Pv t Roadmap

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The 6th Framework Programme

PVT ROADMAP A European guide for the development

and market introduction of PV-Thermal technology



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PVT ROADMAP A European guide for the development

and market introduction of PV-Thermal technology

This roadmap was developed as part of theEU-supported Coordination Action PV-Catapult



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Purchasing value € 25,-Printed copies of this roadmap can be ordered at [email protected] PVT-roadmap can be downloaded without charge at www.pvtforum.org



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This publication presents a roadmap for the marketing and R&D of PVT systems for the short, me-dium and long term, in order to enlarge the long term market penetration of PVT products. Theroadmap is part of the project PV Catapult, supported by the European Union under contract n o

502775 (SES6). More information on the project can be found at www.pvtforum.org

Editors Herbert Zondag, Marco Bakker and Wim

van Helden.

Energy Research Centre of the Netherlands,

Westerduinweg 3, 1755 ZG Petten, the Netherlands

Authors Pascal Affolter,

Solstis, Sebeillon 9b, 1004 Lausanne,

Switzerland

Wolfgang Eisenmann

Institut für Solarenergieforschung Hameln,

Am Ohrberg 1, D-31860 Emmerthal, Germany

Hubert Fechner

Arsenal Research, Faradaygasse 3, 1030 Vienna,

Austria

Matthias Rommel

Fraunhofer Institut für Solare Energiesysteme,

Heidenhofstrasse 2, D-79110 Freiburg, Germany

Anton Schaap

Ecofys, Kanaalweg 16g, 3503 RK Utrecht,

The Netherlands

Henrik Sørensen

Esbensen Rådgivende Ingeniører,Carl JacobsensVej 25D,

DK 2500 Valby, Denmark

Yiannis Tripanagnostopoulos,

University of Patras, Rio, 26500 Patras, Greece

Herbert Zondag

Energy Research Centre of the Netherlands,

Westerduinweg 3, 1755 ZG Petten, the Netherlands



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PVT concepts:

(a) PVT-liquid (b) PVT-air

(a) (b)



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What is PVT?

PVT is a solar energy device using PV as a ther-

mal absorber. By using the heat generated in thePV, a PVT device generates not only electrical, but also thermal energy. Side-by-side systems areoutside of the scope of this roadmap.

The PVT Forum project

Research on PVT is scattered over many (oftenshort-term) projects involving many different ac-tors, but a clear long-term vision was lacking. Itwas considered very useful to bring some of thekey players together to reach consensus on thelong-term outlook for PVT development and toidentify the main bottlenecks. This work has beencarried out within the PVT Forum project, whichis part of the EU-supported project PV-Catapult.The aim of PVT Forum is to lay the foundationsfor a large-scale introduction of Photovoltaic-Thermal (PVT) technology in Europe by meansof this roadmap.

The aim of this roadmap

The aim of the roadmap is to identify promisingmarkets for PVT, and to identify the economi-

cal, policy, legislative and technical bottlenecks.In addition, the roadmap wants to inform the parties in the market on PVT. The roadmap istargeted at a broad range of professionals, includ-ing policy makers, solar manufacturers, install-ers and researchers.

Chapter 1 - Introduction

The present PVT market is very small, but nev-ertheless, PVT has the potential of significantmarket expansion in the near future. Presently,

two commercial PVT air collector manufactur-ers exist, but the number of PV-air collectors in-stalled is very small. For PVT liquid collectors, present commercial activities are even more lim-ited. It is the aim of this roadmap to boost the at-tention for PVT, in order to change this situation.The potential market expansion should be seen inthe light of the EU targets for 2010, that are set at100 million m2 for solar thermal (correspondingto 70 GWp thermal) and 3 GWp for PV. The mar-kets for both solar thermal and PV are growingrapidly. PV-Thermal has the potential to experi-

ence a similar growth and the technical potentialof the technique is large, especially if the marketfor domestic applications can be reached.

Chapter 2 - Overview of modules and systems

PVT devices can be very different in design,

ranging from PVT domestic hot water systemsto ventilated PV facades and actively cooled PVconcentrators. Some of these have a wide appli-cation while others have a more limited market.In addition, the various PVT concepts differ inthe effort that is required to solve the associatedcommercial issues, building integration issuesand technical issues.

Chapter 3 - Present state of PVT market, certi-

fication and R&D

Many manufacturers have participated in thedevelopment, production and marketing of PVTsystems and products. In general, the number of

commercial systems is very small and long-termexperiences with operation of the systems arescarce.

Chapter 4 - Potential markets for PVT

Largely based on the ESTIF report 'Sun in ac-tion - a solar thermal strategy for Europe', anoverall segmentation of the PVT market has been

developed. The largest market potential is foundin the residential sector, now representing 90%of the market. Presently, this market consists

module reliability market building system aesthetics

cost size integration economics

liquid PVT modules glazed ++ + +

liquid PVT modules unglazed + + + + +

air PVT modules glazed + + +

air PVT modules unglazed + ++ + + +

ventilated PV facades ++ ++ + + +

PVT concentrators + +

liquid PVT modules The collector types of PVT systems are typically developed from the

basis of an existing solar thermal collector, which then is equipped with

solar cells on the absorber surface. Two manufacturers presently have

commercial modules.

air PVT modules PVT ai r modules can be manufactured more easi ly, but the market is

smaller. Three manufacturers presently produce PVT air collectors on a

commercial basis.

ventilated PV facades PVT systems belonging to the group of Ventilated PV with Heat Recov-

ery typically have emerged from solutions for specific buildings. How-

ever, standardised systems are becoming available.

PVT concentrators Three commercial systems are available.

Summary

Summary



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largely of domestic hot water systems for single-family houses, but for the future, a growing mar-ket share is expected for solar space heating andfor systems for multifamily buildings. While the

largest potential is seen for domestic hot water systems, possible niche markets are collective tapwater systems, pool heating for (public) swimming pools and autonomous systems, while for the fu-ture space heating and solar cooling may becomea niche market in the commercial sector.

Chapter 5 - Drivers and barriers in the market

The market can be analyzed in terms of driversand barriers for the different actors (decisionmakers, decision influencers, suppliers). In thisroadmap, an inventory has been made for themost promising markets for PVT:

• In the short term, specific actors in the build-ing market may already be motivated to in-vest in PVT (e.g. real estate developers, hous-ing associations, municipalities, energy companies). Multi-family buildings (especially if owned by a housing association) may be animportant early market, due to the limited roof area available, which promotes area efficientrenewable energy applications. Furthermore,interesting niche markets may exist in autono-

mous applications and (public) pool heating.• In the medium and long term, the most prom-

ising application for PVT systems seems to be domestic water heating and space heating.For space heating, it is especially true for advanced houses wanting to cover a large partof the energy needs with solar energy. Com- bination of heat pump and PVT could be a promising concept.

• In the long term, professional application (in-dustry, agriculture) and applications such as

solar cooling will become interesting for PVT.

Chapter 6 - Comparing systems and market

demands

Bottlenecks for the marketing of PVT exist indifferent areas. Technical issues, integration &standardisation issues and general issues such assubsidies and training issues can be distinguished.As main bottlenecks for PVT are identified: un-clear economic viability, lack of warranties andcertification, insufficient legal embedding, lack of training for installers, lack of public aware-

ness and lack of standardization. It is importantthat the reliability and life time of PVT laminatesis thoroughly assessed, which requires further re-

search and dedicated test procedures. Also thePVT system economics need to be clearer.

Chapter 7 - Identification of key developments

The following key developments are identified,and development schemes for the short, mediumand long term are presented:

• Training and education on all levels, from policy makers to customers.

• Integration issues such as plug and play mod-ules, the development of optimized PVT sys-tems and design tools for these.

• Standardization for both performance andreliability aspects

• Aesthetic issues such as an inventory of theaesthetical demands of the different actors,as well as PVT module designs that showflexibility in color and shape, as well as ap- pealing design

• Optimized financing schemes for the variousactors

• Clear and consistent subsidy schemes for thevarious actors

• Technical issues such as stagnation resist-ance, optimization of optical parameters andheat transfer and optimization of PV tempera-

ture coefficient

Chapter 8 - Conclusion

First of all, it should be stated that PVT may beinteresting for a large number of applications andmarket sectors. Customers of PVT productswould include not only homeowners but alsoother groups such as real estate developers, hous-ing associations, energy companies, municipali-ties and owners of public pools, sports facilitiesand hotels. Important sales arguments for PVT

are• only one supplier responsible for all

• eye-catching high profile technique

• provides a green and high-tech image• reduced area and installation costs as com-

pared to side-by-side systems

• renewable energy targets are reached moreefficiently

However, for large scale market penetration of PVT, a number of actions have to be undertaken by the various actors involved. An action plan is

presented below, indicating benefits and chal-lenges for the main actors involved.



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Manufacturers

Benefits of PVT• new and/or enlarged marketsChallenges

• how can the production technologies of PV andsolar thermal be integrated cost-effectively?

• how can plug-and-play integration of PVTinto heating and electrical systems be accom- plished?

• how can PVT modules be produced withsufficient variety in colour and shape?

• how can PVT be promoted effectively?

Policy makers

Benefits of PVT• Renewable energy targets reached more

efficiently and at an earlier timeChallenges• which market support mechanisms are most

effective for PVT?• how should PVT be included in the new

energy efficient building regulations?

• how can research, development and demon-stration of PVT be supported most effectively?

R&D and Test institutes

Benefits of PVT• development requires innovative technologi-

cal solutionsChallenges• what should the performance and reliability

standards for PVT look like?

• which field tests should be carried out to support warranties?

• which technological solutions can be foundto increase the optical and thermal efficiencyof PVT

• which technological solutions can be found

to increase the long-term reliability of PVT?

Architects

Benefits of PVT• new ways to integrate renewables into build-

ings

• less aesthetic problems with integration intothe building envelope, since only one deviceneeds to be integrated

Challenges• how can PVT (and other solar technologies)

become an integral part of the building

design?• which new building concepts are now

possible because of PVT?

Energy Consultancy and engineering

companies

Benefits of PVT• innovative and high profile technology for

demonstration projectsChallenges• what sort of design tools are needed by

architects, installers and engineers?• which new system concepts are now possi-

ble because of PVT?

• what are the best system configurations for given climates and applications?

• which market surveys are required to support the commercialisation of PVT?

Building industry

Benefits of PVT• high profile green product that may be used

to promote the sale of core products• increased energy performance of buildings• reduced payback time compared to PV and

solar thermal side-by-sideChallenges• how can plug-and-play integration of PVT

into the building construction be accom- plished?

• how can prefab building elements be real-

ised that facilitate installation of PVT?

Installers

Benefits of PVT• reduced installation effort

• new or enlarged marketChallenges

• how can plug-and-play integration of PVTinto heating and electrical systems be accom- plished?

• how can the three specialisms (roofing, heat-

ing and electrical installation) be combined?• which targeted solar campaigns are neces-

sary for PVT?

Summary

P h o t o : Gr a mm e r S ol a r



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Table of contents

1. Introduction 11Project aim 11

General introduction of PVT 11

2. Overview of modules and systems 13System overview 13

Classification of thermal demand 13PVT system yield 14

Module overview 15

General module issues 16Liquid PVT collector 18Air PVT collector 19Ventilated PV with heat recovery 20PVT concentrator 21

Autonomous developments in solar-thermal and PV 21

Conclusion

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3. Present state of PVT market, certification and R&D 23Principal products and systems on the market 23

PVT Liquid collectors 23PVT Air collectors 24Ventilated PV with heat recovery 24PVT concentrators 25

Present state of certification 26

Present state of R&D 27

PVT liquid collectors 27PVT air collectors 27

Ventilated PV with heat recovery 27PVT concentrators 28Glazed/unglazed PVT 28Type of PV-absorber 29

Conclusions 29

4. Potential markets for PVT 31Principal segmentation of present potential PVT market 31

Market segmentation for present solar-thermal market 31Market segmentation for present PV market 31

Changes in the market 32

Trends in solar thermal 32Trends in PV 33Trends in the residential sector 33

Market differentiation 34

Solar thermal 34PV 34Subsidy schemes 36

Competitors for PVT systems 37

Conclusion 38

5. Drivers and barriers in the market 39Decision processes 39

Actors and their drivers & barriers 40

Decision makers 40Influencers 45



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Suppliers 47Conclusions 48

6. Comparing systems and market demands 51

General bottlenecks 51Warranties 51Legal aspects 51Aesthetics 52Ease of handling 53Training and awareness 53Green image 54

Grid connected applications 54

Domestic market 55Tertiary market 57

Off-grid applications 60

Consumers 61Professional stand-alone 62Agricultural application 62

Conclusion 62

7. Identification of key developments 63General issues 63

Measuring techniques, standards and certification 63Financing issues 64Subsidy issues 65Awareness and training 66Legal aspects 66

Technical issues 67Stagnation 67Thermal module efficiency 68Temperature dependence of solar cell performance 69

Integration issues 70

Aesthetics 70Development of plug-and-play modules 70Design Tools 71Combining PVT with PV or thermal collectors on a single roof or façade. 71Combining PVT with heat pumps 72Combining PVT with solar cooling 73

8. Conclusions 75Most promising system-market combinations 75

Barriers to overcome 76

Action plan 77

References 79

Glossary 83

Overview PVT products IEA SHC task 35 84



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1. IntroductionPVT roadmap

The aim of the roadmap is to identify promisingmarkets for PVT, and to identify the economi-cal, policy, legislative and technical bottlenecks.In addition, the roadmap wants to inform the parties in the market on PVT. It thereby targets a broad range of professionals, including policymakers, solar manufacturers, installers and re-searchers. This work has been carried out withinthe PVT forum project, which is part of the EU-supported project PV-Catapult. The aim of PVTForum is to lay the foundations for a large-scaleintroduction of photovoltaic-Thermal (PVT)technology in Europe by means of this roadmap.

In order to construct the roadmap, a two-step approach was taken. As a first step, PVT experts,PV and solar thermal industries and other stakeholders were brought together in two work-shops, connected to the PVSEC 2004 in Parisand the Eurosun conference 2004 in Freiburg, toidentify drivers and barriers for PVT. The resultsof these two workshops, that were presented intwo workshop reports, were used as input for the

roadmap presented here.As a second step, the PVT roadmap was written,formulating the necessary actions that should betaken on short, medium and long term in order to enlarge the market for PVT products. Thechapters of the roadmap are written and reviewed by the various participants in PVT Forum. These participants have been selected for this projecton the basis of their contribution to PVT devel-opment over the last years.

General introduction of PVTPVT is defined in this roadmap as a device usingPV as a thermal absorber. By using the heat gen-erated in the PV, a PVT device generates not onlyelectrical, but also thermal energy. Because of this scope, no attention will be paid to side-by-side systems, in which PV is installed next tosolar thermal in the same frame.

PVT devices can be very different in design, rang-ing from PVT domestic hot water systems to ven-

tilated PV facades and actively cooled PV con-centrators. In order to indicate the range of de-vices classified as PVT, some pictures of PVT

devices are shown in Figure 2 and Figure 3.The markets for both solar thermal and PV aregrowing rapidly and have reached a very sub-stantial size. For PV-Thermal a similar growthcan be expected; the technical potential of thetechnique is large, especially if the market for domestic applications can be reached. Given the broad range of application for PVT, which is notonly suitable for domestic hot water heating

(glazed PVT collectors), but also for offices(ventilated PV for preheating ventilation air dur-ing winter and providing the driving force for

Figure 1. Artist impression

of a glazed PVT-liquid

collector, showing both PV

cells and heat transfer

system (source: IEA-PVPS

Task 7 CD-ROM).

Figure 2. Practical examples of PVT liquid devices (left to right: PVT liquid module of

PVTwins, concentrating modules of Vattenfall, unglazed module of ECN)

1. Introduction

Figure 3. Practical examples of PVT air systems (left to right: PVT air modules of

Grammer Solar, ventilated PV facade Scheidegger building by Atlantis Energy, PV air roof ECN)

P h o t o : B .K a r l s s on

P h o t o : A t l a n t i s E n e r g y




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Many types of PVT devices exist, as was illus-trated in chapter 1. In the present chapter, the aim

is to define a number of PVT system classes andto give an indication of the thermal and electri-cal performance. First, an overview of PVT sys-tems will be presented. Next the system efficiencywill be elaborated. Finally, a short overview of points of attention on the module level will begiven.

System overview

PVT is defined in this roadmap as a device usingPV as a thermal absorber. By using the heat gen-erated in the PV, a PVT device generates not onlyelectrical, but also thermal energy.

The electrical yield of the PVT can either be useddirectly or be supplied to the grid. Since storageis not required, it is straightforward to determinethe annual electrical yield. For the annual ther-mal yield, the situation is different. The PVT de-vice is part of a larger heat supply system con-taining other equipment, such as a thermal stor-age and piping. In addition, the user determines

how much heat is used. The thermal efficiencyof a PVT device and the average module temperature depend strongly on these effects. There-fore, the PVT systems overview presented herefocuses on the thermal system. For the various PVTsystems, the thermal yield and the electrical yieldwill both be discussed, including the effect of thethermal system on the electrical output.

Classification of thermal demand

Many applications exist for solar heat, rangingfrom domestic hot water and pool heating to ag-ricultural applications like drying of crops or milk heating for calves. In principle, solar collector systems have a design as shown in Figure 5. Keyelements are the collector, the storage (size rangesfrom zero for direct use systems to a few m3 for weekly storage system) and the auxiliary heater to add as a backup in case of insufficient solar supply.

Various ways exist to classify solar thermal sys-

tems. Here, the choice is made to categorize themwith respect to thermal demand, which has twodimensions: process temperature required and

amount of storage required. The subdivision of the thermal demand is presented in Figure 6. Inthis figure, typical examples of solar thermal sys-tems in these categories are given. It should beemphasized here that the demand by the end user is categorized here, and not the temperature levelthat is provided by the solar collector system.This means that the indicated temperature levelis the temperature level that is produced by thesolar collector and the additional heater (e.g. aconventional gas heater or a heat pump) jointly.Considering Figure 6, it should be kept in mindthat some demands will normally be combinedinto one system (e.g. domestic heating and hotwater).

Each storage level required brings its own tech-niques and problems. Direct application of so-

lar heat may require a good control of the flow,to be able to adapt to variations in irradiance. Atthe other hand, seasonal storage may requiretechniques such as the application of a heat pumpand ground storage or (in the future) thermo-chemical storage.Similarly, each temperature level brings its owntechniques and problems, related to the improved insulation of the PVT module and theassociated issues of increased stagnation temperature and reliability. It should be kept in mindthat PVT is not suitable (yet) for the very high

temperature range, due to the large thermallosses at high temperatures and the wish to re-strict the PV temperature to an acceptable level.

Figure 5. Principal scheme

of PVT system, including

PVT module, storage and

auxiliary heater.

Figure 6. Classification of

PVT systems according to

thermal demand

2. Overview of modules and systems




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PVT system yield

To indicate the yield of a PVT system is notstraightforward. Basically three problems exist:

1. The yield depends on the ambient conditions,especially the irradiation. These conditionsvary strongly with latitude. This implies thate.g. the yield of a collector in Greece will besubstantially higher than the yield of the samecollector in the Netherlands. In addition, theamount of irradiance that is received by thecollector displays a seasonal variation, whichalso depends on the lattitude. These effectsare indicated in Table 1.

2. The collector produces both electrical andthermal output. Therefore, one either has totalk about these two yields separately, or oneshould choose a way to combine both yieldsinto one quantity. There are various methodsto combine the value of electricity and heat(Coventry and Lovegrove, 2003):

• Calculate the total energy by simple ad-dition

• Calculate the primary energy (Fossil fuelenergy required to produce the amount of useful thermal and electrical energy. Thisdiffers from the above due to plant and

heater efficiencies)• Calculate the saved cost from the tariffs

for heating energy and electrical energy• Calculate the exergy

For this report, we prefer to calculate the to-tal yield of the PVT in terms of primary en-ergy, since this provides the fairest way tocalculate the fossil fuel saved. The choice ismade to assume a thermal conversion factor of 1 and an electrical conversion factor of 2½,

corresponding to a heater efficiency of 100%and power plant electricity generation effi-ciency of 40%.

3. The electrical yield of the PVT can either beused directly or be supplied to the grid. Sincestorage is not required, it is straightforwardto determine the annual electrical yield. For the annual thermal yield, the situation is dif-

ferent. Unlike the electrical output, the ther-mal output depends strongly on the thermalsystem design and the amount of heat that isextracted by the user. In the calculations pre-

sented in this chapter, it is assumed that theload is typical for a certain application andthat the system dimensioning is optimised for the load.

Because of these effects, it is difficult to evalu-ate and compare the energy yield per m2 for dif-ferent PVT systems. However, for a given typeof system under a given orientation in a givenclimate, under the condition that the systemdimensioning has been carried out properly, agood estimate can be made. This estimate is pre-sented in Table 2. In this table, various systemsare presented with typical values for PVT, elec-trical yield and thermal yield. The energy yieldis estimated for both the Dutch and the Greek climate. It should be kept in mind that the sys-tems given in Table 2 cannot be compared di-rectly with each other, as they are quite differentconcerning system design requirements (PVTarea required, size of storage tank, etc.), collec-tor type, temperature level and system costs. Nev-ertheless, the table is useful to illustrate some

general trends in PVT systems yield.

From Table 2, several trends can be identified:• The effect of climate is large. The amount of

primary energy saved per unit of collector area is about twice as high in Greece as inthe Netherlands.

• The seasonal variation in the demand mayreduce the annual thermal yield considerably.

• The effect of temperature level on electricalPVT performance is relatively small.

•

The effect of temperature level on thermaloutput is substantial, although this trend isreduced due to the corresponding change inPVT design (over a certain temperature level,insulating covers are used, which increase thecollector performance but also the costs).

• Applications with a heat pump will gener-ally have zero or negative electrical outputdue to the consumption of the heat pump.

• Facade integration reduces both the electri-cal yield and the thermal yield.

• Although the electrical yield is typically 40%

of the thermal yield, in terms of primary en-ergy yield the contributions are almost equal.

• With a few exceptions, the thermal yield per

location latitude annual irradiation ratio irradiation ratio irradiation

horizontal kWh/m2 winter / summer façade/roof 35°

Jerusalem 31º 2101 0.41 0.57

Athens 38º 1567 0.31 0.62Vienna 48º 1113 0.16 0.67

Amsterdam 52º 1046 0.12 0.70

Stockholm 59º 983 0.06 0.75

Table 1. Climatic

parameters for various

countries (source:

Meteonorm). Winter is

defined as November to

January, while summer is

defined as May to July.




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m2 is somewhat lower in a PVT system thanin a conventional solar thermal system, whilethe electrical yield is slightly lower than for a conventional PV module. However, in thecase of PVT, both yields are produced by the

same area! Compared to side-by-side sys-tems, the combined thermal and electricalyield of a PVT system is larger than the combined thermal and electrical yield of a side-by-side system of the same size, allowing for asmaller area and a reduction in installation costs.

• In terms of energy, it is clear that for mostapplications the thermal yield is substantiallyhigher than the electrical yield, which showsthat a conventional PV laminate generates alarge amount of untapped heat. The harvest-ing of this heat has the potential to reduce

both the financial and the energy payback time of the PV considerably, which further illustrates the potential of PVT.

Module overview

The thermal demand that was specified in Figure6 can be covered by several types of PVT collec-tors. PVT modules can be characterized along

several dimensions, such as the type of PV used,whether the collector is glazed or unglazed, whatcollector fluid is used (water/glycol or air),whether concentration is used and what type of module design was used. For practical reasons,in this roadmap, the PVT device classification isused as presented along the y-axis in Table 3,where the effects of glazing and type of PV will be presented as 'general module issues'.

A relation exists between the type of module re-quired and the types of demand as defined in

Figure 6. However, the relation is not a one-to-one. An overview is presented in Table 4.

Table 2. Examples of

systems, with typical yield

(assuming the Dutch and

the Greek climate). For the

electrical performance,crystalline silicon cells are

assumed.


annual PVT annual PVT Annual

yield yield primary

electrical thermal energy

Markets application kWh/ m2 kWh/ m2 kWh/ m2 remarks

Dutch Greek Dutch Greek Dutch Greek

offices solar cooling 90 130 30- 250- 255- 575residences (70-90°C) 50 300 275 625

offices room heating + natural 80 110 20- 50- 250- 310- additional saving on ventilation

ventilation through 40 100 265 350 may be possible during summer

ventilated unglazed PV (season (season

facade (offices) (25-50°C) only) only)

residences, hot water 100 140 200- 550- 450- 850-

apartment (50-70°C) 300 600 550 950

buildings,

hospitals etc room heating + hot 100 140 150- 450- 400- 800-

water (50-70°C) 200 55- 450 900

room heating + hot water including the heat production

combined with heat pump 0 0 200- 500- 200- 500- and electrical consumption of

with ground source 300 600 300 600 the heat pump(50-70°C)

room heating + hot water -20 0 200- 500- 150- 500- including the heat production

combined with heat pump 300 600 250 600 and electrical consumption of

with energy roof and the heat pump

ice storage (50-70°C)

pool heating pool heating outdoor 110 165 150- 200- 425- 810-

(25-50°C) 250 300 525 910

(summer(winter

only) only)

pool heating indoor 100 150 300- 600- 550- 900-

(25-50°C) 400 700 650 1000

industrial car wash (25-50°C) 100 140 300- 400- 550- 900-400 500 650 1000

agricultural crop drying (50-70°C) 100 140 100- 350- 350- 700-

150 450 400 750

(season (season

only) only)



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In separate paragraphs below, the effect of PVtype and glazing are indicated and for the PVTcollector classes as shown in Table 3 some top-ics of attention are given.

General module issues

Glazing

PVT collectors may have a glass cover over theabsorber to reduce the thermal losses. If such acover is present, the collector is referred to as"glazed", otherwise as "unglazed". The terms"glazed" or "unglazed" therefore do not refer tothe glass substrate that may be part of the PVTabsorber!

• Glazed collectors have smaller thermallosses, especially at higher collector fluidtemperatures. For medium to high tempera-ture applications, this results in a much higher

annual thermal yield.• Glazed collectors result in high stagnation

temperatures that may be critical for certaintypes of PV encapsulant (risk of yellowingand delamination). The glazing makes themodule more sensitive to hot spots. Bypassdiodes may get overheated due to the addi-tional insulation. Reflection losses at the glaz-ing reduce electrical performance. Increasedtemperature levels lower the electrical yield.

Table 3. PVT collector

classification.

PVT liquid collector

unglazed module (ECN) glazed module (PVTwins)

PVT air collector

unglazed module (Grammer glazed module (Aidt Miljø)Solar)

Ventilated PV withheat recovery

facade system (TFM) roof system (TFM)

PVT concentrator

stationary module (Vattenfall) tracking module (ANU)




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In the discussion whether the collector should be glazed or not, it is important to find a good balance between the increased thermal yield onone hand, and the reduction in electrical yieldand the issues related to possible degradation onthe other hand.

Type of PV

Several commercial PV technologies exist. Crys-talline silicon has by far the largest market shareof all PV technologies, as shown in Figure 7.Commercial modules have a good electrical ef-ficiency of 10-17% for mono crystalline siliconmodules and 11-15% for multi crystalline sili-con modules, as shown in Table 5. A good elec-trical efficiency is important, since for many applications, PVT produces too much heat relativeto electrical energy.

Amorphous silicon has a significant market share, but much smaller than c-Si. It has a relativelylow electrical efficiency of 4-6% for single junc-tion and 5-7% for triple junction material (Table5). It can be obtained in flexible laminates, in-creasing the design options. The price per squaremeter for a-Si is lower than for c-Si. However,this is compensated for by the lower efficiencyof a-Si; the price per Wp for a-Si is similar to the price for c-Si.

Type of demand Recommended type of PVT collector

high temperature water Use glazed liquid collector, glazed air collector with heat exchanger or concentrator. Also

an unglazed collector is possible as source for a heat pump.

high temperature air Use glazed air collector or unglazed collector/ventilated PV as source for a heat pump.

low temperature water If only summer demand use unglazed liquid collector, if also winter demand use glazed

liquid collector or unglazed collector as source for a heat pump.

low temperature air If only summer demand or high irradiation in winter use unglazed air collector or ventilated

PV. If also winter demand and low irradiation in winter, use glazed air collector or unglazed

collector as source for a heat pump.

Table 4. Relation betweentype of collector and type

of demand.

PVT stagnation temperature

PV laminates are designed for direct insolation and the tempera-

tures that are reached at direct insolation. In a glazed solar ther-

mal collector a transparent cover is placed in front of the ab-

sorber. In this way much higher temperatures can be reached.

Whereas a PV module can reach about 90 °C under direct insola-

tion in hot climates, the absorber of a thermal collector can reach

temperatures of up to 220 °C, with a state of the art spectrally

selective coating. The construction of the thermal collector is

able to withstand these high temperatures. The absorber is fully

welded. Soldered (lead/tin) absorbers are getting rare, because

of the temperature limitation. The backside insulation is also able

to withstand this temperature. It is mostly glass wool with a spe-

cial (non evaporative) binder.

In general a PVT absorber has a higher solar reflectance than a

conventional thermal absorber and also a higher infrared emis-

sion. This means that the PVT absorber will get less hot than a

state of the art thermal absorber with selective coating. A PVT

absorber using standard PV cells will reach temperatures of up

to about 150 °C. Of course, the temperature can be raised by

increasing the solar absorption and decreasing the infrared emis-

sion. In this way the collector efficiency can be improved, butalso the specifications of the bonding technique become more

severe. The solar cells can withstand temperatures around 220

°C without any problem. In this temperature range no diffusion

takes place. But most encapsulation materials used for PV-mod-

ules cannot withstand these high thermal collector temperatures.

Ethylene vinyl-acetate for example oxidises faster at high tem-

peratures and solar irradiation (UV-radiation) than at lower tem-

peratures. The maximum temperature for most polymeric encap-

sulation materials is around 100 °C. Also the durability of the

interconnections of the solar cells will be lower at such high tem-

peratures, even though melting point of the used solder is much

higher (around 250 °C), because of the additional thermal strain

and the fact that the higher temperature increases possible corro-

sion effects (making the solder more brittle).




18

Other PV techniques such as CIS and CdTe areupcoming but have presently a very small marketshare and have therefore not yet been used in PVT.

On the system level, only the effects of climate,orientation and temperature affect the electrical performance of a given PVT system. The mostimportant effects are those of total annual irra-diation - which is much larger for Southern coun-tries as illustrated by Table 1 - and the effect of orientation, which is a function of latitude. Thisleads e.g. to the observation that, from an effi-ciency point of view, facade integration is moreappropriate for Northern countries (as shown pre-viously in Table 1).Of secondary importance is the effect of tempera-

ture. It is different for different types of PV. Ta- ble 6 summarises the temperature coefficients of different PV techniques available on the market.The table shows that for most thin film cells thetemperature coefficients is smaller than for crys-

talline silicon cells, so the losses may be onlyabout half the losses compared to crystalline sili-con cells. However, all cells have negative temperature coefficients which means that the situ-

ation is in principle still the same (less energy produced at higher temperatures).

However, the effect of the power dependence onthe temperature should not be overestimated.During operation (enough daylight) a c-Si PVmodule has an average temperature over the year of about 30-40 oC (depending on the amount of ventilation of the module), whereas a glazed PVTcollector may have an average temperature be-tween 30 oC and 50 oC (depending on the solar fraction). So we can estimate that the electrical power loss will generally be less than about 10%of the total electrical yield.

Liquid PVT collector

The liquid PVT collectors are similar to conven-tional flat plate liquid collectors; an absorber witha serpentine tube or a series of parallel risers is applied, onto which PV has been laminated or glued.

Commercial issues

Hot water has a wide application, is easy to store

and can be used all year long. The flat plate col-lector is very well suited to produce hot water,which is reflected in the fact that of the installedsolar thermal collector area worldwide, flat platecollectors (glazed and unglazed) make up for over 75% (see Figure 8).The collector types of PVT systems are typicallydeveloped from the basis of an existing solar ther-mal collector, which is equipped with PV on theabsorber surface. The cost of the PVT systemcan be assumed to be similar to the cost of thesolar thermal system plus the cost of the PV lami-

nate (including installation), minus the cost of saved materials through integrated production/installation and reduced installation costs.

Table 5. Module

efficiencies of different PV types. Source: Market

survey solar modules 2005

(Photon International,

February 2005)

type of cell range commercial producer highest corresponding cell

module efficiencies per formance modules manufacturer

multicrystalline Si 11-15% Sharp Sharp

monocrystalline Si 10-17% Suntechnics SunPower

HIT cells 16-17% Sanyo Electric Sanyo Electric

ribbon & EFG cells 12-13% Titan Energy RWE Schott

a-Si (single junction) 4-6% Mitsubishi Mitsubishi Heavya-Si (triple junction) 5-7% Sunset United Solar

CIS 9-11% Würth Solar Würth Solar

CdTe 6-9% First Solar First Solar

producer type of cell temperature coefficient (based on power)

(reference) crystalline Si -0.4%/K to -0.5%/K

Mitsubishi Heavy a-Si -0.2%/K

RWE Schott Solar a-Si -0.2%/K

Uni-Solar a-Si -0.21%/K

Kaneka a-Si/µc-Si hybrid -0.23%/KWürth CIS -0.36%/K

First Solar CdTe -0.25%/K

Table 6. Power temperature

coefficients of different PV

techniques.


Figure 7. Market share of

PV technologies 2002

(figure from PV-NET

roadmap, data from P.D.

Maycock)

P h o t o : P

VT WI N S



19

Building integration issues

Building integration is applied successfully for solar thermal collectors, and PVT collectors can be integrated in a similar way.

Technical issues

Special integrated PVT absorbers are required,for which the thermal resistance between PV andcollector fluid should be sufficiently small (especially for unglazed PVT). Leakage or freez-ing may occur in case of faulty design.

Air PVT collector

The PVT air collectors are similar to a conven-tional underflow air collector with a PV lami-nate functioning as the top cover of the air chan-nel. PVT air collectors have the important ad-vantage over PVT liquid collectors that conven-tional PV modules can be used, which reduces

the module costs relative to PVT liquid modules.However, this benefit on module level may becompensated by increased costs and lower an-nual yields on systems level.PVT air collectors can either be glazed or unglazed.

Commercial issues

A problem for air collectors is the limited appli-cation for hot air, especially during the summer when most heat is available. This is reflected in

the installed area of air collectors, that is about1,5% of the total installed solar collector area(see Figure 8). In general, air collectors aremostly applied if the users have a demand for hot air, like in air heating systems and drying of agricultural products.Air heating systems are mainly designed to di-rectly use the air for space heating. However,the opportunity for this application depends di-rectly on the market share of air heating sys-tems, which is low in most countries. A nichemarket is given by preheating of ventilation air for large volume buildings (stores, sport halls,schools, manufacturing halls,...) where tempera-tures in the range of 15 to 25°C are desirable.With the very same air systems, hot water prepa-ration is often possible as well through an air/water heat exchanger, which is done during thesummer season in order to increase the overall performance of the system. Nevertheless, it isdifficult for these systems to compete with a liq-uid collector, because of the cost and the lim-ited efficiency of an air/water heat exchanger.

Other applications for hot air may be solar cool-ing and drying processes.


On the module level, a problem is the high air volume flow required to obtain a good thermalefficiency, and the corresponding items of largediameter tubing, noise and fan losses. The largetubing required may cause problems, especiallyin retrofitting.

Technical issuesThe application of air as a heat transport me-dium has some advantages but also some bigdisadvantages in comparison with water. To startwith the advantages:

• No freezing and no boiling of the collector fluid.

• No damage if leakages occur.

The disadvantages are however rather severe:• Low heat capacity and low heat conductiv-

ity, which result in a low heat transfer.

• Low density, which results in a high volumetransfer.

• High heat losses through air leakage


Figure 8. Installed solar thermal collector area

wordwide (end 2001) in GWp and m2 collector area

(data from Weiss (2004), keynote lecture Eurosun

conference)




20

For direct heating of living rooms, heating air tomore than 60°C is not recommended. Air with atemperature of more than 60°C is starting to burndust particles, which can lead to health problems

in open systems. Also particles of the materialsin the PVT collector may be gassing out at hightemperatures.

Ventilated PV with heat recovery

In conventional PV facades or PV roofs, an air gap is often present at the rear in order to allowthe air to cool the PV by means of natural con-vection (ventilated PV). If this heat can be re-covered from the PV and be used in the building,the PV functions as a PVT collector. Basically,the entire PVT-module infrastructure is alreadyavailable in normal building integrated PV.

Such PV facades, apart from providing electric-ity and heat, have additional benefits as well:• A PV-facade may limit the thermal losses

from the building to the ambient (especiallythose related to infiltration). In addition, thePV facade shields the building from the solar irradiance, thereby reducing the cooling load.

This makes such facades especially useful for retrofitting badly insulated existing offices.

• Air collectors and PV-facades can use their buoyancy induced pressure difference to as-sist the ventilation, if there is no demand for the generated heat.

• Facade integration of PV has the cost incen-tive of substituting expensive facade claddingmaterials.

Similar to PVT air collectors, a problem for ven-tilated PV is the limited application for hot air

during the summer, when most heat is available.An interesting option is the application of the heatfor solar cooling. However, the temperature level

that can be reached by the ventilated PV is notsufficient for direct use in such systems, due tothe large heat losses and the façade orientation.Therefore, ventilated PVT facades are combined

with roof or façade integrated conventional col-lectors to boost the temperature to the requiredlevel for this application.

Commercial issues

Since PV facades are already well established andare largely identical to PVT facades, and sincePV facades replace expensive facade cladding ma-terials, it is expected that the costs on module levelwill be low compared to all other applications.However, on system level the situation may bedifferent; since PV facades are often unglazed, thetemperature levels that can be reached are lim-ited, and the costs of the additional infrastructurerequired may outweigh the benefits of the use of this heat, so low cost systems are mandatory.A difference between ventilated PV with heat re-covery and PVT collectors, is the fact that thissystem is typically designed for a specific build-ing and is not manufactured as a standardisedsystem. Due to the current strong link betweenthis type of PVT and specific building projects,it is very difficult for a non-specialist architect

to provide this option for a specific project. How-ever, this situation may change since several in-stitutes and manufactureres have made an effortto standardise these systems (e.g. Butera, 2005).The application for heating (e.g. preheated ven-tilation air) is limited to climates that have a sub-stantial irradiation during the heating season,which excludes e.g. Northern Europe, although possibilities exist in countries such as the USAand Japan. On system level, the efficiency is lowdue to the seasonal character of the demand. This

may be improved by extending the system to provide hot water or solar cooling during thesummer, but this will strongly increase the sys-tem cost.


At the module level, these PVT systems arehighly suitable for building integration. However,using air systems for ventilating, heating andcooling of buildings generally needs large pipeinstallations and big volumes, because of the poor heat capacity of air. It can therefore mainly be

used in new buildings, introducing air systemsat a retrofitting process is very difficult. For thatreason, only niche markets (sports halls, store-


M a t a r ol i b r a r y-T F M



21

houses, production halls, assembly rooms, etc...)are equipped with solar air systems in signifi-cant numbers up to now.

Technical issuesSince the heat transfer from the PV to the air-flow is generally not very good, the losses to theambient are large and thermal efficiencies aregenerally in the range of 10% to 20% for a well-designed system.Because of health reasons, direct introduction of the heated air into living rooms is not recom-mended. Fungi and bacteria in the duct systemscannot be avoided, as well as dust that will be blown into the living rooms. Although filterscould clean the air, maintenance is difficult andthe pressure drop and therefore the electrical power for ventilation will increase significantly.This is why indirect systems (hypocausts, double wall systems,...) are used for air heating sys-tems in living rooms. However these systems aremuch more expensive.

PVT concentrator

By concentrating, a (large) part of the expensivePV area is replaced by cheap mirror area, which

is a way to reduce the payback time. This argu-ment is the driving force behind PV-concentra-tors. However, this leads to a substantial thermalenergy generation in the solar cells, and if notremoved, a very high operating temperature of the solar cells will be the consequence and theefficiency for solar cells will decrease substan-tially. Therefore, the PV needs to be cooled. If this is done by active means, a PVT concentra-tor results. Different types of concentrators ex-ist, ranging from flat plate concepts with added

reflectors to highly concentrating designs thatstrongly deviate from the flat-plate concept.

Commercial issues

Concentration has the potential of reducing thecost, through replacement of expensive PV area by cheap mirror area. In addition, the PV effi-

ciency increases due to the larger irradiance,which further reduces the payback time. How-ever, up till now the market share for PV con-centrators has been negligible, which is mainlydue to the fact that these systems are rather bulky, disqualifying them for many PV applica-tions.


Large concentration ratios require tracking,which makes building integration impossibleand strongly increases the maintenance costs.Furthermore, not all climates are suitable for high ratio concentration, depending on theamount of diffuse irradiation. This problem isless for low concentration ratios, since a station-ary concentrator can be used, but also in thatcase the collector is thicker than a flat-plate col-lector and the surface uneven in appearance,since the reflectors are not in one plane with thePVT. Aesthetically the concentrating systems provide different reflections and optical effects,which are unusual to the built environment and

which may prevent such systems from being placed visibly in the facade construction. The best option may be to install the concentrator on a horizontal roof (e.g. PVT systems with booster reflector in parallel rows).

Technical issues

The small cell area allows the use of more effi-cient and expensive PV material, such as cellsspecially designed for PVT performance. Thecombination of glazing and reflectors increases

the stagnation temperature, which may lead todegradation of materials. For electrical perform-ance, the uniformity of the irradiance may becompromised, increasing mismatch losses.However, this drawback might be overcome byusing diffuse reflectors.

Autonomous developments insolar-thermal and PV

If we assume that PVT will use state of the artsolar-thermal and PV technology, changes in

these technologies might considerably influencethe development of PVT:


P h o t o : B .K a r l s s on



22

• The PV price will strongly decrease. Thiswould make installation costs more and moresignificant. Since PVT is a means to reduceinstallation costs, this development is prom-

ising for PVT.• The price of solar thermal will decrease more

slowly than the price of PV. This may meanthat in time, the thermal system becomes themost expensive element of the PVT collec-tor. This may shift the emphasis in moduledesign more to thermal efficiency at the costof PV efficiency.

• The market share of vacuum tube collectorsis increasing. This is presently due to low-cost mass-scale production in China. The in-crease in market share will be reinforced dueto an increased demand for space heating andsolar cooling. Due to very high stagnationtemperatures, these collectors are presentlynot suitable for PVT applications. If vacuumtubes would become the dominant market product, this may be problematic for PVT.However, it is expected that flat plate collec-tors will continue to keep a substantial shareof the market (e.g. because of the fact that building integration is easier for flat platecollectors, with the additional benefit of pro-

viding insulation to the building).• Some PVT systems also contain a heat pump.

Future increased efficiency of the heat pump,together with a reduced sensitivity to highsource temperature, will make heat pumpsmore suitable for combination with solar sys-tems functioning as a source for the heat pump.

• In the long run, seasonal storage will becomemore efficient and compact, due to develop-ments in thermo-chemical (TCM) storage.

This will increase the potential for seasonalstorage at the expense of additional costs andincreased technical complexity. However, dueto the costs, the storage capacity should be

minimised, which can best be done by usinghighly efficient solar collectors (vacuumtubes) for loading, since this minimises thetime span over which solar energy is not

available. Since PVT is presently not suit-able for vacuum tube application, such a de-velopment could be problematic. Neverthe-less, this development would influencemainly the market for solar heating, while thelarge market for tap water heating will con-tinue to be served by flat-plate collectors andPVT.

It may be concluded that, although developmentsin PVT system components will influence PVTsystems, PVT will mostly profit from these. The basic advantage will continue to lie in space re-duction and cost reduction (especially if one con-siders the whole chain from manufacturing to mar-keting, logistics installation and maintenance).An exception is the potential future rising mar-ket share of vacuum collectors, a developmentthat may be reinforced by the increasing shareof solar heating, solar cooling and the develop-ment of TCM storage. This development mayrequire dedicated high temperature PVT tech-nologies, which still have to be developed. How-

ever, it is expected that flat plate collectors will play an important role for a long time to come.

Conclusion

A wide range of PVT systems and PVT modulesexists. Some of these serve a wide range of applications while others have a more limitedscope. In addition, the various PVT concepts dif-fer in the effort that is required to solve the asso-ciated commercial issues, building integration

issues and technical issues. Later chapters in thisroadmap will present a priority ranking for theconcepts to be developed and the issues to beaddressed in RD&D, marketing and policy.




23

In this chapter the state of affairs of PVT Sys-tems is analyzed from the point of view of the

market as it was by 2004. For all of the principaltypes of PVT defined in chapter 2, commercialand near-commercial products can be found, al-though their number is small and long-term experiences with operation of the systems arescarce.Many manufacturers have participated in thedevelopment, production and marketing of vari-ous systems and products. The present chapter aims at presenting an overview of this work.However, there is no claim to completeness.

Principal products and sys-tems on the market

Based on the classification presented in the pre-vious chapter, the principal products and systemson the market are split into the following groups:

• PVT Liquid collector

• PVT Air collector • Ventilated PV with heat recovery

• PVT Concentrator

PVT Liquid collectors

Most PVT liquid collectors are developed basedon a commercial solar thermal collector that has been modified to include PV in the surface of theabsorber. The typical thermal performance is simi-lar to the performance of a non-selective type of solar thermal absorber. The electrical efficiency

is around 10%, depending on type of photovoltaiccells used.

Examples of product developments and marketattempts are:• Millennium Electric commercially produces

an unglazed PVT module. Millennium hastaken over this production from Chromagen.

• PVTWINS is a spin-off from ECN, com-mercially producing glazed PVT collectors.This is a continuation of the work done byECN with ZEN Solar and Shell Solar, whotogether developed the PVT system at Re-newable Energy Systems in the UK (seewww.beaufortcourt.com).

• Batec & Racell carried out a PVT develop-ment project during 1998-2001, together with Esbensen, the DTI and Novator. How-ever, due to the collapse of the Danish market,Batec terminated its involvement. Racell con-tinued its involvement in PVT development.

• Solon is developing an unglazed PVT mod-ule for commercial manufacturing. This is acontinuation of the work previously carriedout by Solarwerk on glazed PVT modules.

• Solarwatt carried out a development project

on a PVT collector during 1996/1997. How-ever, problems occurred with the electricalinsulation and when the module failed theclimate tests, the intended demonstration project at Malteser Krankenhaus in Kamenzwas not carried out.

• Zenit manufactured a PVT prototype collec-tor in 1997, but commercial manufacturing

3. Present state of PVT market, certification and R&D


(a) (b) (c)

(d) (e) (f)

Figure 9. (a) Power roll by

Powerlight, (b) PVT

module by PVTWINS, (c)

PVT module by

Millennium Electric, (d)

PVT demonstration system

by ECN, Shell Solar and

ZEN Solar at RES (UK),

(e) PVT collector by

Solarwerk, (f) PVT collector

by Solarwatt.



24

was not carried out.

• Sollektor manufactured a PVT collector dur-ing 1999-2000. A collector was installed andis still running, but commercial production

was not started.• Dunasolar manufactured a PVT liquid col-

lector, but the development was ended whenthe factory was closed in 2005.

• SDA, Sunearth & Unisolar together carriedout a PVT project under PV BONUS during1997-2001, in which they tried to connect aUnisolar laminate to a Sunearth collector.Continuing problems with the flatness of theabsorber and the differences in tolerances be-tween PV and absorber technology stood inthe way of successful production.

• Powerlight The company Powerlight carriedout a PVT project under PV BONUS during1997-2003, in which they developed a PVTconsisting of a flexible Unisolar PV laminatelaminated to a flexible EPDM absorber. How-ever, delamination occurred and the decisionwas taken to postpone the commercial manu-facturing.

• ICEC developed and tested a PVT liquid col-lector in 1999, but this collector is not yetcommercially manufactured.

PVT Air collectors

Compared to the number of PVT Liquid Collec-tor types, only a few PVT Air Collectors have been developed and introduced to the market.However, the level of commercialisation is muchhigher.

Figure 10. (a) PVT air

collector of Grammer

Solar, (b) PVT collector of

Aidt Miljø, (c) Capthel

collector of Cythelia

(photo: Alain Ricaud),

(d) PVT air collector of

Conserval Engineering,

(e) Twinsolar collector

of Grammer Solar,

(f) Autonomous Solarwall

collector.

• Grammer Solar is commercially producinga PVT air collector, which has already beenapplied in a number of large demonstration projects. In addition, Grammer is producing

an air collector with a small amount of PVintegrated for autonomous cottage ventilation

• Conserval Engineering is producing a PVTair collector, in which PV laminates are con-nected on top of their perforated Solarwallmodules. The focus is on PV cooling wherebythe PV yield can be increased. A number of demonstration projects has been realised. Inaddition, also a solarwall air collector with asmall amount of PV is produced for autono-mous cottage ventilation.

• Aidt Miljø also produces an air collector witha small amount of PV for autonomous cot-tage ventilation.

• Cythelia has developed three prototype PVTair collectors, but commercial production wasnot started.


The systems belonging to the group of Venti-lated PV with Heat Recovery typically haveemerged from solutions for specific buildings,

where the primary focus has been building in-tegration of PV and where the need for venti-lation of the PV-systems in order to maximisethe electrical yield has been combined withutilisation of this heat for preheating of venti-lation air, space heating or similar.


(a) (b) (c)

(d) (e) (f)



25

Several projects have been carried out, such asthe Aerni factory (1991, Atlantis energy), theScheidegger building (1993, Atlantis energy),the Cottbus Umweltzentrum facade (1994), theMataro public library (1997, TFM), the multi-family buildings at Skovlunde (Lundebjerg) andCopenhagen (Sundevedsgade) (2000, Cenergia),the Yellow House in Ålborg (2000, Esbensen

Consulting), the eco-canteen of the Fiat research

centre (2003, Secco Sistemi) and recently theroof of the Imagina studio in Barcelona (2004,TFM) and the professional training centre inCasargo (2005, Secco Sistemi). Some of thesesystems use the PVT system only for preheatingof ventilation air (e.g. Imagina studios), whileothers boost the output temperature of the PVTsystem (e.g. by means of conventional solar col-lectors) to make it suitable for solar cooling (e.g.Mataro library).

Attempts have been made to standardise the char-acterization and design of such systems, such asin the European supported project PV-HYBRID-PAS. The Italian company Secco Sistemi is work-ing on a standardised system, together with thePolytechnical University of Milan. As a first application of their system, the CRF ECO-canteenwas realised (Aste, 2004).

PVT concentrators

As described in chapter 2, the PVT concentrat-

ing systems have been developed, based on theidea of using relatively cheap concentrating de-vices to concentrate sunlight on relative expensive

PV solar cells. To avoid too high temperatures,cooling is required. If this is done by active means,a PVT concentrator results. A problem may be thatthe active cooling has to be fail proof.The first commercial PVT concentrators are al-ready available. In the UK Heliodynamics hasdeveloped a commercially available PVT con-centrator, based upon tracking technology. InCanada, the company Menova Engineering

Inc. has developed a commercial PVT concen-trator. Finally, in Sweden, the company Arontis

Solar Solutions has started commercial produc-tion of PVT concentrators. In addition, the Swed-ish company Vattenfall Utveckling AB has de-veloped the MaReCo PVT collector and in thespring of 2004 has carried out a demonstration project of 30 m² of the MaReCo-hybrid inHammarby Sjöstad. However, the developmentat Vattenfall was ended and transferred to thecompany Priono AB, that is trying to commer-

cialise the product.

In Australia, a 300 m2 demonstration project is

carried out with the CHAPS PVT concentrator,a single axis tracking system with a concentra-tion of 37, providing electricity and hot water

Figure 11. (a) Scheidegger

building (Atlantis Energy),(b) Public library, Mataro

(TFM), (c) Imagina PVT air

roof, Barcelona (TFM), (d)

PVT air roof Centro

Ricerche Fiat, Orbassano

(Secco Sistemi), (e) PV air

roof Aerni factory (Atlantis

energy), (f) apartement

building Lundebjerg

(Cenergia, Photo Peder

Vejsig Pedersen).


(a) (b) (c)

(d) (e) (f)

P h o t o : J o e C o v e n t r y-A N U



26

for Bruce Hall, a residential college of the Aus-

tralian National University. The system con-sists of 8 troughs, each being 24 meters long.In the USA, the company Solar Focus is devel-oping the BiSolar PVT concentrator.

Finally, in Canada, Sunwatt was commercially producing the low-concentrating stationary PVTmodules HD100 and HD150 during 1981-1989.Although commercial production was stopped,Sunwatt continues to offer workshops in whichPVT devices are constructed and sold.

Present state of certification

From the market point of view, standardizationand certification of performance and reliabilityare essential requirements to achieve a success-ful market introduction in the building sector. Fur-thermore, reliable performance certification isoften mandatory in order to qualify for supportfrom national support programs, where the finan-cial support to the client is dependent on the effi-ciency of the systems.Performance certification is defined for either solar thermal systems (EN 12975) or for PV

Power systems (IEC 61215), but currently notfor combined systems, for which several addi-tional issues arise:

Performance tests

• The electrical performance affects the ther-mal performance. Therefore, it should beclear whether the characterisation of a PVTmodule should be with or without produc-tion of electricity

• A PVT collector is more sensitive to spectralvariations than a normal collector, resultingin problems with indoor measurements

Reliability• In glazed PVT collectors, the PV may be sub-

ject to substantially higher temperatures thanare prescribed for thermal cycling in the PVstandard IEC 61215.

• Due to the metal rear, short circuiting needsmore attention.

• It should become clear whether the PV testscan be carried out on laminate level, or should be carried out on PVT module level

The development of proper certification proce-dures for PVT would improve the competitive

position of PVT-systems in the market. There-fore, new developments in this field are veryimportant for successful commercialization of PVT systems in the future.Presently, as a part of the EU supported Coordi-nation Action PV-Catapult, a draft is made for a performance test for flat-plate PVT liquid mod-ules with crystalline silicon cells. In addition, adiscussion paper has been written on reliabilityissues for these modules. For more information,see www.pvtforum.org. It is foreseen that in thefuture, this will gain more official status and will

be extended to thin film cells, air type PVT andconcentrating PVT.

Figure 12. (a) MaReCo

PVT concentrator of

Vattenfall, photo: Bjorn

Karlsson, (b) PVT

concentrator of Heliodynamics, (c) PVT

concentrator of Solar

Focus, (d) PVT

concentrator of Arontis, (e)

CHAPS PVT concentrator

of the ANU, photo: Joe

Coventry, (f) Power-Spar

PVT concentrator of

Menova Engineering, (g)

PVT concentrator module

of Sunwatt, photo:

Richard Komp.


(a) (b) (c) (d)

(e) (f) (g)

An integrated

concentrating PVT air

collector was installed by

Sunwatt in 1987 and is

still running.

P h o t o : S un w a t t -Ri c h a r d K om p



27

Present state of R&D

R&D on PVT liquid modules started in the 1970'sand, with a dip during the 1980's, continued un-

til today. Most of the research is on thermal mod-ule efficiency optimization, and to a lesser ex-tent on systems studies and economical aspects,while the number of studies on reliability aspectsand optical optimisation is very small. Since2000, also a small number of life cycle assess-ment (LCA) studies has been carried out.

PVT liquid collectors

A number of PVT prototypes have been con-structed, such as a sheet-and-tube PVT collec-tors (De Vries, 1998), channel type PVT collec-tors (Zondag et al. 2003), PVT collectors with plastic absorbers (Sandnes, 2002), thermosyphonPVT collectors (Agarwal & Garg, 1994; Chowet al. 2005) and ICS PVT collectors (Krauter,2004). Glazed and unglazed PVT liquid collec-tors were compared by Tripanagnostopoulos etal. (2002). Often, the PVT prototypes were con-structed by the connection of a commercial PVlaminate to a commercial solar thermal collector A weak point often was the thermal resistance of

the connection, especially for unglazed collec-tors (the thermal insulation due to the glazingmakes the collector less sensitive to the heat re-sistance between the PV and the collector fluid).Often, the performance of unglazed collectorswas severely degraded due to this internal ther-mal resistance (Sudhakar and Sharon, 1994; Vander Ree, 1996).Glazed PVT collectors can produce high temperature heat directly, and are therefore suitable

for direct heating of tap water. Various systemsstudies on glazed PVT systems were carried out(Zondag, 2001). In addition, a study on the stag-nation temperature of a glazed PVT collector

was carried out by Zondag et al. (2002), whileLCA studies have been carried out by Frankl etal. (2000) and Tripanagnostopoulos et al. (2005).Unglazed PVT collectors have a lower outputtemperature and are therefore often combinedwith a heat pump in system studies (Ito et al.,2004; Bakker et al., 2005; Nishikawa et al.,1993; Gasner and Wen, 1982). However, the dependence of unglazed PVT on the market pen-etration of the heat pump may cause problemsfor the marketing of unglazed PVT.

PVT air collectors

Only a few studies have been carried out intoPVT air collectors, which is probably due to thelimited market share of solar air heating. Per-formance studies for single channel glazed andunglazed PVT air collectors were determined(Tripanagnostopoulos et al., 2002). Also LCAstudies have been carried out on these collec-tors (Tripanagnostopoulos et al, 2004). Compari-sons of single channel and dual channel PVT

air collectors were carried out by Sopian (1997)and Hegazy (2000).


In the 1990's, with the coming of PV facades,also the research into ventilated PV started. Thefocus here was on the thermal efficiency of thefacade, ranging from the simple statement of measured values to sophisticated flowsimulations and the establishment of effective cor-

relation functions for the heat transfer (Brinkworth, 2000; Sandberg and Mosfegh, 1998;Bazilian, 2001; Eicker, 2003) to module perform-



P h o t o : S ol on-B e r n d L i t z e n b ur g e r



28

ance studies (Bazilian et al., 2002; Strachan et al.,1997) and design methods (Infield et al, 2004).

A point of attention is the fact that the internalheat resistance is more critical than in the case

of liquid. Therefore, research has been carriedout to increase the heat transfer by means of finsetc (Tripanagnostopoulos, 2001). Literatureoverviews of heat transfer increase methods for PV-air modules are presented by Kelly (2000)and Hodge and Gibbons (2004).Systems studies are few. However, importantwork was carried out within the European project


PV-HYBRID-PAS, in which a number of exist-ing buildings were simulated with a hypotheti-cal PVT system (PV-HYBRID-PAS, 2000;Wouters et al, 1997). In addition, studies were

carried out for residential buildings in HongKong (Ji and Chow, 2003), for the Mataro library (Mei et al, 2003) and for the BrockshillEnvironment Centre (Cartmell et al., 2004).Studies on ventilated PV providing heat for so-lar cooling have also been carried out (Eicker et al., 2000; Butera et al., 2005). Because of the fact that the temperature level of the ven-tilated PV was too low for direct use in solar cooling, the temperature level needed to beincreased by conventional solar thermal air collectors or by a cogeneration plant. Eicker (2000) found that over the period of July-Sep-tember, the 225 m2 ventilated PV facade pro-vided 14% of the required heat, while the 300m2 ventilated PV roof provided about 35%. Theremaining 51% of the required heat was pro-vided by150 m2 of conventional air collectors.Adhikari (2004) found that the 160 m2 venti-lated PV façade could provide about 28% of the heat required in the CRF solar cooling sys-tem, while the remainder was provided by acogeneration plant.

PVT concentrators

The PVT yield could be increased by means of reflectors or even parabolic troughs. Studies have been carried out on the optimisation of the reflec-tor design (Brogren, 2003). In addition, modulestudies have been carried out, comparing a lowconcentration PVT with diffuse reflectors to con-ventional PVT (Tripanagnostopoulos, 2005).Also LCA studies have been carried out on these

collectors (Tripanagnostopoulos, 2005).Tracking modules were studied and developedat the Australian National University (parabolic trough with a concentration of 37) (Cov-entry, 2005) and at the University of Lleida(Fresnel mirror with a concentration of 11)(Rosell et al., 2005), while static concentrat-ing modules were developed for wall integra-tion at the Universities of Lund and Uppsala(asymmetric parabolic reflector with a concen-tration of 3) (Gajbert et al., 2003; Helgessonet al., 2004).

A CPC dual channel PVT-air collector with aconcentration factor of 1,85 was studied byOthman et al. (2005).

P h o t o : Ar on t i s - J o a k i mB y s t r om

I m a gi n a S t u d i o-T F M



29

Glazed/unglazed PVT

The effect of glazing on the efficiency curvewas measured by Tripanagnostopoulos et al.

(2002), for both air type and liquid type PVT.However, the glazing does not only affect the performance but also the stagnation tempera-ture. In case of unglazed PVT, the stagnationtemperature of the PVT module will be simi-lar to conventional PV temperatures and addi-tional problems do not arise. However, for glazed PVT, the stagnation temperature isstrongly increased by the glazing and can ex-ceed 120 °C. This may be critical to the en-capsulant, e.g. when EVA is used (Zondag etal., 2002; Affolter et al., 2000).

Type of PV-absorber

A small number of studies has been carried outinto the absorption of PV over the entire solar spectrum (and not just the part of the solar spec-trum that can be used to generate electricity). Thistopic is important in order to improve the ther-mal performance of the PVT (Affolter, 2000;Platz et al, 1997; Santbergen, 2005).In addition, the fact that the PV absorber is not

spectrally selective has a strong negative effecton the PVT performance. Some studies have ad-dressed the spectral selectivity of PV materialand TCO's, but since the PV needs to be pro-tected from moisture and is embedded in an en-capsulant, spectrally selective characteristics of the laminate top glazing seem more relevant.However, studies into the possibilities of spectrally selective glazing have not been pub-lished.

Conclusions

Many PVT developments have been started over the years and a few of these have now resulted

in commercial or near-commercial applications.• Most types of PV-thermal collector are by

now commercially available, ranging fromPVT liquid collectors, both glazed andunglazed, to PVT concentrators.

• Ventilated PV-systems are commerciallyavailable, but generally the design of thesesystems is not standardised and the designand installation is carried out by specialisedcompanies for specific buildings. However,this situation is changing since several insti-tutes and manufacturers have made an ef-fort to standardise these systems.

Standardization and certification of performanceand reliability are well defined for either solar thermal systems (EN 12975) or for PV systems(IEC 61215), but currently not for PVT systems.It is necessary for the commercialization of PVTto pay attention to the additional issues that arisein PVT systems, in comparison to separate PVand solar thermal systems. Initial steps in de-veloping dedicated PVT tests were taken within

the EU supported Coordination Action PV-Cata- pult.

With respect to PVT research, the scope is gen-erally very module efficiency oriented and veryfew studies on issues such as reliability are pub-lished.




30



31

The first three chapters of this roadmap serve asa general introduction of PVT from a theoretical

and a practical point of view. The last five chap-ters of the roadmap serve as an inventory of whatshould be done in PV-Thermal, resulting in anaction list. In order to set priorities for PVT, oneshould start with the commercial potential for PVT systems. Due to the large variations in prod-uct type, concepts, user demands etc. it is impor-tant to split the market in different segments inorder to understand the conditions, requirementsand potential for each of the segments. The iden-tification of promising markets then serves as a basis for the systems to be developed and theactions that should be carried out for this.The aim of the present chapter is to give this mar-ket overview, identifying interesting market seg-ments for PVT. In addition, future developmentsfor these segments wil be given and regional vari-ations will be indicated. Finally, an inventory of competing technologies will be made.

Principal segmentation of pre-sent potential PVT market

PVT is a combination of PV and solar thermal.It can therefore be expected that the combinedtechnique is mainly interesting for the marketsegments that solar thermal and PV have in com-mon. Therefore, the present analysis starts withan overview of market segmentation for solar thermal and PV.

Market segmentation for present solar-thermal market

The market development for solar thermal in the

EU is presented in figure 13. The European So-lar Thermal Industry Federation (ESTIF) indi-cates that in 2004, the EU presented 9% of the

solar thermal newly installed capacity, world-wide (the booming Chinese market accountingfor 78%, Israel and Turkey together for 8% andthe rest of the world for 5%).

For solar thermal, in 2003 the roadmap 'Sun inAction' has been developed by ESTIF. TheESTIF market segmentation is presented in Fig-ure 14. Note that only glazed collectors are takeninto account here, which mainly implies that themarket for outdoor pool heating is not taken intoaccount.

The largest market segment is here defined as

the residential sector, with 90% of the market.The remaining 10% consists of tertiary (8%),industrial (<1%) and other (<2%). The indus-trial thermal demand consists largely of hightemperature heat, for which PVT collectors areless suitable than for lower temperature appli-cations. It seems therefore logical to concentrateon the residential market, while tertiary appli-cations such as public pool heating may provideinteresting niche markets.It is of importance to map the tertiary sector fur-

ther in order to find interesting niche markets.As an example, the Dutch market is presentedhere, as analysed by Warmerdam (2003). In thisreport, an analysis of large solar thermal sys-tems is presented, subdivided into market seg-ments. In the tertiary market, the largest seg-ments are presented below:

• Public swimming pools (58% of tertiary,90% of which for pool heating)

• Campgrounds (15% of tertiary, of which35% for pool heating)

• Homes for the elderly (13% of tertiary)• Recreational and sports (5% of tertiary)

• Hotels (1% of tertiary)

Figure 14. Market

segmentation for solar

thermal (ESTIF roadmap -

sun in action).

4. Potential markets for PVT


Figure 13. Newly installed solar thermal capacity in

Europe. (Source: ESTIF).



32

• Other utility (8% of tertiary, of which 95%for tap water and 2% for cooling)

In addition, for industrial applications, the fol-lowing market segments were specified:

• Agricultural (66% of industrial, of which 60%for drying)

• Car wash (1% of industrial)

• Other industrial (33% of industrial, of which

97% process heat)

Market segmentation for present PV market

Until now, only the market for solar thermal has been analysed. However, since PVT is a combi-nation of PV and thermal, also the market for PVdeserves attention.

An overview of the PV-market is presented infigure 15. This figure displays two important points. The first is the large size and clear growth

of the PV market. The second is the fact that withrespect to the PV market, the largest market shareis given by grid connected distributed systems.

Although the exact distribution of PV systemsover the various market segments 'residential','tertiary' and 'industrial' (as defined previouslyfor solar-thermal) is not clear, it is clear that a

large proportion of this market is presented byresidential systems. Since this is also a sector that corresponds to the largest share of the solar thermal market, the combination of PV and so-lar thermal seems to have good opportunities.In addition, it is clear that a substantial part of the PV market is in autonomous applications.Since PVT would be very suitable for autono-mous use as well (PV driving the collector pumpor fan), it is worthwhile to explore the potentialof PVT for autonomous applications, which can be expected to be a small but profitable niche.Possibilities could be autonomous air heating sys-tems for off-grid cottages or desalination systems.

Changes in the market

Trends in solar thermal

In the near future, changes are expected, such asa growing share of multi-family buildings and agrowing share of solar heating. Especially thegrowing share of multi-family buildings may be

an interesting development for PV-Thermal,since the available roof area per household will be more limited for such applications, which isfavouring area efficient solutions such as PVT.In the longer future, it is to be expected that in-dustrial applications and solar cooling will be-come more important. Solar cooling may be spe-cifically interesting because it would open opportunities in the office market, that presentlyhas very limited application for solar heat. Astudy into the potential of solar thermal in the

Netherlands for the year 2010 was carried out by Ecofys (Warmerdam, Zegers and Voskens,2001). In this report, tap water heating and solar heating are seen as having the largest potential,of respectively 39% and 45% of the total poten-tial for solar thermal, followed by solar cooling(7% of total) and industrial heating (6%). Theother applications, such as drying (3%) and poolheating (0.2%) are much smaller.A detailed study has been carried out into theindustrial potential for solar thermal collectorsin the Netherlands (Van de Pol & Wattimena,

2001). This study indicated substantial savingsin energy demand for several industries. The larg-est savings were found in washing of clothes

Figure 15. Cumulative

installed PV power in the

reporting IEA countries4

by application (MW).

Source: IEA task 1 report

2002.

Figure 16. Main terrestrial

PV market segments

(source: EPIA Roadmap)


4Australia, Austria, Canada, Denmark, Finland, France, Germany, Israel, Italy, Japan, Korea, Mexico, the Netherlands, Norway, Portugal, Sweden,Switzerland, Spain, the UK and the USA.



33

(10% savings), vegetables and fruit (6%), meat(5%), textiles (4%) and breweries (3%). How-ever, the solar thermal potential in terms of col-lector area required does not so much depend on

the energy savings, as on the total energy demandof these industries, and more particularly on thesize of the industrial branch, which will vary fromcountry to country. Taking this into account, inthe Netherlands, the largest potentials in termsof potential industrial collector area are seen for dairy (24% of area), meat (17% of area), paper & cardboard (14% of area) and vegetables & fruit(10% of area). Possibly, this may present addi-tional opportunities for PV-Thermal. However,although industrial applications will becomemore important, their market share can be expected to remain very small as compared to thedominant domestic market.

Trends in PV

The share of grid connected distributed PV power shows a clear growth (Figure 15). Since thismarket coincides largely with the potential mar-ket for PVT, PVT could benefit from this devel-opment as well.Important in the longer run is the fact that PV

has shown a substantial and consistent decreasein price over the last decennia. It is to be expectedthat this trend will continue in the long run, al-though it might be temporarily halted due to the present shortage of feedstock material. In addi-tion, in a liberalised market, the utilities will in-creasingly charge their customers higher rates for periods of peak demand. As electricity produc-tion by PV is often in phase with demand peaks,this will support the growth of PV.In its roadmap, EPIA depicts a scenario in which

PV becomes competitive with conventional peak power in Spain in about 2010, while it will be-come competitive with bulk power around 2030(see Figure 17). This has two consequences:• Since PVT has a shorter economic payback

time than PV, PVT will be competitive even before PV.

• When PV becomes competitive, PV roofs will become the rule rather than the exception, andthe resulting 'battle on the roof' (not enougharea for PV and solar thermal next to eachother) will strongly increase the market for

PV-Thermal systems.

Trends in the residential sector

The energy performance of houses has shown acontinuous improvement since the late 1970's,due to increased levels of insulation and, morerecently, heat recovery from ventilation air. Dueto this effect, the heating demand for new houseshas been reduced strongly over the last decen-nia. Since the amount of heating is strongly re-duced and is shifted towards the heart of winter,

this reduces the possibilities for solar heating.However, for countries with sufficient irradianceduring the heating season, advanced houses mayoptimize their energy performance by using aventilation air heat-recovery system, with a cen-tral ventilation air inlet. In this case, we can eas-ily imagine that the ventilation system could beintegrated with a domestic air heating system,in which a PVT air collector could function as asolar heater and could prevent freezing of theheat recovery unit at the same time. If this col-

lector would e.g. be an integrated facade col-lector, it would contribute to the thermal insula-tion of the house as well.With respect to hot tap water, however, a slowincrease in per capita consumption can be ob-served, due to increasing comfort demands anddecreasing household size. This indicates a largefuture potential for domestic water heating, atask for which PVT liquid collectors are highlysuitable.In the building sector of the future it is very likelyto become mandatory to have a certain percent-

age of the total energy supply to be covered with building integrated solar solutions, which will provide a push for standardized solutions for the

Figure 17. Price

development of PV (source:

EPIA roadmap, RWE

Schott Solar).




34

built environment. A vision for the future of the building sector should include having roofs asactive solar elements, covering most of the en-ergy needs of the building, regardless its divi-

sion into heat and electricity needs. Whereas of-fice buildings might need more electricity, pri-vate houses generally use more low temperatureheat. In any case, the overproduction shouldmainly be converted into electricity since onlythis energy can be stored efficiently by feedingit into the electric grids.Another trend is the fact that, due to high instal-lation costs, the use of prefabricated elements isgrowing. In time, fully prefabricated roofs could become standard in which solar energy systemssuch as PVT are already integrated. This wouldstrongly reduce the amount of installation timeneeded. In order to facilitate this development,the standardization of PVT in terms of size andshape, corresponding to the conventional stand-ards in the building sector, is important.

Market differentiation

In the previous paragraphs, a general overviewof the PVT-market has been presented. However,it is to be expected that not all PVT systems are

suitable for all regions. It is therefore importantto obtain some overview of the differences be-tween regions.

Solar thermal

For solar thermal applications, large regional dif-ferences may occur, due to differences in climate,legislation and subsidies, as shown in figure 18.

• In Greece, 99% of the installed collector areais for domestic hot water production, whileabout 1% concerns large centralized solar sys-tems, mainly for tap water heating in hotels

(ESTIF roadmap, 2003).• In Israel, since 1980 an obligation exists for

the installation of solar DHW systems in allnew buildings below a height of 27 meters,with the exemption of hospitals and indus-trial buildings. This has lead to the presentsituation in which 85% of the households areusing a solar system. In Israel, residentialDHW systems account for about 50% of themarket (75% of which is replacement), whileindustry (16%), the public sector (14%) and power generation (12%) also have significantshares (ESTIF roadmap, 2003).

• In the USA 96% of the solar thermal heatingis pool heating. Also here, the residential mar-ket has a share of 90%, while the commer-cial market has another 9%. The share of tapwater heating is only 2% and is insignificantcompared to the level of fossil tap water heat-ing (ESTIF roadmap, 2003).

In general, the economy of PVT systems depends on local conditions, particularly with

respect to the cost of the fuel it replaces. Thisfuel may be either electricity (Greece), oil(Austria, Germany) or natural gas (the Nether-lands). This will influence the overall revenueand therefore the design and operation mode of a PVT collector.For the future, it can be expected that in SouthernEurope, a substantial potential exists for coolingapplications and solar thermal power systems.However, these applications still need further de-velopment. With respect to agricultural drying, the

potential will differ from country to country, depending on the agricultural production.

PV

With respect to the PV market, it can be seenfrom Figure 19 that the share of grid connectedversus autonomous systems varies greatly.


Figure 18. Installed solar

thermal capacity per

capita in 2004 (data from

Weiss, 2006).



35


POTENTIAL OF PVT MARKET IN SOUTHERN EUROPE

Greece: The existing thermal collectors are 3.5 million m² (2.5GWth) and regarding photovoltaics, the existing installed PV

power is about 3.5 MWp. The electric water heater is the main

competitor to the solar water heater and the main solar thermal

product is the thermosyphon water heater. The current annual so-

lar thermal market in Greece is about 200.000 m2 per year includ-

ing also hotels studios, etc. The systems are covered usually with

warranty of up to 5 years. The basic solar thermosyphonic system

is composed of a 1.8 to 4.0 m 2 collector area and a hot water stor-

age tank of 120 to 250 litres. Domestic water heaters are distrib-

uted mainly through the retailers or wholesalers. They are regarded

as standard (finished) products like fuel boilers, burners, heating

elements etc. The large systems are mostly installed by the manu-

facturers or through large distributors who have capacity to cover

the engineering needs of the project.

There are two main priorities in the energy policy in Greece: first

the completion of the basic infrastructure for natural gas and the

gradual penetration of the market by it and the second is the de-

regulation of electricity and natural gas market, which is expected

to be completed by 2006. Solar water heaters are contributing a

lot to the security of supply of electricity. Due to the extensive use

of electric air conditioners, the electricity network is working at

close to breakdown during several days in summer. The situation

is more critical in those islands whose electricity network is not

connected to the mainland network. It is estimated that the in-

stalled capacity for the generation of electrical energy would have

to be increased by approximately 10% if no solar water heaters

existed.Considering the wider application of solar energy systems and the

target for 2010 with the penetration of PVT systems, we estimate

that many of them could be installed on existing buildings replac-

ing the old thermosyphonic systems. Considering the existing col-

lector surface area, a 10% replacement of it with PVT systems

could result to a 15-25 MWp additional installed power respec-

tively, provided that the PV subsidy is extended also to small do-

mestic systems, which is presently not the case.

Cyprus: The contribution of solar energy to the total energy con-

sumption in Cyprus is 4.5%. This energy is used mainly in the

domestic sector (93.5%) for hot water production. There is one

solar water heater for every 3.7 persons in the island, which is a

world record. Typical solar water heaters in Cyprus are of the

thermosyphon type and consist of two flat-plate solar collectors

having an absorber area between 3 to 4 m2, a storage tank with

capacity between 150 to 180 litres and a cold water storage tank,

all installed on a suitable frame. The estimated collector area in-

stalled up today including central systems in hotels and hotel apart-

ments is about 560.000 m2 (0.4 GWth) out of which 540.000 m2

are installed in houses and flats. The average quality of solar wa-

ter heating systems is acceptable and the solar water heater in

Cyprus enjoys a very good reputation. The industry of solar wa-

ter heaters expanded very quickly and today reaches an annual

production of about 30.000 m2 of collectors (about 30 manufac-

turers). Applications of photovoltaics in Cyprus are very limited.

The people are very familiar with solar energy systems and this

makes easier the replacement of the old thermosyphonic systems

with PVT. Apart from the thermosyphonic PVT units, the air-cooled PVT systems are less useful for application in Cyprus, as

it is also for Greece, because space heating in buildings is neces-

sary only 4-5 months annually. PVT water heating systems can

be considered a viable solution as they can effectively combine

the electricity production with water all year and space heating

during winter. The feed-in subsidy of 0.20 €/kWh is very promis-

ing for the PVT system owners, as this amount is very attractive

considering the current price of the grid-electricity (0.12 €/kWh).

In addition, the contribution of the PV produced electricity would

be helpful for the economy of the country, as in this way a signifi-

cant amount of imported oil for the electrical power stations can

be avoided. Considering an initial replacement of 10% of the old

thermosyphonic units by the new PVT systems, an amount of about

3 to 5 MWp, depending on the PV module type, will be intro-

duced in the electricity grid of the island.

In particular, it can be seen that countries likeGermany, Japan, the Netherlands, Denmark, theUK, Austria and Switzerland have a share of over 80% grid connected systems, while other coun-

tries, such as Mexico, Norway, Canada, Israel,Finland, Sweden, Australia, France and Portu-gal have shares of over 80% off-grid systems.Obviously, although grid connected has the larg-est market share, for a number of countries off-grid applications may also present an interestingmarket. Since autonomous systems are likely to be more cost effective than grid connected applications, it may be relevant to pay specific at-

Figure 19. Installed PV

power in the reporting IEA

countries by application

(%) in 2002. Source: IEA

task 1 report 2002.



36

tention to autonomous applications in the fieldsof residential, recreational, agricultural, des-alination, etc. as an interesting niche market.

Subsidy schemes

For regions not connected to the grid, PV can be cost effective already, replacing a dieselgenerator or avoiding long supply lines or ca- bles. However, PVT is dedica ted mainly to buildings (because of the thermal yield) andhas therefore to focus on regions with electric-ity supply. In regions with electric grid con-nection, PV systems are nowadays mainly notcost effective without subsidies. For pushingPV - as it is one of the most promising elec-tricity sources for the future – many cities, re-gions and federal authorities have introducedsupport schemes, based on grants or on the veryeffective feed-in-tariff system. Incentives ex-ist in Europe and Japan, but also in most of theUSA and many other countries worldwide. Theglobal PV development, which shows an an-nual increase of more than 30%, dependsstrongly on these incentives.Although the cost effectiveness of solar ther-mal systems is much better, they also mostly

need subsidies as incentives for customers tofavour solar instead of conventional heatingsystems.Because of this, it is important to make an in-ventory of subsidy schemes in order to assesshow these will work out for PVT.

PV subsidies

PV subsidies may be along two lines:

1. Output related grants. Over Europe, there

seems to be a general trend towards feed-in tariffs. In general, such subsidies would be suitable for PVT systems as well. Incountries with high feed-in tariffs, however,it is economic to optimise the generationof electricity as far as possible, which pro-motes unglazed PVT systems in which thePV efficiency is increased at the expense of thermal efficiency.

2. Fixed grants. In regions where there is no sub-sidy or only grants for PV installations, thevalue of PV reflects only the electricity price

if the electric energy can be directly used inthe house. Assuming that the subsidy is only based on the nominal power of the laminate,

it may well be the case that the electricaloptimisation of the system becomes less important and that the focus will shift to the ther-mal performance of the system.

Solar thermal subsidies

Solar thermal subsidies may also be along twolines:

1. Output related grants. Generally, output re-lated grants are presently not used for so-lar thermal, since the owner of the systemdoes not deliver energy to anyone else.However, it can be expected that in the fu-ture, such grants will be introduced alongwith a permanent control on the yield, be-cause it is a way to ensure that the owner of the system feels responsible for the func-tioning of the system. This development isreinforced by the expectation that in the fu-ture, large professional customers (e.g.housing associations) may only want toinstall systems with a guaranteed annualyield. In Germany, there are initiatives for a "solar-thermal feed-in law". For PVT,such a development would be very inter-esting, since a grant based on the real out-

put of the system would make PVT less dependent on the threshold conditions thatmay be attached to fixed grants (see below).As in the case of PV, the additional cost of monitoring may promote larger installa-tions, which may favor centralized instal-lations e.g. for high-rise buildings.

2. Fixed grants. This grant may be applicable per area installed. However, such a schemefavors large areas of low-cost low-effi-ciency collectors (which may favor large

areas of unglazed PVT). However, in or-der to stimulate technological developmentof thermal collectors, other subsidy systemsexist that set a periodically increasing mini-mum threshold for the thermal efficiency,which should be met in order to qualify for the subsidy (e.g. in Germany). However,the threshold level is based on the perform-ance of good solar thermal collectors. Sincethe thermal efficiency of PVT is lower thanthat of solar thermal collectors (among oth-ers because of the simultaneous production

of electricity), such a scheme generally implies that PVT does not qualify for the so-lar thermal support.




37

From this discussion it can be derived that thesubsidy scheme might influence the design andoperation mode of a PVT collector.

Competitors for PVT systems

The broad definition of what is a competitor toPVT depends on the choice that a customer hasto make (shall I reach my prescribed energy rat-ing through a PVT or through an energy recov-ery unit?, shall I make a PVT facade or would amarble facade be more attractive?, shall I havePVT on my roof or just buy green electricity?).However, although these are very realisticchoices, such a broad definition of 'competitor'is not feasible here and a narrow definition will be used of an apparatus that also generates fullyrenewable power and heat. This gives the fol-lowing competitors:

• PV and solar thermal side-by-side. These products have been on the market muchlonger and presently have a clear advantagein terms of market size and associated lower production costs. Typical products are tradi-tional solar thermal collectors, photovoltaic power systems and trombe walls. Side-by-

side systems of solar thermal and photovoltaicsystems are likely to become the direct competitor to PVT Systems. It can be expectedthat more and more installation and mount-ing systems will be developed combiningsolar thermal and photovoltaic power systemswith roofing and facade systems respectively.For larger building integrated systems, a highflexibility can be expected towards combin-ing various sizes of solar thermal panels withvarious sizes of photovoltaic panels, thus pro-

viding the option to change the thermal toelectrical power ratio. For the more advancedsystems easy cabling and connections will bedeveloped as integrated part of the mountingsystems. In order to keep up with this com- petition, it is important that enough attentionis paid to the flexibility and ease of installa-tion of PVT systems.

• Biomass and PV or TPV domestic cogene-

ration plants. A biomass and TPV plantwould be fully independent of the amount of irradiance, which would make it a very reli-

able system for all-year use. However, TPVis still firmly within the R&D area. An alter-native would be to combine PV and biomass,

with the additional benefit of a certain levelof complementary use. The main disadvan-tage of biomass is the more difficult transport and operation. Since comfort (includ-ing ease of operation) is of major concernfor most consumers, this option will mostlikely be a competitor for autonomous sys-tems only. Autonomous PVT systems maythen be more appropriate for applications depending on summer use or sunny areas,whereas biomass & TPV systems may be

more appropriate for winter use in areas withlow irradiation.

• Heat pump combined with PV or green

electricity. For a well-insulated house, a PVroof will provide sufficient electrical energyto run a heat pump that provides the full heat-ing of the house. This may be more economi-cal than a PVT tap water and space heatingsystem, especially if PV prices continue todecline or if the cost of green electricity isfurther reduced. In Switzerland for example,

a 200 m

2

family house corresponding to thestandardized label “Minergie” can be heatedup with a burner power of only 4kW or less,with annual oil or equivalent consumptionof about 800 liters. For such low energy buildings, it is becoming more and more easyto cover 100% of the heat with a heat pump.This is a popular option in Switzerland,where 60% of the electricity consists of hydropower. This has some implications for PVT, since a heat pump needs an energysource:

− Energy roofs are now coming on the mar-ket, that function as the source for a heat


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Table 7. Main niche

markets for the short,

medium and long term.

niche markets

short term collective tap water systems for campgrounds, sports, homes for the elderly, hospitalsand hotels, pool heating for (public) swimming pools, autonomous systems

medium term space heating systems and solar cooling systems for the commercial sector

long term niche markets in industry, e.g. clothes washing or processing of agricultural productssolar drying systems and greenhouse heating systems for agriculture


pump. If such roofs would be covered withPV, an unglazed PVT collector would re-sult in which the cells are very effectivelycooled. A point of attention is the amountof storage that is required for the match-ing of the solar input and the demand.

− Earth coupled heat pumps may decline in performance if the soil freezes, a condi-tion that may occur if a sufficiently largecluster of houses is using heat pumps. Alsoregulations may prohibit the net extrac-tion of heat from the soil. Unglazed PVTwould be a very interesting option for re-generating the soil, with the additional benefit of doing part of the tap water heat-ing, thereby reducing the electrical de-mand of the heat pump.

Heat pumps are particularly suitable for spaceheating, but less so for tap water heating. Inaddition, heat pumps also provide the possibility for cooling. Therefore, this developmentis a very good candidate for office applica-tions, and in the long run could replace largesolar thermal space heating systems. Also

solar cooling could in the long run be replacedwith an electrical heat pump driven by PV.For hot tap water applications, however, so-lar thermal can be expected to remain the bestoption.

Conclusion

In this chapter, an inventory has been madefor the most promising markets for PVT. It wasseen that the largest market is in domestic applications. Given the continuing efforts for reducing the energy demand in the residentialsector, this market is expected to grow sub-stantially over the decades to come. For thefuture, it can be expected that the share of multi-family houses will increase and that so-lar space heating will become increasingly

important.Apart from the domestic market, several nichemarkets exist, as represented in Table 7. How-ever, it should be kept in mind that these nichemarkets are much smaller than the domestic mar-ket, which should be the main target for PVT.



39

In the previous chapter, an overview was givenof the potential of the markets that could be in-

teresting for PVT. However, PVT will not auto-matically gain access to these markets. It is important to keep in mind that only a minority of the customers are technology lovers or engineers.It is not the cleverness of the PVT concept thatwill be the main driver but only the induced gainsoffered by this technology. The perception of which are the main gains of PVT will differ for the different groups involved.Therefore, it is important to ask what is requiredof PVT to qualify for the different market seg-ments. What are the bottlenecks to the introduc-tion of PVT on these markets and how can these be addressed? What are the perceived benefitsand how can these be optimised?This chapter will give a detailed overview of thedifferent actors relevant for the markets indicatedin the previous chapter, and show which driversand barriers are especially relevant for them.

Decision processes

In chapter 4, a number of markets were identi-

fied as interesting for PVT. The main market wasseen in systems for the domestic market, for which the increasing importance of solar heat-ing and multi-family buildings was indicated. Niche markets were identified for the short termin collective tap water systems (e.g. for sports

and hotels), pool heating for (public) swimming pools and autonomous systems, for the medium

term in space heating systems and solar coolingsystems for the commercial sector and for thelong term in solar drying systems and green-house heating systems for agriculture and nichemarkets in industry.

For each market defined in chapter 4, the deci-sion making process to install PVT technologywill be analyzed below. Within the decision process, the following groups should be ad-dressed:

• The decision maker

• The suppliers• The influencers

The decision maker may be a homeowner, ahousing corporation, a company, a real estatedeveloper etc. Suppliers can be the manufacturer (a PV or a solar thermal company), the installer,an engineering company or an energy companyacting as an intermediary. Influencers can be of several types such as the installer (again), the

architect, the municipality, a financing organi-sation or the national government. All these ac-tors have their own drivers and barriers for theimplementation of PVT. An overview is pre-sented in Table 8.

Table 8. Decision chains

for PVT

type of market market decision maker influencer supplier

size

domestic single family house •••• home owner, housing association, instal lat ion solar thermal

real estate developer company manufacturer

private pool heating • home ownerautonomous • home owner energy company PV manufacturer

recreational

multi family house ••• real estate developer, home owners municipality PVT assembler

association, housing associationarchitect

services hotel • hotel owner,

recreational company national installation

real estate company government company

office • real estate developer,

real estate company, commercial energy

municipality, company bank company

campground • campground owner

public pool heating •• municipality, recreational company consumers building

home for the elderly/ • municipality, foundation organisation company

hospital

sports facility • municipality, sports associat ion farmersindustrial car wash/laundrette • company organisation

agricultural drying barn, stables • farmer

5. Drivers and barriers in the market




40

Actors and their drivers & bar-riers

This paragraph presents a list of the relevant ac-

tors with their respective interests. They are dis- patched in the three categories: decision makers,influencers and suppliers. It was tried to answer the following questions:

• Why would these people want PVT or not?

• What is restraining them or pushing them on-wards?

Decision makers

Homeowners: domestic applications

A large number of renewable energy installationsis commissioned by homeowners that want tohave solar energy systems on their own houses.This is typically an existing home. The PV may be commissioned any time, while a solar ther-mal installation is typically commissioned at thetime of renewal of the central heating boiler.In countries with high feed-in tariffs, PV has be-come a profitable investment, which motivateshomeowners into the commissioning of large PV-systems. For such large PV-systems, the result-

ing battle-on-the roof between PV and solar ther-mal presents a good marketing argument for PVT.However, also in areas where no high feed-intariffs exist, PVT may be interesting for home-owners. For a private homeowner, energy priceis not the unique criterion for making the deci-sion, but also other factors are of importance,such as lifestyle, image and perceived benefits,as well as the effort required of him in terms of preliminary work for application, installation andmaintenance. An important issue at this time is

to have energy delivery at a ‘solar price’, that isnot sensitive to conventional commercial fuels.A private owner considers the whole budgetrather than the specific energy price. In this approach, the fact to have more area than a stand-ard solar collector system could even be an ad-vantage, since more roof area will be coveredwith solar roofing elements. The commercialis-ing of PVT systems will be assisted by creatingadd-ons on the system that motivate the consum-ers to choose for the system for other reasonsthan price only.

Aesthetics, uniformity, functionality, life duration,roof protection, water tightness, ethics, autonomyand prestige are a number of non economical top-

ics that can help a homeowner to take the deci-sion to invest in solar energy. For PVT systems,the arguments are the same, but PVT will presenta different offer that will be interesting to people interested in advanced technologies, as wellas people having a more limited roof area.Other important topics are the reliability of thesystem and the ease of handling and maintenance.The required maintenance should be minimal,the reliability should be very good and thereshould be good after-sales services to solve prob-lems as quickly as possible.In addition, PVT could be interesting to decrease

the dependence of consumers on weak electric-ity grids. Although the availability of the elec-tricity supply in Europe is mainly very good, thisfeature may be interesting for remote Europeanregions or in other parts of the world with weak grids. And even in areas with a highly reliablegrid, homeowners will still feel pride in beingless dependent on the public grid, which may bea sales argument for PVT.

Homeowners: private pool heating

People having a pool can increase the utilisationseason of the pool by means of a heating sys-tem. Since pool owners are only a small fractionof the larger group of homeowners, we assumethat this option doesn’t represent a large market. Nevertheless, pool heating may be an interest-ing niche market that in some countries, such asthe USA, has a substantial size.Among pool owners, the use of pool collectorsis very popular and the decision to use a solar pool collector is primarily economic. For private pool heating, people are ready to invest an

amount corresponding to the heat expenses for heating up the pool during 1 to 3 years, i.e. be-tween 3000 and 6000 EUR. This application is


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very popular since it needs a small investmentand offers a short payback time.A user wanting to invest in a photovoltaic systemwill have the possibility to choose for PVT, al-

lowing him to gain heat for increasing the seasonof the pool. If the PVT system heat output is dedi-cated to pool heating, the cost of the PVT heatingcomponent (the difference between the cost of thePVT and a standard PV installation) should notovercome the approximate price of standard poolsolar thermal system. For a 50 m2 pool, one hasabout 3000 EUR over cost, i.e. 60 EUR/m2 for theturnkey thermal system connected to a PV sys-tem. This is quite low but the price should be inthis range in order to ensure success.An interesting optimization can be found if onePVT collector system is installed for both poolheating and tap water heating. This system will be a standardized domestic hot water PVT sys-tem not only dedicated to the pool.

Homeowners: autonomous applications

A small subgroup of homeowners may be inter-ested in PVT systems for autonomous applica-tions, such as tap water heating or room heatingfor off-grid cottages, or applications in mobilehomes. In addition, water desalination systems

may be of interest in island applications or inarid near-sea areas, both for single-family andcollective use. In general, these systems will besmaller than conventional domestic systems. For autonomous applications, the issue of econom-ics is reduced. In addition, for mobile applica-tions or small portable systems, the lifetime may be less critical than for domestic application. Atthe other hand, issues such as easy installationand maintenance may become more important.

Housing association

Housing associations are responsible for a sub-stantial part of the building stock and realise large building and renovation projects. Originally,

many housing associations were semi-govern-mental, but a large privatisation development hastaken place. Nevertheless, many housing asso-ciations are still motivated to integrate solar en-

ergy into their building and renovation projects.For these companies, PVT could be a very in-teresting option, because of the possibility to re-alise “two-in-one” with the associated reductionof project management and planning required,due to the fact that one company is responsiblefor both PV and thermal, and because of the pro-motional aspect of PVT, due to the fact that it isa new and attractive technology.Furthermore, the stock of housing associationsconsists largely of multi-family buildings, for which PVT may be especially suitable due tothe limited roof area available, which providesinsufficient area for side-by-side systems. Thereare opportunities for large-scale newly builthousing projects, but the reconstructions, be-cause of the high potential, should be not for-gotten. The occupants profit from the solar gainswhile the housing association has to pay the in-vestments but does not profit directly from thelower energy bills. Therefore, an issue for hous-ing associations is the question to what extentthey can compensate the investments by an in-

crease in the rent, which is often legally boundto certain limits. If the installation of a solar en-ergy system is part of a large-scale renovation,this may increase the possibilities. In addition,other business models may circumvent this prob-lem. As an example, the housing associationowning the PVT system may sell the electricaland thermal yield to the energy company, thatsells the heat back to the occupants in the formof supplying it to the collective heating system,while the electricity may be sold elsewhere as

green electricity. In this case, the occupant doesnot experience an increase in rent, but also not adecrease in energy costs. Another possibilitywould be that the housing association just leasesroof area to the energy company, while the en-ergy company remains the owner of the PVTsystem.

Municipality

The municipality owns buildings, that it canchoose to upgrade with solar technology. These buildings may be offices, but also municipal

swimming pools or school buildings.The motivation for such plans may be the pro-filing of the municipality, possibly in combina-





42

tion with the fulfilment of obligations to the na-tional government. In addition, the municipalitymay want to invest in demonstration installationsfor motivating private people and organisationsto install solar energy systems themselves. Inthese cases, the choice for PVT would have theadvantages of providing a high profile solar tech-nology, a single warranty responsible and a re-duction of project management and planning re-quired in comparison to installing PV and solar thermal separately.

Real estate developer

A real estate developer may have an independ-ent motivation for the installation of solar en-ergy systems, for different reasons:

• because he is obliged to fulfil certain build-

ing energy performance criteria as stipulated by the national government and/or municipal authorities and can do this cost effectivelywith solar energy systems.

• because he expects it will help the sale of thehouse: at a time of oil price increase combined with an increasing sensitivity to envi-ronmental problems, to offer a turn key housewith an integrated solar system is a way of

promoting a house. This effect is even more prominent in the case of high feed-in tariffs.

• because he wants to profile himself with agreen image.

In that case, the PVT application can be a goodway of integrating solar energy in the building project. In the case of a building company offer-ing a standardized PVT system, the advantagefor the PVT supplier is to be without competitor.This approach is at the same time cheaper (PVTsystems purchased / produced in bulk, lower in-stallation costs for a large number of systems).Combined with other (renovation) measures onthe roof and of the installations, the costs can beeven lower. The advantage for the real estate de-veloper is to have a single warranty responsibleand a reduction of project management and plan-ning required in comparison to installing PV andsolar thermal separately.

Real estate company

A real estate company owns e.g. office build-ings that are rented to companies. Most real es-tate companies are purely commercial, but notall of them (e.g. governmental buildings are usu-ally owned by a governmental real estate com-

pany). In addition, funding companies, such as a pension fund, may have a large participation ina real estate company, and may not have exclu-sively commercial aims (e.g. green funds).For very commercial real estate companies, theremay be limited interest in the independent com-missioning of solar energy applications. How-ever, less commercial real estate companies (gov-ernmental real estate company, green funds) mayhave targets for realising a certain percentage of solar. For these companies, PVT could be a very

interesting option, because of the possibility torealise “two-in-one” with the associated reduc-tion of project management and planning re-quired, due to the fact that one company is re-sponsible for both PV and thermal, and becauseof the promotional aspect of PVT, as it is a newand attractive technology. Similar to the case of housing associations, real estate companies donot profit themselves from a reduction of theenergy bill; in principle the profit goes to thecompanies renting the building. However, alsohere, other business models may remedy this situ-

ation (e.g. the real estate company selling theyield to an energy company, that sells it back tothe occupant). Finally, it should be stated that in


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43

the case of sufficiently high feed-in tariffs, PV becomes profitable which can be expected tochange the position of the very commerciallyoriented real estate companies radically. PVT

could profit from this, especially if also a feed-in tariff for heat is introduced.

Hospitals and homes for the elderly

Hospitals and homes for the elderly are oftenowned by foundations. These may be motivatedto use solar energy, to save on water heating costs.Since hospitals not only have a large hot water demand but a substantial continuous electricitydemand as well, PVT may be an interesting op-tion. A strong point of PVT may be the 'two-in-one' effect of PVT, reducing the administrative burden and having a single warranty responsible. Finally, hospitals require back up systemsin case of breakdown of the electricity supply.Part of this backup capacity could in principle be in the form of PVT.

Owners of public pools, sports facilities,

hotels and campgrounds

The owners of public pools, hotels, sport facili-ties and campgrounds can be of different types.• Public pools may be owned directly by the

municipality. In that case, the municipalityhas the primary decision to install a solar energy system on the building. For possiblemotivation of the municipality, see the cor-responding paragraph above.

• Hotels may be owned by real estate compa-nies and rented to an entrepreneur or recrea-tional company (see real estate company)

• Public pools and hotels may be owned bycommercial companies, such as large recrea-tional companies

•

Campgrounds and hotels may be owned by private persons.

• Public sports facilities may be owned by themunicipality, a commercial entrepreneur or a sports association.

• Non-public sports facilities may be owned bycommercial or non-profit companies.

Since the motivation of municipality and real es-tate companies for the installation of solar en-ergy was already presented above, it will not re- peated here.

For recreational companies and private persons,the aim will be threefold: the economical return,the increased comfort level and the public im-

age. Especially the larger companies may bevery interested in highly visible solar energytechniques as a means to promote themselves.It should be mentioned here that for outdoor

pools, presently low-cost plastic absorbers areused. It will be difficult to compete with theseabsorbers, especially since the lifetime of thePV may not be compromised. For indoor pools,however, glazed collectors are used, which maygive better possibilities for PVT.

Industry

For the industrial market, the final energy costwill be of paramount importance. If there arelegal conditions making solar energy profitable,industries with funding possibilities may investinto PVT systems as a way of reducing tax on

profits. Without interesting financial conditions,only industries that want to promote themselveswith a green image and/or have an official andtrue willingness to cover their needs with re-newable energies will consider PVT technologysolutions.For this reason, the challenge for the PVT sys-tem is to achieve maximum thermal and electri-cal efficiency, with heat at high temperature leveland this at minimized cost. For higher tempera-ture levels, a PVT concentration system seemsthe most appropriate type of PVT module. How-

ever, it is to be expected that this will be a smalland - due to the high temperature levels - tech-nically difficult market for PVT systems.


A u s t r i a S ol a r & S onn e nk r a f t B e t r

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Farmer

Depending on their field of activity, farmers needa lot of hot air, hot water and electricity.

• Hot air may be needed for crop drying or manure drying

• Hot water may be needed for preparingwarmed milk for young pigs or calves, floor heating of stables on heating of greenhouses

They will primarily install solar energy systemsfor economic reasons, and the issue of a shorter payback time will be more important than theheight of the initial investment required. Theymay have enough skills and time available (e.g.during winter season) to do solar installationsthemselves. For all these reasons, farmers willlook for a quality product easy to mount.If there are legal conditions making solar energy profitable, PVT is for this reason an interesting proposition for them. However, if a specific sup-

port scheme is not available, PV itself may inmost cases not be able to compete with wind tur- bines. In that case, the use of PVT becomes lessinteresting.In the cases in which PV is an interesting option,it may be difficult for PVT systems to competewith separate PV and solar thermal systems; thereoften is no space constraint and, in addition, thecollectors presently used for agricultural drying purposes are very cheap, low-tech collectors;since the PVT-air systems only replace low-costcollectors, the economic margin is small and it is

not yet clear if PVT-air collectors could success-fully compete. Nevertheless, a modest nichemarket may be present here, e.g. for off-grid dry-

ing purposes, where the PV may be used to drivethe fan. An asset may then be the cooling of thePV, which increases the PV efficiency.

Energy companyFor energy companies, renewable energy is ahigh profile new market. In the liberalised en-ergy market, energy companies may look for ways to promote themselves and to provide ad-ditional services. Solar energy may provide in-teresting opportunities for this.Due to the fact that PVT is a high profile greentechnology, PVT is expected to be an interestingtechnique for energy distribution companies.These companies may then commission PVTsystems and deliver the solar energy to the cus-tomers. Energy companies therefore are inter-esting partners in the development of PVT, sincethey can afford to start new products and are in-terested in diversifying their market.Finally, energy companies prefer to diminish peaks in electricity demand. The electricity pro-duction costs for an energy company are for amajor part determined by the peak electricity de-mand of the customers. This asks for a form of demand side management in which the energycompany invests at the site of the customer to

reduce the peak load of the whole system. Incountries with a hot climate, the peak in the elec-tricity consumption is during the summer, dueto the airconditioning load. PVT has a doubleeffect in peak reduction, since the PV part pro-duces electricity, whereas the thermal part can produce solar cooling or hot water (which low-ers the electrical demand in countries with elec-trical water heating). The solar cooling optionwill be appropriate for professional buildingssuch as offices and schools, which have a cool-

ing demand during the day, while the hot water option may be more appropriate for domestic application (people taking a shower in the eveningafter coming home from work).Energy companies may be interested to promotethe installation of PVT systems in order to re-duce the total investment in the whole electric-ity production, transportation and consumptionchain. Since in most countries energy companiesare now active in a liberated market and there-fore do not consider the whole chain as their re-sponsibility, it will take some steering action

from the general governments to help the energycompanies in this direction.




45

Influencers

National government

The government is highly motivated to promote

solar energy, on the basis of the Kyoto agree-ments and the related EU targets to which thegovernment has committed itself. PVT technol-ogy can play a large role in achieving the Euro- pean long-term goals for renewable energysources. Initial estimates indicate for a PVT mod-ule a cost reduction of roughly 10% as comparedto a combination of the separate modules. TheEuropean targets for PV and solar thermal for 2010 are 3 GWp and 100 million m2 (= 70 GWpthermal), respectively. If the complete power of 3 GWp would be realised by installing 30 mil-lion m2 of PVT, 30 million m2 (= 21 GWp ther-mal) of solar thermal would be installed simul-taneously. With the aforementioned potentialsavings for PVT, the large-scale introduction of PVT in Europe can generate a cost reduction of roughly 3 Billion Euros on a European scale.Therefore, it is to be expected that governmentswill actively support PVT.The national governments have a very large in-fluence on the promotion of solar energy throughvarious means:

• The government may issue direct and indi-rect subsidies for different groups such ashomeowners and companies for the imple-mentation of renewable energy.

• The government may influence different eco-nomical sectors by specific regulations.

− Building sector: In many countries, thenational government has set energy per-formance criteria to which new buildingshave to comply. Until now, not all energy

performance criteria also include the con-tribution of renewable energy. However,this will change since the European Par-liament has accepted the Energy Perform-ance Building Directive (EPBD), pre-scribing that the general framework for the calculation of energy performance of buildings has to take into account activesolar systems and other heating and elec-tricity systems based on renewable energysources. Member States have to bring intoforce the regulations necessary to com-

ply with this directive at the latest on 4January 2006.

− Energy companies: The clearest example

in which the national government can actas an influencer through the energy companies is the establishment of the feed-in tariff (e.g. as in Germany), which

obliges energy companies to purchaserenewable energy in its service area andfixes the price at which this energy is to be purchased. However, also other meth-ods have been used. As an example, inthe Netherlands, during the 1990’s anagreement existed on solar energy imple-mentation between the Dutch govern-ment and the Energy distribution companies, resulting in a situation in whichthe energy companies actively subsidisedsolar water heaters and were involved ina substantial share of the new installa-tions of solar water heaters, either byrenting solar heaters or by mediating inthe sale.

As indicated before, care should be taken thatthe requirements for these subsidies or specificdetails in the legislation do not inadvertently ruleout PVT systems.

Municipality

Often, there are targets on the municipal level

for solar energy, originating from the nationalgovernment or from municipal policy. Typically,the municipality gives out plots to real estatedevelopers, to which targets for solar energy areconnected. In order to qualify for the bidding,the real estate developer has to make a plan inwhich the prescribed contribution of solar en-ergy is realised. In this way, large new city dis-tricts may be realised with a substantial solar contribution. In general, customers are ready to pay a bit more for the house (mortgage), if they

decide to buy the house anyway, so this is a veryefficient way of promoting solar energy.Municipalities act also as influencer throughregulations about constructions. These regula-tions and the associated procedures are crucialsince they define the possibilities to build or modify buildings and the effort this takes. Atthe moment, in some locations, it may still bequite difficult to modify building aspects sincethe local regulations tend to be very conserva-tive, imposing barriers to new technologies or unconventional materials. From this point of

view, PVT technology gives a unique selling proposition for a combined solar system withuniform aspect on the roof. Possibly, munici-




46

palities could consider offering simplified pro-cedures for specific solar systems like PVT (evenwith big surface).At the other hand, municipalities may offer sub-

sidies for solar energy that motivate consumersto install solar energy systems. Care should betaken that the requirements for these subsidiesdo not inadvertently rule out PVT systems.As argued also in the previous paragraph, for municipalities, PVT may be an interesting andhigh-profile possibility of realising their own tar-gets with respect to the implementation of renew-able energy.

Financial sector

Renewable energy systems typically need highinvestments and long payback times. For thisreason, financing is a crucial issue for estab-lishing projects. It is important to generateways of low interest funding.Furthermore, there is no primary reason why acommercial bank would be interested in such ac-tivity, unless it would for them be a means to sellother financial products as well. It may be inter-esting for banks to facilitate constructions suchas a solar energy system being part of the mort-gage. There is no reason why a commercial bank

would prefer standard solar systems over PVTsystems, so PVT may be an interesting optionfor the future enlargement of their market.Furthermore, a number of banks have startedgreen funds, for which more relaxed criteriafor money lending to solar energy systems may be applicable.In addition, the government and the bankingsector together may generate financial con-structions (e.g. ‘green mortgage’), in which the banking sector provides reduced interests to

customers for green energy projects, in whichthe reduction in the interest is financed by thegovernment.

Installation company

The installation company plays a key role sincethey have contact with the end customers and/or end users. The installation company is the pri-mary influencer for many solar energy installa-tions. The installer is often the main advisor onwhat system should be installed, and if he ad-vises against the application of solar, this opin-

ion will generally be followed. Since the installer also acts as supplier, further information on hisrole will be provided in the next paragraph.

Energy consultancy and engineering

companies

Energy consultancy and energy engineering companies have an important role due to the influ-

ence they can have on the choice and design of the energy system in larger building projects. Itis expected that they will be open to new tech-nologies, since they are well equipped to copewith new techniques, and may see PV-Thermalas an option to promote themselves with a newhigh profile technique, in order to improve their market position.

Architect

The architect is a very important person in thedevelopment of a building project. The buildingowner is rarely experienced in building construc-tion. For this reason, he relies on the knowledgeof the architect.Solar energy represents an option that is not ab-solutely necessary for the operation of the build-ing. Since the solar system is rarely the uniqueenergy source, the architect prefers often to sim- plify the project by using a conventional system,that allows to save budget for other requirementsand that gives more liberty for “dressing” the building.

From the viewpoint of the architect several pointsare necessary:

• PVT system should represent an added-valuethat helps selling or promoting the building

• PVT products should be flexible in shape,easy to implement and aesthetically pleasing

• PVT systems should be profitable, helping the building owner paying back his investment.

Consumers organisation

A speciality of consumers’ organisations is to

make comparative tests of products. As soon asPVT systems will be available on the market,consumers organisations will compare PVT sys-


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tems with conventional solar systems. In thiscomparison, the main criteria will be price, payback time, reliability and ease of maintenanceand operation.

For PVT, it is important that the performanceshould be given in such a way that a fair comparison is made with conventional solar thermaland PV systems. In addition, the reliability needsto be sufficiently assured. This underscores againthe importance of clear testing procedures dedi-cated to PVT. Furthermore, the commercialisingof PVT systems will be assisted by creating add-ons on the system that motivate the consumersto choose for the system for other reasons than price only.

Suppliers

The conventional solar energy business is at themoment in a phase of high growth. The increasein market volume presents the possibility to re-structure its distribution chain. Companies in-volved in the heating and in the construction sec-tor have started to offer solar thermal systems as part of their standard product range [ESTIF, April2003]. This evolution should inspire PVT tech-nology to reduce its maturing phase and to struc-

ture its distribution chain so as to enable a fastdevelopment at an early stage.

PV manufacturer

For PVT products close to photovoltaic products,PV companies may be interested to add the manu-facturing of PVT products to their portfolio, andthe PVT products will be distributed using thesales channel of PV photovoltaic. As an addi-tional advantage, the PV manufacturer alreadyhas most of the equipment that is required for the

manufacturing of the PVT laminate (such as lami-nators, tabbing and stringing equipment, etc.).A problem for this approach might be that thePV manufacturing companies are very prudentto make changes in their products because of thehigh demands on product quality; it is difficultto change the production process for specific op-tions and the quality process is very expensive,since any change will require new tests with thenecessary test certification reports. For the shortterm, this problem is further enhanced by the present lack of feedstock material, which results

in PV manufacturers that focus on their main products and are very hesitant to offer specialfeatures.

However, the situation will improve when, from2007 onwards, the feedstock problem is relieved(Photon International, 2004; 2005). This may re-

sult in PV companies trying to expand their market again and offering more special prod-ucts. PVT could then be a very interesting op-tion to enhance the green image of PV even fur-ther and open new markets. An advantage of PV-air systems is that conventional PV laminatescan be used, which eases the constraints pre-sented by the quality certification.

Solar thermal manufacturer

For a solar thermal manufacturer, PVT would

offer the possibility to upgrade the image of his products and to profit from the booming PV mar-ket - and especially the feed-in tariffs that have been introduced in many countries.A problem may be the fact that the solar ther-mal manufacturer has to invest in expensive pro-duction equipment such as laminators, has to buy prefabricated elements such as solar cells (in-cluding tabbing) and has to produce cell matri-ces at the same quality level as commercial PVmanufacturers.Such investments will only be done if the manu-

facturer is convinced that the PVT system brings perspectives from both a production and a mar-keting point of view.




48

PVT assembler

A high investment is required to obtain all theequipment required for the production of PVT.Therefore, possibilities may exist for assembly

companies, that outsource the manufacturing of specific parts of the PVT system. The assembler could e.g. buy absorbers from a solar thermalmanufacturer and commission a PV manufacturer to laminate these into PVT modules, after whichthe assembler integrates the combined moduleinto a collector casing. Additional synergy isobtained when the assembler is the same personas the solar thermal manufacturer or the installer.It is to be expected that the first companies start-ing a PVT product will be specialised assemblycompanies wanting to open new market sharesand looking for a unique selling proposition.

Installation company

Installers are not always keen on solar energysystems, especially if they have limited experi-ence in installing such systems. Since the number of solar installations is not very large comparedto conventional installations, an installer may bereluctant to invest in specialised training for so-lar energy installations, a problem that may beaggravated further by strong market fluctuations

due to inconsistent government policies. These problems may even be more serious for PVT sys-tems, since PVT has - at present - a very smallmarket and, since a PVT system is a combina-tion of a solar thermal and a photovoltaic sys-tem, very broad skills will be necessary for en-suring installation safety and quality.However, the problem could be reduced if theamount of training is limited, because the sys-


tem is well designed and easy to mount. The skillsrequired should be the same as compared to con-ventional solar energy systems, and preferablyeven less. This implies a strong emphasis on

plug-and-play systems. In this case, the cost/ben-efit ratio for the installer is reduced and he willsooner be motivated to sell it and thus helpingits dissemination.

Building element supplier

Building companies may be interested to add PV-Thermal to their portfolio, especially if this is ameans for them to sell other products as well.PV-Thermal could be especially interesting for them as a high profile green technology. Build-ing companies may then develop and supply pre-fabricated building elements that allow for easy plug-and-play integration of PV-Thermal into the building process and circumvents the need for additional roof- and facade work by installers.

Conclusions

From the previous paragraphs, a number of conclusions can be drawn.Very important for the commercialization of PVT will be the installers and the national gov-

ernment, while energy companies, homeown-ers, real estate developers, housing associa-tions and municipalities also have a large in-fluence. Municipalities and national govern-ment can be expected to be interested in PVTas a source for employment and publicity. Fur-thermore, parties such as energy companies,real estate developers, municipalities or the na-tional government may be very motivated toapply solar energy because of legal obligationsthey may have. However,awareness is a prob-

lem, as only few people are informed on PVT,mainly in the R&D sector.The barrier presented by the high initial cost isfor most parties of limited concern, due to suffi-cient financing options. Only for homeowners,and to a lesser extent for small entrepreneurs(small farmers, small recreational companies)this may be a problem.Quality and ease of installation should be important concerns for the development of thePVT collector, followed by appearance, greenimage and economics. The product reliability is

an important issue that should receive specificattention, among others through dedicated reli-ability test standards. In addition, installers need

B e a uf or t c o

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Table 9. Market

development

characteristics for the

short, medium and long

term.

assistance with the necessary investments intraining and equipment which should be mini-mised through optimized PVT design).Manufacturing by a PVT assembler is a logical

solution, while solar thermal companies may beinterested but might view the required invest-ments as too high.As a conclusion, we see that a number of actorsexist that may be very motivated to apply PVT.Important actors in the short run are real estatedevelopers, housing associations and municipali-ties, while in the longer run also homeownerswill play a crucial role. Based on chapter 4 andchapter 5, the following conclusions can bereached:

• In the short term, specific actors in the build-ing market may already be motivated to in-vest in PVT (e.g. real estate developers, hous-ing associations, municipalities). Multi-fam-ily buildings (especially if owned by a hous-ing association) may be an important earlymarket, due to the limited roof area available,which promotes area efficient renewable en-

ergy applications. Furthermore, interestingniche markets may exist in autonomous applications and (public) pool heating.

• In the medium and long term, the most prom-

ising application for PVT systems seems to be domestic water heating and space heat-ing. The dominant sector for this applicationis the large market segment of single-familyhouses, both newly built and existing.

• In the long term, professional application (in-dustry, agriculture) and applications such assolar cooling will become interesting for PVT.

It should then be concluded that the primary tar-gets should be as described in table 9.Considering the full marketing chain, we haveto emphasize that the PVT assembler and in-staller will anyway play a major role since theywill answer all technical questions to customers(real estate developer and end customer), givethe requested warranties and ensure after-saleservice.




50



51

In chapter 5, an overview was presented of thevarious drivers and barriers for the actors in the

different PV-Thermal markets, as presented inTable 9. In the present chapter, the link is made between these markets and the correspondingPVT systems and modules, indicating the differ-ent issues relevant for the market introductionof PVT. In the first half of this chapter, generalmarketing bottlenecks will be indicated. In thesecond half, specific bottlenecks on systems andmodule level will be examined.

General bottlenecks

Warranties

One of the most important issues for a new mar-ket is the reliability of the products. Even thoughthe market might be very small in the beginning, bad products can destroy the image of this tech-nology extensively. Experience from other mar-kets shows that even a few bad products can beresponsible for a significant market reduction ina young market. Therefore, this issue should re-ceive special attention.

A lack of standardisation exists for measuringand modeling the performance of PVT and for testing the reliability. Up to now, some PVT sys-tems were measured according to existing stand-ards for thermal collectors and/or PV modules.However, the interrelations were not taken intoaccount sufficiently. So far, the scientific basisof monitored PVT-systems is weak. Long–termexperience with detailed results is totally miss-ing so far. From the first experiences, the demandfor future research will increase significantly.

This work is specifically important since it helps producers in determining appropriate warrantiesfor PVT, which is a prerequisite for PVT mar-keting.The process to start standardisation activities isgenerally mainly driven from industry. However,the market is small, and in addition, the weak cooperation and exchange of experience between producers of thermal collectors and PV modulesis a barrier for the development of reliable PVTcomponents. Pre-standardisation work seems to be necessary in order to classify existing prod-

ucts, to develop a certain quality level as well asto harmonise the products in order for the manu-facturers to become acquainted with PVT sys-

tems in due time. As long as there is no real mar-ket, guidelines and recommendations might be

sufficient to assist the process of keeping a highlevel of system and component quality. Later on, standardisation will be unavoidable, consid-ering the positioning of the work item at thestandardisation committees since it is referringto CEN/ISO from the thermal point of view aswell as to CENELEC/IEC from the PV aspect.

Legal aspects

Legal aspects play a role in the marketing of PVT on several levels:

1. qualification aspects (e.g. qualification for subsidies, qualification for regulations re-garding energy performance of buildings,energy targets for specific market actors (e.g.municipalities, energy companies, real estatecompanies, housing associations and others))

2. regulations regarding procedures for instal-lation.

3. regulations regarding building codes

Qualification aspectsFor the market introduction of PVT, it is impor-tant that PVT qualifies for the support regula-tions developed for other forms of solar energy(particularly PV and solar thermal). This maynot always be the case; sometimes special re-quirements are set (e.g. a minimum level of ther-mal efficiency) that impede the extension of existing regulations to PVT.In addition, it is important that PVT, as well asother solar energy techniques, is acknowledged

as an appropriate technique to satisfy energy performance targets. Countries differ in theamount of freedom they give in order to obtaina good energy performance, allowing a broader or narrower range of options to obtain a low fos-sil energy consumption. It is important that PVT(and other solar energy techniques) are supported by such regulations.

Installation procedures

In most countries PV systems but also solar ther-mal systems have to be commissioned by a spe-

cialist. For PV this is mainly an electrician, whilefor thermal applications a plumber does this job.It is to be expected, that for a PVT system both

6. Comparing systems and market demands




52

experts have to make the commissioning. Sinceone of the main advantages of PVT systems isthe potential for reduced mounting time compared to side-by-side systems, it is of paramount

importance that this potential advantage is notcancelled by a legal regulation prescribing bothPV and thermal experts to do the installationseperately.

Building codes

PVT collectors are new on the market, combin-ing two techniques that are normally regarded asseparate techniques, subject to different sets of regulations with regard to building codes, sub-sidy issues, energy performance directives etc.The fact that these two techniques are combinedinto one, means that PVT devices have to follow both sets of regulations. However, it is to be expected that PVT will not always fit into theseregulations very well.

Aesthetics

Aesthetics is important for most PVT market seg-ments, as indicated in chapter 5.For a small group of technique-lovers, that mayfunction as ‘early adopters’, the high tech image

of PVT may be important. Especially the electri-cal applications have a “high tech component”-image. PVT systems could profit from this, sincethe joint use by combining two renewable tech-nologies and the high standing of PV is broughttogether in one high tech component.For the general acceptance of solar systems, theaesthetic quality of the collectors on the build-ing is decisive. In particular, aesthetics is impor-tant for home-owners, architects and real estatedevelopers. Only for industrial and agricultural

applications, as well as for energy companies, isaesthetics considered to be of lesser importance.

Optical appearance is of crucial importance for solar products in order to become a standard product and should be taken into account latestat a stage when the market development leaves

the stage of the “early adopters”. An importantaspect of the enhancement of the aesthetical appearance of PVT systems is building integration(BIPVT). Since one of the potential advantagesof PVT is better aesthetics as compared to a combination of separate techniques, this advantageshould be strengthened by developing flexibleand plug-and-play BIPVT elements. Similar tothermal and electrical solar installations, PVT hasthe obligation to become an integral part of the building mainly by being used as part of the building envelope and overtaking additionalfunctions like rain protection or shading. Avoidedcosts for facades and roof tiles can then be takeninto account when calculating the overall costsof a PVT system. For these reasons, BIPVT isexpected to be an important future development.The fact that BIPVT will be important leads to anumber of design issues:

• Since one of the advantages of PVT systemsis to reduce the ‘battle on the roof’, PVT willoften be applied in cases where PV and solar

thermal together take more than the availableroof area. Therefore, it may be assumed thatPVT devices will often be applied in systemsthat cover the whole roof.

• Fully “prefabricated PVT roofs”, which areonly assembled at the site, could be a prom-ising trend towards “active roofs”. Large pre-fabricated elements (whole facades, largeroof parts) with integrated PVT elementscould lead to a standardised building conceptwhere PVT is a substantial part of each

(mainly south oriented) building envelope.• BIPVT products will only be accepted if they

Figure 20. Building

integration and aesthetics

(a) PVT has an aesthetical

advantage over separate

systems (b) colour and

flexibility is important for

building integration


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are flexible concerning size, colour, framing,fittings, etc. Architects are much more openminded to use solar elements, if the choice incolour is not stricitly limited to black and dark

blue. Therefore, linked to existing investiga-tions with coloured thermal absorbers andcoloured solar cells, coloured PVT collectorsshould be investigated.

Research in PVT has to take into account the de-sign of the collector, from glazing to framing, aswell as the integration of the collector into the building envelope, which may be in the form of replacing parts of the building envelope by pre-fabricated PVT building elements.

Ease of handling

It is of paramount importance that a PVT systemcan be installed by one person, so that it is notrequired to have both an electrician and a plumber on the roof. Connection to both electricity andwater must be easy to handle. The need for optimisation, simple connection and installation procedures is therefore quite high. Developmentefforts have therefore to be made in terms of simple plug and play-components. Similar efforts are

currently made within both the concerned indus-tries (PV and solar thermal). However, the PVTsystems need additional efforts aiming at ena- bling either the plumber or the electrician to in-stall a PVT system completely in short time. Inaddition, the development of BIPVT compo-nents, as described in the previous paragraph, willalso be an important step in this development.

Training and awareness

Training of installers and engineers

PVT is so far no item in education and training.Since the market is more or less negligible, it isobvious that there is currently no need for in-

structing plumbers and engineers. Later on, theextension of existing solar trainings to PVT, based on long experiences in the solar sector andother related issues, seems to be easy. (e.g. the“Certified Austrian Solar thermal engineer &installer”). Optimal timing for the commence-ment of these trainings seems to be crucial inorder to have from the very beginning high qual-ity systems operating. However, only if the newtechnology is already visible on the market, in-stallers will apply for this training. First “proto-type trainings” and demo-installations joined byscientific institutes could act as demonstrators

for the early installers. If the development is pro-ceeding and first products have successfully en-tered the market, joint efforts of producers andindependent education schemes are needed toregularly train the professionals for installingthese products with high quality. The branch or-ganisation for installers and engineers may playan important role in promoting such trainings.Specific attention must be paid to the aspect,that the profession of an electrician and a heat-ing installer is quite different; dealing with a

PVT collectors means to be educated in both professions in order to avoid the situation inwhich two professionals are required to installa PVT-collector. Addressing the question of the business branch (plumber/electrician) could leadto a fundamental change in general educationof these craftsmen, by teaching them the basicsof each others business or by providing a groupof people with specialised training, allowingthem to commission both. Possible legal restric-tions need to be considered here as well. In ad-dition, a strong effort has to be made to reduce

these additional training requirements as muchas possible by plug-and-play design of PVTmodules.




54

Training of architects

Also for architects, training in the use of solar energy in general, and of PVT in particular, isimportant to show them the possibilities and po-

tential of such techniques. The branch organisa-tion for architects may play an important role in promoting such trainings. In addition, softwarefor architects should be developed, to facilitatethe integration of PVT in both the building de-sign and the energetic design of the building.Preferably, this should come as a module that can be added to existing design software.

Awareness

So far, the market pull towards PVT systems isnot very strong. On the one hand, only expertsare informed about PVT, while on the other hand,very few commercially available PVT systemsexist.It is important to distinguish different phases inthe awareness generation.

• First phase: target group in the first stage must be the policy makers, in order to create the proper conditions for PVT market introduc-tion, in order to stimulate manufacturers of thermal or electrical solar components to de-

velop such products, mainly with assistanceof research institutes involved in both tech-nologies. In addition, installers, architects andother professionals may be informed of thefact that such a product is under development by means of publications in technical jour-nals etc.

• Second phase: only after appearance on themarket, public awareness should be createdin order not to confuse the existing market by talking about a product of tomorrow.

With respect to the message that should be com-municated, it seems to be of paramount impor-tance to focus strictly on the advantages of PVTas compared to PV and/or solar thermal. In do-ing so, it is important to target specifically onmisconceptions that exist among actors relevantfor the marketing of PVT (e.g. overestimation of the importance of the temperature effect on thePV efficiency). The following arguments should be emphasised:

• cheaper manufacturing of the element itself,• more total energy gain per m²,

• reduction in installation costs and mainte-

nance costs

• regarding the whole value chain of PVT, alsoreduced marketing and logistic costs should be considered carefully.

Green image

The image of solar systems is generally high,mainly because of the environmental aspect of using renewable energy. For PVT, the impres-sion of “too much technology” could have anegative influence, as well as the fact that PVand thermal are competing for the same sourceof primary energy and therefore threaten to re-duce the efficiency of PVT systems compared tothe individual technologies. Research efforts dur-ing the design process of a PVT device shouldtherefore aim at optimising the yield (thermaland electrical). LCA studies may help to promotethe green image of PVT relative to a combina-tion of the separate technologies.

Grid connected applications

A relation between markets and systems can begiven. In order to realise the potential of PVTsystems, it is important to focus on the main

markets. The present paragraph focuses on themain grid-connected markets, while the follow-ing paragraph will give a short overview for thesmall but potentially interesting off-grid nichemarkets. An overview for the main grid-con-nected markets is presented in Table 10.

• For glazed PVT liquid collectors, the mainmarket is seen as the domestic hot water mar-ket, being by far that largest market segmentas indicated in chapter 4. Interesting niche

markets are seen in the tertiary market for applications such as homes for the elderly,hospitals and sports buildings. It is expectedthat these PVT systems will be less suitablefor domestic heating, keeping in mind the re-duced thermal efficiency as compared to con-ventional solar thermal collectors, which willlower the performance during the heating sea-son, especially for the short heating seasonexperienced in low-energy buildings.

• For unglazed PVT liquid collectors, the mainmarket is seen in the combination of this col-

lector with a heat pump for space heatingapplication. The main future markets wouldthen be the domestic market, again because




55

of the size of this market, and the tertiary mar-ket, because it is to be expected that the heat pump will become increasingly popular here

due to the cooling it can provide. A smaller specific market is seen in PVT pool collec-tors.

• For glazed PVT air collectors, unglazed PVTair collectors and ventilated PV facades, themain market is seen in utility space heatingduring the winter. In the future, this may becombined with preheating air for solar cool-ing during the summer. However, this willrequire an additional source of heat such as booster collectors to reach the required tem-

perature level. This system may be especiallyrelevant for low energy houses with a centralheat recovery ventilation unit, where the ven-tilation air can be integrated with the domes-tic air heating system. Although the domes-tic market is large, it is expected that this will be a niche market due to technical limitationsof such systems and the difficult competitionwith liquid collectors.

• For concentrating systems, the main marketis seen in large professional high-tempera-ture applications. Therefore, solar cooling in

the tertiary sector is seen as having the larg-est potential.

Domestic market

General issues

For consumers, the issues of quality, ease of han-dling, a feeling of autonomy and appearance areof primary importance and financing is an important bottleneck.

• Quality of the system is very important. Astrict quality chain from tested componentsto monitored systems but also well trainedinstallers and planners are needed. Qualitylabels are important in order to make such ahigh quality process visible for the customer.

The systems should be warranted for at leastas long as the backup heating system andgood after sales services are mandatory. Inaddition, the owner should have an indica-tion about how well the system is perform-ing.

• Installation of the system needs to be easy plug-and-play, in order to reduce the instal-lation costs and allow for only one installer carrying out the full installation. In addition,maintenance requirements should be negli-gible.

• It should be made as easy as possible for theconsumer to purchase these systems, by re-ducing the required amount of paperwork to


Table 10. Relation

between market segments

and PVT systems for grid

connected applications.

Future main markets are

indicated in red, niche

markets in yellow.



56

a minimum. Preferably the opportunity of pur-chase should be a standard opportunity on boiler replacement and assistance should be provided in the subsidy applications.

• Appearance of the system is of increasing importance. Building integration will becomeincreasingly standard due to real estate de-velopers applying solar energy in newly builthousing projects as part of the energy per-formance requirements. Therefore, prefabPVT building elements should be developed.

• Financing methods are required that lower thefinancial burden on the consumer, rangingfrom inclusion of the system in the mortgage,to solar contracting and lease of the system.

• Cost reduction of the PVT system is impor-tant to increase the market penetration. Allfurther efforts in development of glazed PVThave to carefully consider that cost reductionis an important argument for the applicationof PVT. In addition, the yield per Euro in-vested will become a criterion on which con-sumers organisations will start to comparesolar thermal, PVT and PV modules, whichis an incentive to increase the module effi-ciency.

Module related issues

General issues

• The aesthetics of flat-plate PVT is generallygood. For the future, large PVT areas, whichcould cover the whole roof or parts of the fa-cade could make buildings more attractive,especially if we think of the highly appreci-ated effect of PV, due to the appearance of the solar cells. The existing approaches in thePV technology with differently coloured cells

and foils (blue, green, red, grey,...) will openup an attractive field for innovative architects.Development should focus also on adding

other functions (e.s. shading) that widen thespectrum of possible applications.

• For concentrating PVT, the aesthetics are lessdue to the problematic building integration

of such systems. This reduces the applica-tions for such systems to collective applica-tions where they can be put on the flat roof.

• In order to improve the cost efficiency, thethermal efficiency of PVT should be further increased. In particular, the absorption andemission values should be improved.

Single family tap water heating (Glazed liquid

PVT)

• Further R&D is required to minimise the ef-fect of the high collector temperatures on thelifetime of the PV.

• In addition to prefab elements for the newly built market, standardised plug-and-play PVTwater heaters should be developed for add-on in existing buildings. It is important thatthese have sufficient aesthetic appeal.

• Because the area required for solar tap water heating is much less than the roof area of aone-family house, it is recommended to de-velop systems in which the PVT can be combined with PV in a side-by-side system.

Collective tap water heating (Glazed liquid

PVT, concentrating PVT)

Collective tap water systems for multifamily buildings may be a large niche market for glazedglazed liquid PVT collectors, and could be a mainmarket for concentrating PVT collectors. Due tothe larger system size, tracking may become eco-nomically feasible.

• Glazed liquid PVT. The same considerations

hold as in the case of single family tap water heating.

• Concentrating PVT. Concentrating PVT col-lectors are less suitable for building integra-tion. However, they may be positioned on flatroofs of multifamily buildings. An advantageis their low loss factor that allows for good performance under low ambient tempera-tures. Failsafe methods need to be developedto prevent stagnation temperature damage toPVT concentrators (out of focus movementfor tracking collectors or high temperature

resistant materials for non-tracking collec-tors). In addition, for tracking systems, sys-tem reliability and the corresponding main-


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tenance may be problematic, but this issuecould be reduced if not the individual inhab-itants but a professional body such as a hous-ing association is responsible for this.

Space heating and tap water heating

(Unglazed PVT with heat pump)

• The system reliability may be compromised by the heat pump. It should be taken into ac-count that many heat pumps can only work efficiently with source temperatures below20°C, although, in case of higher collector outlet temperatures, it is technically possibleto add cold water. In addition, the lifetime of the heat pump might be shorter than the expected lifetime of the PVT collector.

• Compared to glazed PVT collectors, the temperatures in the collectors are lower whichshould be of advantage for the lifetime; thelifetime of the product will benefit fromthe reduced operating temperature since thecollector materials will be less thermallystressed. However, the strict requirements for quality and reliability require more attentionon the reliability of unglazed PVT systemsas well.

• For unglazed collectors (both conventional

and PVT collectors) good building integra-tion techniques have to be developed. Prom-ising developments are e.g. the Rheinzink energy roof and the EMA collector systemdeveloped by ISFH.

• For most applications, the heat pump elec-tricity demand is substantial and will prob-ably exceed the electrical production of thePVT system. This may cause an image prob-lem due to the fact that the origin of the elec-tricity for the heat pump needs to be taken

into consideration. Although in Europe theliberalisation of the electricity market opensthe opportunity to change the electricity supplier and switch to a “Green Electricity” supplier, the higher cost of this electricity wouldinfluence the profitability of this application.

Pool heating (Unglazed liquid PVT)

• This application will have to compete withlow cost plastic pool collectors side-by-sidewith PV. This will be very difficult, especiallysince a long lifetime is required because of

the PV. With the present techniques it is fore-seen that it will be very difficult to make thisapplication profitable. However, in the future,

flexible absorbers may successfully be combined with cheap polymer PV techniques.

Component related issues

• Inverter: PV systems linked to the grid arenowadays mainly not able to continue theelectricity supply if the main grid is shutdown. This currently also leads to a break-down of the heating or cooling supply, sincethe pumps for the heating/cooling system arealso not operational. In future, PV inverterscould have the standard feature to continueoperation in times of solar radiation but nogrid supply. For PVT, such systems are thenmuch more reliable and will especially in re-gions with weak electricity grids becomevery attractive. Inverters should be devel-oped that do not switch off when the publicgrid fails. Attention should be paid to con-trols that do not violate the prohibition onislanding1 . In addition, the design of the PVsystem must be chosen appropriately to beable to fulfill the needs of the heating/cool-ing system autonomously.

• A good monitoring system should be devel-oped showing the yield of the system. Pref-erably, the monitoring device should not

work on batteries but be connected to the elec-tricity grid and show values that are of inter-est to the consumer (e.g. savings, if possible).

Tertiary market

General issues

Parts of the tertiary market are owned directly by the municipality and the national government.Since these parties may be very interested in pro-

moting solar energy, they may have targets for solar in which PVT could fit very well. In addi-tion, real estate developers and possibly hous-ing associations will be forced into the applica-tion of solar energy by energy performance di-rectives from the municipality or the nationalgovernment. This may create a substantial terti-ary market for solar energy systems, includingPVT. In addition, PVT has the additional ben-efit of being a high profile technique, which mayalso attract parties in the tertiary sector and may be regarded as a sales argument by real estate

developers.


1Islanding is the situation in which the PV continues to deliver power while the main power is switched off. This is presently not allowed, basedon the idea that if someone switches off the main power, there should not be any power left on the grid that can present an electrical hazard.However, it is reasoned here that there are ways around this, e.g. by allowing the inverter to continue functioning in case of public grid failure, but to make sure that the inverter is switched off if the main power switch in the house is turned off.



58

• Legislative measures are very important,since the potential contribution of PVT should be properly represented in the energy per-formance directives, in order to profit from

these.• For commercial applications, aesthetics are

very important and building integration is animportant issue, but for municipality and gov-ernment these criteria may be less strong.

• Due to the fact that systems are typicallymuch larger and more custom made, the is-sue of standardisation and plug-and-play isless prominent for this market.

• Issues with respect to operation and mainte-nance may be less problematic than for con-sumers, since a maintenance staff will nor-mally be present and may routinely carry outthese tasks. This also allows for more com- plicated systems.

• For new buildings, prefabricated PVT build-ing elements need to be developed, in order to facilitate large-scale integration of PVT as part of project development schemes.

• For retrofit applications, financing construc-tions may be an issue. Although the initialcost will normally not be a problem, the department budget system may cause problems,

since it may not be clear from which budgetthe money should come. Standard financingsolutions for this issue may be required.

Module related issues

Tap water heating (Glazed liquid PVT,

concentrating PVT)

A large niche market exists for tertiary sector buildings with a large tap water demand, such asswimming pools (showers!), homes for the eld-erly, hospitals, hotels, sports buildings etc.

• The issue of stagnation temperature is less problematic than in the domestic sector,where people may go on holidays during thesummer, since most of these tertiary applica-tions will still have a substantial hot water demand. Nevertheless, also for this applica-tion, further R&D is required to minimise theeffect of the high collector temperatures onthe lifetime of the PVT.

• Also here, the difficulty of building integra-tion would limit the application of PVT con-

centrators systems that can be located on flatroofs.

Public pool heating (Glazed and unglazed

liquid PVT)

For swimming pool application we have to dif-ferentiate between two applications: heating of outdoor pools (only in times of high ambient temperatures) and heating of indoor pools (also intimes of colder ambient temperatures). For thefirst case, unglazed non-insulated solar thermalmodules, usually made of rubber or plastic, arethe best, cheapest and well-established solutionfor swimming pool heating. This is obvious, sincethe system is only operational in times of highambient temperatures; a cover as well as insula-tion is basically not advantageous for this appli-cation. However, for the second case, glazed col-lectors are often applied.

• Unglazed liquid PVT. Experiences fromGermany and Austria show, that in recentyears the market for pool application is sig-nificantly decreasing, which might offer PVTalso only a small market segment. For stand-ard swimming pool collectors the efficiencycan reach values of 85% or more, but the ab-sorber is also able to gain energy from the air (without solar radiation). By using a PVTcollector, care should be taken not to reduce

this gain by adding PV at the upper surface.Generally, in case of swimming pool heat-ing, if the pool is uncovered and used only intimes of high temperatures, the competitionwith the cheap established absorbers seemsto be quite heavy. However, in countries withPV feed-in-tariffs, an unglazed PVT as a so-lar roof is already attractive – even in eco-nomic terms- whenever the roof of a public bath has to be renovated. Due to the relativelylow water temperatures, PV is cooled effi-ciently during the sunny season. Gains re-

ceived from the PV system could enable con-tracting models for financing. Depending onthe PVT construction, a metal absorber might


P h o t o : A u s t r i a S ol a r &T e uf

e l & S c h w a r t z



59

be necessary instead of the rubber or plasticabsorbers normally used, which causes fur-ther expenditures for heat exchanger, pipingand separate collector circuit compared to a

standard solar absorber which can be directlyoperated with chlorinated water.

• Glazed liquid PVT. A different situationoccurs, if the pool is indoor and used alsoin times of moderate temperatures. In thatcase, the PVT collector has to competemainly with standard glazed thermal col-lectors instead of cheap plastic collectors.A problem may be that during the summer,indoor pools are typically closed for main-tenance, leading to prolonged stagnation periods.

Office space heating (Unglazed PVT with heat

pump, PVT air systems, ventilated PV)

Due to the relatively large electrical demand of offices, compared to the thermal demand, it isrecommended that side-by-side systems of PVTand PV should be developed for this market.

• Unglazed liquid PVT with heat pump. For office applications, heat pumps are highlysuitable due to the added possibility of sup-

plying the cooling load. For the function of space heating, PVT may well serve as thesource for the heat pump (storage is requiredsince the thermal output of the collector willfluctuate while the heat pump needs a con-stant heat supply). In addition, the high day-time office electricity demand will largely co-incide with the time of the PV energy deliv-ery, resulting in optimal use of the PV. Fur-thermore, the high profile of the techniqueand the targets for energy performance in of-

fice buildings will stimulate the implemen-tation of such techniques.

• Ventilated PV. From the energetic point of view, this application is probably the mostefficient way to use PV and cool the facadein order to have double temperature effect:

By actively cooling the facade, one directlycools down the building by avoiding directsolar radiation on the walls and one also re-duces the temperature of the PV modules,which leads for most PV cells to an increaseof the PV-efficiency. Furthermore, facade in-tegration is very well developed. Designtools need to be developed in order to facili-tate wider application of this technique. Also,system control (volume flow rate, collector outlet temperature) needs to be developed.An interesting additional option may be thecombination with solar cooling (see below).

• PVT air collectors. These collectors aremore efficient than ventilated PV and thecontrol is better developed. Therefore, asmaller area is required, which makes thesecollectors more suitable if space is limited.Also here, solar cooling may provide an in-teresting option. Because of the higher effi-ciency of glazed collectors in comparison toventilated PV, the need for booster collec-tors is reduced.

Solar cooling (concentrating PVT, PVT air

collectors, ventilated PV with additional

booster)

Cooling is about to become the main market inlow energy applications. Also in moderate cli-mates like mid-Europe, the demand for coolingis increasing significantly. Mainly due to the in-creasing desire for comfort, but also due to in-creasing internal heat gains and improved insu-lation levels in office buildings, cooling becomes

more and more necessary. Solar cooling has al-ready shown its functionality in various appli-cations. Many, mainly larger systems for offices,are already equipped with solar cooling systems.


P h o t o : B .K a r l s s on- V a t t e nf a l l

P h o t o : A u s t r i a S ol a r & S i k o S ol a r V e r t r i e b gm

b H



60

• Availability of space might be an item for of-fice buildings, to combine heat and electric-ity production. In case of countries where PVis subsidized well, the roof is used for the PV

system and might offer no further space for asecond system for heating and/or cooling.Therefore the combination within a PVTmodule will be attractive especially for of-fice buildings with a high cooling load.

• Energy companies may be interested in sup- porting such a system, since solar cooling cansignificantly contribute to peak load shavingof the electricity system. Nowadays, in sev-eral Southern European countries, the elec-tricity peak loads are mainly in summer, whenall cooling systems are operational. The com- pression system needs a lot of electricity thatleads to high peaks.

• Solar cooling will be required only during thesummer. For concentrating PVT liquid mod-ules, the economy of the system would bestrongly improved if the system could also be used for hot water, possibly supplementedwith space heating during the winter. Thismakes the system especially suitable for ter-tiary applications that do not only have a cool-ing load but also a significant tap water de-

mand, such as hospitals and old peopleshomes.

• For ventilated PV or PVT-air collectors, thecombination of solar cooling with space heat-ing seems the most logical. That would makesuch systems especially suitable for tertiaryapplications with relatively low hot water de-mand, such as offices and public buildings.Further studies into system optimisation for solar cooling are required.

• For the case of concentrating PVT, an issue

is the weak possibility for building integra-tion; improved concepts for such applicationswould be welcome.

• In concentrating systems, stagnation tempera-tures are enhanced. For tracking systems,moving the system out of the sun will be nec-essary, affecting the electrical yield.

• For ventilated PV combined with conven-tional air collectors (for boosting the tempera-ture level up to the required minimum temperature of about 60 ºC for solar cooling), anissue is the combination of both types of col-

lectors into one system. Standardised build-ing integration systems need to be developedfor these combinations.

Component related issues

• For PVT concentrators, techniques for officefacade integration should be further devel-oped, with corresponding components.

• For ventilated PV, standardised building inte-gration systems combining ventilated PV withconventional air collectors need to be further developed, with corresponding components.

Off-grid applications

Although the off-grid market is small, the competing technologies are mainly diesel genera-tors in the field of electricity and biomass, oiland standard solar applications in heating andDHW, which makes this market an interestingniche for PVT applications. Niche marketscould be in recreational applications such asmountain huts (either privately owned or com-mercially exploited) and mobile homes or vans. Other niches could be in desalination in-stallations (e.g. for island application other near-sea arid areas), which could be small scale(individual households) or large scale (entirecommunities). Finally, agricultural applica-tions such as drying should be considered. Anoverview between different systems and mar-

kets is presented in Table 11.A problem for PVT in this market is the com- petition with separate PV and solar thermalsystems. At the one hand, space constraints will be less problematic and aesthetic demands will be reduced. At the other hand, installation andtransport costs are much more important,which might be an important advantage for PVT.Due to the fact that long-term absence may be prominent in this market and maintenance and

replacement is expensive, it is important that




61


systems are very reliable or do-it-yourself. Inaddition, the problem of theft may need spe-cific attention.

Consumers

Consumers can choose for hot water systems androom heating systems. Since transport and in-stallation may be problematic and costly, the sys-tem needs to be simple and easy to mount, pref-erably by the owner himself. This requires sys-tems with a high degree of prefabrication thatare relatively small. A point of attention is thetheft risk during the prolonged absence of theowner, that it should be possible to secure thesystem, or (for small systems) to store it awayduring the owners absence.

• PVT air systems present a very good match, being able to provide ventilation with heatedair also in the absence of the owner and thereby protecting the house from moisture problems.This system is already on the market.

• Water heating applications may be problem-atic. First of all, off-grid applications willmostly not be connected to the water pipingsystem either, which implies that for appli-cations such as showering, natural water will

be used (e.g. from a rainwater tank or well)for which the water quality may be low, re-quiring robust pumps and filters. If the owner is absent for long periods, long stagnation periods and also freezing may occur.

− For small-scale use, this may lead to small portable plug-and-play collectors that can be connected to a fixed water storage dur-ing presence of the owner, and can be

decoupled and stored during his absence.− For larger systems, installation costs may

be an obstacle. Although do-it-yourself systems seem promising because of thehigh transport and installation cost asso-ciated with autonomous applications, thismay compromise the safety and reliabil-ity of the system, especially with respectto the freeze protection. In order to en-hance the reliability, it may be requiredthat the system is drained during the ab-sence of the owner. The irregular loadmay result in long stagnation periods.Combined with the fact that cottages will be used mainly during the summer sea-son this suggests that unglazed PVT sys-

tems may be the most appropriate.• An interesting application can be PVT sys-

tems for water desalination. Such systemsmay be of interest for island applications or other near-sea arid areas. They can be scaledfrom individual family systems to collectiveapplications, e.g. for small communities. For these systems, autonomous PVT systemsmay be of interest, e.g. for reverse osmosis,

Table 11. Relation between

market segments and PVT

systems for off-grid.




62


general issues certification

financing schemes,

subsidy issues

awareness

technical issues reliability issues (e.g. stagnation temperature resistance)

efficiency issues (optics, heat transfer, temperature effect on PV)

integration issues aesthetics

plug-and-play PVT

design tools

combined PVT & PV systems

combined PVT & heat pump

combined PVT & solar cooling

Table 12. Priority issues

for PVT market introduction

in which electricity is used to drive the pumpwhile the thermal yield is used for heatingthe inlet water. It is an important asset thatsuch systems can be manufactured as plug-

and-play stand-alone systems. Attentionshould again be paid to the issues of reliabil-ity and theft.

Commercial stand-alone

Professional stand-alone applications may becampgrounds or mountain huts. This sector willhave the same demands as consumers, but theconstraints are less severe. Initial cost will be less problematic and load patterns may be much moreregular, although still showing a strong seasonal peak. This will increase the economy of thesesystems. Also here, PVT systems for water puri-fication may be an interesting niche market inisland applications or arid areas.Hot water systems will be more suitable than for autonomous consumers, while the technical prob-lems are reduced, due to professional installa-tion, easing the use of glycol systems.

Agricultural application

Drying with solar energy mainly in the agricul-tural sector might become an interesting market.

Especially in regions with no electricity supply,drying combined with PV electricity productionmight become a further promising niche of PVTapplications.

Hay drying with solar air collectors was alreadydone some decades ago, however, the market penetration was very weak. In any case, the total potential of this market segment seems to be quitemodest.The main function of the PV will then be to drivethe fan, which limits the required PV area rela-

tive to the required solar thermal area. Whether glazed or unglazed systems will be used dependson the temperature level required, but for manyapplications, unglazed will be the most appropriate. The increased electrical yield due to thecooling of the PV may allow a smaller PV area,increasing the profitability of the system as compared to separate PV and solar thermal.

Conclusion

Based on the promising markets for PVT and theappropriate market-system combinations, anumber of issues were identified as priorityissues for the market introduction of PVT. Anoverview is presented in table 12, while anaction plan for these issues will be defined inchapter 7.

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63

In chapter 6, a number of issues were identifiedthat should receive attention in order to assist

the commercialisation of PVT. A number of gen-eral issues were identified, together with anumber of technical issues. In the present chap-ter, a detailed action plan for these issues is pre-sented. Separate paragraphs are dedicated to each

of the subjects and each paragraph is concludedwith a development scheme distinguishing the

short, medium and long term. A schematic over-view of these issues is shown in Table 13. A rank-ing (ranging from 1-5) has been added to indi-cate the importance of the various issues for thedifferent PVT module development trajectories.

General issues

Measuring techniques, standards andcertification

Existing international standards are EN 12975and ISO 9806 for thermal collectors as well asIEC 61215 for PV modules. These cover reli-

ability and performance verification proce-dures and electrical safety issues. So far, testsof PVT systems at laboratories are conductedaccording to own procedures and/or accordingto standards for testing thermal solar collec-tors, which makes a comparison of test resultsvery difficult.Energy performance under different climaticregions is still an open issue.Close combination of PV cells with large me-tallic structures (the absorber and heat ex-changer installation) poses new demands on the

construction and electrical system design. Elec-trical hazard protection, leakage current limi-tation, capacitive coupling to ground and cor-

Table 13. Schematic

overview of issues for PVT commercialisation

rosion from moisture are critical issues, whichare only partly covered by standards.The energy rating of PVT collectors is a completely new topic. Electrical and thermal per-formance have to be evaluated into a combined rating, with a separate rating for ther-

mal performance and electrical performanceat defined temperatures and from one or morecombined tests. To evaluate the total perform-ance, the primary energy savings or the CO

2

emission reduction can be used as a rankingcriterion. The problem with that however isthe dependence on the fuel mix and efficiencyfor electricity generation, which is differentfrom place to place. An extra complication isthat the electric and thermal performance areinterrelated, because of the temperature dependent output of the PV cells.

Other issues that should at least be addressedare the stagnation resistance of the PVT col-lector and the thermal shock resistance.

7. Identification of key developments


Type relevance

liquid glazed •••••

liquid unglazed •••••

air glazed •••••

air unglazed •••••

concentrator •••••

ventilated PV •••••



64

short term banking, government • Develop financing schemes that facilitate the purchase of PVT systems.

• Develop financing schemes that take into account the departmental

structure of companies.

medium term – –

long term – –

short term R&D institutes • Develop a comprehensive performance test method for PVT systems

• Develop a stagnation test method

• Develop a thermal shock test method

• Develop an integrated ranking criterion for the evaluation of the PV plus

the thermal performance of the PVT system.

• Carry out long-term PVT reliability and performance tests

medium term R&D institutes, • Develop standards and certification methods for

certification institutes, standard PVT collectors (flat plate liquid, c-Si)

manufacturers • Develop test methods for non-standard PVT systems

(advanced PV concepts, PVT concentrators, PVT-air)

• Make recommendations for improved PVT certification,

based on long-term test results.

long term R&D institutes, • Develop standards and certification methods for non-standard

certification institutes, PVT systems (advanced PV concepts, PVT concentrators, PVT-air)

manufacturers

Table 14. PVT certification

development scheme.

Table 15. PVT financing

development scheme.


Financing issues

For renewable energy systems in general, mostcosts are upfront whereas for the competing fos-sil systems most of the costs are during opera-tion in the form of energy costs. This can be agreat hurdle for a renewable energy system totake, especially for PV that is at the moment still

far from being cost effective in grid connectedapplications. For PVT, although the economicsare better, the upfront cost are even higher thanfor PV since the additional thermal system alsoadds to the price.

For homeowners, the easiest way to overcomethe financial hurdle of the upfront investment isto incorporate the PVT investment in the mort-gage of the building. In this way the payment isspread over about 30 years. In general interest

rates on mortgage loans are rather low, becauseof the low risk involved since the house servesas the security of the loan. Other options are the possibility of leasing or renting a system.

For companies, for the case of retrofit, financ-ing constructions may also be an issue. Althoughthe initial cost will normally not be a problem,the department budget system may cause prob-lems, since it may not be clear from which budgetthe money should come. Standard financing so-lutions for this issue should be developed.

Type relevance



air glazed ••

air unglazed ••

concentrator ••

ventilated PV ••



65

short term government, municipality • Make sure that existing subsidies do not exclude PVTmedium term government, energy companies • Develop subsidy schemes for potential customers of PVT systems

(especially home-owners), which are reduced periodically.

• Develop training subsidies for installers

long term – –

Table 16. PVT subsidy

development scheme.


Subsidy issues

To overcome the hurdle of the upfront invest-ment also subsidy schemes could be created. This

can be in the form of an investment subsidy, atax credit or a feed in tariff. The exact form isless important than the right amount (not toomuch, not too little) and the reliability of the sub-sidy scheme. In case of PVT, the energy yield of the system would suggest to allow the full PVsubsidy (or feed-in tariff) plus a part of the solar thermal subsidy, due to the lower thermal yieldof these systems. However, if one would reallywant to push this technique, because of its effi-ciency and its potentially high contribution to theEU targets, one could allow a bonus, e.g. in theform of the full solar thermal subsidy.

Subsidy schemes have to run for many years other-wise the effect can even be very harmful. Becauseof subsidy schemes private investors are temptedto invest in PVT production facilities and all can be lost when the subsidy scheme is stopped after say 5 years. The private investors will be very re-

luctant to invest in renewable energy again.It is also good to introduce a yearly reduction of the subsidy, in which technical, industrial andmarket progress is incorporated (learning curve).

It also makes clear that the ultimate aim is tocome to a cost effective system.

• For installers, training subsidies could facili-tate their involvement in PVT, speeding upthe commercialisation.

• For the government, the driving force will be CO

2reduction, employment and innova-

tive production.

• Municipalities will have a similar outlook as the national government, but will befocussing more on promotion of the municipality, which makes high profile techniquessuch as PVT especially interesting.

• For utilities the driver will be especially toreduce peak load demand. PV and especiallyPVT have a strong influence on the peak power demand in countries where air condi-tioning demand is responsible for this peak power demand.

Type relevance




air unglazed •••


ventilated PV •••



66

Table 17. PVT awareness

development scheme.


Awareness and training

Although a number of PVT market products ex-ist, PVT has a very small market share. This im-

plies that

• awareness for PVT is small at all levels (from policy maker and installer to consumer). Thelow level of knowledge impedes a fast mar-ket penetration of PVT, and raises barriers dueto the fact that the specific characteristics of PVT are not taken into account in legal regu-lations and subsidy issues.

• installers do not have specific training for theinstallation of PVT systems. Apart from thegeneral issues related to PV and solar ther-mal, specific PVT issues are the moduleweight and the combination of electrical andthermal connections (connecting module toinverter properly, connecting module to hotwater system). Ideally, only one installer would be required to install a PVT module,taking care of both the electrical and the ther-mal installation. Since most installers do nothave both skills, this implies that the systems

should be as much as possible plug-and-play,so that only limited training is required, butin addition, installers should be trained to dothis installation properly. It is to be expectedthat in the first phase, manufacturers will dothe installation themselves or will give dedi-cated training to selected installers, whileseparate craftsmen will be required for elec-trical and thermal.

Essential for awareness are the experiences fromdemonstration projects. A sufficient number of such projects should therefore be carried out.

Legal aspects

As indicated in chapter 6, due to the fact thatPVT is a new technique, it may not fit well

into existing regulations (e.g. energy perform-ance of buildings, subsidies, prescribed instal-lation procedures, building codes). It is impor-

tant that an inventory is made of this potential problem, and that awareness is raised at policymaker level to repair such problems in exist-ing regulations and to prevent new problems

in future regulations (e.g. when the new EUenergy performance directive comes into forcein 2006).

short term PVT manufacturers, installers•

Installer instructed by manufacturer • Awareness campaigns should be targeted at policy makers level

to obtain support for PVT and to ensure that PVT is properly

represented in building energy performance directives

• Field tests should be carried out.

medium term PVT manufacturers, installers • Internal training in large installation companies, provided by PVT

manufacturer

• Solar thermal craftsmen also making electrical plug and play

connections

• Awareness campaigns should be targeted at decision makers

and decision influencers level (consumers, real estate developers,

architects) to ensure the implementation of PVT

• Demonstration projects should be carried out.

long term -

Type relevance







Type relevance









67


short term PVT manufacturers, • Inventory of bottlenecks in existing regulations

installers, policy makers • Awareness campaigns should be targeted at policy maker level

to obtain support for PVT and to ensure that PVT is properly represented

in building energy performance directives

medium term policy makers•

Action should be undertaken to repair regulations that unfairly put PVT ata disadvantage

long term −

Table 18. PVT regulations

development scheme.

Technical issues

Stagnation

In general, PV systems and solar thermal systemsshould be able to withstand direct insolation with-out active cooling, because active cooling systems(pumps and fans) can fail, as power can fail. Thisis also very important for glazed PVT systems andlow-concentration PVT systems.For high concentration PVT systems, it is sim- ply not possible to design them in a stagnation

resistant way; these systems depend on out of focus movement in case of stagnation. Thismeans that a failsafe mechanism should be foundfor out-of-focus movement, that also functionsin times of power failure.

• Investigations have to be carried out and toolshave to be elaborated in order to know ex-actly and reliably the temperatures in all components of PVT absorbers. This concerns thestagnation situation in order to prevent the

complete destruction of a PVT device. But italso concerns the normal operating mode inorder to improve existing constructions andto develop new constructions of PVT absorb-ers.

• A way to overcome the stagnation problemof PV modules in a thermal collector is bynot using standard solar modules but by con-necting bare solar cells to a thermal collec-tor. In this way only the solar cells should beable to withstand the high temperatures, aswell as the interconnection of the cells, the

electric cabling and the bonding material. Thesolar cells still need to be bonded to the ab-sorber, but the requirements for the bonding

material will be strongly reduced, comparedto full encapsulation. However, techniqueshave to be found to seal the cells from mois-ture (or to produce PV that is intrinsicallymoisture resistant), to accommodate the dif-ference in thermal expansion between the PVcells and the absorber and to ensure a suffi-cient level of electrical insulation betweencells and absorber. Possibly, alternative ab-sorbers may be found that have a lower ex-

pansion than metals. The expected lower thermal conductivity may be compensated by the application of fully wetted absorbers.In addition, thin film PV techniques may beused that are less brittle than PV cells.

• Another way is to find stagnation tempera-ture resistant encapsulants. Encapsulantshave to fulfill a number of requirements, suchas being highly electrically resistant, prevent-ing corrosion of the metal contacts of the PVcells and being able to accommodate to the

difference in thermal expansion of the (c-Si)solar cell and the (mostly) copper thermalabsorber. The simplest bonding techniquethat can resist 150 oC is silicone. However,silicone has a low heat conductivity, so the bonding layer should be thin.

• For PVT concentrators, effective stagnation protection should be developed that is ableto move the collector out of focus at timesof power failure. This may be a batterycharged DC system that is fed by the PV.Possibly, gravity based controls could be

developed that move out of focus if external power is not applied.

Type relevance


liquid unglazed •


air unglazed •


ventilated PV •



68

short term R&D institutes, • Development of tools to investigate exactly and reliably the temperatures

PVT manufacturers in all components of PVT absorbers

• Develop high temperature resistant encapsulation techniques

(e.g. silicone-based).

•

Develop an electric insulation, interconnection and cabling techniquewhich can resist elevated temperatures

medium term R&D institutes, • Develop moisture sealing techniques that allow for the use of

PVT manufacturers unencapsulated solar cells.

• Optimise encapsulation techniques for heat transfer

• Develop effective stagnation protection for PVT concentrators

long term R&D institutes, • Develop roll-to-roll moisture resistant PV

PVT manufacturers • Integrate the solar thermal absorber fully with PV

Table 19. PVT stagnation

resistance development

scheme.


Thermal module efficiency

The efficiency of PVT can be optimised further by improved thermal insulation and improved op-tical efficiency. This may lead to an improvementin the economics of PVT. However, any improve-ment in the thermal efficiency will also lead toan increase in the stagnation temperature, andtherefore makes the issue of stagnation resistantPVT more critical. PVT efficiency can be improved in a number of ways:

• With respect to the development of coveredPVT-modules the recent achievements of anti-

reflective glass (AR-glass) are important andoffer positive development aspects. If normalsolar glass is used as a cover, the reflectionlosses are about 9%, but with an AR-glassthe reflection losses are only 4%. The appli-cation of an AR-cover will lead to improvedthermal and electrical PVT efficiency. In ad-dition, anti-reflective glass opens the optionof using double glazed PVT collectors, withsubstantially higher thermal efficiency thanthe present generation of glazed PVT. Recent

results from thermal collector developmentsshow that a double glazed AR collector hasabout the same conversion factor hι as a sin-gle glazed collector with normal solar glass.As the heat losses of a double glazed collec-tor are also reduced this means that doubleglazed AR collectors with (non-selective) PVcells as absorbers may have a thermal per-formance as good as state-of-the-art singleglazed collectors with selective absorbers to-day. The development possibilities in connec-tion with AR glass have to be investigated

under the special conditions and requirementsof PVT collectors (materials, stagnation con-dition, construction aspects).

• A standard solar thermal absorber has a veryhigh solar absorption and a very low infra-red emission (solar absorption coefficienttypically 93 to 95 % and thermal emissioncoefficient typically 5 to 10%). This is calleda spectrally selective absorber. Present dayPVT modules are not spectrally selective, dueto the loss of transmission associated withspectrally selective coatings for glazing thatcould be used as superstrate in PVT absorb-ers. Therefore, PVT absorbers have relativelyhigh thermal radiation losses. If suitablespectrally selective coatings could be devel-

oped, or if use could be made of the spectralselectivity of the solar cell techniques them-selves (e.g. if bare cells could be used, whichrequires alternative moisture protection tech-niques), the thermal efficiency can be improved

• PV concepts should be developed that areoptimised not only for electrical but also for thermal performance; an effort should bemade to minimise the reflection of the PV,also for solar radiation with energy below the bandgap. This requires research into tech-

niques to lower the longwave reflection atthe silicon interface, as well as improved lighttrapping for long wave radiation.

The heat transfer from the PV to the collector medium is very important. Especially for unglazed PVT, this thermal resistance has a largeimpact on the thermal efficiency. In addition, theelectrical efficiency is negatively affected dueto relatively high absorber temperatures. The heattransfer is affected by two issues:

• The thermal resistance of the bonding tech-

nique. With respect to the bonding technique,care should be taken to minimise the thermalresistance, e.g. by means of additives to the

Type relevance


liquid unglazed ••••



concentrator •••

ventilated PV ••••



69


encapsulation or bonding to increase the heattransfer, and by making these layers as thinas possible without compromising the elec-trical resistance and the accommodation of

thermal stresses.• The heat transfer resistance to the collector

fluid. For collector liquids (water, glycol) thisis generally not a problem, but for all solar air collectors, including PVT-air collectors,a good heat transfer from the PV panel to theair in the cavity behind the panel is crucialfor the efficiency of the system. As is knownfrom all the development work in solar ther-mal air collectors, there are numerous waysto enlarge the heat transfer, by for exampleridges or fins. These ridges or fins or other structural elements should be integrated with

the backside of the PV panel.

Finally, the solar thermal absorber could be in-tegrated fully with PV, for example by produc-

ing PV with a metal foil (thermal absorber) as asubstrate. A starting point could be the a-Si tech-nology developed by United Solar Systems andCanon. Here, an a-Si thin film layer is depos-ited on a sheet of stainless steel of about 0.1mm thickness. The process is “roll to roll”, thelength of each coil may reach 100 m, the widthis about 0.3 m. Critical issues are corrosion pro-tection of the fragile thin layer of active mate-rial and electrical insulation of the active mate-rial, cell to cell as well as cells to “ground”.

Temperature dependence of solar cellperformance

Most solar cells are made of crystalline silicon(either poly- or mono-crystalline). With this ma-terial the electricity production decreases with in-creasing temperature. The temperature coefficientis about 0.4-0.5% of (electric) efficiency reduc-tion at every oC temperature increase. In a (cov-ered) PVT application the temperature is higher

over an average year than with standard PV mod-ules. The power reduction due to increased temperature can be reduced by switching from c-Si to

Table 20. PVT efficiency

optimisation development

scheme.

short term PVT manufacturers, • Apply solar cells with a high solar absorption

R&D institutes • Develop double covered PVT modules with AR-glazing

• Develop highly transparent low-e coatings

• For PVT-air add heat transfer enhancing structures (for example metal fins) to

the backside of the PV module

• For PVT-air produce a highly turbulent flow in the air cavity to improve the

heat transfer.

• Develop bonding techniques for minimal heat resistance between PV

cells and collector fluid.medium term PVT manufacturers, • Develop dedicated PVT cells by optimisation of the solar absorption

R&D institutes of PV cells

• Apply highly transparent low-e coatings

PVT manufacturers • Integrate the heat transfer enhancing measures in the production

technique of the PV module.

• Develop modules in which the PV cells and the absorber are fully

integrated (deposition of thin-film PV on metal substrate).

long term PVT manufacturers, • Apply dedicated PVT cells with optimised solar absorption

R&D institutes

Type relevance


liquid unglazed ••


air unglazed ••


ventilated PV •

a-Si or to another material with a better tempera-ture coefficient. However, then PVT cannot makeuse of the good electrical efficiency of c-Si.



70

short term PVT manufacturers, • Product development using standard interconnection techniques for the

installers electric cabling and the thermal connections (air and water).

• Comply to all the requirements for systems using the combination of

electricity and water outdoors

medium term PVT manufacturers, • Work on definition of standard and test procedures of integrated inter

installers connection techniques

long term PVT manufacturers, • Real plug and play systems

installers • Integration of the water lines with the electric cabling


Table 23. PVT plug-and-

play connection

development scheme.

Integration issues

Aesthetics

Aesthetics is an issue of major importance for groups as varied as homeowners, companies, realestate developers and architects. It is importantto establish criteria for good PVT design. In ad-dition, flexibility in shape and colour, as well asan optimal fit to the building stream should beobtained.

Development of plug-and-play modules

One of the main advantages of a PVT system isthe reduction in installation time required. Thiscan only be realised when the interconnectionswith the electrical and heating systems arestraight forward and can be applied fast. In thecase of PVT liquid the interconnection has also

to comply with additional demands when combining water and electricity in the same system.The system should be installed by just one in-staller and not by a separate electrical installer and a thermal installer.Most of the work will be product development

using existing interconnection techniques. On thelong term, new interconnection techniques might be developed where the electric cabling and thehydraulic system will be integrated.

short term - -

medium term PVT manufacturers, • Inventory of the aesthetic requirements of homeowners, architects and

Consultancy, archit ects other relevant groups

• Development of PVT systems that are flexible in size and colour, as well as

uniform in appearance.

• Development of industrially designed PVT modules

long term PVT manufacturers • Testing and commercialisation of aesthetically optimised PVT modulesthat allow for flexible integration

Table 22. PVT aesthetics

development scheme

short term PVT manufacturers • Carry out economic optimisation studies for diferent types of PV in PVT,

taking into account the operation temperature of the PVT

• Investigate in real applications by how much really the electric output is

reduced by increased cell temperatures in installed field systems

medium term PVT manufacturers,•

Find ways to lower the PV temperature during stagnation conditions.R&D institutes

long term PVT manufacturers • Develop thin film PV techniques with better high temperature performance

R&D institutes

Table 21. PVT

Temperature dependence

development scheme.

Type relevance





concentrator •••


Type relevance



air glazed ••••

air unglazed ••••

concentrator ••••


P h o t o : A u s t r i a S ol a r &

Br a m a c D a c h s y s t e m e I n t e r n a t i on a l



71


Combining PVT with PV or thermalcollectors on a single roof or façade.

The thermal side of the covered PVT collector will be used mostly for domestic hot water. Another application is a so-called combi system, whichdelivers a large part of the hot water demand anda small part of the space heating demand. For bothapplications, the required PVT area is limited bythe heat demand of the house. This is a big differ-ence between thermal solar systems and grid con-

nected solar PV systems, since the PV area on a building is only limited by the available roof andfacade area. To optimise a solar system it might be necessary to combine PVT with standard PVin a single plane. Therefore, roof-mounting tech-niques have to be developed in which PVT andPV can be combined in any ratio and in any shape.In addition, the combination of PV and PVTshould also have an aesthetic appearance. Thereare differences between the two that hamper anaesthetic appearance. The PVT collector isthicker than the PV module and (because of the

glass cover above the PV) the impression of shineand colour is different. The simplest solution isto develop PVT dummies. These have the same

appearance as PVT collectors but produce onlyelectricity. Of course PVT dummies are moreexpensive than standard PV laminates, so thisis not the optimal solution. On the longer term,aesthetically matched roofing systems for PVand PVT should be developed. This can even bea contrasting match in which the differences arehighlighted but are forming aesthetically a goodcombination.Finally, simulation tools have to be developedfor the dimensioning of solar systems in which

PV-modules, thermal collector modules and PVTmodules can be combined to fulfill the require-ments of the building in the best way.A similar problem appears when PVT air sys-tems for space heating are extended to provid-ing solar cooling as well. Since solar coolingrequires higher temperature levels than mostPVT air collectors will be able to provide, thePVT collector array is often combined with an ar-ray of conventional solar air collectors to boost thetemperature level. For the commercialisation of suchsystems, it is important to develop standardised and

aesthetically matched roofing and façade systemsfor PVT combined with solar thermal.

Design tools

Good design tools are essential for the appli-cation of PVT systems. Design tools facilitate

the implementation of the PVT system in the building development process. The designtools have to range from rules of thumb andspreadsheet based models to more sophisti-cated models like a full physical simulation of the yearly performance.The whole range of design tools should be de-veloped focusing on the target group which will

use the design tools.

• Dimensioning tools should be developed for architects, in which they can easily dimen-sion the PVT roof to fit in their building de-

sign. These tools should also have the possibility to make a visualisation of the PVT roof on the building.

• Sophisticated performance modeling toolsshould be developed for engineering companies, in order to make detailed calculationsof the PVT system yield. These tools can be based upon the TRNSYS simulation model.

short term R&D institutes, • Develop rules of thumb and spreadsheet based models for standard PVT

PVT manufacturers, modules (PVT liquid, flat-plate)

engineering companies, • Develop dimensioning aids for the architects as well as a visualisation

architects aid for standard PVT modules (PVT liquid, flat-plate)

• Develop a PVT module for the TRNSYS platform for standard PVT

modules (PVT liquid, flat-plate)

medium term R&D institutes • System optimisation with full physical models.

PVT manufacturers, • Develop PVT design tools for non-standard PVT modules

engineering companies, architects (PVT concentrator, PVT air)

long term R&D institutes, PVT manufacturers, • System optimisation with full physical models for non-standard

engineering companies, architects PVT modules.

Table 24. PVT design tool

development scheme.

Type relevance

liquid glazed •••

liquid unglazed •••

air glazed ••••




Type relevance

liquid glazed •••

liquid unglazed •••

air glazed •••

air unglazed •••

concentrator •




72

Combining PVT with heat pumps

PVT, and especially unglazed PVT, functions bestat low temperature applications because of the rela-tively large heat loss and the negative effect of temperature on PV cell performance. An interestinglow-temperature application is the combination of an unglazed PVT module with a heat pump. Byusing a heat pump, the low temperatures of theuncovered PVT collector can be used for higher temperature applications like space heating or do-mestic hot water.For such a system, a large storage will be required

between the heat pump and the solar supply. Twooptions are either an ice storage (of about 2 m3)that could be placed in the attic (Spoorenberg &Traversari, 2003), or a ground storage, where aground heat exchanger could be used for extract-ing energy from the soil during the winter and re-generating the soil during the summer (Bakker etal., 2005).However, the combination with a heat pump willalso set additional demands. Due to the lower mod-ule temperatures, condensation may occur on the

modules (front side and rear side), and even theformation of ice can occur on the PVT panel over longer periods. This has an influence on the elec-trical yield of the system. Of course, the formation

of ice can be prevented by keeping the PVT mod-ule above 0 oC, or reduced by introducing meltingsequences over specific intervals in time. However,in both ways thermal energy is lost.

• All interconnections and cabling must be re-sistant against ice over longer periods. On thelong term it might be possible to develop non-stick coatings, which can prevent ice form-ing at the PVT surface.

• The influence of the more severe stress con-ditions in the PVT due to condensation andice forming has to be studied.

• The advantage of increasing the temperatureof the heat source with a PVT should be ana-lysed in detail in order to confirm if the PVTis a good complement to a conventional heat pump system. An analysis should be madecomparing PVT to other heat source concepts.Simulations should be done with differentdata (climate, house properties, comfort need,etc…) concerning all regions of the futurePVT market.

• Appropriate heat-pump technology working

at elevated and more dynamically varyingtemperatures (compared to heat exchangers buried in the ground as a heat source for theheat pump) has to be developed.

Table 26. PVT with heat

pump development scheme.

short term R&D institutes, • Establish under what conditions PVT is suitable as additional component

PVT manufacturers to a heat pump system.

• Set up field systems using available heat pump technology.

• Develop melting sequences. Develop module temperature control to

prevent freezing.

medium term R&D institutes, • Development of appropriate heat-pump technology

PVT manufacturers • Development of uncovered PVT modules that withstand condensation

and icing conditions

long term R&D institutes, • Develop non-stick coatings to prevent ice forming on the PVT module.

PVT manufacturers


Table 25. PVT & PV

combined system

development scheme.

short term PVT manufacturers • Develop dummy glazed PVT with only an electric production

• Develop unglazed PVT collectors, looking like standard PV.

• Develop simulation tools for the dimensioning of solar systems with combinations of

PV-modules, thermal collectors and PVT-modules.

medium term PVT manufacturers • Develop aesthetically matched roofing systems for PV and PVT. This can even be a

contrasting match in which the differences are highlighted but are forming aesthetically

a good combination.

• Develop aesthetically matched roofing systems for solar thermal and ventilated PV or PVT air

collectors for solar cooling applications.

• Develop roof mounting systems in which PV and PVT can easily be combined in varying ratios

long term PVT manufacturers • Develop complete integrated and aesthetically matched PV/PVT roofing systems.

Type relevance

liquid glazed •

liquid unglazed ••••

air glazed •


concentrator •

ventilated PV •



73


short term R&D institutes, • Market analysis for solar cooling, including Southern countries

PVT manufacturers • Systems studies on PVT cooling

• System optimisation of ventilated PV or PVT air collectors with booster

collectors for solar cooling

• Demonstrate combination of highly concentrating PVT with single effect

cooling

medium term R&D institutes, • System optimisation of highly concentrating PVT with single effect cooling

PVT manufacturers • Develop aesthetically matched roofing systems for solar thermal and

ventilated PV or PVT air collectors for solar cooling applications.

long term R&D institutes, • Combination of highly concentrating PVT with double effect cooling

PVT manufacturers

Table 27. PVT coolingdevelopment scheme

(see also issues related

to PVT concentrator

development).

Combining PVT with solar cooling

Special PVT topics are the integration with a sin-gle or double effect sorption cooling system.

Whereas a single effect sorption system can reacha COP (Coefficient of Performance) of around 0.7at driving temperatures of around 70 to 90 oC,double effect sorption chillers can reach a COPof around 1.3 at temperatures of around 130 to150 oC. The higher COP of double effect is veryattractive, but the solar cells and thermal absorber must be able to withstand temperatures of about150 to 200 oC.Because of the relatively high temperatures, so-lar cooling can best be provided by concentrat-ing PVT, due to the lower thermal losses at hightemperatures for this technique.There are two possible development routes:

• Low concentration (mostly smaller than 3)for areas in which beam as well as diffuseinsolation should be collected. This systemis mostly placed in a fixed orientation.

• High concentration for areas in which only beam insolation should be collected. Thesesystems are mostly tracking the sun over oneor two axes.

Solar cooling will probably be needed only partof the year, so it is interesting to combine solar

cooling with hot tap water and possibly spaceheating.

Although PVT concentrators are the best PVT

candidate for providing the high temperaturelevels required for solar cooling directly, thisis not the only consideration, since attentionshould also be paid to the optimisation of thesystem yield on an annual basis. From this perspective, it is an interesting option to ex-tend a PVT air system, used for space heatingduring the winter, with the option of provid-ing solar cooling during the summer. How-ever, since such systems cannot directly pro-vide the temperature level required by the so-lar cooling system, an additional booster sys-tem is required, e.g. in the form of conven-tional air collectors.

Type relevance

liquid glazed •

liquid unglazed •

air glazed ••

air unglazed ••


ventilated PV •••

P h o t o : J o e C o v e n t r y-A N U



74



75

8. Conclusions

8. ConclusionsPVT has a large potential. PVT systems can beapplied in a large share of the present solar ther-

mal market, including domestic hot water sys-tems, as argued in chapter 4. In addition, PVTcan supply a significant contribution to the EUtargets for the implementation of renewable en-ergy, as argued in chapter 5. It should be con-cluded that PVT is a very promising techniquethat deserves efforts from target groups rangingfrom policy makers to installers.

Most promising system-mar-ket combinations

In this roadmap, an inventory has been made for the most promising markets for PVT:• In the short term, specific actors in the build-

ing market may already be motivated to in-vest in PVT (e.g. real estate developers, hous-ing associations, municipalities). Multi-fam-ily buildings (especially if owned by a hous-ing association) may be an important earlymarket, due to the limited roof area available,which promotes area efficient renewable en-ergy applications. Furthermore, interesting

niche markets may exist in off-grid applica-tions and (public) pool heating.

• In the medium and long term, the most prom-ising application for PVT systems seems to be domestic water heating and space heat-ing. For space heating, it is especially truefor advanced houses wanting to cover a large part of the energy needs with solar energy.Combination of a heat pump and PVT could be a promising concept.

• In the long term, professional application (in-

dustry, agriculture) and applications such assolar cooling will become interesting for PVT.

The requirements of the different markets leadto different PVT systems:

• For glazed PVT liquid collectors, the mainmarket is seen as the domestic hot water mar-ket, being by far the largest market segmentas indicated in chapter 4. Interesting nichemarkets are seen in the tertiary market for applications such as homes for the elderly,hospitals and sports buildings. It is expected

that these PVT systems will be less suitablefor domestic heating, keeping in mind thereduced thermal efficiency as compared to

conventional solar thermal collectors, whichwill lower the performance during the heat-

ing season, especially for the short heatingseason experienced in low-energy buildings.Off-grid, niche markets may exist for recrea-tional applications or desalination systems.

• For unglazed PVT liquid collectors, the mainmarket is seen in the combination of thiscollector with a heat pump for space heatingapplication. The main future markets wouldthen be the domestic market, again becauseof the size of this market, and the tertiarymarket, because it is to be expected that theheat pump will become increasingly popu-lar here due to the cooling it can provide. Asmaller specific market is seen in PVT poolcollectors.

• For glazed PVT air collectors, unglazed PVTair collectors and ventilated PV facades, themain market is seen in utility space heating.In addition, glazed PVT air collectors willhave a niche market in domestic space heat-ing combined with tap water heating througha heat exchanger. Although the domesticmarket is large, it is expected that this will

be a niche market due to technical limita-tions of such systems and the difficult com- petition with liquid collectors. Finally, aninteresting niche market exists for autono-mous air collector systems for the ventila-tion of cottages.

• For concentrating systems, the main marketis seen in large hot tap water systems for multifamily buildings or tertiary applications.A large niche market may be solar cooling inthe utility market. In off-grid applications, a

niche may exist for desalination systems.

B e a uf or t c o ur t -RE S



76

Barriers to be overcome

A number of barriers were identified for PVT.An overview is given below.

Table 28. Barriers to PVT

and how to remove them

Action plan

In the previous paragraphs a number of actionshas been defined. In order to present these ac-tions in the most effective way, the action plan below attributes these actions to the appropriate

actors, indicating both benefits and challengesfor the main actors involved.

Manufacturers

Benefits of PVT• new and/or enlarged marketsChallenges• how can the production technologies of PV and

solar thermal be integrated cost-effectively?• how can plug-and-play integration of PVT

into heating and electrical systems be accom- plished?

• how can PVT modules be produced withsufficient variety in colour and shape?

• how can PVT be promoted effectively?

8. Conclusions

barriers ... ... and how to overcome them

lack of cert if icat ion Dedicated PVT testing and rel iabi li ty standards have to be made, taking into account PVT

specific issues such as stagnation temperature resistance of the PV.

unknown legal status An inventory has to be made, to find out how well PVT f its in with nat ional energy

regulations, building codes and regulations regarding installation, and bottlenecks should

be removed.

lack of financing schemes Financing schemes need to be set up, in order to help consumers finance the high initial

cost of PVT.

unclear subsidy schemes An inventory of existing subsidy schemes should point out if PVT fits in sufficiently well. For

the future, dedicated PVT subsidies should be set up. Subsidies should be considered to

facilitate training courses for installers and architects.

lack of awareness In the short run, awareness should be raised on the level of policy makers and solar energy

professionals, to facilitate the introduction of PVT. In the near future, this should be exten-

ded to decision makers (consumers, real estate developers, etc) in the form of targeted

marketing campaigns.

improved economics Thermal module efficiency should be improved and module- and installation costs should be

reduced. For the reduction of the installation costs, the development of plug-and-play

connections is important.

opt imised systems Combination of PVT with heat pumps, combination of PVT with PV, combination of PVT with

solar cooling. Design tools should be developed.

bui lding integrat ion Aesthet ics should be improved. PVT modules should be developed that are suf ficiently

flexible in colour and size, as well as uniform in appearance. Design tools and prefab PVTbuilding elements should be developed.

improved rel iabil ity Stagnation temperature res is tance should be suffic ient ly high.

Policy makers

Benefits of PVT

• Renewable energy targets reached moreefficiently and at an earlier time

Challenges• which market support mechanisms are most

effective for PVT?• how should PVT be included in the new

energy efficient building regulations?• how can research, development and demon-

stration of PVT be supported most effectively?

R&D and Test institutes

Benefits of PVT

• development requires innovative technologi-cal solutions

Challenges• what should the performance and reliability

standards for PVT look like?• which field tests should be carried out to sup-

port warranties?



77

• which technological solutions can be foundto increase the optical and thermal efficiencyof PVT

• which technological solutions can be found

to increase the long-term reliability of PVT?

Architects

Benefits of PVT• new ways to integrate renewables into build-

ings

• less aesthetic problems with integration intothe building envelope, since only one deviceneeds to be integrated

Challenges• how can PVT (and other solar technologies)

become an integral part of the buildingdesign?

• which new building concepts are now possible because of PVT?

Energy consultancy and engineering

companies

Benefits of PVT• innovative and high profile technology for

demonstration projectsChallenges• what sort of design tools are needed by

architects, installers and engineers?• which new system concepts are now possi-

ble because of PVT?

8. Conclusions

• what are the best system configurations for given climates and applications?

• which market surveys are required to support the commercialisation of PVT?

Building industry

Benefits of PVT• high profile green product that may be used

to promote the sale of core products• increased energy performance of buildings

• reduced payback time compared to PV andsolar thermal side-by-side.

Challenges• how can plug-and-play integration of PVT

into the building construction be accom- plished?

• how can prefab building elements be real-ised that facilitate installation of PVT?

Installers

Benefits of PVT• reduced installation effort

• new or enlarged marketChallenges• how can plug-and-play integration of PVT

into heating and electrical systems be accom- plished?

• how can the three specialisms (roofing, heat-ing and electrical installation) be combined?

• which targeted solar campaigns are neces-sary for PVT?



78



79

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GlossaryExergy

The amount of energy that can be transferred

to work and is not converted to entropy.

Heat pump

A device that can bring heat from a low temperature level up to a high temperature level(e.g. a fridge). A heat pump needs external power to function (electricity or heat).

Heating season

The part of the year in which heating is re-quired. This depends on climate and buildingtype.

Hot spot

The fact that a non-functioning PV cell heatsup due to dissipation of the power of the other cells in the string.

ICS

Integrated collector storage; a system in whichthe collector and the storage tank are integratedinto one device.

Mismatch lossSolar cells operating under diferent illuninationor temperature will have different power curves.When connected in series or in parallel this leadsto reduced total efficiency, known as mismatchloss.

Season factor

If the thermal PVT yield is only harvested partof the year (e.g. a swimming pool that is onlyused during the summer), the annual yield of

the collector can be determined by means of a

Glossary

season factor, which is defined as the irradia-tion over the period of use, divided by the irra-

diation over the whole year.

Stagnation temperature

The absorber temperature that is reached if heat is not actively withdrawn from the collec-tor (e.g. due to pump failure or full storage).Typical stagnation temperatures for unglazedPVT may be as high as 80 °C, whereas typicalstagnation temperatures for glazed PVT may be as high as 130 °C.

Spectral selectivity

The phenomenon that the absorption is high inthe solar part of the spectrum and low in thethermal part. Because the thermal absorptionis low, so is the thermal emission, which limitsthe radiative losses. PVT collectors are typi-cally not spectrally selective, unlike conven-tional thermal collectors. This results in higher radiative losses for PVT.

Solar fraction

The ratio of used renewable energy over total

used energy.

Staebler-Wronski effect

Light-induced degeneration of the efficiencyof amorphous silicon.

TPV

Thermo-photovoltaics: devices for the conver-sion of thermal radiation into electricity. Al-though the name is similar, PVT and TPV arefundamentally different types of devices.



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The matrices of PVT manufacturers and PVT products presented below are part of the Photo-

voltaic/thermal Solar Energy Systems, report IEA

Table 29. PVT

Commercial standard

products. (Source: IEA

SHC task 35)

Overview PVT products IEA SHC task 35PVPS T7-10 and updated as part of IEA task 35on PV/Thermal Solar System. For more infor-

mation see www.iea-shc.org/task35



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Table 30. PVT product

research overview.

(Source: IEA SHC task 35)

Overview PVT products IEA PVPS T7

Figure 21. (a) Powerlight

(PowerTherm), (b) Cythelia

(Capthel collector; photo:

Alain Ricaud), (c) Solar

Focus (TERC)

(a) b) (c)



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Table 31. Overview of

PVT products for specific

projects (Source: IEA SHC

task 35)

Figure 22. (a) TFM

(Mataro library), (b)

Atlantis Energy

(Scheidegger building),

(c) Atlantis Energy (Aerni

factory), (d) Esbensen

Consulting Engineers

(Yellow house), (e)

Australian National

University (Bruce Hall), (f)

Crowder College (Solar

Decathlon 2002 house).

(a) b) (c)

(d) (e) (f)



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For more information, see also the PVT platform at the ECN website (www.ecn.nl).

Table 32. PVT contact

information (source: IEA

SHC task 35).



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