PERFORMANCE ANALYSIS OF DIFFERENT GRID CONNECTED ROOFTOP SOLAR POWER PLANTS

PREPARED BYK. NAGA VENKATESH,ROLL NO. 15MSE007M.TECH 2ND YEAR,ENERGY SYSTEMS & TECHNOLOGY-FOCUSED ON SOLAR

GUIDED BYHOD OF SOLAR DEPARTMENTDr. INDRAJIT MUKHOPADHYAY

1. INTRODUCTION RENEWABLE ENERGY SCENARIO IN INDIA  

India’s overall generation capacity as of November 2016 stands at 308.83GW, of which approximately 262.165GW comes from conventional energy sources and 46665MW from renewable energy sources.   Table 1: Grid connected installed capacity from all sources as of April 30, 2016

Source Installed Capacity (MW) Share

Coal 187,252.88 61.12%

RES MNRE 44,236.92 14.44%

Large Hydro 43,112.43 14.07%

Gas 25,057.13 8.18%

Diesel 918.89 0.30%

Nuclear 5,780.00 1.89%

Total 302,833.20 100.00%

 

Source Total Installed Capacity (MW) 2022 target (MW)

Biomass Power(Biomass & Gasification and Bagasse Cogeneration)

4932.33 *10,000.00

Small Hydro Power 4324.85 5,000.00Solar Power 8874.87 100,000.00Total 46665.53 175,000.00Waste-to-Power 114.08 *10,000.00Wind Power 28419.40 60,000.00

 Table 2 : Installed Grid Interactive Renewable Power Capacity in India as of April 30, 2016 (RES MNRE)

Regions

Northern Region

Western Region

Southern Region

Eastern Region

North Eastern Region

Islands and others

Total

 

MW’s

2,097.72

2,464.91

3,766.46

184.98

5.37

106.77

8,874.18 

Table 3: Grid Connected Solar PV plants in India

The total installed solar roof top power plants in India is 500MW out of 8874.87MW. Our target is to install 22GW solar roof top power plants by 2022.

2.1 Overview of Grid Connected Roof Top Solar PV system

The main Blocks include in solar power plants is:

1.SOLAR BLOCK(DC) Module mounting structure dc cable Solar modules

2.Power Block Solar Inverter

3. Power Evacuation block AJB ACDB AC CABLES

4. Measuring Block Whether monitoring system Energy Meter

3. Methodology

it includes study of different type of performance parameter, various losses and affect in energy generation, life cycle of Solar Module, revenue generation for grid connected solar PV project and analysis of project case studies with recommendation to improve the performance of existing plant in design side with include selection of plant balance of system, like Cable, inverter, module, module mounting structure, protection equipment and compare the design with actual report with existing plant equipment.

Designing parameters means Proper String connection, selection of cables according to Temperature and proper tilt angle of the structure

4. Different Types of ROOFs Available in INDIA

Maximum Possibilities Of roofs Present in India

1. Plain roof Facing exactly south and some Azimuthal towards West or east direction shown in below figure.2. Tilted roofs with East-West Direction and some azimuthal towards east or west direction shown in below figure.3. Tilted roofs with north-south Direction and some azimuthal towards east or west direction shown in below figure.4. Some roofs are with ellipsoidal shape.

Flat roofEAST-WEST roof

NORTH-SOUTH roof

5. Performance of the solar power plants

The performance of solar power plants is best defined by the Capacity Utilization Factor (CUF), which is the ratio of the actual electricity output from the plant, to the Maximum possible output during the year. Which is normally 17 to 23% for all the solar roof top power plants.

PR=Where Ptpv is Thermal loss factor for PV. And It can be calculated by using the below formula Where Tc is Standard Temperature. NOCT is Normal operating condition Temperature Β- Power Temperature coefficient of the module.

6. Factors Effecting on the Performance of the solar power plants

1) Quality of the modules

2) Tilt of the modules and Azimuthal angle of the modules.

3) Temperature

4) Irradiation

5) Inverter Efficiency.

6) Other losses in the system

6.1 Quality of the Modules

Photovoltaic converters are semiconductor devices that convert part of the incidentSolar radiation directly into electrical energy. The most common technologies that are available in the market is showing in below figure.

Mono Crystalline silicon (Wafer based silicon)

15-20% 40rupees/Wp

Poly Crystalline silicon (Wafer based silicon)

15-17% 30 rupees/Wp

Thin films (a-si) 6-9%  CdTe (Thin film) 9-11%  CIS/CIGS 10-12%  

Table 4: Type of the modules and it's Efficiency

Module model

Rating of the module

Efficiency (%)

Voc(V)

Isc(A)

Vmpp(V)

Imp(A)

Canadian solar (Mono Crystalline)

320Wp 16.69 45.60 9.13 37.20 8.610

Canadian solar (Poly) Crystalline)

320Wp 16.67 45.3 9.26 36.8 8.70

Renesola solar (Poly Crystalline)

320Wp 16.5 45.6 9 37.4 8.55

Trina solar (Poly)

320Wp 16.58 45.8 9.10 37.2 8.61

Topsun solar Mono Crystalline solar

320Wp 16.58 45 8.93 37.8 8.49

Rec solar (Poly Crystalline)

320Wp 16.41 46.1 8.99 37.8 8.48

phono solar 320Wp 16.59 46.4 8.95 38 8.64Pana sonic 240Wp 19.31 52.4 5.85 44.3 5.5Kyocera solar

315WP 14.37 49.2 8.5 39.7 7.9

Waaree solar

300Wp 15.47 45 8.89 36.1 8.39

Table 5: Module and it's Technical Dimensions

Present so many companies are manufacturing solar modules with different efficiencies and different Vmp and Isc. But the modules rating is same. Here I am showing the table below which contains different companies of poly crystalline modules with its efficiency and its current and voltage ratings.

6.2 Change in Tilt of the Modules and different Azimutal angles of the modules

Before going to this concept, first we have to know that “why we have to face the modules in south direction”?

Northern hemisphere includesUnited statesCanadaRussiaAll parts of the EuropeIndia(south Asia region)Southern hemisphere includesNewzilandAustraliaBrazilMadagascarArgentina

6.2.1 Different tilt of the Modules on the same roof

S.No

Plant capacity

Tilt

Annual Production

Specific production No. of units

per day per Kwp

change in generation with optimised tilt(no of

units/year)(kwh/Kwp/year)

1 57.6KWp 22 94233.6 1636 4.482191781 1958.4

2 57.6KWp 20 94752 1645 4.506849315 1440

3 57.6KWp 18 95212.8 1653 4.528767123 979.2

4 57.6KWp 16 95616 1660 4.547945205 576

5 57.6KWp 13 96192 1670 4.575342466 0

6 57.6KWp 10 96076.8 1668 4.569863014 115.2

7 57.6KWp 8 96019.2 1667 4.567123288 172.8

8 57.6KWp 4 95558.4 1659 4.545205479 633.6

9 57.6KWp 0 94809.6 1646 4.509589041 1382.4Table 6: Chennai 57.6KW capacity with different

tilt angles.

S.No Plant capacity Tilt

Annual Production

Specific production No. of

units per day per Kwp

change in generation with optimised tilt

(no of units/year)

(kwh/Kwp/year)

1 57.6KWp 25 96134.4 1669 4.57260274 57.6

2 57.6KWp 23 96192 1670 4.575342466 0

3 57.6KWp 20 96019.2 1667 4.567123288 172.8

4 57.6KWp 17 95616 1660 4.547945205 576

5 57.6KWp 13 94752 1645 4.506849315 1440

6 57.6KWp 10 93830.4 1629 4.463013699 2361.6

7 57.6KWp 5 91814.4 1594 4.367123288 4377.6

8 57.6KWp 0 89164.8 1548 4.24109589 7027.2

Table 7: Ahmedabad 57.6KW capacity with different tilt angles.

S.NoPlant capacity

Tilt

Annual Production

Specific production No. of

units per day per Kwp

change in generation with optimised tilt

(no of units/year)

(kwh/Kwp/year)

1 57.6KWp 0 79718.4 1384 3.791780822 8294.4

2 57.6KWp 5 81964.8 1423 3.898630137 6048

3 57.6KWp 10 84556.8 1468 4.021917808 3456

4 57.6KWp 15 86054.4 1494 4.093150685 1958.4

5 57.6KWp 18 86918.4 1509 4.134246575 1094.4

6 57.6KWp 22 87494.4 1519 4.161643836 518.4

7 57.6KWp 25 87667.2 1522 4.169863014 345.6

8 57.6KWp 28 87897.6 1526 4.180821918 115.2

9 57.6KWp 31 88012.8 1528 4.18630137 0

10 57.6KWp 35 87379.2 1517 4.156164384 633.6

Table 8: Jalandhar 57.6KW capacity with different tilt angles.

1.From that different tilts we can conclude that placing of the modules with latitude angle will gets more generation compared to all other tilts.

S. No

City Average Radiation

Ambient Temperature

Optimum tilt

1 Jodhpur 5.52 26.1 26.32 Jaipur 5.52 26.1 26.83 Varanasi 4.88 25.1 25.34 Patna 4.83 25.3 25.65 Shillong 4.54 16.5 25.66 Ahmedabad 5.35 27.5 23.17 Bhopal 5.23 25.3 23.38 Srinagar 4.10 13.6 34.19 Delhi 5.09 25.1 28.610 Ranchi 4.70 24.3 23.411 Kolkata 4.50 26.9 22.512 Bhavnagar 5.70 27.2 21.813 Nagpur 5.12 27 21.114 Bombay 5.03 27.5 19.115 Pune 5.41 24.7 18.516 Hyderabad 5.67 26.7 17.517 Visakhapatnam 5.13 28.4 17.718 Chennai 5.36 28.8 1319 Bangalore 5.47 24.1 1320 Dehradun 5.32 11.4 30.321 Ludhiana 5.23 22.6 30.922 Manali 4.59 -1.6 32.323 Allahabad 5.79 25.9 25.524 Darjeeling 4.80 9 27.125 Kota 5.08 25.4 25.226 Vadodara 5.29 27.5 22.327 Bhubaneswar 4.82 26.9 20.328 Machilipatnam 4.95 28 16.229 Mangalore 5.08 27.3 12.930 Coimbatore 5.12 26.2 1131 Jalandhar 5.39 20.4 31.332 Bhatinda 5.08 23.4 30.233 Ajmer 5.14 5.14 26.5Table 9: Different locations with their

optimised tilts and Average Radiation

Calculations show that for modules faced towards the equator, and with a tilt angle equal to the latitude, yearly reflection losses relative to STC are about 1%.

2.As optimised tilt increases, the structure cost is increases and weight of the area on that roof increases and total cost of the project is also increases.

6.2.2 Different Azimutal angles of the building with same tilt of the module

1) Flat roof with different Azimutal angles towards west and east

S.NoPlant capacity(KWp)

Roof Azimutal(-ve (East side) +ve (West side)

Annual Production

Specific production

No. of units per day per Kwp

change in generation compared to south

(no of units/year)

(kwh/Kwp/year)

1 462 45 739200 1600 4.383561644 32340

2 462 40 746130 1615 4.424657534 25410

3 462 30 755832 1636 4.482191781 15708

4 462 20 763686 1653 4.528767123 7854

5 462 10 769692 1666 4.564383562 1848

6 462 5 771078 1669 4.57260274 462

7 462 0 771540 1670 4.575342466 0

8 462 -5 771540 1670 4.575342466 0

9 462 -10 770616 1668 4.569863014 924

10 462 -20 765996 1658 4.542465753 5544

11 462 -30 759528 1644 4.504109589 12012

12 462 -40 748902 1621 4.44109589 22638

13 462 -45 743820 1610 4.410958904 27720Table 10: Solar Generations with different Azimutal angles.

In India some of the buildings are facing south and some of the buildings are having some azimuthal angles towards west or East and how much generation is coming from that buildings if we install the solar power plants over there and we can observe that differences in generation between south facing buildings and azimuthal buildings.

2) Tilted roof (North-South) with different Azimutal angles towards west and east

Figure 6-2-2: North- south roof

S.NoPlant capacity(KWp)

Roof Azimutal(-ve(East side) +ve (West side)

Annual Production

Specific production

No. of units per day per Kwp

change in generation compared to south

(no of units/year)

(kwh/Kwp/year)

1 462 45 767382 1661 4.550684932 8778

2 462 30 771540 1670 4.575342466 4620

3 462 20 773850 1675 4.589041096 2310

4 462 10 775236 1678 4.597260274 924

5 462 5 775698 1679 4.6 4626 462 0 776160 1680 4.60273

9726 0

7 462 -5 776160 1680 4.602739726 0

8 462 -20 775698 1679 4.6 4629 462 -30 774312 1676 4.59178

0822 1848

10 462 -45 771078 1669 4.57260274 5082

Table 11: Solar Generations with different Azimutal angles.

Observation:-

If you take all of the above roofs we can observe that, exactly facing south modules are getting more generation compared to facing the modules with some Azimutal angles towards East or West. East-south Roof is getting more generation compared to West-south direction.

Example:

Consider the building Flat, they want to Extend that that flat roof as Slanted, and The Azimutal Angle of the Building Is 45deg towards west, in how many Possibilities we can Place the Modules on that roof and In What Possibility We will get Max Generation??

East-West Roof

1) East- Facing Modules South, West- Facing Modules South2) East, West- Facing Modules Along the roof.3) East- South Facing, West- Along the roof4) East- Along The Roof, West- Modules Facing south.

Only East- Roof

1. East Roof- Modules placing in south Direction2. East roof – Modules Placing Along the roof

Only West- Roof

1. West Roof- Modules Placing in south Direction2. West roof- Modules Placing Along the roof

Modules placing Plant size(kWp

PR(%)

Annual Energy(Mwh/year)

Specific Production(Kwh/Kwp/Year)

East roof + Remaining        East-along the roof 44.8 76.7 64.76 1445

East- south facing-1 34.6 71.4 49.28 1426         West roof + Remaining        

West-Along the roof 49.4 76.4 76.24 1547West-South facing 32.32 76.8 51.39 1606         East+West+Remaining        

East-West(Along the roof)) 49.28 76.6 74.05 1503

East-West(South facing) 33.9 75.6 52.4 1545

East-Along the roof, west-south 41.6 76 62.53 1503

west-Along the roof, East-south 41.6 75.3 63.07 1516

From the above table we can say that West Roof, facing Modules south Is getting more generation compared to all other cases. But total power plant size will be decreases compared to Placing the Modules along the roof.

6.3 Temperature

Module performance is generally rated under Standard Test Conditions (STC): irradiance of 1,000 W/m², solar spectrum of AM 1.5 and module temperature at 25°C. All electrical parameters of solar module depend on temperature. The module output decreases with increase in temperature. The loss of power as defined by Temperature coefficients. This effect can be seen in the sample V-I characteristics, obtained from the specification sheet for commercially available module.

Figure 6-3-1: Voltage and Current W.r.t Temperature

Typical values of temperature coefficient for for crystalline silicon are as follows: γ (Pmpp) typical values for crystalline modules is -0.4 to 0.45%/K γ (Pmpp) typical values for amorphous modules is -0.2 to 0.23%/K γ (Pmpp) typical values for CdTe modules is -0.24 to 0.25%/K Therefore thin film modules will certainly give higher performance at elevated temperature when compared to crystalline silicon.

As the Temperature increases, the module voltage and power decreases and Voltage drop of the cables(DC & AC) increases in the power plant.

Module model

Rating of the module

Efficiency (%)

Voc(V)

Isc(A)

Vmpp(V) Imp(A) β(V/deg) β(nA/

deg)β(W/deg)

Canadian solar (Mono Crystalline)

320Wp 16.69 45.6 9.13 37.2 8.61 -0.173 0.02 -0.45

Canadian solar (Poly) Crystalline)

320Wp 16.67 45.3 9.26 36.8 8.7 -0.165 0.05 -0.43

Renesola solar (Poly Crystalline)

320Wp 16.5 45.6 9 37.4 8.55 -0.147 0.03 -0.4

Trina solar (Poly)

320Wp 16.58 45.8 9.1 37.2 8.61 -0.153 0.03 -0.41

Topsun solar Mono Crystalline solar

320Wp 16.58 45 8.93 37.8 8.49 -0.167 0.01 -0.45

Rec solar (Poly Crystalline)

320Wp 16.41 46.1 8.99 37.8 8.48 -0.141 0.03 -0.4

Table 12: different solar modules with their Temperature Coefficients

Voltage, Current and Power Equations W.r.t Temperature.

Where Voc- Open Circuit voltage Pmpp- MPP Power

Vmpp- Maximum power point voltage

T1- Standard temperature

Isc- Short circuit current

T2- Practical Condition

Impp- Maximum power point current

Till now we have observed the characteristics of Module specifications with temperature. Both DC cables AC cables are also Depends on the Temperature. As the Temperature Increases, The Resistance of the Both DC cable and AC cable is increases, and the voltage drop of the power plant is also Increases.

So Temperature is also one of the factor for selection of the cables. According to MNRE rules we have to implement the solar Roof-top Power plants Less than 2%. If distance is very high from string to inverter then we have to use Parallel runs for decreasing the Voltage Drop.

DC Voltage Drop: - PV Modules to Inverter

AC Voltage Drop: - Inverter to Metering Panel.

As the temperature increases , the resistance of the cable also increases.

Where β is Temperature coefficient of the copper and it varies with Temperature.

T2- Final Temperature

T1- Initial Temperature

% DC Voltage Drop =

Where 2 Represents for both +ve and –ve DC Cable

I Represents String Current under Practical Condition

R represents Resistance under Practical condition

L represents Length of the one cable.

V Represents Total voltage across the string under practical condition.

% AC voltage Drop =

Where I represents Inverter output current A- Power factor

R represents Resistance of the AC cable under Practical condition

L represents Length of the one cable.

V represents output Voltage of the Inverter Normally 415V.

LENGTH OF THE AC

CABLE

SIZE OF THE

CABLE(INV TO

ACDB)

No.of

runs

Inverter o/p current(considering

Derating Factor)

Voltage drop

% percentage voltage drop(UPF)

Resistance of AC cable per metre@45 DEG

64C,25 Sqmm CU 1 90.90909091

0.725193439

0.174745407

0.000767622

64C,25 Sqmm CU 1 90.90909091

0.725193439

0.174745407

0.000767622

64C,25 Sqmm CU 1 90.90909091

0.725193439

0.174745407

0.000767622

64C,25 Sqmm CU 1 90.90909091

0.725193439

0.174745407

0.000767622

75

3.5C,120 SQmm,2 run AL 2 363.6363636

6.316200916

1.521976124

0.00026743

75

3.5C,120 SQmm,2 run AL 3 363.6363636

4.210800611

1.01465075

0.00026743

Table 13: AC Voltage Drop Calculation of one real solar power plant

TOTAL VOLTAGE DROP(2 runs) 1.696721531

TOTAL VOLTAGE DROP(3 runs) 1.189396156As we Increase the No. of runs of the cable, there is a possibility of decrease the AC voltage drop of the

Total plant size. And always we have to maintain Voltage drop below 2%.

6.4 IRRADIATION

Beam Radiation – solar radiation received from the Sun without being scattered by the atmosphere and propagating along the line joining the receiving surface and the sun. It is also referred as direct radiation. It is measured by a pyrehiliometer.

Diffuse Radiation – the solar radiation received from the Sun after its direction has been changed due to scattering by the atmosphere. It does not have a unique direction and also does not follow the fundamental principles of optics. It is measured by shading pyranometer.

Total Solar Radiation – the sum of beam and diffused radiation on a surface. The most common measurements of solar radiation is total radiation on a horizontal surface often referred to as ‘global radiation’ on the surface. It is measured by pyranometer.

Extraterrestrial radiation- the intensity (power) of the sun at the top of the Earth's atmosphere. It is usually expressed in irradiance units (Watts per square meter) on a plane normal to the sun.

As the irradiation changes, the o/p current changes and the power of the solar plant is changes. As the irradiation increases, the o/p power is also increases and the performance of the solar power plant increases.Below I am showing that a graph between voltage and power with different irradiations.

Below I am showing irradiation data for different locations.

Figure 6-4: PV power, Irradiations vs Time of the day

6.5 INVERTER

A solar PV inverter is a type of electrical inverter that is made to change the direct current (DC) electricity from a photovoltaic array into alternating current (AC) for use with home appliances or to be fed into the utility grid.

These inverters may be standalone inverters, which are used in isolated systems, or grid tie inverters which are used to connect the power plant to the grid.

The currently available grid connected inverters have efficiencies of 96 to 98.5%, and it depends on designing conditions. Before going to design string layout we should have to know the inverter technical specifications.

Two types of Inverters are present in India. They are

1) String and central Inverters

2) Micro Inverter

Model RPI-M50AManufacturer DELTAInput Max. DC 1000 VDC input Voltage Range 250-1000 VNominal DC Voltage 600Start Up Voltage 250 VMaximum Input Current 50 A * 2MPPT 2String/MPPT 5Output Power 50000 VAMax. Output Current 73 AMax. Voltage Range 3Ph 200± 20%Efficiency 97.8 %/ 97.6 %

Efficiency of the Inverters are Effected due to

1) String Mismatch losses (Partial shading)

2) Unbalancing MPPT

3) Different orientations are giving to one MPPT.

4) Unbalancing in the strings

5) String Voltage is not equal to Nominal MPPT voltage Mentioned in a data sheet.

Consider one Example, 5 strings are connecting to one MPPT, Due to Parapet wall shadow is coming on the 2 modules of one string that means 2 modules will be shut down (V=0), That means string Voltage is decreases and it is not Equal to other strings voltage.

So always while we are designing the solar power plants we must have to do shadow analysis and that should be below 2%.

6.5.1 String Mismatch losses (Partial shading)

Delta 30KW Inverter has 2MPPT’s and 6 String Inputs. We can unbalance the MPPT’s are in ratio of 67% and 33%.

Suppose my plant size is 34.56 Kwp (Delta 30Kw Inverter is enough and module rating is 320Wp.)

Possibilities of the strings: - 18*6 (Balanced)

20*3, 16*3 (wrong connection)

19*5, 13*1 (unbalancing the MPPT)

6.5.2 Unbalancing MPPT

6.5.3 Different orientations are giving to one MPPT

6.5.5 String Voltage is not equal to Nominal MPPT voltage Mentioned in a data sheet.

If the power plant designing string voltage is not equal to the Nominal MPPT voltage, then there is a chance to decrease the efficiency 1 or 1.5%

6.6 OTHER LOSSES IN THE SYSTER

6.6.1 Degradation of the Modules:

6.6.2 Soiling loss

Normally the power Degradation of the modules is 0.5% during 1st year and 0.8% during second year……

If we see the power plant after 24 years, the generation is 60% of the 1st year.

Soiling loss is 2% (Normally cleaning monthly one time)

Soiling loss in Industrial areas is 4% (cleaning monthly one time)

Soiling loss is 0.45% (normally cleaning weekly one time)

Total System Size = 291.84 kWp FINALGHI = 1942

Global Horizontal Irradiation 1942Global Incident in Collector Plane 1.8%Near Shadings: Irradiance Loss -0.4%

IAM Factor on Global -2.9%Soiling Loss Factor -1.5%

Effective Irradiance on Collector 1883Collector Area 1750

PV Conversion Efficiency at STC 16.67%Array Nominal Energy (at STC Efficiency) 549.28

PV Loss due to Irradiance Level -0.2%PV Loss due to Temperature -9.0%Year-1 Annual Degradation -0.5%

Module Quality Loss 0.4%LID - Light Induced Degradation -2.0%

Module Array Mismatch Loss -1.0%Ohmic Wiring Loss -0.5%

Inverter Loss During Operation -1.70%Inverter Meter Accuracy Error 0.0%

AC Ohmic Losses -0.8%System Unavailability 0.0%

Expected Energy Injected Into the Grid 469Total Irradiated Energy 577

System PR % 81.3Expected Specific Generation Value 1607

Expected Generation of the Solar power plant without using PV SYST software by considering all the losses which are occurring in Power plants and this plant is Located at Chennai.

7. Example of Real Power Plant analysis: -

Future scope: -

• The future scope of this work is to Evaluate the solar power plants Performance with different types of orientations and different Azimutal angles.

• Making a new formula for solar power generation according to variance in tilt angles and Azimutal angles of the building, and finding out the various techniques to develop the performance of the solar power plants.