Absolute Cavity Pyrgeometer (ACP) and InfraRed Integrating ...Integrating Sphere (IRIS) Comparisons...

Absolute Cavity Pyrgeometer (ACP) and InfraRed Integrating Sphere (IRIS) Comparisons for CIMO

Meeting in the National Physical Laboratory (NPL), UK

Ibrahim RedaPrincipal Scientist

NREL/PR-1900-70458

November 15, 2017

NATIONAL RENEWABLE ENERGY LABORATORY 2

• Why the ACP was developed.• The ACP Measurement Equation.• The Revised Calculation of the Throughput (τ).• Field measurement process.• Results of four comparisons between NREL’s ACPs

and POMD’s IRISs.• Absolute atmospheric-longwave-irradiance versus

the Irradiance measured by PIR with traceability to WISG.

Overview


Few years ago experimented with calibrating pyrgeometers outdoors independent from the traditional methods using blackbodies. The result of this experiment was published in 2006. The pyrgeometer was installed outdoor on aluminum plate connected to circulating temperature bath, by lowering the pyrgeometer’s body temperature, while the incoming longwave irradiance is stable, the slope of the outgoing irradiance versus the pyrgeometer’s thermopile output is the outdoor net irradiance responsivity (RSnet), independent of the absolute value of the atmospheric longwave irradiance. To evaluate this method, the calculated irradiance using the derived coefficients was compared to the irradiance measured using a pyrgeometer with traceability to the World Infrared Standard Group (WISG). Based on results from four pyrgeometers calibrations, the method agreed with the WISG within ±3W/m2 for all sky conditions.

Why ACP: When the article was reviewed, reviewers suggested removing the word ABSOLUTE since the

Pyrgeometers had domes.

Why the ACP was Developed

Reference: I. Reda, J. R. Hickey, J. Grobner, A. Andreas, T. Stoffel. “Calibrating Pyrgeometers Outdoors Independent from the Reference Value of the Atmospheric Longwave Irradiance”. Journal of Atmospheric and Solar-Terrestrial Physics, Vol. 68 (12) August 2006 pp. 1416-1424.


The Measurement Equation

where:- Watm is the atmospheric longwave irradiance (W.m-2)- K1 is the reciprocal of the ACP’s responsivity (W.m-2.uV-1)- Vtp is the thermopile output voltage (uV)- ϵ is the gold emittance = 0.02925- K2 is the emittance of the black receiver surface- Wr is the receiver irradiance (W.m-2)- Wc is the concentrator irradiance (W.m-2)- τ is the ACP’s throughput, NIST characterization

K V W W K Wtp atm c r1 21 2* * ( ) * ( ) * *= + + − −τ ε ε

KW K W

Vc r

tp1

21 2=

+ − −( ) * ( ) * *ε ε∆ ∆∆

WK V K W W

atmtp r c

=+ − − +1 22 1* ( ) * * ( ) *ε ε

τ

- By cooling the ACP case temperature, and since Watm is stable, then,

- Then the atmospheric longwave irradiance is,

Since Wnet = Win – Wout , then,

Reference: Reda, I.; Zeng, J.; Schulch, J.; Hanssen, L.; Wilthen, B.; Myers, D.; Stoffel, T. Dec. 2011. “An absolute cavity pyrgeometer to measure the absolute outdoor longwave irradiance with traceability to International System of Units, SI”. Journal of Atmospheric and Solar-Terrestrial Physics, 77 (2012) 132-143. http://dx.doi.org/10.1016/j.jastp.2011.12.011


• τ is the ACP’s throughput- During NIST characterization τ was calculated using

K1 = 0.2667, which resulted in τ values from 90.1% to 93.5%.- Since the pyrgeometer has no dome, the correct K1 value

was given to NIST to recalculate τ with K1 = 0.0784, which resulted in τ = 99%.

The Revised Calculation of the Throughput

Reference: Z. Jinan, L. Hanssen, I. Reda, J. Scheuch. “Preliminary Characterization Study of a Gold-Coated Concentrator for Hemispherical Longwave Irradiance Measurements”. Reflection, Scattering, and Diffraction from Surfaces II: Proceedings of SPIE Conference, 3-5 August 2010, San Diego, California 12 pp.


1. The ACP is deployed outdoor under clear sky conditions.2. Once stabilized with the outdoor environmental conditions, the self calibration starts to calculate K1.3. K1 is then used to calculate τ (see ACP article),

τ = 0.004903 ∗𝐾𝐾1+.004419.007548∗𝐾𝐾1+.004242

4. The atmospheric longwave irradiance is then calculated using the Measurement Equation in slide 4.5. Steps 2 through 4 are repeated every 1 to 2 hours based on the outdoor conditions.

Field Measurement process


Results of First Comparison between ACPs and IRISs-Davos


Results of Second Comparison between ACPs and IRISs-Davos

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18:57 19:21 19:46 20:19 20:43 21:18 21:42 22:06 22:43 23:07 23:42 0:06 0:33 1:05 1:29

W/m

2

UTC

Night-Time IR irradiance measured at PMOD by ACP, IRIS, & WISG on October 2&3, 2013(~15 mm H2O vapor column)

W(ACP-6) W(IRIS-2) W(IRIS-3) W(IRIS-5) W(WISG)


Results of Third Comparison between ACPs and IRISs-Davos


Results of Fourth Comparison between ACPs and IRISs-SGP

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32020

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Irrad

ianc

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/m2 )

CST

Nights on October 16, 17, 18, 23, 24, 25 & 26, 2017

ACP95F3 ACP96F3 PIR 31197F3 IRIS1 IRIS2 IRIS5


Results of Fourth Comparison between ACPs and IRISs-SGP, cont.

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Irrad

ianc

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/m2 )

CST

Average of 2 ACPs, Average of 3 IRISs, and PIR

Average ACP Irradiance Average IRIS Irradiance PIR 31197F3


Results of Fourth Comparison between ACPs and IRISs-SGP, cont.

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Irrad

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/m2 )

CST

Average of Absolute Irradiance Versus PIR w.r.t. WISG

Average of Absolute Irradiance PIR 31197F3


• The difference between the irradiance measured by the ACPs and the IRISs is within ± 3 W/m2, which is within the stated uncertainties of the ACPs and IRISs.

• The irradiance measured by the PIR with traceability to WISG is lower than the absolute atmospheric-longwave-irradiance by 3-5 W/m2.

Conclusion


Set-up at DOE-ARM-SGP

Julian, Craig (SGP), Mike (NREL), Allison, and Chuck PIR, ACPs, IRISs, PIRs, and CG4s

Fifth comparison will be held at SGP from November 27th to December 8th, 2017

Absolute Cavity Pyrgeometer (ACP) and InfraRed Integrating ...Integrating Sphere (IRIS) Comparisons...

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