pvlib
FS spectral correction: parameters lack a reference
The first solar spectral correction function spectral.mismatch.spectral_factor_firstsolar provides coefficients for a single cdte product, see here.
The coefficients are different from those found in the primary reference, the 2016 IEEE PVSC paper by M. Lee and A. Panchula [2].
The backstory: this python code was ported from a function provided to PVLib for Matlab by the primary author, Mitchell Lee. The Matlab function was updated by M. Lee with parameters from his 43rd PVSC presentation. It appears that the finalparameters did not make it into the PVSC paper.
The Matlab code has comments that include a set of parameters for FS modules older that Series 4-2, but these parameters aren't those appearing in the paper, either.
I think we need to add a new reference, private communication with M. Lee, to memorialize the source of the built-in parameters. I can't find [4] anywhere, which might contain the parameter values. [4] appears to be a non-public work product from TUV to a client.
Credit to Larry Pratt at Groundwork for identifying the documentation issue.
[4] has a table containing values that match pvlib, but they are rounded to four decimal places, and the text says they were provided to TUV by the customer (First Solar).
@cwhanse unfortunately not. Could someone or some organization lobby First Solar to make public a document listing the coefficients?
I can reach out to to the PlantPredict team, I know they have a contact over there.
The CdTe coefficients are listed in Lee et al., Accuracy of CdTe PV Energy Predictions Using Spectral Corrections:
M was calculated for all timestamps using (2) with the relevant module coefficients as published in [17]: b0=0.86273, b1=-0.038948, b2=−0.012506, b3=0.098871, b4=0.084658, and b5=−0.0042948.
Notably, the cited [17] is the MATLAB PV_LIB...
I was unable to locate a source for the non-CdTe coefficient sets.
