In my experimental trials with SAM's CEC Performance Model with database (DB) and with user-entered specs (UES), I can't see where the model is taking account of anti-reflective glass, different responses to low-light, and LID (light-induced degradation.
For example, when I model any of the 4 SunPower X22-370 modules either with DB or UES, I always get Nominal POA losses of -2.796% for "reflection (IAM)." But I get exactly the same Reflection losses for Hyundi S290MI panels, which have no anti-reflective glass and much worse absorbtion of low-light (including their spectral response), and much worse LID (light-induced degradation). How can this be right?
On the other hand, the Nominal DC Energy "Module" losses for SunPower appear as -3.866, while for the Hyundais it is -6.459% (2.953% worse).
I leave the other inputs for these 2 panels identical for comparison purposes, so there is no need to consider shading, soiling, mismatch, diodes, etc.
I read the thread between Paul Gilman and pstuder of 6/13/16 and 6/14/16, which confused me further. It said the Module Loss includes IAM (but so does Reflection, according to the Losses report), spectral-related losses, temp-related losses, and "losses associated with converting light to electricity" (which sounds like everything).
If Module Loss is the place where differences of A/R glass, low-light (including IAM), and LID are being reflected, that would mean that the only difference between the best and the worst panels in this respect was 2.953%. That doesn't seem remotely accurate to me.
My reading suggests that the difference between top-quality A/R glass and plain glass is about 3%. The combination of high-transmission glass and cells that respond optimally to low-light and red-spectrum conditions is up to 1%. That differences in LID can easily be 2% - 3% from the best to the worst panels. These add up to 6% - 7% at the very least, and there are other differences in IAM and other losses between these SP and Hyundai panels as well.
Comparing that minimum of 6%-7% with the 2.953% difference in Module losses mentioned above leaves a minimal discrepancy of 3%-4%, and I'm not sure that covers all the differences.
However, when I lower the TCP on the Hyundai panel from its spec of -.45%/degree C to the -.29%/degree C of the SP panel, Hyundai's Module loss drops to BELOW the SP one: it goes down to -3.481%.
That suggests that all (and then some) of the difference between SP's & Hyundai's Module Loss is accounted for merely by the TCP, leaving no differences remaining to account for A/R glass, low light, and LID.
I'm confused.
By the way, I also checked the resulting annual energy figures as I went along, and they correspond pretty closely to these differences in Module Loss. This reassures me that the model isn't accounting for these other differences somewhere else.
My conclusion is that the CEC models, both DB and UES, do not account for these light factors at all. They should account for them in the Reflection (IAM) loss, but that is stuck at -2.796%. They do not, despite the forum thread, account for any of them in the Module Loss, which only reflects the TCP, and that is a temperature-variant factor, unlike the light factors I've been talking about.
This suggests that the SP panels are probably at least 6% - 7% better than the CEC models report, which is quite a large discrepancy.
Perhaps I've missed something. I've tried to search the instructions and forum, but haven't found any answers.
Or maybe this is a known problem that just hasn't yet been addressed.
Other than this, I very much appreciate the terrific work your team has done on both PV Watts and SAM.
