Actually Vic, wouldn't the true measure be the difference between typical heat degradation of racked panels and these direct mount panels?
Yes, and that isn't the only variable though. For comparison, I looked up a similar panel to the one I have (which is no longer made... they keep getting more and more watts!):
https://www.solarwho...ne-solar-panel/
which has a a temp coeff of -.41%. Not quite as good as the ones you are using. (.05% difference)
I note that various manufacturers have better temp coeff ratings than others...
https://news.energys...re-overheating/
Take that with a ton of salt though, as it appears most of the info on the www indicates it is darn hard to actually determine the temperature of a solar cell during operation https://core.ac.uk/d.../148682287.pdf AND that it is worthwhile to cool a solar array if possible. This paper uses standard solar panels, not flexible ones, and has a readable approach to their testing:
http://www.satnac.or...osters/44.pdf. What I see in the last graphic in that paper is that PV temp roughly follows air temp, given the free-air mounting on an angle so the heated air can rise/flow over the panel.
I still think that mounting flexible panels with no air space under them is not optimal. On a sailboat's Bimini (which is where I think this idea started) heating wouldn't be as much of an issue.