Number crunching

Yeah, real-world performance is likely to have multiple factors affecting the power output, not just temperature coefficient spec of the panels. Nonetheless, it would be very nice to be able to tell the loss (or gain) of power generation is due to temperature or something else. My panel has 25 years efficiency loss warranty, but I am a bit skeptical any manufacturer actually honer such claims ever. I will have to ask for warranty documents on my system to read the small prints, but how can an owner demonstrate such loss of efficiency over years?

 

"how can an owner demonstrate such loss of efficiency over years?" With the handheld photon counter discussed here earlier would be one way.

 

Certainly I will keep record of Daily Light Integral (DLI) and total kWh generated from the system for that day and hand calculate the production efficiency. But I wonder what percentage of owners would have such device and keep the record over the span of warranty period? I wish efficiency of the panel is displayed somewhere in the built-in data logging capability. I have not found such functionality on my PV system.

And even if I can demonstrate generation efficiency loss by comparing kWh/DLI, it does not take into account for temperature difference. So that means, I would also need to keep record of daily temperature.

There maybe more factors that affect power generation. So, it would be easy for a manufacturer to deny even a legit warranty claims, I would think.