FoxESS Community - Owners & Installers Forum

I had 12 x 480w Jinko panels installed in April last year and regularly saw output peaking at just under 6kWh. This year so far, I have just about never seen over 5kWh on any day and certainly never over 5.8kWh. This is odd to me. I am in the south of England and it has been very hot, but, from the datasheet, the panels only lose about 10% efficiency when the temperature goes from 25DegC to 50DegC. Is this expected? Is there anything I can do to troubleshoot?

I have had a number of firmware upgrades this year. Could they be causing the problem?

I see a similar reduction in hot weather. Seems about par for the course.
There is a recent discussion here viewtopic.php?t=3398 and there are others if you do a forum search.
Inverter efficiency can also drop off if it is overheating.
Here's another recent thread viewtopic.php?t=3298&sid=3c1c92cde45796 ... f45026b25f

I am just surprised that it has never been high this year, even outside the heatwaves.

Have you cleaned the panels at all since being installed?

Or do they get the rain shower cleaning treatment

"Natural cleaning". I'm in a small rural town, so not much pollution so I was thinking of cleaning them every other year, but output 20% down in a year? Is that expected if you don't clean them?

NickJH wrote: ↑Sat Jul 11, 2026 10:10 pm "Natural cleaning". I'm in a small rural town, so not much pollution so I was thinking of cleaning them every other year, but output 20% down in a year? Is that expected if you don't clean them?

Temperature is the most likely candidate, panels derating above 25C as much as 0.5% per degree depending on the make and install - that’s comfortably a 10-20% decrease in output with these consistent high temps.

The panels will have had pollen earlier in the year, and Saharan sand from the ‘weather bomb’ and without heavy rain they won’t have had chance to clear, I clear mine yearly but in all honesty i’ve never seen an obvious improvement afterwards, it just makes me feel better

I did clean my panels just a few days ago, with the day before having the same temperature as cleaning day.
It did improve the output, but it's not day & night, perhaps a ~5% increase at best.

I dare say there are panels that have been on a roof for many years without any cleaning, apart from the rain. Mine are easily accessible, so they get a clean with pure water twice a year.