Charge rate on a hot day

[nschizzano]

(2x) 100w panels, total 200w. I am getting 50w to 67w Watts or so on full sun, but very hot and humid out. 81F to 87F. Is this the watts I should be getting with that heat? In Ottertail city Minnesota, from about mid June untill today(july22 2024). In may I rebuilt
/updated my system I was getting 187w on full sun. Displayed On my old eppever mppt. I now have a new Litime MPPT. And a new LItime bat. Was it perhaps the changing of my system? Like an error or issue? Or is the the weather? Slightly Stressed and confused. I kinda want all those 200 watts right now. Running my generator alot now.. So I tested each panel, giving 16.5v to 19.5 volt full hot humid sun, w/ slight haze out. The back of the panel says 21v (max). Renogy panels. Thanks.

 

[JWLV]

STC (Standard Test Condition) is 25C or 77F. Solar panels are rated at STC. So 81F to 87F is not too far off from STC and should not affect your solar panels much at all. There's probably something else wrong if you're only getting 50w to 67w, but it's probably not the weather.

Are your two panels connected in series? If not, then that must be the problem.

 

[740GLE]

Also hot and humid also means hazy, you may see blue sky but that moisture hanging in the air is getting in the way.

 

[Mattb4]

... So I tested each panel, giving 16.5v to 19.5 volt full hot humid sun, w/ slight haze out. The back of the panel says 21v (max). Renogy panels. Thanks.

The 19. 5Voc would be low but in the margin of error. 16.5Voc would suggest a panel problem either from shade, bad weather or damage.

 

[Suijkerbuijk]

Wy update your mppt ?
If it works fine wy update it ?
It can that the new Litime MPPT use other settings and just use a slow charge function.

See if both settings are the same or adjust the float a little higher .

 

[sunshine_eggo]

STC (Standard Test Condition) is 25C or 77F. Solar panels are rated at STC. So 81F to 87F is not too far off from STC and should not affect your solar panels much at all. There's probably something else wrong if you're only getting 50w to 67w, but it's probably not the weather.

Are your two panels connected in series? If not, then that must be the problem.

Except that solar panels are rated at CELL temperatures, not ambient. In 20°C ambient with only 800W/m^2 irradiance, the CELLS will be about 45°C, so a typical panel is going to lose ~7-8% Voc/Vmp due to cell heating, so the 21.5Voc panels should measure about 19.5Voc when the panels are at full operating temperature in sunny conditions (20°C ambient, 800W/m^2). If conditions are hotter or more intense than 20°C ambient or 800W/m^2, voltage will be even lower.

The 16.5V panel is a concern.

I would test performance of each panel individually in the MPPT.

I would also confirm charger is not in absorption mode limiting output due to nearly charged battery by adding a notable load to draw battery voltage down and encourage more PV output.