Working temperature of Solar Panel

What is temperature of the panel which should be used for worst case calculation of efficiency during a high summer in Mediteranian countries ?
Thanks Toshko

Probably 45C I think @dominof.

Thanks a lot Marty. You think probably on outside temperature because the temperature of the panel could rise maybe much more than 45C ( I suppose) ??? Or maybe due to the construction of panel temperature does not rise much above the ambient temperature (if there is enough space underneath to cool down).
Generally, for standard panels with power temperature coefficient of -0.4%/K, temperature increase of 20C makes 8% less power which is not number to neglect.

I think the rules here is to use ave daily temp at 3pm (say 20C), plus a factor depending on how the panels are mounted. If they have a frame that offsets them from the roof (and gets good cooling air flow) that factor is 25C (hence using 45C). If it’s flat on the roof, then that factor should be 35C (so you would use 55C).

To cut to the important number, in hot Australian climates, I think people generally use a temperature derating of 5%.

As a general guide you could use the NOCT values from the solar panel specification sheet… Although these are generally for temperate climates, not arid desert regions.

The internal cell temperature can be as high as 80 degC with a very hot 40 degC ambient temperature and little wind, so about a 15-20% loss can be expected in these extreme temperatures. However you should do all estimated generation calculations based on the average peak sun hours (PSH) of your location and average temperatures.

Below is the spec sheet for LG Neon 2 panels showing the STC power rating and the NOCT power rating below.


Wow that’s a massive difference. I thought STC was ambient temp not module temp. So you can expect a 20% loss in a perfectly nice 20C day? That’s seems like a crazy high derating?

But it’s also only using 800W/m2, which would be maybe ave across the day for decent install?

Dear Svarky, thanks a lot for explanation and contribution to this discussion.
It’s more clear now and calculation I supposed is.
Maybe we should install the PV panels inside a water containers and get hot water and better performances. I do not know are PV panels can sustain continous immersion in water (back side only). Do you think manufacturers specify this parameter ??
Regards Dominof

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Dear Marty,
It’s nice that we clarify this issue because the numbers we get from data sheets are very optimistic. Thanks again for your support. Regards

Hi Dominof ,

  1. you can also choose to have a lighter colour for your roof material .It will reflect some heat rather than absorb ( Also getting ready for Bifacial panels as when its become more affordable )
    and I notice new houses has more black or dark colour roof

  2. I notice from Specification The Silver frame performance has a 5 watts higher than the black frame of the same make & model, But customer preference for the better look than performance

Marty you wouldn’t normally get a 20% loss on a 20 degC day, but around 10-12% loss is pretty standard (with no wind).
The STC is based on 25 degC ambient temperature at midday (1000W/m2) for a few seconds. In real world the internal cell temperature increases to 35-40 degC within 5-10 minutes and derates accordingly, this is normal and why is makes more sense to oversize the PV as much as possible.

The Thermal imaging camera shows this really well… could be a good article here! :wink:

Dear SHS,
Thanks for the piece of advice. Unfortunately color of my roof is dark.