camelot-forum.co.uk

Apologies if this has been covered, I searched and looked a few pages deep but found nothing.

My test 295w Perlight 54 cell panels feel like they are under performing. Prior to today I've rarely seen them produce much more than 400w's total either in series or independently as they are now), it was easier when I had them side by side on the same inclination and angle but now I've tried to optimise one of them for testing taking them both as a whole the over all generation seems lower than expected until today.

This morning it was terrible, cloud everywhere and cooler, but now the sun is mostly out for us. But I'm seeing much better results than I would have expected. Its quite a bit cooler today and I have the feeling that it might be or at least might partially be down to the panel temperatures. I've read that the voltage can increase with much colder temps but assumed the generation was fairly consistent.

Do some panels work better in cooler weather than others? I'm tempted to grab a new 400w+ panel just to compare the PV generation as a percentage to see how it measures up. You cant have enough panels after all

Currently DC1 is the south facing panel and DC2 is the SW facing, both are raised to a similar angle roughly 35-40 degs elevation. Its likely that had both panels been next to each other I would have been seeing 420w+ ish, I've only seen peaks into the 400's then it tailed off pretty sharpish even in clear/sunny skies making me think about the temps.

My local supplier has some discounted 410w Canadian Solar panels that seem quite competitive or maybe even some 575w's both physically quite a bit larger than my small 295's but different brand and possible characteristics. I think the mounting points are fairly consistent across panels so hopefully it would just be a swap out.

Obviously if its not that then then larger panels might just be better ^^

Its a fact that panels are more efficient at lower temperatures and lose power output as they get hotter.
It's also a fact that you get more generation in the summer even though it's warmer because the sun is above the horizon for longer, and is passing through slightly less atmosphere...

Your observations seem perfectly normal to me!

Panels get very hot and derate significantly in summer. The primary driver for the amount of generation in summer is simply the length of the days. At midday on the sunniest day in august you should expect to be generating 75% of your array's rated kWp.

dan_b wrote: ↑Thu Sep 28, 2023 3:20 pm Its a fact that panels are more efficient at lower temperatures and lose power output as they get hotter.
It's also a fact that you get more generation in the summer even though it's warmer because the sun is above the horizon for longer, and is passing through slightly less atmosphere...

Thanks for the reply, I knew about the higher voltages and to not over panel is cooler conditions etc, thats typically a feature of electronics in general I guess. I didn't really phrase it very well.

Do some brands or maybe particular models within brands perform better than others in various weather conditions ?

ie: I f I had 3 different brands of panels all in the same location, elevation, efficiency and type (Mono Crystalline for example), would they all produce near on the same output at 10, 20, 30 degs C, for example ?

I guess what I'm trying to discover in a very round about way, is there a preferred panel for certain conditions?.

Is it a case of people choosing JA Solar over Eurener or Perlight over Canadian Solar due to personal preference or to add to an existing system, or is it that one had a particular deal on at the time or availability of brand X was just in short supply.

I've heard a few stories of people getting a quote with brand xyz panels and being delivered brand ABC panels, if they are all pretty much the same I'm not sure I see an issue. But if brand X performs better in cooler temps like the UK then I can see why it would be an issue.

Stinsy wrote: ↑Thu Sep 28, 2023 4:26 pm Your observations seem perfectly normal to me!

Panels get very hot and derate significantly in summer. The primary driver for the amount of generation in summer is simply the length of the days. At midday on the sunniest day in august you should expect to be generating 75% of your array's rated kWp.

Ok, that makes sense and does tie in to my observations. 440w is about the best I saw out of the 2 x 295w panels so that does tie in to what I have seen.

I guess the same questions applies though, are some panels better in hot climes and conversely some better in in cooler climes?

Your question is a good one - but I suspect none of us really has the ability to test the theory properly as for that we'd need

- a large site
- a large number of different panels of equivalent size and nameplate power output from different manufacturers to test
- per panel (or per string) monitoring and the ability to log
- lots of money for the hardware for the above points!
- lots of time to assess the generation over the whole year...

Trouble is, by then you've already bought and installed it all!


I suspect for the majority of installs these days the primary issues are
- price per kWp
- are they the right physical size for the array
- actual stock availability

The most important thing is getting panels installed in the first place. With a good orientation and lack of shading. Ultimately the odd lost watt here and there from panel X vs panel Y doesn't really matter that much in the grand scheme of things.

The actual change on power is fairly small and does vary a bit between different panels - a quick check of some datasheets:
for a jasolar perc cell 410w, claimed -0.35%/°C Pmax
For a canadian solar heterojunction cell panel of similar size, claims -0.26%/°C Pmax

The real difficulty i find though, is that it is very hard to judge what is a true clear blue sky vs a slightly hazy blue sky - and that tends to make a bigger difference. Truly clear skys do seem to be a rarity now - possibly due to the increasing scale of wildfires in the last few years.

Some comparisons of the Temperature Coefficient's on panel brands here,
https://www.solarquotes.com.au/blog/the ... mperature/

For clear blue sky's you need a cold front to have just gone through to clear the dust out of the atmosphere which builds up with high pressure. We get more cold fronts passing in spring and autumn than summer.

dan_b wrote: ↑Thu Sep 28, 2023 4:49 pm Your question is a good one - but I suspect none of us really has the ability to test the theory properly as for that we'd need

- a large site
- a large number of different panels of equivalent size and nameplate power output from different manufacturers to test
- per panel (or per string) monitoring and the ability to log
- lots of money for the hardware for the above points!
- lots of time to assess the generation over the whole year...

Trouble is, by then you've already bought and installed it all!


I suspect for the majority of installs these days the primary issues are
- price per kWp
- are they the right physical size for the array
- actual stock availability

The most important thing is getting panels installed in the first place. With a good orientation and lack of shading. Ultimately the odd lost watt here and there from panel X vs panel Y doesn't really matter that much in the grand scheme of things.

I think you may be right, my biggest issue is smallest size with bang for buck with my roof, I just have to wake up every day saying to myself "something is better than nothing". the rely on off peak to charge a big lump of batteries, I wont be saving the planet anytime soon but it would make running costs less.

Are there any decent PV review sites out there? - Due to cost and so many variables I suspect most would be heavily guided by sponsors.

Perhaps we need a Linus Tech Tips for solar who is a tad less clumsy

Marcus wrote: ↑Thu Sep 28, 2023 5:34 pm The actual change on power is fairly small and does vary a bit between different panels - a quick check of some datasheets:
for a jasolar perc cell 410w, claimed -0.35%/°C Pmax
For a canadian solar heterojunction cell panel of similar size, claims -0.26%/°C Pmax

The real difficulty i find though, is that it is very hard to judge what is a true clear blue sky vs a slightly hazy blue sky - and that tends to make a bigger difference. Truly clear skys do seem to be a rarity now - possibly due to the increasing scale of wildfires in the last few years.

Thanks, I was going to ask whether higher or lower Pmax was better or worse but just found something on a Canadian Solar datasheet that explained it.

"Lower temperature coefficient (Pmax): -0.29%/°C, increases energy yield in hot climate" - I'm now wondering whether that lower co-efficient means its not so good in winter/cooler climates and a higher one is better? A leap to far?