Panels overheating or simply not suited for hot weather?

[Tay]

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.

A good read that, despite 12 years old the theory is the same.

The key is a low coeffecient (As a higher rating would means less output per Deg C over (or under I presume) its typical sweet spot of 25 Deg C, high output, small size within the capabilities of your chosen inverter.

ta

[John_S]

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

I had not realised that the range was so large.

I have now had my panels for 13+ years. I have tried to measure degradation over that period but with no clear results.

However, it is clear that there there is a very good correlation between sunshine hours (at Heathrow, ten miles down the M4 from me) and kWs produced. Trouble is that it can only be easily measured on an annual basis.

In my data logging, I have found that the kWhrs produced per kWp of my panels is also inversely correlated to the number of sunshine hours. This makes sense. Sunshine hours is a proxy for average temperature and a higher temperature means less kWhr per kWp.

One day I shall post my conclusions on degradation on this forum, but at the moment there are none.

Sure, there is a lot of noise in the data, is it clear bright sun, or hazy sun? is it morning or afternoon sun (I suffer from early morning shading in the summer and lots of winter shading and my roof faces about 20 degrees west of south)? etc. But the trend is clear.

However, give me more sunshine hours, especially in the summer, to be happy.

John

[sharpener]

However, give me more sunshine hours, especially in the summer, to be happy.

John

If there are any going spare I would prefer mine to be in the winter!

I would have found it difficult to insist on a particular brand of panel on grounds of tempco and perhaps it is more important to choose a size which enables you to get the best utilisation of the roof area. Last year I contacted over 20 potential installers over a period of six months and despite being flexible about type and size was not able to get the second bank installed until November. Callidus quoted me for 10 x 385W panels which would have given me a bit more output, but cancelled the day before they were due to come.

It would have been nice to get new panels with self-coloured aluminium frames to match the old but things have moved on and it would have put too much of a constraint on the project. The new all-black panels look inconspicuous on the slate roof but it would have been nice if the rails had also been black, or even if the fitters had brought proper end caps for them!

I think other differences can also be more important. E.g. I get as much power from the 8 x 405W (3.24 kW nom) as I do from the original 16 x 230 (3.68 kW nom), though one is measured at DC by the Victron MPPT and the other by an AC meter so it may just be measurement error. And it is not because the original panels are dirty or degraded, their annual yield is still as much as when first installed in 2011.

[Tay]

However, give me more sunshine hours, especially in the summer, to be happy.

John

If there are any going spare I would prefer mine to be in the winter!

I would have found it difficult to insist on a particular brand of panel on grounds of tempco and perhaps it is more important to choose a size which enables you to get the best utilisation of the roof area. Last year I contacted over 20 potential installers over a period of six months and despite being flexible about type and size was not able to get the second bank installed until November. Callidus quoted me for 10 x 385W panels which would have given me a bit more output, but cancelled the day before they were due to come.

It would have been nice to get new panels with self-coloured aluminium frames to match the old but things have moved on and it would have put too much of a constraint on the project. The new all-black panels look inconspicuous on the slate roof but it would have been nice if the rails had also been black, or even if the fitters had brought proper end caps for them!

I think other differences can also be more important. E.g. I get as much power from the 8 x 405W (3.24 kW nom) as I do from the original 16 x 230 (3.68 kW nom), though one is measured at DC by the Victron MPPT and the other by an AC meter so it may just be measurement error. And it is not because the original panels are dirty or degraded, their annual yield is still as much as when first installed in 2011.

I think the key for me is going to be trying to find a happy compromise between size and output. And I suspect I may be in a similar position to you when it comes to when somebody can install

Actually getting somebody to commit to coming out and conducting a proper review instead of telling me that 16 panels will give me X power, I'd be happy (I can do that bit, its not hard), if I was happy going on the roof and and some 100lbs lighter I might have considered that option too!!, my brother in law is a bit of a monkey for this type of stuff but I wouldn't trust him to do this stuff.

If I cant get panels installed for some time I might just go down the big battery route myself (but a static rather than what I have got right now. Time will tell I guess and that might decide AC coupled or DC coupled too.

But it has given me time to think about stuff and ask questions. Also I'd probably just grab some larger temp panels and get stuck into the micro inverter route until I'm able to get a static solution but do less playing and more just leaving the damned things alone ^^

[sharpener]

Actually getting somebody to commit to coming out and conducting a proper review instead of telling me that 16 panels will give me X power, I'd be happy (I can do that bit, its not hard), if I was happy going on the roof and and some 100lbs lighter I might have considered that option too!!, my brother in law is a bit of a monkey for this type of stuff but I wouldn't trust him to do this stuff.

If I cant get panels installed for some time I might just go down the big battery route myself (but a static rather than what I have got right now. Time will tell I guess and that might decide AC coupled or DC coupled too.

Most of the people I talked to did virtual surveys based on google sat view plus photographs. To cross check their recommendations I counted the slates and also measured the whole roof at ground level. PV-GIS is good at the macro scale and there is an app on the Midsummer website which enables you to plan the panel layout and do a materials take-off.

Starting at this point in the year then maybe getting on with the battery is a better move though. There is something to be said for having some of both AC and DC to maximise the efficiency and avoiding double conversions.

[Ken]

Over thinking it.
There is probably a bigger variation in efficiency of different panels. Just look at the spec sheets.
The best panels are those whose size allows you to mount the most kwp

[Stinsy]

I'm not sure all this matters so much on a domestic array intended fro self-consumption. On the hottest days in summer you tend to generate more than you can use. Far more important is how the panels perform in bright-overcast conditions. Small variances here would make a big difference to how your array performs.

Ig you're building a commercial array in Tunisia or whatever then this metric is more important.

[Tay]

Most of the people I talked to did virtual surveys based on google sat view plus photographs. To cross check their recommendations I counted the slates and also measured the whole roof at ground level. PV-GIS is good at the macro scale and there is an app on the Midsummer website which enables you to plan the panel layout and do a materials take-off.

Starting at this point in the year then maybe getting on with the battery is a better move though. There is something to be said for having some of both AC and DC to maximise the efficiency and avoiding double conversions.

I've got freebie access to an app called Pylon, pretty slick too, also uses sat imagery but I'm not 100% convinced about the sizing, but I might be wrong, its geared more towards the professional reseller/designer side of things, but it was pretty good for me to have a play around with various inverters and and generally muck about with it.

Free to use for single (or perhaps 2, I cant remember) location designs but as I said geared towards the pro's that might do many different designs/locations/regions etc, has tons of panels preconfigured and heaps of extras.

What I dont want though is somebody to arrive with a bunch of panels and go "Ahhh, but you've got xyz roof tiles we cant do that!!" because I know I dont have a cookiecutter roof. I'd rather people not wing it on the day.

Hopefully I'll know about access to funds next week or so, so, not long to wait now.

[Tay]

Over thinking it.
There is probably a bigger variation in efficiency of different panels. Just look at the spec sheets.
The best panels are those whose size allows you to mount the most kwp

idle hands and all that

You are probably right.

[Tay]

I'm not sure all this matters so much on a domestic array intended fro self-consumption. On the hottest days in summer you tend to generate more than you can use. Far more important is how the panels perform in bright-overcast conditions. Small variances here would make a big difference to how your array performs.

Ig you're building a commercial array in Tunisia or whatever then this metric is more important.

I figured as much, but in order to eick as much power out of this roof as possible and stay married I need something perhaps slightly non standard, I'll probably need everything generated to charge the batteries but still have the EV tariff to fall back on.