Degradation of domestic solar panels

JKenH

ispookie666 said:

@QrizB
Will need to put scaffolding up for any change and that would be significant cost (likely a years FIT payment).   Might wait till a few more degrade or die completely to consider changing them.    I'll have to  check the M215 micro inverter spec sheet to find out if newer panels would be ok.  

Have there been any further developments with your panel problems? I am like you am reluctant to put up scaffolding until things get worse as I doubt I could get anyone in to look at i5 given how busy solar installers are. I can’t see the problem being investigated and fixed the same day so it would need to be up for a while. 

I did buy a very, very, long pole and gave mine a wash but it didn’t change anything. 

QrizB

JKenH said:

On the east roof, which has 6 panels on each string, DC1 measured 218v and DC2 176v.

On the west roof which has 7 panels on each string, DC1 was 216v and DC2 251v.

OK, so that sounds like one faulty panel on each roof.

• East roof: 218 / 6 = 36.3 then 36.3 x 5 = 182 (quite close to 176)
• West roof: 251 / 7 = 35.9 then 35.9 x 6 = 215 (very close to 216)
  

 Are these 54-cell panels? A typical 60-cell panel has a Voc of around 40V, but 54 cells will give a Voc of about 36V which is what you're seeing.

In theory, the faulty panels should be hotter than the good ones (since it's not turning 300W of sunshine into electricity) but I have no idea whether you could detect that from the ground with a thermal camera or whatever.

JKenH

QrizB said:

JKenH said:

On the east roof, which has 6 panels on each string, DC1 measured 218v and DC2 176v.

On the west roof which has 7 panels on each string, DC1 was 216v and DC2 251v.

OK, so that sounds like one faulty panel on each roof.

• East roof: 218 / 6 = 36.3 then 36.3 x 5 = 182 (quite close to 176)
• West roof: 251 / 7 = 35.9 then 35.9 x 6 = 215 (very close to 216)
  

 Are these 54-cell panels? A typical 60-cell panel has a Voc of around 40V, but 54 cells will give a Voc of about 36V which is what you're seeing.

In theory, the faulty panels should be hotter than the good ones (since it's not turning 300W of sunshine into electricity) but I have no idea whether you could detect that from the ground with a thermal camera or whatever.

Thanks. Interesting thought. I do have an infra red thermometer but it needs to be around 20cm from the panels and I’m not good with heights. 

Voc is quoted as 39.6v for my panels. I did a Voc check on my freestanding solar panel (which I use to charge my PPS) and found it varied depending if it was in sun. Would you expect that? 

Edit: presumably my panels are wired in series to get that Voc so wouldn’t  a failed panel affect the out put from the others? The poor string on my East roof is now around 76% of the good string. 

ispookie666

@JKenH - No, just left it.  My cut off would be half the panels degrading.  Only need 5 more.  
I am presuming it is the panels rather than problem with the micro inverter. 

QrizB

JKenH said:

Voc is quoted as 39.6v for my panels. I did a Voc check on my freestanding solar panel (which I use to charge my PPS) and found it varied depending if it was in sun. Would you expect that?

Yes, shading, clouds etc. will affect Voc, and so will temperature. On a cold but bright winter's day a panel can exceed the notional Voc and so you always need a bit of headroom between the string voltage and the max inverter voltage, in case you exceed it. (This is more frequently a problem in DC off-grid systems where you pay more for higher-voltage controllers so there's a temptation tyo cut corners.)

Edit: presumably my panels are wired in series to get that Voc so wouldn’t  a failed panel affect the out put from the others? The poor string on my East roof is now around 76% of the good string. 

In principle the bypass diodes will replace the failed panel with a short circuit, so the current from the good panels can still flow but wihout gaining voltage from the failed one. That seems to be what's happening here, although you might expect the loss to be 17% (1/6th) not 24%.

JKenH

The degradation is gradually creeping up. For a long while it was around 17% but today it is just over 25%

ispookie666

I hope it's just unfavorable conditions rather than deg.  If the latter, that's way higher than quoted figures(I presume these were installed in 2018?). 

JKenH

ispookie666 said:

I hope it's just unfavorable conditions rather than deg.  If the latter, that's way higher than quoted figures(I presume these were installed in 2018?). 

They were installed in 2018. I don’t think it’s unfavourable conditions. There is no shading on that roof after 06.00 and the panels are clean.