Faulty Inverter or Panels?

spikemuk

I'm hoping somebody out there could give me some advice on an annoying problem that I am having with my Solar PV system

The installation is a 4KW PV solar installed on a bungalow at the end of 2011. The installers have since gone into liquidation. The system consists of two strings of 10 panels each on a south facing 30 degree roof with no shade issues, I had an ABB inverter installed three years ago to replace the faulty Aurora PVI 3.6 inverter under the warranty period. Since installation the generation figures have been slightly lower than before but I put this down to cloudier weather and deterioration of the solar panels. However when I checked the inverter I noticed that whilst string 2 was working fine, string 1 had the correct voltage (360v) (sorry, on my original post I incorectly stated this as 330v) but the ampage was zero and hence not generating any output. The inverter appeared to be working fine and had no error messages. When I rebooted the system, string 1's zero ampage corrected itself and the outputs continued correctly for the rest of the day. However, on checking the next day the string was fine in the morning, but at about midday stopped working again - a reboot got it working.

A more detailed observation of the display showed that the two strings work fine until the total output reaches 3588W, then string 2 continues to increase output (up to 3000W), whilst the voltage and ampage for string 1 starts to drop. Once the string 1 ampage reaches zero, the string 2 output then returns to around 2000W (if sunny), but string 1 output then remains at zero for the rest of the day. However, if I reboot the inverter at this point, then both strings operate correctly for the rest of the day. If its an overcast day, the problem doesn't seem to occur and both strings run fine for the whole day.

I got in touch with ABB and they first suggested that there is an earth leakage on string 1 and to check for condensation or poor connection on the wiring from the panels. I did this and found nothing. They now suggest that it is probably a faulty panel on string 1 and I would need an electrician to find which one is faulty. However local electricians need to have scaffolding put up to do this (even though the installation is on a bungalow), and of course the question of whether to upgrade to solar edge whilst there is scaffolding up now comes to mind.

I'm still convinced that it's the replacement inverter that's at fault as there was no problem with the panels and their connections under the previous inverter. The reduced output has only occurred ever since the new inverter was installed and I think it is unlikely that a panel would become faulty at exactly the same time - hence I'm apprehensive at getting scaffolding put up to test the panels if the fault is likely to be elsewhere.

Any suggestions out there?

1961Nick

spikemuk wrote: »

I'm hoping somebody out there could give me some advice on an annoying problem that I am having with my Solar PV system

The installation is a 4KW PV solar installed on a bungalow at the end of 2011. The installers have since gone into liquidation. The system consists of two strings of 10 panels each on a south facing 30 degree roof with no shade issues, I had an ABB inverter installed three years ago to replace the faulty Aurora PVI 3.6 inverter under the warranty period. Since installation the generation figures have been slightly lower than before but I put this down to cloudier weather and deterioration of the solar panels. However when I checked the inverter I noticed that whilst string 2 was working fine, string 1 had the correct voltage (330v) but the ampage was zero and hence not generating any output. The inverter appeared to be working fine and had no error messages. When I rebooted the system, string 1's zero ampage corrected itself and the outputs continued correctly for the rest of the day. However, on checking the next day the string was fine in the morning, but at about midday stopped working again - a reboot got it working.

A more detailed observation of the display showed that the two strings work fine until the total output reaches 3588W, then string 2 continues to increase output (up to 3000W), whilst the voltage and ampage for string 1 starts to drop. Once the string 1 ampage reaches zero, the string 2 output then returns to around 2000W (if sunny), but string 1 output then remains at zero for the rest of the day. However, if I reboot the inverter at this point, then both strings operate correctly for the rest of the day. If its an overcast day, the problem doesn't seem to occur and both strings run fine for the whole day.

I got in touch with ABB and they first suggested that there is an earth leakage on string 1 and to check for condensation or poor connection on the wiring from the panels. I did this and found nothing. They now suggest that it is probably a faulty panel on string 1 and I would need an electrician to find which one is faulty. However local electricians need to have scaffolding put up to do this (even though the installation is on a bungalow), and of course the question of whether to upgrade to solar edge whilst there is scaffolding up now comes to mind.

I'm still convinced that it's the replacement inverter that's at fault as there was no problem with the panels and their connections under the previous inverter. The reduced output has only occurred ever since the new inverter was installed and I think it is unlikely that a panel would become faulty at exactly the same time - hence I'm apprehensive at getting scaffolding put up to test the panels if the fault is likely to be elsewhere.

Any suggestions out there?

It might not prove much, but you could swap strings around on the inverter & see what happens?

DREKLY

Hi Spikemuk, to me, it sounds like the inverter, if a panel went down, the problem would be there all of the time, not coming
and going dependent on level of output.
Panels are pretty reliable things, barring stone damage by a vandal, Of course, Solaredge does continually monitor all the panels via their optimisers, so that may be the way to go...
I am puzzled as to how you have TWENTY panels, only producing a max of 4 Kw ??
I have 16 x 250 watt panels doing the same (which will all be removed later this year, should you be interested ! ).
No doubt more knowledgeable solar experts will add their knowledge soon, there are some great guys on here.

EricMears

DREKLY wrote: »

I am puzzled as to how you have TWENTY panels, only producing a max of 4 Kw ??

No great puzzle there - the clue was in the installation date. Back in 2011, 200Wp would have been a 'medium' sized panel; my 250Wp panels were about as big as you could get.

Dave_Fowler

The fact that re-booting the inverter corrects the problem suggests very strongly that the problem is in the inverter. The panels can't know you've re-booted the inverter. However:-

The only puzzling thing is the low voltage (330V) on string 1 when the current is zero. This seems low for 10 panels when there is no current. Check the specification of the panel's open circuit voltage. Most (but not all) panels are about 40 to 45 V open circuit, so 10 panels in series would be 400 - 450V open circuit.

Dave F

spikemuk

Thanks for the replies. As someone has pointed out the panels were from 2011 and hence of a lower spec than more modern solar panels. The panels are each rated at 185W and 36V, hence each string of 10 panels produces 360V and up to 1.85kW apparently, however if the readout on the ABB inverter is to believed the one string suddenly rises from 2kW to up to 3kW during the short period that the voltage starts to drop on the other string, but once that string reaches 0kW, then the other string reverts back to 2kW and stays like that for the remainder of the day, unless a manual reboot is performed, then both strings go back to close to 2kW each.
Thank you for the advice to swap the inputs over for string 1 and 2. I did this and according to the inverter, the other string of panels are now the problem string, and the string of panels which I was told had a faulty panel in it, is now working fine. I will be getting in touch with ABB again as this surely indicates that the inverter is at fault.

spikemuk

Just a quick update, ABB have agreed to replace the inverter under guarantee, which is a good outcome.

spikemuk

Final Update - The inverter has now been replaced under guarantee and that appears to have fixed the problem; both strings from the solar panels are now operating with similar output values resulting in an overall increase of about 30% in output.