Solar PV Issue…

[DJN008]

Evening,

Hi there hope everyone is well. I have a question for something that I have never seen before on a fault find, and wanted to get your opinions on it if you have the time please.

Six panels up on the roof, connected the two MC4’s below in the house together (just before the inverter for continuity), so testing for faults up on the roof. I am getting good readings of 3.90A end to end, and 256V. All going well so far…

I then connect the ends together, and the Amps and Voltage drop to about 0.8A & 41V. How can this be, could a faulty panel be there, therefore providing resistance?

I/R on the circuit was well above 500Meg, continuity showed +/- at the DC isolator. What are your thoughts on this anyone please, other than what I have mentioned?

Thank you.

 

[Richard-the-Ninth]

1)Why were you there?
2) What did they say is wrong/not happening?
3) How old is the installation?

 

[binky]

Plug into the inverter, it will soon tell you if there is a fault. Did you check for clouds....
what test gear are you using?

 

[DJN008]

The installation is less than a year old, String One is fine, String Two is the issue. Inverter just reads what I have found up on the roof. As I mentioned before 3.90A up on the roof, and when connected together it all drops out. Using clamp meters, multimeter you name it.

The only thing I can possibly think of, and bit of a long shot here…could one of the panels have been wired in the factory with reverse polarity, so when connected it is giving resistance..? At the end of the day, these panels are prewired so no chance of messing up the +/-‘s, unless it was wired incorrectly during manufacture..?

 

[binky]

The installation is less than a year old, String One is fine, String Two is the issue. Inverter just reads what I have found up on the roof. As I mentioned before 3.90A up on the roof, and when connected together it all drops out. Using clamp meters, multimeter you name it.

The only thing I can possibly think of, and bit of a long shot here…could one of the panels have been wired in the factory with reverse polarity, so when connected it is giving resistance..? At the end of the day, these panels are prewired so no chance of messing up the +/-‘s, unless it was wired incorrectly during manufacture..?

Factories are fully automated, so I very much doubt incorrect polarity. 99% of panel issues are failed connectors, ie the ones put on badly by the installers. Try swapping the strings at the inverter, it could also be a failed MPPT.

 

[DJN008]

Binky,

Thank you for your input, much appreciated. What I just don’t understand though is that when the circuit is split, I.e. the positive MC connector in one hand, the negative MC connector in the other hand, and test I am getting decent ampage. I then connect and the amps decrease to almost nothing. I even re-crimped these two MC4’s and still getting the same issues. Changed the strings at the inverter, and still nothing, but I expected this as there was no decent Amps when not connected to the inverter. Regarding the panels, I appreciate that the panels are made by machine, but the crimping of the MC4’s is done by hand I’m pretty sure, as they also cable-tie the leads before despatch. Very strange, but will update once I have been back there, and found the fault…

 

[binky]

Binky,

Thank you for your input, much appreciated. What I just don’t understand though is that when the circuit is split, I.e. the positive MC connector in one hand, the negative MC connector in the other hand, and test I am getting decent ampage. I then connect and the amps decrease to almost nothing. I even re-crimped these two MC4’s and still getting the same issues. Changed the strings at the inverter, and still nothing, but I expected this as there was no decent Amps when not connected to the inverter. Regarding the panels, I appreciate that the panels are made by machine, but the crimping of the MC4’s is done by hand I’m pretty sure, as they also cable-tie the leads before despatch. Very strange, but will update once I have been back there, and found the fault…

I don't quite understand that either, other than perhaps when connected to the mppt, which is altering things to get power, then a dodgy connection is failing under actual load. MC4s I was thinking of will be end of the strings on the roof. It's very common for installers not to use MC4 spanners and fail to do the back nut up properly, which in turn allows moisture ingress and eventually burns out the pins via corrosion. Also worth looking at the panels themselves for any 'oddities' like snail trails, burn marks etc etc. I did have one job where you couldn't see anything from the gorund, and even with a scaffold up there was no immediately obvious panel defects, but a quick inspection of the individual panels revealed shattered glass and lots of burn marks - panel had overheated in numerous spots due to bird poo. If visual checks reveal nothing obvious with panels or MC4s, I would test individual panels by removing them from the array which will also allow inspection of the back sheets and junction boxes. Plan B, use a bypass connection lead, easy to make one yourself, and try the string with one panel wired out at a time, or wire out half the array then individul panels, similar to splitting a ring main to find a fault.

 

[DJN008]

Great advice, thank you. I was thinking something similar. Removing each panel, testing each panel, or half the array. Would you see scorch marks on the back of the panel on the white sheeting for example? Thanks again.

 

[binky]

Great advice, thank you. I was thinking something similar. Removing each panel, testing each panel, or half the array. Would you see scorch marks on the back of the panel on the white sheeting for example? Thanks again.

scorch marks are visible from the the front and back.

Can't say I'm great at fault finding as I have had very little trouble with my own work, I used to encourage my staff to work carefully rather than have too return to a job - saves £600 for scaffolding and time.

 

[SPECIAL LOCATION]

Can't say I'm great at fault finding as I have had very little trouble with my own work, I used to encourage my staff to work carefully rather than have too return to a job - saves £600 for scaffolding and time.

Is that like the old phrase.... "More Haste, Less Speed" ?

 

[binky]

Is that like the old phrase.... "More Haste, Less Speed" ?

More or less, a well fitted pv system should be good for 30+ years bar the inverter dying at some point. To get that level of reliability, you can't just throw it on a roof and hope for the best. Plus scaffolding at around £600, or more, puts a very large hole in any profits if you have to return to fix anything, and all systems came with a 6 year warranty under MCS rules. It's why I would always recommend checking out any PV company, and directors, for changing their company name on a regular basis...

 

[DJN008]

The saga continues…
Was back on site, and we found a faulty Tigo optimiser. It was making a clicking noise, which according to their website it shouldn’t do that. Removed this one from the string, and a second one which was also faulty.

So…we then then put all the panels back together, completed the circuit just before the inverter, and we got a good amp reading, but almost zero Volts.

What are your thoughts?

Thank you.

 

[binky]

Remove any more Tigos, never did like them. My argument has always been to avoid adding failure points to the roof unless you really have to. The fact they are there possibly explains your weird results. Does the customer have a monitoring gadget for the Tigos?

 

[DJN008]

I’ve never had an issue with Tigo’s before I must admit, but it would make sense to remove them for sure. Another day on the roof…
I have access to the TAP device for the optimiers, but to be honest it doesn’t really reveal any useful data.

 

[binky]

I’ve never had an issue with Tigo’s before I must admit, but it would make sense to remove them for sure. Another day on the roof…
I have access to the TAP device for the optimiers, but to be honest it doesn’t really reveal any useful data.

I've never had anything to do with Tigo, but sounds like a dodgy batch that has failed for some reason. Or incorrectly fitted. Kind of makes sense with some of the test results you've been getting. Is there any shade issues to justify having them?

I would also be looking at the Tigo warranty, they maybe liable for cost of repairs.

 

[DJN008]

There is very little shading, but they fitted the automatic shutdown type for safety. Thank you for your reply.

 

[binky]

There is very little shading, but they fitted the automatic shutdown type for safety. Thank you for your reply.

so not needed then...