Question about fault finding.

[dansk]

If i have 12 panels wired as two strings of 6 in parallel, and i do an VOC to confirm the correct voltage, and i do Isc to check for double Isc - how can i confirm that both strings are functioning if the irradiance is low.

I have wired it from the inverter in two core, out onto the roof into branch connectors were both strings plug in at that point.

 

[BruceB]

The strings really need testing individually at the branch connectors I would say to confirm they are producing similar currents.

Or if you do not want to test on the roof, then test inside but disconnect one string at a time at one branch connector on the roof (whilst no current flowing)

 

[dansk]

OK - thought as much, is there not a way to verify by doing Isc at the inverter to confirm?

I almost know one bank of panels isnt producing as the customer is getting half of the expected generation, and the MC4's i've used i have had issues with since his install - but i just wanted to do a quick test to prove it to myself.

Luckily i can get on the roof without scaffolding, so i will isolate and disconnect and trace it to the string in question.

I would like to know for the future, is there a formula for Isc and irradiance - like voltage and tempreture to compare against?

 

[BruceB]

OK - thought as much, is there not a way to verify by doing Isc at the inverter to confirm?

Theoretically with performance curves and an irradiance meter, but personally I am not convinced by the utility of the latter most of the time.

 

[Gavin A]

You can probably tell fairly reliably in strong sunlight, but in weak light I reckon it'd be pretty unreliable.

 

[dansk]

at least im not going mad!

 

[Gavin A]

at least im not going mad!

you're doing well if you're not tbf

 

[dansk]

Gavin - another question - any experiance of over voltage with NPG? Ive been to a customer today who system has been cutting out, it did it 5 times yesterday and the inverter has exceeded 261 volts, the current steady state voltage is 250v, im about to phone NPG but thought i would ask you, also it happended to them last sunday also. BD16 postcode.

All last week in the glourious sunshine the system was fine.

 

[Gavin A]

yeah, we've had it a few times.

My advice would be if possible to download the fault info from the inverter so you can give them chapter and verse of how often it's gone over voltage as well as the voltage readings.

Report it as an overvoltage fault on their line, and explain you've got evidence of it happening repeatedly this week, with a peak of 261 V recorded, and that you're certain the problem is at their end and not as a result of the PV installation.

They should send an engineer to fit a monitoring device which they'll leave in position for 2 weeks, and should then adjust the tapping on the transformer if the monitoring proves that there is a significant over voltage issue and there will be no problems from them dropping the tapping.

We've actually installed a system for a yedl engineer covering over that way, who has since apparently become that areas go to person within YEDL for these issues, so if you've got any problems let me know.

the number we ring to report this stuff is 0845 6024453, and remember to report it as an over voltage fault on their line to ensure you get put through to the right department and don't end up getting billed for it etc.

 

[dansk]

Thank you very much - very helpful, im 99.9% sure thats the issue, the install is nothing wacky, just the usual, and we downloaded the data today and its clear to see.

Thanks

 

[dansk]

To finish off this thread - fix the fault, dodgy MC4 as i thought - i placed a sheet over one bank of panels to see which side was work fine, then traced back to the connections and found it. New MC4 (+), tested and plugged back in, then started up and placed the sheet over one bank then the other at the same time as watching the generation dip and come back up on both sides - lesson learnt here, test string before inserting into branch connectors when its a dull day as it was in November - and i offered to pay the half of generation they lost out on (£135)

Happy customer again.