Recognising a duff panel

[pjcomp]

Theory's great but it's only when a problem comes up you really start to learn things..... My relatively low number of installs to date have gone to plan so I'm hoping a few of you out there have hit more problems than me.

Just put up a 14-module rooftop, two strings of 7x245W panels. Al lthe panels checked OK on the ground. When it came time to connect up, one string gives me 242V, the other one 172V. The arithmetic says I've got two duff panels in the second array.

Questions: Am I missing a bit or does it indeed indicate two duff panels? If they tested OK on the ground, what should I be looking for in retest (I'd prefer to have a few ideas before I start pulling the array apart)? All suggestions gratefully received.

PJ

 

[SolarCity]

I'd say a more likely culprit would be incorrect polarity in one of the panels - your results are consistent with this.

 

[pjcomp]

Thanks Biggs - had an issue with this manufacturer a few months ago when all their panels were wired back to front (male plug for neg, female for pos) so this might have slipped through again somehow. Got any suggestions for pinpointing which one it might be?

PJ

 

[SolarCity]

It depends how easy the plugs are to get to. I'd disconnect the array so I had both ends at the array. I'd plug a fly lead into one of the ends and go down the line checking the voltage. What make of panel are they?

 

[pjcomp]

OK, update, big thanks to Biggsy, and one worth noting to anyone else reading this.

It was indeed a panel with revers polarity - or to be more precisse, six panels with reverse polarity.

Of the 14 panels delivered, six had a different version of MC4 connectors; not the end of the world to swap a couple with standard ones to connect up. What eventually transpired, however, after a lot of to-ing and fro-ing with the suppliers, turns out these six were wired back to fornt, ie the male connectors were neg and the female were pos. thus the one in the 7-string that was the "correct" way round was the one with, efectively, reversed polarity. So, a bit of panel juggling on the roof and plug changing, and a properly working array. Phew.

Another one to clock up to experience.

PJ

 

[beefheart]

good thread, what make of panel, i will teach the apprentice the finer points of polarity checking on every panel not just the basics

thanks

 

[Graeme Harrold]

You should be checking polarity when ground testing, good find though.....

 

[SolarCity]

To be honest, I never check polarity with the panels. I test that I get a feasible voltage and Isc and that's it. I will definitely keep my eye on polarity from now on though - not that you should have to. Panels aren't cheap and I'd be interested to know which manufacturer are throwing out these shoddy modules.

 

[Graeme Harrold]

You would think everything is OK concidering the flash tests conducted off the production line.....................

 

[pjcomp]

The panels were DelSolar, made by Delta, perhaps more relevant the reversed connectors were by Tyco. It's not the first time I've been bumped with "non-standard" MC4s so that alone didn't set off alarm bells

PJ

 

[malcolmsanford]

Doesn't your meters give you a -(minus) indication on the read out scale on DC voltage if the polarity is reversed??

 

[SolarCity]

Yeah, it does. But I don't pay attention to it when I'm testing each panel. Incorrect polarity is not a fault I thought would be likely. Now I know better.

 

[malcolmsanford]

Biggs when I did the Ecoskies course they made us go out and do the panel tests VOC Isc etc, all Ok. Then we were brought back inside and did some more work and then split into groups to do a string.

The guy brought out several panels for us to wire and we started, 2 of us testing and 2 stringing. luckily I was testing and one panel showed the -(minus) on the Dc range so I dished it. Any way he came out and asked ok, and we told him yes gave him all the reading of each panel and then the string, and he asked did we have a problem, I said yes one panel had reversed polarity, and he was so ****ed that we found it as it was his little test !!!!