Faulty 1/3 of panel question

[sw15]

Hello all

I have a Lg neon 2 black solar panel.

I bought it second hand knowing it was faulty - quite cheap.

The seller told me it was down on power by about a third.

There is a plastic box on the back with some diodes in it.

There are 3 panels in series connected in series with diodes.

With no load on a bit of a dull day two of the 3 cells were a very similar 12v and one was only 7v.

My question is this.

When panels go faulty do they go high internal resistance?

I could leave it as it is or I could just have the two good panels in series and dump the faulty 7v panel.

To test it with load scientifically I would have to buy a small collection of high power resistors which I don't really want to do.

I could even separate off the 7v faulty array and use it for a separate system, put in a boost and use it to keep the starter battery topped up?

Thanks for reading my first post!

 

[binky]

I would expect a failing set of cells to go high resistance, although, to be frank I doubt anyone has really bothered to check, and I doubt anyone can give you any guidance on test values. Faulty panels get binned and replaced, and that's all we need to know in the trade.

What I would be concerned with is why a top quality panel has failed in the first place. Is there any signs of thermal damage to any of the cells looking at the front? Is there any damage to the glass, or any other signs of what has caused one string of cells to deteriorate?

 

[sw15]

Hi all

binky and his comments/suspicions are all correct

The panel was replaced by the installer and I bought the duff one that was rejected.

Also, again correct by binky there is a patch of slight discolouration that is visually not that bad.

If I got a piece of cardboard I could work out what bit of the panel was what circuit.

Then if I could prove the discoloured bit was high impedance, I could potentially cut it out, and replace the duff bit with a short.

can anyone suggest what power resistors I buy for dummy loads? 1R ? 2R?

the voltages I have read are cloudy day but no load.

But I am not using the panel in a big domestic system. I’m using it on a motorhome.

 

[sw15]

It could be true that as little as 5% of the panel is duff and high impedance..

 

[binky]

Then if I could prove the discoloured bit was high impedance, I could potentially cut it out, and replace the duff bit with a short

Have a look at how thin the busbar wires are, I would say you have 2 chances of making that work, plus you would have to cut through the backsheet and try to reseal it.

The cells are usually arranged in 6 rows across the panel, with 2 rows per circuit, making 3 circuits, hence you have 3 bypass diodes in the junction box. You would be better off disconnecting the bypass diodes and working out which 2 circuits are good, and reconnecting to suite, leaving the duff circuit out. You'll end up with a panel that's probably still more powerful than most fitted to campervans.

 

[sw15]

This is an image of the previous owners control system

 

[binky]

This is an image of the previous owners control system

Very nice, but no use for solving your problems