Troubleshooting seemingly dead solar panel

[LifesBetterWhenYoureBeating]

Hi everyone,

A couple days ago I noticed one of my solar panels had stopped working. I disconnected the panel from the controller and measured the voltage directly on the junction box (on the panel's metal tabs, before the diodes) and it was oscillating between 11-13v with the whole panel area exposed to midday sun, so I thought the panel was gone, but as a last shot I thought I'd disconnect the junction box from the panel's metal tabs and measure the voltage there. I wasn't hopeful as I thought the diodes had no effect since I was measuring the voltage before them, but this time I measured 20+v, so I installed a new junction box hoping it'd bring the panel back to life. Now I'm getting only 11-13v again, though

Is it expected that I get such different voltage readings with/without the diodes connected? If not I could try and confirm it once again but that would require undoing the soldering in the junction box so I thought I'd ask first.

If the diodes are expected to affect the voltage that much, does it mean the panel is really gone?

Thanks in advance!

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[Scubaseas]

From memory which is admittedly hazy, diodes will drop your voltage .5V to .8V.

[Kelkara]

While you're waiting for the solar panel experts to weigh in ... here's something else to consider ... did you measure the current at any location? a short circuit will pull down the voltage considerably.

[senormechanico]

Panel probably has a high internal resistance due to bad connection(s) from whatever.
It will read high voltage with no load, but drop dramatically with even a very light load.

[LifesBetterWhenYoureBeating]

Originally Posted by senormechanico

Panel probably has a high internal resistance due to bad connection(s) from whatever.
It will read high voltage with no load, but drop dramatically with even a very light load.

Is this a common failure mode for panels?

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[team karst]

Voltage is half the story. Measure Isc; short circuit current from the panel in full sunlight. That spec is likely on the panel itself.

[senormechanico]

Originally Posted by LifesBetterWhenYoureBeating

Is this a common failure mode for panels?

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I have a couple of old panels which died in that fashion.
They are still under warranty, but the company is no longer in business.

[LifesBetterWhenYoureBeating]

I don't know how but the panel voltage is now back to 21v and it's generating power, but as soon as I connect the mppt or the multi meter to measure (short circuit) current/voltage, a small burned spot (shown on photo) on the back of the panel starts smoking

Any ideas what that is and whether it'd be safe to try and fix it myself?

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[Scubaseas]

Originally Posted by LifesBetterWhenYoureBeating

I don't know how but the panel voltage is now back to 21v and it's generating power, but as soon as I connect the mppt or the multi meter to measure (short circuit) current/voltage, a small burned spot (shown on photo) on the back of the panel starts smoking

Any ideas what that is and whether it'd be safe to try and fix it myself? Attachment 272710

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If you loose all the smoke it won't work anymore. Personally I would not try fixing it.

[senormechanico]

That's very likely the problem.
Either dig into it to try to jump the bad connection, or dump it for a new one.
Or, just wait for the fire to start!

[donradcliffe]

Its not worth losing your boat, plus all your dock neighbors. That hot spot can develop into a fire. Are the panels flexible or rigid?

[LifesBetterWhenYoureBeating]

Originally Posted by donradcliffe

Its not worth losing your boat, plus all your dock neighbors. That hot spot can develop into a fire. Are the panels flexible or rigid?

It's rigid

I thought hot spots would only cause an efficiency loss. Can they all develop into a fire? I'm not going to keep this panel but I have a second identical one that may have hot spots as well



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[donradcliffe]

I did watch a flexible panel catch a bimini on fire. From the research I could find, theoretically if there are more than 2 panels in parallel there is enough energy available for the spot with high resistance to melt and ignite. I wouldn't want to test that theory on my boat.

[team karst]

Even just 150 watts in a few sq inches would make that spot quite hot i propose . When coupled to other panels, i dont know if series or parallel is worst case. Seems to me parallel adds to MPPT current; series adds Voltage to mppt. I would suspect this bad panel has a spot of very thin (too thin) metal plating causing the hot spot. But i dont have any history of analyzing bad panels.

[senormechanico]

While I have (and replaced) a couple of defective Aurinco 100 watt panels, they never developed hot spots. It might be because they were assembled on aluminum sheet, but that's just speculation on my part.
I took them off the boat and found if I flexed them slightly concave instead of slightly convex as they had been mounted (amas) they performed normally.


Aurinco is no longer in business, but I managed to talk to someone who had worked there. He said they found out too late, that the panels were not as flexible as they thought. I followed their recommendations for installation, but...at least the boat didn't catch fire !


Additional: I have a total of five panels, 600 watts all in parallel (fingers crossed).