Troubleshooting seemingly dead solar panel

[LifesBetterWhenYoureBeating]

Originally Posted by 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.

I'm getting ~3A of short circuit current but only 7.3v instead of the expected 21v. What can we conclude from that?

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[Jammer]

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?

That is a high-resistance connection.


I would replace the entire panel. A repair would involve cutting away enough of the backsheet to get at sound foil and then soldering in a repair and sealing it.

[betwys1]

Originally Posted by 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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Connect a car headlamp bulb to the solar panel with no other connections. You will find the voltage droops from off-load - probably considerably, compared with a good panel. Possibly an internal bad connection.

[Kolchac]

If you use diodes (as I understand) to connect solar panels to each other, you are doing wrong. Solar panels are not batteries. The solar panel is a matrix of diodes, and you can connect all panels in parallel directly. Just pay attention: if one panel generates 20V, and another 12V, and you connect them in parallel, the output will be 20V, and the 12V panel would be locked. When you connect them to a battery, and the voltage dropped to 13V, only one 20V panel would charge your battery, and another 12V panel would be still locked by 13V. If the voltage on the battery drops to 10V, 12V panel will be open and both panels will charge the battery.

[LifesBetterWhenYoureBeating]

Originally Posted by Kolchac

If you use diodes (as I understand) to connect solar panels to each other, you are doing wrong. Solar panels are not batteries. The solar panel is a matrix of diodes, and you can connect all panels in parallel directly. Just pay attention: if one panel generates 20V, and another 12V, and you connect them in parallel, the output will be 20V, and the 12V panel would be locked. When you connect them to a battery, and the voltage dropped to 13V, only one 20V panel would charge your battery, and another 12V panel would be still locked by 13V. If the voltage on the battery drops to 10V, 12V panel will be open and both panels will charge the battery.

I was talking about the diodes in the junction box of the panel.

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[team karst]

Series panels should have a bypass diode installed in each. Parallel panels should have blocking diodes on each. Series/parallel gets both. A single panel system needs no diode, as long as its not working directly into a battery.

ps: just noticed that vid link. Did i get it right [emoji41]

[betwys1]

Probably better to take with a pinch of salt, posts beginning "As I understand it" or "I believe". Try looking at this video clip on bypass and blocking diodes.

https://www.youtube.com/watch?v=-x_6OLdAods

You likely have a high resistance internal connection in your panel.

[sinnerman]

Be careful trying to salvage old uncertain solar panels.

Under the previous owner, my boat had a serious cockpit fire from a shorted/ malfunctioning solar panel.

The resulting fire burned the cockpit, bimini, mainsail, boom etc. The fire department had to be called to the scene.

New replacement solar panels are cheap by comparison...

[LifesBetterWhenYoureBeating]

I've already discarded the defective solar panel, so this thread can probably be closed

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