This has happened to me. 15 year old panels, one string was producing less power than the other when they should have been exactly the same. A trick for finding a bad panel without having to disconnect anything is: (1) Have a display of the watts produced on the string handy (like on your mobile phone) so you can monitor it while you are up on the roof. (2) Then simply cover each panel in the string individually with a big piece of cardboard and write down the production in watts after it settles down. Remove the cover, let the watts recover. Move onto the next panel. Repeat. The panel that has the least effect on power production is likely to be the bad panel (or related wiring). In my case one panel had fried due to water ingress.... a few cells were discolored and on the back there was a line of burn marks from where the current overheated the backing due to the damaged cells. -Matt
Wait until you have one bad diode and they all have the same voltage and amperage. Happened to me this past spring. What happens when a diode shorts is the panel is fine by itself but becomes a load for the rest of the 2S2P array. What I did to figure out which one was bad was put them in a 3S and swapped in the fourth panel one by one. When I added the bad panel in the 3S and saw the performance drop, I had my culprit. I replaced the diodes with bigger ones and it's now my best panel.
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Cracked solar panel do work if the crack doesn't affect the pn junction of the cells
This has happened to me. 15 year old panels, one string was producing less power than the other when they should have been exactly the same.
A trick for finding a bad panel without having to disconnect anything is:
(1) Have a display of the watts produced on the string handy (like on your mobile phone) so you can monitor it while you are up on the roof.
(2) Then simply cover each panel in the string individually with a big piece of cardboard and write down the production in watts after it settles down. Remove the cover, let the watts recover. Move onto the next panel. Repeat. The panel that has the least effect on power production is likely to be the bad panel (or related wiring).
In my case one panel had fried due to water ingress.... a few cells were discolored and on the back there was a line of burn marks from where the current overheated the backing due to the damaged cells.
-Matt
Nice idea!
Wait until you have one bad diode and they all have the same voltage and amperage. Happened to me this past spring. What happens when a diode shorts is the panel is fine by itself but becomes a load for the rest of the 2S2P array. What I did to figure out which one was bad was put them in a 3S and swapped in the fourth panel one by one. When I added the bad panel in the 3S and saw the performance drop, I had my culprit. I replaced the diodes with bigger ones and it's now my best panel.
looks like a raccoon fell on that one. impressive that it still works.
LOL! It might have. Several of my panels look beat to hell and still work fine. Those used San Tan Solar panels are a great buy.