One Reddit user spotted three newly darkened cells on a 2-year-old solar panel. The panel still produced power, but the main worry was about reduced output.
The discussion quickly turned to whether the change was merely cosmetic or evidence of a developing fault.
Here's what to know
The issue surfaced in a Reddit post, where the owner described a ground-mounted DMEGC panel showing three dark areas that appeared to line up with individual cells. The original poster wrote: "Three cells have darkened suddenly … No cracks I can see front or back."
Among the replies, one commenter asked whether the panel had shown any slight voltage drop and advised inspecting the busbars closely, while another said: "Micro crack can make such a thermal profile."
The responses suggested the marks might be more than a simple cosmetic issue.
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More background
The original poster said cloudy weather made it hard to tell whether production had been affected. They also explained that the panel was wired in series with another module, so they planned to test it separately in full sun.
In the comment thread, someone else suggested checking the back of the affected area for heat, since unusual warmth can point to a developing failure: "IF micro crack is the cause, In day time, when the temperature is high enough, micro-crack will generate a heat. touch the backside of the cell. (power loss become worse when become warmer due to the thermal expansion)."
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An unchecked panel issue can reduce production and cut into the utility-bill savings that made solar attractive in the first place. If the module is only 2 years old, documenting the issue early could also help if the seller or manufacturer needs to review a warranty claim.
What can be done?
A sensible next step is to test the panel on its own in strong sunlight, compare its voltage, and use an infrared thermometer if available to see whether the darkened section is running unusually hot. If those checks suggest the panel is underperforming, contacting the seller would be a good next move.
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The mystery remains unsolved for now.
"For me those dark cells are not normal," one commenter said, while the original poster noted: "It may just be something I have never noticed before and be ok."
Where can I learn more?
These stories cover weather-related performance risks, cleaning mistakes, and new findings on solar-cell durability.
• Researchers found temperature swings can trigger failure in next-generation perovskite solar cells.
• Tests showed common cleaning products can harm solar panels instead of helping them.
• Scientists reported an increase in the durability of perovskite solar cells with a new tweak.
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