A solar owner in southern Spain ran into a deceptively tricky problem when dust began dragging down the output of nearly flat solar panels.
Cleaning them seemed like the obvious solution, but there was a catch: Tap water left behind stubborn mineral marks, creating a new headache.
That raised a bigger question for solar owners everywhere: When does cleaning actually improve solar output, and when can a rinse make the problem worse?
Here's what to know
In a Reddit thread on r/solar, the original poster said, "My panels are part of a solar carport/pergola and they're virtually horizontal, at about 3deg tilt. I'm in the south of Spain where we barely get any rain but we do get a lot of wind."
Even after a medium-power wash and a pass with a squeegee, the panels dried with mineral residue from mains water; the owner had turned to cleaning only after noticing output slip about a year after installation.
The next question was whether changing the rinse would help, including trying distilled water or vinegar.
Several replies focused on keeping the process simple and paying attention to water quality.
"I use soft water to rinse my panels and avoid hard water deposits," one commenter said.
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Another suggested, "Water and a microfibre mop (to get the reach)."
Not everyone agreed that washing panels is always worth the trouble. Still, one commenter in a dusty area reported a clear improvement, writing, "The day before I cleaned my peak was 5.2 kW. The day of it was 5.9 kW."
Because lower solar output can mean relying more on electricity from the grid, going solar is one of the best ways to save money on home energy. If you're considering panels, EnergySage lets you get free solar installation estimates and compare quotes.
More background
Systems tilted only around 3 degrees do not shed dust and debris as easily as steeper rooftop arrays, and the original poster's combination of wind and limited rainfall means grime may linger instead of being naturally washed away.
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A different commenter said the payoff was minimal on a much larger setup, writing, "I can't tell you on my 42kw setup I saw almost no change from dirty and clean panels," and noting in the thread that the cleanup took most of the day.
For homeowners deciding whether solar is worth the upfront cost, transparent pricing tools can matter as much as maintenance advice. With EnergySage's help, the average person can save up to $10,000 on solar purchases and installations.
EnergySage's solar map shows the average cost of a home solar panel system by state, plus details on solar panel incentives for each state, which can help homeowners get the best price for rooftop solar panels and access available incentives.
What can be done?
For panel owners dealing with similar buildup, the safest routine discussed in the thread was fairly straightforward: Use a soft brush or microfiber tool, clean gently, and avoid rinse water that leaves mineral residue behind.
"Really you should be rinsing them with deionized water," one commenter said.
That approach can help protect the glass while restoring output that might otherwise be lost to dirt and dust.
Adding battery storage to a solar setup is also one of the best ways to protect your home during outages, save money on energy, and go off-grid. You can explore EnergySage for information about home battery storage options, including competitive installation estimates.
Where can I learn more?
For a closer look at what affects solar output, these stories explore how dirt, rain, and different cleaning methods play out in the real world.
• On rooftop arrays, dish detergents and cleaners can leave solar panels worse off.
• Homeowners found that a simple rinse unlocked roughly 5% more power from dusty panels.
• Across Reddit, solar owners pushed back on the most 'out there' myths still confusing homeowners.
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