A Southern California solar owner who expected steady savings from a new solar-and-battery setup instead noticed a worrying drop-off: peak output had fallen by roughly 10% in just one year.
The homeowner took to Reddit's r/Solar community to ask whether others had experienced similar reductions and what they did to address them. The other Reddit users suggested the issue may have less to do with panel degradation and more to do with something much simpler: dust.
Here's what to know
According to the Reddit post, the owner thought the drop-off seemed unusually steep because they had read that annual degradation should be closer to 0.5%.
The original poster also said their 19-panel system with a Powerwall 3 was peaking at about 5.7-5.9 kW rather than the roughly 6.5-6.7 kW they had seen before, trimming clear September production by around 4-5 kWh.
When another user asked whether the panels had ever been cleaned, the OP replied: "No. My installer told me it wasn't really needed."
Shortly after that, dust buildup emerged as the likeliest explanation in the replies. One commenter said that "both not cleaning them and the normal vagaries of weather could easily account for 10%," while another wrote: "Wash your panels. It will help."
What can be done?
Before assuming there is a hardware defect, commenters suggested checking a few basics, like comparing output across the same month or season, inspecting for new shade, and looking for visible dirt buildup on the panels.
In a dry climate, careful cleaning, or even waiting for heavier winter rain, may help show whether dust is the real problem.
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Where can I learn more?
Dust, weather, and changing conditions can quietly chip away at rooftop solar output over time.
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