How to clean solar panels, and whether you need to
Dust and pollen cost some power. Whether washing pays depends on where you live and how dry it gets.
For most home systems, occasional rain does most of the work and a professional cleaning rarely pays for itself. A study of 186 California PV sites measured an average soiling loss of 0.051% of output per dry day; 26% of sites lost more than 0.1% a day, and nearly flat panels lost more (Mejia & Kleissl, 2013). Pollen is the exception: NREL found rain did not wash it off fully.
What a dry season costs
A 7 kW system through a 150-day dry spell at the study's average rate, and what one wash half-way through would recover at the local energy charge:
| City | Lost over the spell | Recovered by one wash | Worth about |
|---|---|---|---|
| Chula Vista, CA | 190 kWh | 95 kWh | $44 |
| San Diego, CA | 189 kWh | 94 kWh | $44 |
| Oceanside, CA | 187 kWh | 93 kWh | $43 |
| Carlsbad, CA | 184 kWh | 92 kWh | $43 |
| Bakersfield, CA | 185 kWh | 93 kWh | $34 |
| Clovis, CA | 183 kWh | 91 kWh | $33 |
| Fresno, CA | 182 kWh | 91 kWh | $33 |
| San Jose, CA | 179 kWh | 89 kWh | $33 |
| Tucson, AZ | 197 kWh | 98 kWh | $15 |
| Phoenix, AZ | 193 kWh | 97 kWh | $14 |
| Glendale, AZ | 193 kWh | 97 kWh | $14 |
| Chandler, AZ | 193 kWh | 96 kWh | $14 |
| Tempe, AZ | 193 kWh | 96 kWh | $14 |
| Gilbert, AZ | 193 kWh | 96 kWh | $14 |
| Scottsdale, AZ | 192 kWh | 96 kWh | $14 |
| Surprise, AZ | 196 kWh | 98 kWh | $14 |
| Peoria, AZ | 195 kWh | 97 kWh | $14 |
Estimate: loss grows by 0.051% a day and resets with rain; production from NREL PVWatts; value at the city's typical energy charge. Your roof may be dirtier or cleaner.
Even in Chula Vista, one wash recovers about $44 of power. Compare that with a cleaning quote.
When cleaning is worth it
- Heavy pollen. In North Carolina, NREL measured output down by as much as 15% in peak pollen season and estimated annual losses on the order of 10% without planned cleaning (NREL).
- Nearly flat panels, which shed dirt poorly.
- Bird droppings, ash or farm dust that sit on part of a panel.
How to clean safely
- Check the manual first. The panel maker's instructions set what you may use; the wrong method can void a warranty.
- Stay off the roof. Use a soft brush or sponge on an extension pole and plain water from the ground.
- No pressure washer, no abrasive cleaners, and not on hot glass in the middle of the day.
- Snow: it usually slides off tilted panels. Don't climb up to clear it; a soft roof rake from the ground, if the manual allows.
How to know if dirt is the problem
Compare this month's output with the same month last year in your monitoring app, or with the monthly numbers for your city in how to tell if solar panels are working.
Run your own numbers
Enter your ZIP and bill to see what a system would make and save where you live.
Keep reading
- How much electricity a solar panel produces — Daily, monthly and yearly output per kW and per 400 W panel, city by city.
- How long solar panels last — Lifespan, how much output drops each year, and what a 7 kW system still makes in year 25 in each city.
- How to tell if solar panels are working — Monthly output to expect in your city, and the checks that catch a problem.
Installer records by city: solar companies in Phoenix, solar companies in Tucson, solar companies in San Antonio, solar companies in Austin, solar companies in San Diego, solar companies in Fresno, solar companies in Chandler, solar companies in Scottsdale, solar companies in Gilbert, solar companies in Glendale, solar companies in Tempe, solar companies in Peoria, solar companies in Surprise, solar companies in San Jose, solar companies in Bakersfield, solar companies in Clovis, solar companies in Chula Vista, solar companies in Oceanside, solar companies in Carlsbad, solar companies in Toms River, solar companies in New York, solar companies in Elizabeth, solar companies in Yonkers.
Updated 2026-09-22.