The numbers
How much does cleaning actually help?
The size of the gain depends on how dirty the panels were and how they are mounted — but the measured results are real and well documented:
The reason flat and low-tilt panels gain the most is simple: steeper panels get a gravity-assisted rinse when it rains, while flat ones trap standing water, mud, and dust that never washes off on its own. Across typical U.S. installations, untreated soiling costs about 0–7% per year, but heavily soiled systems lose 20–25%, and in extreme conditions losses reach 30–50% — all of which cleaning recovers. See the full loss and recovery data →
The biggest wins
When cleaning makes the biggest difference
For a steeply tilted residential roof in a rainy stretch, rain does a lot of the work. Cleaning delivers the clearest gains in these situations — several of which are common across Rocklin, Roseville, and the rest of Placer County:
- After wildfire smoke or ash. Ash can cut output up to 30% instantly, and it does not rinse off cleanly.
- Heavy tree pollen. Sticky spring pollen resists rain and can drop production up to 15% at peak season.
- Flat or low-tilt panels. They never self-clean and can nearly double their output after one wash.
- Biological growth. Mold, algae, and lichen films cause persistent 2–10% losses that rain cannot remove.
- Near dust sources. Homes close to farmland, construction, or busy roads soil far faster than average.
The cost of waiting
What happens if you don't clean them?
Soiling does not just cost you energy today — the losses compound the longer you wait, and during long, sunny summer days (when your system should produce the most) a soiled panel costs you the most kilowatt-hours and the most money. Sticky pollen and biological films build into a layer that rain can no longer touch, so the loss becomes permanent until someone cleans it.
⚠ Wildfire ash is the real danger
Wildfire ash is alkaline and corrosive. Left on the glass, it reacts with morning dew and humidity and chemically etches the cover glass permanently, ruining the anti-reflective coating that the panel depends on. Guidelines call for cleaning ash off within 48 to 72 hours. In a fire-prone region, this is about protecting the panel itself, not just this month's production.
Do it right
The right way to clean — so you don't cause damage
Cleaning helps only when it is done correctly. Done wrong, it can permanently damage the panels and void the manufacturer warranty. The key rules:
- Never pressure wash. Even on low settings, pressure forces water past the seals, causing internal corrosion.
- Never walk on the panels. It creates invisible micro-cracks that destroy cells over time — and a footprint-shaped crack pattern voids your warranty claim.
- Use pure water. Deionized or reverse-osmosis water leaves no hard-water spots or residue.
- Clean cool, not hot. Cold water on sun-heated glass can crack it, so clean in the cool morning, evening, or on overcast days.
How Cable Pressure Washing and Solar Panel Cleaning cleans solar panels
We clean with water-fed poles and deionized water, low pressure, no soaps, cool hours only, and we never step on your modules. We work from the ground when the array is safely in reach and from the roof when it is not. It is the method that recovers the most output while protecting both the glass and your warranty.
The math
What a cleaning costs vs what it recovers
Around here the math is easy to run. Our solar panel cleaning is $15 per panel with a $200 minimum, so a typical 20-panel home system is a flat $300, quoted in writing before we start.
Set that against what soiling takes. A system losing even a mid-single-digit percentage produces its worst numbers on the long summer days when it should produce its best, and under California's NEM 3.0 net billing rules, reduced export rates make every peak-hour kilowatt more valuable than it used to be. A soiled panel during a high-value afternoon window is the most expensive kind of dirty.
You do not have to take the averages on faith. The solar ROI calculator estimates the lost kWh and lost bill value for your own panel count and ZIP code, and the statistics page carries the sourced study data behind every figure on this page.
Timing the visit matters too. The highest-value clean in Placer County is late spring, right before the long high-output months, with a second look after ash season in heavy smoke years. The seasonal cleaning calendar maps the whole year.
Common questions