Solar

Does Rain Clean Solar Panels? The Honest Answer

If your installer told you 'the rain takes care of it,' they were wrong. Here's what 30 years of independent solar research actually shows.

March 28, 2026 6 min read

It's the single most common thing solar customers in LA tell us: "My installer said rain would clean the panels." It's well-meaning advice. It's also flatly wrong, and it's costing Los Angeles homeowners thousands of dollars a year in lost solar production.

What the research actually shows

Independent studies — including landmark research from UC San Diego and Google's own work on its solar arrays — consistently document 15–30% production losses on uncleaned panels in Mediterranean climates like Los Angeles. The losses compound over a dry season. By October, a panel that hasn't been cleaned since spring is producing significantly less than the brochure promised.

And yet the rain narrative persists. Why?

Why rain doesn't actually clean panels

Three reasons:

LA gets only 12–15 inches of rain a year, and almost none between May and October. The dirtiest months get zero help.

Light rain is worse than no rain. It moistens the dust just enough to make it stick into a hardened film, then dries before it can wash anything away.

Rain leaves its own residue. Atmospheric pollutants and the minerals from your roof drain across the panel surface, creating tiger-stripe staining along the bottom edge of every module.

What actually accumulates on LA solar panels

We see the same things every job: a fine layer of basin dust (worst near freeways and construction), eucalyptus and palm pollen (sticky, baked-on), bird droppings (acidic, can permanently stain), irrigation overspray residue (calcium and chlorine), and wildfire ash during smoke events. None of this washes off in a 0.2-inch winter sprinkle.

How much does it cost you?

The math is simple. A typical 7 kW residential system in LA produces about 11,000 kWh per year. At LADWP or SCE residential rates of roughly $0.30/kWh (with TOU), that's $3,300/year of value at full output. A 20% production loss costs you about $660 per year. Over a 25-year panel lifespan, that's $16,500 — for the cost of two annual cleanings at $200–$300 each.

What proper cleaning looks like

Solar panels need to be cleaned with purified (deionized) water and soft brushes — not pressure washers, not chemical cleaners, and ideally not city tap water (which leaves its own mineral deposits as it dries). All major panel manufacturers specify this in their warranty terms. Pressure washing in particular can crack the protective glass and void coverage.

Most LA homes need cleaning twice a year — once in late spring after the pollen settles, once in fall before the dry-season grime bakes in. Homes near construction, under tree cover, or with large arrays often benefit from quarterly service.