Most homes in Southern California do well with one or two solar panel cleanings a year. If your panels sit under trees, near dirt or construction, or where birds like to perch, plan on three or four. Local weather matters too. Our summers are dry, so dust has months to build up before a good rain shows up.
Here’s how to work out the right schedule for your house.
What decides how often panels need cleaning?
Five things do most of the work: what’s around the house, how steep the panels are, whether birds use the roof, how close you are to dust, and where you are relative to the coast.
| Your situation | Typical schedule | Why |
|---|---|---|
| Flat street, few trees, steep tilt | Once or twice a year | Light dust, and the slope sheds some of it |
| Oaks, eucalyptus, pepper or jacaranda nearby | Three to four times a year | Pollen, tassels, blossoms and sap land on the glass |
| Near a dirt lot, construction or open hillside | Every three to four months | Fine dust arrives nearly all year |
| Near a freeway or busy road | Two to three times a year | Road grime and exhaust film build up on the glass |
| Birds roost on the roof | Clean as needed, and look at proofing | Droppings dry hard and sit on the glass |
| Low tilt or flat array | Two to three times a year | There’s less slope for dirt to slide off |
| Close to the coast | Two to three times a year | Marine layer moisture and salt-air film hold on to dust |
These are starting points, not rules. A tract home in Granada Hills might need less than an oak-shaded house in Calabasas, and the numbers above shift with your own roof.
Why doesn’t rain keep panels clean?
It helps a little, but not enough. Rain rinses off loose dust. What stays behind is a different problem. Dust and pollen turn into a thin paste when they get wet, and as the panel dries the minerals in that paste stay on the glass as a film. You’ll often see a grimy line along the bottom edge of each panel where the water stopped running.
The first storms of the season are the worst for this. Our dry months leave a lot of dust on the roof, and the first light rain turns it to mud instead of washing it off. A good soaking later in winter does better, but it still isn’t the same as cleaning by hand.
What does the calendar look like?
The rainy season runs roughly November through March. Spring brings pollen. Summer is dry and dusty. Fall brings Santa Ana wind days. That gives you a few natural windows.
Late spring, after the pollen. Pollen coats the glass and sticks when morning dew hits it. Cleaning in May or June clears it out before the long dry stretch.
Early fall, before the rains. Months of summer dust and any bird activity are on the glass. A cleaning before the first storm means the rain doesn’t turn that layer into paste.
After Santa Ana winds. These hot dry winds blow dust, leaves and small debris onto roofs. If a strong wind event follows a cleaning, a heavy coat of fine dirt may be on the panels again by morning.
After ash. If there’s been a wildfire nearby, wait for the ash to settle before you do anything. We cover the details in solar panels and wildfire ash.
How do you know panels need cleaning?
Look for the signs before you decide on a schedule.
- A visible film or haze on the glass, seen from the ground on a sunny morning
- Droppings on the panels
- A grimy line along the bottom edge of each panel
- Leaves, pollen or blossom stuck to the glass
- Production that sits lower than on similar sunny days from earlier in the year
Please don’t climb onto the roof to look. From the ground, a pair of binoculars works fine, and the monitoring app tells you plenty on its own.
What should I track in my monitoring app?
Your app already holds most of what you need. Pick a few clear, sunny days and write down the daily production number. Then, after a cleaning, pick a few similar sunny days and compare. Don’t compare a sunny day to a cloudy one, because weather will swamp everything else.
A few habits help.
- Note the date of each cleaning so you can line it up with the graph
- Compare days with similar weather and season
- Watch for a slow drift down over several weeks, which can point to buildup
- Watch for a sudden drop, which usually isn’t dirt, and check with your installer if you see one
If you want to dig into what the numbers mean, read does cleaning solar panels increase output.
Does where I live in the valleys matter?
Yes, a bit. Homes in Chatsworth and Simi Valley that back onto open hillside see more dust through the dry months. Canyon Country and Valencia in the Santa Clarita Valley mix new construction and open land, which kicks up dust. Tree-heavy neighborhoods see more pollen and leaf debris. Check the city page for your area for what we see there.
Does the coast change anything?
A little. Near the coast, the marine layer settles over the roof most mornings, and that dampness helps dust stick to the glass. Inland valley homes get the opposite problem, with hot dry months where dust piles up and nothing moves it. Either way, a film builds. It just forms a bit differently, which is why the table above puts coastal homes at two or three cleanings a year.
What if I’m not sure which row I fit?
Most homes fit more than one. A house near a freeway with a few oaks and a flat array has three reasons to be dirty. In that case, use the shortest schedule that applies. It’s easier to stretch a schedule later than to catch up on a heavy buildup.
A simple way to test it is to start with two cleanings a year and watch the glass. If you see a film building up well before the next visit, add another. If the panels still look fine at each visit, you can leave it alone. Your monitoring app will show you the same thing from the production side.
Do windows and skylights follow the same schedule?
Roughly, yes. Dust, pollen, ash and hard water spots land on windows the same way they land on panels, so many homeowners book window cleaning on the same visit. We’re already on the property with purified water, and the glass dries clean without spots.
Can a plan keep me on schedule?
Most people don’t forget that panels need cleaning. They lose track of when. Our membership plans are free to join, and we pick the visits (quarterly, twice a year or annually), schedule them and send a reminder first. If you’re not sure which fits your roof, we’ll look at the trees and the setup and tell you.
Next step
Cost depends on the roof, so see what changes the price before you ask for an estimate. Or just ask us. Call (818) 913-1626, Monday through Saturday, 7am to 7pm, read about solar panel cleaning, or see every area we cover.