How Often to Clean Solar Panels in the Inland Empire

Short answer: most homes need panels cleaned once or twice a year, and more often when rain is rare and dust is heavy. The Inland Empire has both, so two cleanings a year, one after the windy season in spring and one before it in early fall, is a reasonable start. Add a mid-summer visit if your monitoring app shows output drifting down.

We clean panels on single-story roofs from the ground, with a water-fed pole and pure water, for $6 a panel and a $110 minimum. We never walk on a roof.

Why dirty panels make less power

Dust, ash and pollen settle on the glass and block some sunlight from reaching the cells. Rain washes some of it away, but in a dry climate the film builds for months. Researchers have measured this, and the size of the loss depends on where you are, the tilt of the panel, how long since the last rain and what kind of dirt it is.

We read the text of both papers, and they study large systems and test modules more than rooftops at one house. None of them says your panels have lost any particular amount. Treat them as evidence that the effect is real, and use your own numbers to decide.

The Inland Empire calendar: long dry spells and a windy season

By one modeled data set (NASA data summarized by WeatherSpark, not NOAA records), Ontario has a rainless period from about April 22 to October 20.

That is a six-month stretch with almost nothing to rinse a panel.

Santa Ana winds are the other half.

Seasonal winds typically blow in from October to December, according to the state emergency services office.

The South Coast Air Quality Management District, the regional air agency, says two things about wind and dust.

Gusty Santa Ana winds can lift dust and soil into the air.

South Coast AQMD issued a windblown dust advisory for the Inland Empire.

The Santa Ana wind guide goes through it.

Put the two together and the calendar writes itself. Summer builds a film with no rain. Fall and winter add wind-blown dust and ash. A cleaning in March or April starts the dry season clean. A cleaning in September or early October clears the summer film before the windy months. A third visit in mid-summer is for homes near freeways, warehouses, dirt lots, construction or trees.

What outside guides say about frequency

The Bob Vila solar cleaning guide, updated May 2026, is a general guide, not a Southern California one.

The Bob Vila guide says cleaning solar panels once or twice a year is typically enough.

Homes whose roofs have little to no slope may also need more frequent cleaning.

A cleaning may be necessary after a nearby construction project is completed to remove any dust.

We could not open an NREL or Department of Energy statement on residential cleaning frequency, so we do not quote one.

A fair summary: once or twice a year is the baseline, and a dry, dusty place sits at the higher end.

Does a cleaning pay for itself? Do the math with your own numbers

You can check this in about ten minutes with your solar monitoring app. Write down your production for a clear day just before a cleaning, and again for a similar clear day just after. The difference is what the film was costing you.

Here is a made-up example to show the arithmetic, not a promise. A 16-panel array costs $110 to clean with us. If a kilowatt-hour is worth $0.30 to you, $110 buys back about 367 kWh. If the cleaning adds 60 kWh a month (an invented number, only for the example), you get that money back in about 6 months. Use your own electricity rate from your bill, and your own before-and-after numbers. If the app shows no change, you do not need a cleaning yet.

We do not promise a percentage. We promise clean glass.

Cleaning panels yourself: what the care guides say

If you decide to do it yourself, from the ground, here is what we could confirm from pages we opened:

Bob Vila: The best times to clean solar panels are cool, cloudy, and mild in temperature.
Bob Vila: Never apply cold water to hot panels.
Bob Vila says high-pressure cleaning is likely to create fine cracks on their surfaces.
Also start with a soft brush and a hose, and check your manufacturer's instructions.
First Solar wrote these cleaning guidelines for its utility-scale thin-film modules.
Do not apply water that is more than 20°C warmer or colder than module surface temperature.
Water pressure must not exceed 35 bar (500 psi) at the nozzle.
They also say not to use abrasive cleaners, to squeegee hard water off to prevent scale buildup, and they warn of the potential for electric shock. Those are for a different product than your roof, but the cautions apply in spirit.
Pressure and soap limits differ by maker. Look up your own panel's manual before you pick a method.

The real danger is the roof, not the water. A wet roof is slippery. We clean from the ground with a pole and never climb. If your array is on a second story or a steep roof, a pole from the ground cannot reach it, and the safe answer is to hire someone who is trained to work there, not to go up yourself.

Why pure water

Tap water in the Inland Empire is moderately hard to very hard depending on the supplier, and it dries and leaves mineral spots. Pure water has the dissolved minerals taken out, so it dries without leaving a film and needs no soap. One maker of window-cleaning tools says pure-water pole cleaning is done from the ground and without drying and polishing. We use the same pure-water pole on panels as on windows. See the hard-water guide for the local numbers.

What we charge, and the limits

Panels are $6 each with a $110 minimum visit, single-story roofs only, from the ground. Windows and panels in the same visit are 10 percent off. The plans that discount window visits (15% every 3 months, 12% every 4 months, 8% twice a year) apply to the whole visit.

Panels	One-time price
8	$110
12	$110
16	$110
20	$120
24	$144
30	$180

We do not clean panels on a second-story roof, we do not walk on roofs, and we do not use detergents or soaps on panels. If your pole cannot reach your array from the ground, we tell you before the visit.

Common questions

How often should I clean my solar panels in Southern California?

Once or twice a year is the baseline most guides give. In a place with long dry spells and a windy season, such as the Inland Empire, two cleanings a year, spring and early fall, is a reasonable start.

Does rain clean solar panels?

Some, but not always all of it. Ontario has almost no rain from late April into October.

Can I clean my own solar panels?

From the ground, with a soft brush and low-pressure water, in the cool part of the day, and following your panel maker's instructions. Do not use a pressure washer, and do not go on the roof if it is steep, high or wet.

Will cleaning void my warranty?

High-pressure cleaning may. Check your manual. We use a soft brush and low-pressure pure water.

How do I know if cleaning helped?

Compare your monitoring app's output on similar clear days before and after. If nothing changed, your panels did not need it.

Where this applies

We work in every place within 15 miles of Ontario: Ontario, Upland, Montclair, Chino, Rancho Cucamonga, Claremont, Alta Loma, Eastvale, Pomona, Etiwanda, Chino Hills, Jurupa Valley, La Verne, Norco, Fontana, San Dimas, Diamond Bar, Corona, Walnut, Rialto, Covina, Glendora.

Related services: Solar panel cleaning, Plans, Instant quote.

More guides

Sources

Mejia and Kleissl (2013), "Soiling losses for solar photovoltaic systems in California," Solar Energy (UC San Diego). “Soiling can have a large effect on... the largest solar resource”
Ilse, Micheli, Fayad et al. (2019), "Techno-Economic Assessment of Soiling Losses and Mitigation Strategies for Solar Power Generation," Joule 3(10). “soiling is estimated to have reduced global solar power production by at least 3%-4% in 2018”
WeatherSpark, "Average weather in Ontario, California" (modeled NASA MERRA-2 data; rainless period). Verified from an archived copy, since the live page is script-rendered. “The rainless period of the year lasts for 5.9 months, from April 22 to October 20”
Cal OES, "Impending Santa Ana winds bring increased fire risk," October 14, 2023. “seasonal winds typically blow in from October to December”
South Coast AQMD news release, December 9, 2023 (gusty Santa Ana winds lift dust and soil). “gusty Santa Ana winds, which can lift dust and soil into the air”
South Coast AQMD news release, December 9, 2023 (gusty Santa Ana winds lift dust and soil). “south coast aqmd issues windblown dust advisory for the inland empire”
Bob Vila, "Solar panel cleaning cost" (frequency, method, cautions). Updated May 11, 2026. “cleaning solar panels once or twice a year is typically enough”
Bob Vila, "Solar panel cleaning cost" (frequency, method, cautions). Updated May 11, 2026. “a cleaning may be necessary after the project is completed to remove any dust”
Bob Vila, "Solar panel cleaning cost" (frequency, method, cautions). Updated May 11, 2026. “The best times to clean solar panels are cool, cloudy, and mild in temperature”
Bob Vila, "Solar panel cleaning cost" (frequency, method, cautions). Updated May 11, 2026. “Never apply cold water to hot panels”
Bob Vila, "Solar panel cleaning cost" (frequency, method, cautions). Updated May 11, 2026. “high-pressure cleaning is likely to create fine cracks on their surfaces”
First Solar, Module Cleaning Guidelines, Rev 3.4 (utility-scale thin-film modules; pressure, temperature, hard water, shock cautions). “do not apply water that is more than 20°C warmer or colder than module surface temperature”
First Solar, Module Cleaning Guidelines, Rev 3.4 (utility-scale thin-film modules; pressure, temperature, hard water, shock cautions). “water pressure must not exceed 35 bar (500 psi) at the nozzle”

Written by Foothill Home Services. Local prices on this page are our own draft rates from the price list the quote tool uses. Where we quote an outside page, the quote is linked in the sources above, and we last checked this page on October 13, 2026. Other outside figures are described as the source reports them.

How often should you clean solar panels near Ontario and Rancho Cucamonga?