Solar panel cleaning in Las Vegas: does it pay, and how to do it safely

Sometimes, and you can find out for your own roof in a week without guessing. Record a few clear days of production, clean the panels safely or have them cleaned, and record a few clear days after. The difference is what cleaning is worth to you. NREL's data says the typical yearly loss from dirt is a few percent, but some sites lose much more, and droppings behave very differently from dust.

What the studies actually measured

Solar marketing is full of cleaning numbers. Here is what the published data from the National Renewable Energy Laboratory says, and what it does not.

Across monitored US systems. NREL's 2024 fleet study extracted soiling losses for 255 systems that showed measurable soiling, meaning more than 1 percent. Among those, annual soiling losses typically ranged from 0 to 15 percent, and the median was 2 to 3 percent.

In the Southwest specifically. A 2023 NREL paper picked 16 Southwest sites from the same soiling map, chosen because they had soiling losses above 1 percent, and modeled 20 years of rain and dust. Average losses at those sites ranged from 4.3 to 15.5 percent a year. Those are large ground-mounted plants chosen for being dusty, so they are a ceiling for a dusty site rather than a forecast for your house.

In NREL's own estimator. PVWatts, NREL's free public calculator, assumes a default 2 percent for soiling.

Two honest conclusions follow. For many roofs, the loss is a few percent a year, which may not cover a paid cleaning. For some roofs, especially near construction, unpaved lots or open desert, it is much more. The only way to know which roof you have is to measure it.

One more detail from the 2023 paper: when a system has more panel capacity than inverter capacity, the inverter caps output on the best hours anyway, so some of the dust loss disappears into that cap. A system that clips on clear spring afternoons may gain less from cleaning than you would expect.

Why rain does not do it here

In most of the country, rain cleans panels for free. NOAA's climate normals for the Las Vegas airport put annual rain at 4.19 inches. The standard soiling model the 2023 NREL paper used treats a day with more than 2.5 millimetres of rain as a cleaning event and lets dust build up steadily between them. Here, the gaps between those days are long.

A light summer shower can make things worse, not better, turning a film of dust into mud streaks that dry in the sun.

Dust versus droppings

These are different problems.

Dust is an even film. It dims every cell a little. The loss grows slowly and cleaning restores most of it.

Droppings are opaque. One covered cell can drag down a whole string, and a covered cell can heat up. Nobody can give you a percentage for droppings without knowing which cells are covered. If you see spots, cleaning is only half the answer, because the spots come from birds, and birds in Las Vegas usually mean something living under the array. Pigeons under your solar panels covers the clean out and the critter guard that stops it coming back.

The water problem

Las Vegas tap water is hard. The Las Vegas Valley Water District puts it at 280 parts per million, or 16 grains per gallon, which it classes as very hard. The minerals are calcium and magnesium.

That does not hurt you, but it matters on glass. Water that dries on a hot panel leaves its minerals behind as white spots, the same way it does on a shower door. A panel that has been washed badly with hard water many times can look worse than a dusty one.

Panel makers know this. One major manufacturer's installation manual asks for water with low mineral content and near neutral pH. Practical ways to get there:

• Wash in the early morning, when the glass is cool and the water does not flash dry.
• Finish with a rinse of filtered or deionised water if you have it.
• Do not let the panels air dry in full sun.

How to clean without voiding the warranty

Read your panel maker's manual before anyone touches the glass, because the same manual that sets the rules also says what voids the warranty. The manual we opened for this page, CSI Solar's installation manual for standard modules, is typical. It says damage from inappropriate cleaning voids the warranty, and it asks for:

• No dry scraping or rubbing. It causes micro scratches in the glass.
• No abrasive cleaners, degreasers or unapproved chemicals. Only substances the manufacturer approves.
• Soft, non-abrasive tools. A soft cloth, sponge or soft bristle brush, made of non-conductive material.
• A pressure limit. That manual sets a maximum water pressure of 4 MPa. A pressure washer can exceed a limit like that, and a garden hose does the job without the risk.
• Avoid the hottest hours. Cold water on hot glass is thermal stress.

It also says what every licensed electrician will tell you: the voltage and current in an array during daylight are enough to cause a lethal shock, and cracked or damaged modules are a shock hazard, worse when wet. Look for cracked glass before you spray anything. If you see any, stop and call someone.

Stay on the ground

Cleaning from the ground with a hose and a soft brush on a pole is fine if you can reach safely. Climbing is not.

Tile breaks under foot, and dust on glazed tile makes it slippery. OSHA's fall protection rule requires protection for residential construction work 6 feet or more above a lower level. A homeowner on a ladder with a hose is not working to that standard, and a broken tile under an array is the start of a roof leak under your solar panels.

When to hire someone

Hire when your own before and after numbers say the gain is worth the fee, or when the job is one you cannot do from the ground. Ask anyone you hire:

• What water they use, and how they avoid spotting.
• What tools touch the glass.
• Whether they walk on the roof, and how they protect the tile.
• Whether they will look under the array for birds and nesting material while they are up there.

We do not publish a cleaning price, and we will tell you if your numbers say it is not worth doing.

Measure first, clean second

1. Pick three to five clear days in a row and write down daily production from your inverter or app.
2. Clean, or have the panels cleaned.
3. Write down the next three to five clear days.
4. Compare the averages.

If production barely moves, dust was not your problem. If your system is well short of what the contract promised, the cause may be something else entirely, and solar producing less than promised walks through the other suspects. If you do not know where to find the production numbers, your app and NV Energy's figure explains which one to use.

We recheck this page annually. Last checked 2026-09-28. If a number here has moved, tell us and we will fix it the same week.