Maintenance tips

Maintenance schedule: How often to clean solar panels

The question of cleaning solar panels strikes controversy. Can the rain do the job for me or do I still have to add panels to my cleaning list? And how often to clean solar panels? Let’s clear up the subject.

To clean or not to clean? Points of view

Long ago in 2007, Google assembled a huge solar panel installation at their headquarters in Mountain View and faced the hard question, “How often should solar panels be cleaned to run effectively?” They conducted an experiment: left some flat panels on carports and some rooftop tilted ones unwashed for 15 months. When they cleaned the carport system, the panels' production rose by 36%. Rooftop PV modules didn’t show a substantial increase in power and experts concluded that rain can take care of the panels that are tilted. 

The American Chemical Society confirms that dirt and dust pollution accumulated on solar panels can reduce their performance by 17–25%, especially in desert regions. Rain can’t wash away traces of air pollution though. In areas with low precipitation, a rare rain just turns a layer of dust into mud.

Asking Reddit

Numerous threads on Reddit with a wide range of views only confirm that the question is hot. Many homeowners don’t clean their panels for years and are fine with it:

“Personally I don’t consider cleaning worth the effort even when fairly dirty (as in after dusty winds, spring pollen, etc.) I only see a negligible drop in power, and rain usually cleans them off soon enough so the barely noticeable hit in production isn’t worth risking my neck.” – nocaps00.

While for some the drop in production is substantial, they choose against cleaning. The reason is simple — getting up on the roof is too difficult.

“I know mine are filthy up there, I can tell our production is less than last year by a good margin. The problem is we have a two story house and the panels are on the side that there is no good way for me to go up there and scrub them.” – chepnut.

Most admit that dirt is a problem seeing a 30-50% drop in production:

“Cleaning panels depends on location and debris from leaves to bird crap. Living in Los Angeles we get bird crap and dust layer every 6 months. Power output drops from 30% to 50%. In areas with lots of rain, the problem of cleaning becomes less of a factor. I want to say a good rule of thumb is if your power output drops then more than 30%, it's a good idea to check and clean if necessary.” – Kaptainkid1.

And here's the comment that best explains why neither rain nor occasional hosing down are enough to keep solar panels clean:

“I took a trip up to the roof on a day when I was bored. Yes, the panels were dusty (I’m in southern California)...OK, [I said to myself], I’ll wash off my 27 panels with a hose and call it a day...I’ve had these panels for about 8 years. I was surprised to find a jump in power of roughly 10%!

Just for fun, I got down to one panel and rubbed my finger on the panel. There was a film that a garden hose didn’t get off! I bought a window washing thing, and took another trip up to the roof... It was not all that hard, took about 30 minutes. I picked up another few percentage points in power. Let’s call it 3 panels worth. That’s a lot of power.” – hmspain.

We believe that rain alone is not enough for cleaning your panels, no matter where they are installed. You can order a service instead of doing it yourself — learn about the costs in our article!

How often do I need to clean solar panels? Check these factors

In general, it’s recommended to clean solar panels every 6 to 12 months, even if they appear visually clean. But the geography of the United States is diverse, ranging from arid deserts to polar humid coasts and everything in between. In some regions panels require more frequent cleaning than others:

Drylands: Frequent heavy rain can keep your panels relatively clean, but if rain is a rare guest in your home, you’ll have to handle it yourself.
Desert: Desert areas may have another problem – sand. If your panels are buried under a pile of sand and the wind fails to blow it, high performance is out of the question.
Coastline: Those living on the coast face salt deposits on the panels and the seagulls contributing to the problem. Even rain won’t help here, you have to deal with the problem yourself.
Big cities: Life in a big city jammed with cars or in an industrial area surrounded by factories and plants can also affect how often solar panels need to be cleaned. Pollutants in the air can settle on the panels’ surfaces and build up a layer of grime that can reduce their performance over time.
Wildfire regions: Cleaning becomes especially important in areas like California, Oregon or Washington where you experience a lot of wildfires. Ash settles on the panels and rain has a hard time washing it away.

Every 6 to 12 months – 

how often to clean solar panels in general

Is it time? Signs that your solar panels need cleaning

It’s not hard to figure out whether it’s time for cleaning. Here are the two clear signs that your panels need a proper wash:

Visible dirt and dust: If you see a layer of dirt, dust, leaves, bird droppings, or other debris covering the surface of the panels, it’s a clear sign that they need cleaning.
Reduced energy output: A decline in panels’ electricity generation which you can’t explain by changes in weather or seasons, may be caused by dirt or debris.

Cleaning is an essential part of solar panel maintenance. But before grabbing a cloth and a hose, check out our article on how to clean solar panels properly.

Years of experience in translation and a love of nature help Julia find the right words to encourage going solar. She joined the team in 2023 and is happy to make her contribution to a greener future.

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