What to do about dirt, ash, or dust on your solar panels

[This post was revised on Feb. 17, 2021 to update information about the significant ash fall experienced in the Easy Bay in Sept. 2020.]

From time to time, a customer will call and ask what kind of regular cleaning or maintenance is needed for solar panels. For both solar electric and solar pool panels, if a tree or large branches should fall on your panels, contact us. But what about for plain old dirt? Or dust? Or ash from fires?

For pool panels, don’t worry about it. For solar electric panels, Mother Nature usually delivers enough rain or wind to clean off your panels. But in the event of very heavy or continuing ash fall, you can expect a decrease in your solar panel production.  Some estimates (such as from studies by the Department of Energy) indicate that very dirty panels could cause losses of around 8-10%.  We performed a test in Oct. 2020 on our own home and found that removing ash and dust from our panels improved production on those panels by at least 12%. That’s enough to warrant cleaning panels by hand rather than waiting for a strong rain storm. The ash layer was heavy enough that a cloth was used in addition to a garden hose. It is not clear how much heavy rain would be sufficient to clean this amount of ash from the panels (without human help). In January and February of 2021, Corda Solar cleaned panels for a number of customers. Our staff members found that in spite of several rain events, a sticky, oily ash layer was still firmly adhered to panels and needed scrubbing to come off.

Energy Sage, in their article on the topic, says rain will usually suffice to clean your panels UNLESS there is heavy particulate matter accumulated on them. If you decide to hire a contractor to clean them, make certain that they NEVER step on the panels and be careful to choose a reputable company that is properly licensed and insured. If you decide to clean them yourself, do so safely, from the ground, using an ordinary garden hose (NOT A PRESSURE WASHER!). Make sure to spray the panels early in the morning before the heat of the day. Solar panels are rugged and designed to be outdoors, but they are also made of glass and do not like sudden temperature changes (like cold water being sprayed on them on a sunny day). 

(Smoky air can reduce production, too. On Sept. 9, 2020, the air in the Bay Area was so thick with smoke that the sunlight at midday on what should have been a cloudless, sunny day was the equivalent of the light just after sunset. Solar production at our home was less than 20% of what it should have been on that particular day.)

Please note that Corda Solar does offers solar panel cleaning service only on a seasonal basis (not during the hot summer).