How to clean solar panels
November 4, 2020

Whether you have photovoltaic (PV) modules or flat panel solar thermal collectors, you can achieve the highest energy output from your solar panels by carefully scheduling a proper and safe cleaning once or twice a year. Solar panel soiling occurs in all environments and can be considerable if your system is located near a freeway, farm, factory, construction site or a stand of trees. In this era of massive wildfires and power shutoffs, it is more important than ever to keep your panels clean so they can perform optimally during the short winter days or if used for charging batteries. Waiting until after the height of wildfire season has passed could be the best time of year to have your solar panels cleaned.

For some real world insight, I asked Koralie Hill, Director of System Performance at Sun Light & Power, about cleaning photovoltaic modules and solar thermal collectors. Her extraordinary experience shed a great deal of light on this important subject.


Does wildfire ash pose any special cleaning requirements? 

Fire ash seems to fall in larger clumps and builds up faster. Thankfully, ash is easier to "brush off" especially if addressed right after it falls. Dust from highways or fields is constant and tends to be finer.


How much PV power is lost due to soiling after a year in a typical urban neighborhood? 

 It depends on the exact location, angle of the array, and proximity to the source of dust such as ongoing construction. I've seen output drop from 8-30%


 How often should solar panels be cleaned in a rural or agricultural area?

 It really depends on the size of the array. The larger the array and the installation, the more power will be lost due to dust build up. If customers are interested in maximizing power output, they should consider cleaning modules one-two times per year


Can customers rely on the weather to clean their solar panels? 

I tell our customers that rain will help remove superficial dirt, dust, and ash on modules, but rain alone will not remove all of the built-up grime. Module cleaning will help increase power production if you thoroughly remove all of the buildup.  


Are there any special cleaning requirements for solar thermal collectors or evacuated tubes? 

Solar thermal flat plate collectors are cleaned much in the same way as solar PV modules. We do not recommend that customers try to clean evacuated tubes themselves because these are far more delicate. 


Does Sun Light & Power plan to offer cleaning services?

SLP can coordinate module and panel cleaning, but we do not perform this service ourselves.

ash covered solar panel 

Basic Solar Panel Cleaning Guidelines:

Don’t put yourself at risk! If you have a steep roof or the solar panels are inaccessible, we recommend that you hire a professional cleaning service. However, we urge you to hire only those who can produce proof of insurance.

Modules should be washed when they are cool (early morning or after sundown). Use only mild, biodegradable dish soap and a nonabrasive scrubbing device. Never stand or lie on your solar modules. The extra pressure can cause invisible breakage that can permanently degrade your module performance. Do not use a pressure sprayer to wet the modules - a regular garden hose nozzle is sufficient. There are many soft-bristle brushes available with extension poles that may be connected to a regular garden hose. 

Soft water and gentle cleansers are crucial for properly cleaning and protecting your solar panel investment. Use only water with a low mineral content at ambient temperature. Pass the water through a water softener or use distilled water. If grease is present, an environmentally friendly cleaning agent may be used with caution. Never use aggressive or abrasive cleansers/chemicals such as alkali chemicals including ammonia based solutions to clean solar panels.

The employee owners of Sun Light & Power would like to thank Director of System Performance Koralie Hill and Superintendent Anukene Warda for their contributions to this blog. Please visit our solar panel cleaning page for more details on how to clean residential and commercial PV arrays.

clean solar panels 

Seamas Brennan is Marketing Coordinator at Sun Light & Power.

Have you cleaned your PV modules or solar thermal collectors lately? 510.845.2997

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