Dirty solar panels? If you have a residential solar energy system installed, you may be wondering how to clean it to keep it running in top form.

Rain typically cleans the panels for you, but in drought-stricken areas like ours, you may have been told to clean your solar panels every few months to remove accumulated pollen, dirt, dust and bird droppings to increase energy efficiency.

But in most cases, you won’t need to clean your solar panels often, if at all, according to Evergreen Solar, the national council for solar power growth.

In a 2013 study at University of California, San Diego, researchers concluded that cleaning solar panels often isn’t worth the cost. Dirt and debris build-up can affect how much sunlight gets through, but the resulting decrease in efficiency is minor.

During the study, panels in California that hadn't been cleaned or rained on for 145 days during a summer drought lost only 7.4% of their efficiency. Overall, for a typical residential solar system of five kilowatts, washing panels halfway through the summer would translate into a mere $20 gain in electricity production.

For larger commercial rooftop systems, the financial losses are bigger, but still rarely enough to warrant the cost of washing the panels, the university researchers said. On average, panels lost a little less than 0.05% of their overall efficiency per day.

In Santa Rosa, the average cost for hiring a professional to clean your solar panels is $90, and in Rohnert Park, it’s $130, according to home services website Thumbtack.

So, it might be better to just skip the cleaning process all together, unless they are very dirty.

If your panels are in need of a deep cleaning, however, the simplest and safest way to clean your residential solar panels, according to Evergreen Solar, is with a bucket of soapy water and a washcloth or soft scrubbing sponge, to ensure you do not scratch the panels. Avoid using laundry detergents or anything with harsh chemicals; just use dish soap or plain water.

Also keep in mind that you shouldn’t use any type of high-pressure water sprayer because it can damage the panels.

Solar panels can get extremely hot when the sun is beating down on them, so it’s best to pick a cool, overcast day to clean them. That not only protects you from burns, but if you’re attempting to clean the solar panels when it’s extremely hot out, the soapy water will evaporate quickly and may leave a residue on the panels, which can minimally reduce their effectiveness.

You can also hire a professional to clean them for you, but what you get back cost-wise in your energy bill does not exceed the amount you need to shell out for this work.

It’s best to let the rain — whenever it eventually comes — take care of your solar panel cleaning and save yourself the hassle.

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