Do you need to wash your solar panels?

It’s a good question and one with a lot of different answers. Companies specializing in cleaning solar panels generally say: Yes – you have to clean your rooftop solar panels and you have to clean them regularly. Some say panels need an annual scrub, others say quarterly. One company selling an automated washing system says panels should be washed every couple of weeks.

They cite a National Renewable Energy Laboratory study that found dirty panels produce 25 percent less electricity than clean ones.

Skeptics, however, argue the companies are just trying to sell their services and that washing or paying to have panels washed is a foolish waste of money and/or effort.

Maybe you will need to wash, maybe you won’t

As with most debates, there’s validity and hogwash on both sides.

NREL’s official line on the subject is that “solar panels may need to be cleaned in climates with infrequent rainfall.”

Since most solar panels are mounted on a slope, rainwater will rinse dirt, debris and bird droppings off of them the same way it cleanses your windshield when you leave your car parked outdoors in the rain.

Of course, you sometimes get dirty rainstorms or blowing dust that will stick to your windshield, leaving it dingier than it was before the rain. The same thing can happen to your solar panels.

Most of the time, those dirt spots will wash away in the next rain. But if you live in a place with a lot of wind and debris in the air or infrequent rain, washing or having your solar panels washed will likely be a requirement. It could even be a stipulation of your solar panel warranty depending on your dealer and location.

It’s your call

Be wary of people telling you that you have to wash your solar panels. They could be trying to sell you a service you don’t need – or they could know what they’re talking about. There’s no way to know for sure until you can see for yourself.

You might put off signing a maintenance contract until you have a chance to watch your electricity generation and get a look at your solar panels to see just how dirty they will get. Clean them or have someone clean them and see for yourself if the cleaning made a big difference in your panels’ power production. If cleaning increased your system’s output, it might be worth contracting for regular cleaning services.

How to do it

Even if you don’t need to wash your panels regularly, it might not be a bad idea to give them a little TLC and inspection every few years.

If you are going to clean your solar panels yourself, use water, a gentle soap like dishwashing detergent and a soft brush to get the buildup out of the corners. Avoid harsh chemicals, abrasive scrubbers and pressure washers, which could damage your solar panels.

And be careful up there.