Whether to clean solar panels is a great question we get with every solar power installation we do. Our answer is simple: Century Roof and Solar does not actually recommend cleaning solar panels more than once annually. And in the Bay Area, one good winter rain will do the job for you!
Homeowners and commercial property owners are happy to hear this: This keeps them from climbing on their roofs unnecessarily, or paying for extra cleaning services they don’t need.
To Clean Your Solar Panels One Good Winter Rain Will Do
The owner of Century Roof and Solar, Tony Diaz, is an instructor for one of the top solar energy training schools in the world, Solar Energy International or SEI. SEI and the Department of Energy partnered about 10 years ago to quantify the additional solar generation benefit gained by cleaning solar panels, to better guide their students on how to maintain solar panel installations. Here is what they found:
- If you clean the panels one time a year in June, you will get 4% more annual production.
- If you clean the panels 4 times a year (quarterly) you will get 6% more annual production.
With this information, we can see that the sweet spot is cleaning the panels only one time a year.
At first glance 4% additional annual generation seams exciting right? But do the math.
- Let’s say that your annual solar generation is 7000 kilowatt-hours (kW-hr) per year.
- A 4% increase by cleaning would equal to an extra 280 kW-hrs.
- Then you would multiply the kilowatt-hours by your average cost per kW-hr that you are still paying the utility.
- Let’s say on the high end that your cost per kilowatt-hour after solar is still 20 cents a kilowatt hour, then your total extra annual monetary value for cleaning the panels will be $56.
Given this calculation, we teach students at SEI that cleaning solar panels is not very beneficial and not really worth the risk of having a property owner venturing to a high place to wash an electrical device. Now if a panel or two have some type of opaque material on the glass such as a tree leaf or a gigantic bird stool, then yes, that should be cleaned off. Those substances are a “hard shading” material. But, the general buildup of annual dust from the environment really does little to block out the visible light spectrum that causes the electron movement in silicon solar cells.
We had many consumers call our office last summer concerned that their panels needed cleaning due to the ash from the fires. But researching the monitoring history of our own solar system on our office and homes, as well as past customers’ homes, proved that the ash had little to no effect. In fact, many of the systems for which we reviewed and compared their annual energy “harvest” showed that many systems generated more energy this year than last. It is opaque objects that truly affect solar generation, and ash is not opaque.
Rely on Mother Nature to Clean the Dust Off Solar Panels
I know that consumers’ perceptions are that cleaning solar panels is beneficial, especially due to local entrepreneurs advertising panel cleaning services. But as you can see from the above calculation, the numbers are just not there to warrant the expense and or effort to clean off solar panels. Besides, there is no better way to clean the dust off a solar panel than letting good old Mother Nature drop rain from 30,000+ feet up in the sky!
Now we just need to pray for decent rain this winter so we can all get our solar panels clean and ready for June 21, the longest day of the year with up to 15 hours of sunlight!