Clean Solar Panels: should you?

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Should you clean solar panels?  Probably not.  Should somebody?  Maybe.  Is it included in your service?  That depends.  Can you avoid it?  Quite possibly.  Let’s take a look at the different scenarios.

Sun Through Glass

Solar modules are topped with a sheet of glass.  I’ve heard the installers say, “we have glass on the roof,” meaning that they’ve completed the rails and conduit and have begun attaching the modules.  “Glass on the roof,” signals that the job is almost done.

Solar modules are clean on day one.  Over time, the glass gets dirty, like the windshield of your vehicles when left outdoors in a parking lot or the driveway.  [Technically, solar panels are enclosed in modules and stay clean.]

In Pleasant Hill, small bird sits on my finger recovering from collision with clean glass.
A clean window temporarily stunned this bird.  Maybe that’s why birds prefer dirty glass.

Tree sap, pollen, pollution, dust and dirt, bird droppings, and the footprints of inquisitive squirrels, raccoons, cats, and roof rats, all contribute.  Solar installed near freeways or other areas of high traffic is susceptible to even higher accumulations of exhaust and road dirt.  On Mars, dust is the biggest problem for panels.

This past year, I noticed my skylights had white spots on them.  I haven’t climbed up to inspect them, but I imagine I need to clean my solar panels, also.  I believe a nearby fire may have dropped ash which stuck to the dew on the surface of the skylight.

Reduction in Production

As you can imagine, dirt blocking the amount of sunlight passing through the module’s glass to the solar panels, causes a reduction in production.

Should solar modules be cleaned?

Early solar adopters and solar-nerds (thanks, guys!) can get fanatical about monitoring and maximizing output of their system.  It’s not average behavior, but it is normal. I’ve seen a few who did the same before they had solar, producing elaborate spreadsheets of electric usage bought from the Utility.  Some of them have been known to climb on the roof to clean the glass.

Designed for Dirt

However, most solar companies simply over-size the system enough to allow for an accumulation of dirt.  It makes sense, because there is a usually a production guarantee, and they don’t want under-production, either. If they can pad the production and still save you money, why not?

The highest output will be when you PTO (get permission to operate) and as time goes by, the production drops a little bit.  If you have as much electricity as you need, then don’t worry about it.

Third Party Considerations


“See that electric meter back there?  They buy from the Utility.

If you are under an agreement with a PPA or leasing company, or in any case, have a remaining solar manufacturer’s warranty, your agreement with the solar company will probably spell out a certain amount of guaranteed production.  If you need more energy, then the first step should be to compare your production to the guarantee.

Should you find that it has fallen below, or if you simply want it to produce more, it’s worth a call to see what they say about your options for improving production.  After ruling out equipment failure or new sources of shade, they should be able to steer you in the right direction.

If your system is producing significantly less than it should, and it is owned by another party, they may be willing or eager to clean it for you.  Call them.  If you own it, and it is still under warranty, they may want to evaluate its performance before recommending cleaning.

Cleaning Clean Solar Panels Won’t Help

Dirt is one cause of increased supplemental purchases from the Utility, but sometimes people go a bit crazy when they first get solar and start leaving all the lights on.  Cleaning dirty solar panels (really modules) helps, but cleaning clean ones won’t.

Don’t Void the Warranty

Before you climb up on the roof or hire someone, be aware that a third party may also prohibit cleaning, or limit what products are used.  Third parties could include the manufacturer, the service company (if any), or the actual owner of the system.  Check with them, first.

Monitor Production

“The family on this side has solar.”

There have been stories of system failures where the first sign of trouble was an electric bill that suddenly jumped up.  At the very least, glance at your bill each month to see what’s happening.

Keep in mind we’re only talking about electricity, here, not gas, and production is seasonal, so each month is different.  Someone like me, in your local area, should be able to help you evaluate your system if you need it.  PG&E has a Solar Hotline for solar customers; they can help with reading your bill, but not with your solar equipment.

If you have an account with PG&E, they will only bill you once a year at “True-up” for your electric purchases from them.  That’s why you need to check the NEM pages each month, to see your anticipated annual bill.

If, however, you purchase your electricity from MCE or another aggregator, you may be charged for generation purchases, monthly.

Basically, just because the total amount billed seems normal, you still need to glance at the details showing credits and charges being deferred.

Monitoring Services Need Monitoring

Any type of solar agreement may or may not include third-party monitoring, depending on what was offered at the time.  Consult the documentation of the agreement.  There may even be more than one party monitoring, depending on the set-up and type of deal.  But don’t assume they will catch production issues before you do.

Many of them also provide customers with their own monitoring software or apps.  If you have one, it’s worth checking it once in a while.  Solar is reliable, with no moving parts.  However, the quality of monitoring services really depends on who is doing it—and they may be monitoring thousands of systems, or might have closed their doors.

PG&E also has ways to monitor what you buy from them, which can be useful.  However, they don’t monitor how much your system is producing or how much your household is using, only what you get from them.  If you get electricity from MCE or another CCA, their billing may complicate the calculations.  PG&E can provide the number of kWh you buy, but the dollar amounts will only include the distribution and delivery charges, not the generation charges from another provider, if any.

Clean Solar Panels the Easy Way

The easy way is if it’s someone else’s job.

For many people, that’s one of the main appeals of having a PPA.  It’s also one of the reasons a PPA has a rising rate over time (just like the Utility, only limited by agreement, not politics)—they assume they may someday have to send someone out to clean your solar panels at future labor costs.

Also remember, if you have a PPA, you may be paying for what the system produces. Clean solar panels might increase your total payment, as well as the production, so think twice about washing them if your system is too big and you have a PPA agreement.

In any case, if the company doesn’t attribute the production loss to an equipment failure or other cause, they may simply clean the solar panels or suggest you clean them, depending on the terms of your agreement.

Maximum vs Adequate

If you are producing more than you use, ask yourself if producing more has any value this year, since in most cases the excess is not worth much, and some credits may be reset to zero at true-up.  It may make sense to wait until they get dirtier, and Utility rates increase.

On the other hand, your extra will be sold to your neighbors, and it’s clean and green, so there is still a benefit to all of us.

If you are producing less than you use, then what are you paying the Utility to supplement your system?  If it’s only a small supplemental amount, the above still applies.

After all the foregoing, if you decide to take responsibility to clean your own solar panels, you have the option of using a solar-cleaning service, or doing it yourself.

How Often Do Solar Modules Need Cleaning?

Once you determine you want to clean them, how often is really up to you.  You will have to balance the cost in time or money against the amount of electricity produced.

Over time, as Utility electric rates go up, the value of the increased production does, too, but so may the cost of labor.

There are services that clean solar panels.  Some people call them once a year, before or after rainy season. 

However, even if you rarely wash your car, you probably wash the windshield more often than once a year, even if just using the built-in wiper fluid system and the wipers.

A large white heron studies my neighbor's pool
Pool cleaner prepares to remove mosquito fish from my neighbor’s pool in Contra Costa.

How often then becomes a question of how important it is to you to maximize production.

If you find yourself having to buy more and more electricity from the Utility each year, cleaning might be a good idea.Just make sure whoever cleans your solar panels is insured and knows what they’re doing.  Insurance companies charge higher premiums for any worker that climbs up on a roof, for a reason.

Self-Cleaning” Solar Panels/ Modules

All of which makes “self-cleaning panels” an attractive option. Treat them once, and assuming a bit of wind or rain from time to time, you can have solar panels guaranteed not to need further cleaning for 20 years! No ladders needed by you, and treated panels outperform untreated ones, year after year.

Have you ever cleaned your own solar modules? Did you see an improvement?  If so, please comment below, and Bookmark, Like, Share, or Subscribe.  Contact me with questions or suggestions.

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