CAUTION: READ MANUFACTURER INSTALLATION, SAFETY, AND MAINTENANCE INSTRUCTIONS BEFORE CLEANING OR MAINTAINING YOUR SOLAR PANELS. PARTICIPATING IN SUCH ACTIVITIES INVOLVES THE EVER-PRESENT RISK OF PERSONAL INJURY, PROPERTY DAMAGE, AND LOSS. THE USE OF HARSH, INDUSTRIAL-STRENGTH CLEANING MATERIAL OR SHARP INSTRUMENTS TO CLEAN OR MAINTAIN YOUR SOLAR PANELS MAY VOID PRODUCT GUARANTEES OR WARRANTIES.
Do solar panels need regular cleaning to maintain top efficiency or does the occasional rainstorm get the job done?
The truth is, it depends. In some cases, rain or snow may clean most of the dust buildup, but in certain conditions, it could do more harm than good. In both dry climates and more humid ones, environmental factors, different types of dust, and location and installation factors will all influence:
How much dust buildup will collect on buildings over time.
How much of an impact dust buildup will have on the energy production of solar panels.
Whether rainfall will wash the dust off enough to restore panels to at least 95 percent of top performance levels.
Does rain help or hurt? How much?
In a study conducted in Spain, researchers measured an average performance reduction of only 4.4 percent after a year’s worth of dust buildup. Most solar panel owners could probably live with that. But the study also found that in "long periods without rain, daily energy losses can be higher than 20%.”1 So, in a dry climate where dust buildup is the main issue, the problem remains pretty simple: a lack of rain results in dust buildup that might get progressively worse the longer the dry spell lasts.
Meanwhile, normal rainfall can rinse away dust and keep solar panels producing at around 95 percent of their maximum capacity. That conclusion might lead you to assume that solar panels in climates with frequent rainfall should require less maintenance. Not so fast! Most of the time there’s more to the equation than just dust. Pollen, bird droppings, leaves, ash, and a hazy film that can form when smog or smoke hang heavy in the atmosphere can all combine into a layer of surface soiling, which may or may not wash away in the rain. Here’s a report from Renewable and Sustainable Energy Reviews2 that digs into the many complex variables involved. The research concludes that allowing rain to do the work of cleaning solar panels is a fine decision if, and only if, you live in the right kind of place, such as:
A place where dust makes up most of the buildup that forms on solar panels.
A place where the makeup of the dust is such that rain will effectively wash it away.
A place where it rains with the right frequency to keep dust buildup from depleting the energy production of solar panels.
Think about it: if rain was really an effective method of cleaning, then why is the car wash everyone's first stop when a rainstorm ends? With the wrong combination of pollutants, a little rain might not clean anything. It could just become the base ingredient that combines a collection of contaminants into a kind of slurry. Case in point: the account of one family living in a temperate rainforest where the climate completely rules out dust as a problem. Three years after installing their solar panels, they noticed a 10 percent performance drop. When they called local installers to ask about cleaning services, they got a canned answer about how the frequency of rain in their area should prevent any significant buildup from forming. But when a window washer who they eventually hired went up to clean their panels, he found a sticky brown haze that he said wasn't likely to rinse off in the rain. Then once the panels were cleaned, the homeowner claimed that productivity jumped back up by 20 percent, exceeding their original production level by 10 percent!3
If rain won’t do the trick alone, how do you determine if cleaning is worthwhile?
If you’ve had solar panels for a while—a year, maybe more—you’ve most likely noticed how their energy production varies from month to month due to weather changes and the sun’s changing position overhead as the seasons progress. With a little bit of experience monitoring your solar array, you’ll learn how much fluctuation to expect over the course of a year. If you start noticing reduced output at a time when weather patterns seem on par with what you’ve come to expect, dirty panels could be the main factor. If or when that happens, consider these questions:
Do your panels lie pretty flat—between zero and five degrees? If so, they may accumulate more surface soiling than others.
- Do you live downwind from a highway, airport, or farmland? If so, the air in your area may carry high amounts of dust.
- Is rainfall sparse enough to allow heavy dust buildup? If so, your panels may need to be at least sprayed off with water.
- Do you live in an area prone to pollution from industrial smog or wildfire smoke? If so, you may find a hazy film on the surface of your solar panels that may not rinse off.
- Is your house surrounded by tall trees? If so, you may find a buildup of fallen leaves and/or bird droppings on your panels.
- Have you just come through a season of high pollen count? If so, you may find a sticky residue that prevents rain from washing dirt and dust away.
- Is your local climate humid enough for moss to grow around your home? If so, you can’t assume rain is keeping your panels clean? Rain may be the problem.
Ideally, you want to clean your panels in a way that tips the balance between cost, effort, and the potential efficiency improvements in your favor. If it seems clear that your panels need to be cleaned one way or another, the next step is to determine the best way. At that time, consider this next list of questions, based on your observations.
Does the buildup seem to be mostly dust or are there more sticky substances like bird droppings, pollen, and smoke in the mix?
Is it possible to spray your panels off with a garden hose from the ground or will you need a ladder?
Is there a safe way—either by ladder or otherwise—to climb onto your roof if necessary?
Are your panels mounted far enough from the edges of the roof that you can move around and position yourself to safely reach each one?
Do your roofing materials and roof pitch create a safe platform to work from? Or is it too high, steep, fragile, and/or slippery?
Tips on cleaning solar panels
Cleaning your solar panels shouldn’t cost an arm and a leg, nor should it be an overly complicated process. When it’s possible, spraying them off from the ground is easiest and best. But the stickier the buildup, the more likely it is that you’ll need cleaning tools and supplies to wipe your panels down from up close.
For minimal surface soiling made up mostly of dust, try hosing your solar panels off from the ground.
If your panels seem to be underperforming, your roof isn’t too high, and your consideration of environmental factors leads you to conclude that a simple accumulation of dust is likely the problem, try hosing your panels off from the ground first. It’s the safest, easiest, and most low-cost solution, which makes it the one with the highest return. Just remember, if your roof is low enough to be sprayed from the ground but high enough to require a pressure washer or a nozzle to concentrate the hose pressure, be sure not to blast your solar panels directly with harsh, high-pressure pulses of water. Hitting the dirty surface with high pressure may create scratches. And scratches will cast tiny shadows on the photovoltaic cells underneath the tempered glass layer, permanently depleting the energy output of your solar panels.
For heavier buildup, use soft scrubbers, mild soapy water, and a squeegee to wash your solar panels.
Cleaning supplies you’ll need:
- A soft brush and squeegee long enough to reach from wherever you’ll be working.*
- A water hose long enough to reach your panels.
- A bucket filled with water and a little mild soap.**
*Pro tip: If you don’t have adequate tools on hand, you can find inexpensive, all-in-one, window washing tools with a soft scrubber to gently clean glass on one side, and a squeegee on the other mounted on an extendable pole, like this.
**Pro tip: You can find specialty, biodegradable solar panel cleaners, like this, packaged in a disposable hose mixing sprayer.
- Fill your bucket with clean water and add a small amount of soap.
- Rinse solar panels with clean water to clear away loose dirt.
- Use soft scrubber and soapy water from the bucket—or mixing sprayer—to gently wash the surface of the panels.
- Rinse solar panels with clean water from the hose a second time.
- Squeegee panels dry.
- Follow the same process, changing your position as needed, until all panels are clean.***
***Pro tip: Be careful to avoid touching the sides or underside. Also, avoid contact with any wiring harnesses and/or cables.
It’s important to remember that solar panels get hot in the middle of the day, so it’s best to schedule your cleaning time at dawn or dusk or on overcast days when their surface will be relatively cool. If you were to wipe your panels with soapy water while they’re hot, the water would instantly evaporate creating a film that would require additional cleaning steps to remove.
Sometimes it’s cheaper, safer, and easier to call professional cleaners.
Maybe you’ve considered the variables involved, taken stock of the resources you have on hand, and concluded that cleaning your solar panels on your own is not for you. For example, maybe you’ve realized:
- Your roof is too high, too steep, or too slippery to walk on.
- You don’t own a ladder or adequate cleaning tools and the idea of buying and storing a bunch of gear you may only use once a year makes no sense.
- You have physical limitations that make climbing ladders and scrambling around on rooftops a sketchy proposition.
- You’d simply prefer not to be the one who does all that work.
For plenty of solar customers, professional cleaning can be the most worthwhile option. At that point, the obvious choice is to call the company that installed your panels in the first place to ask if they offer cleaning services. They should have information regarding your roofing materials, roof pitch, square footage of your solar array, and either photographs or digital renderings of how your solar panels are laid out across your rooftop. Armed with all that information, it should be very easy for them to give you an accurate price estimate right over the phone or at least point you in the right direction.
Depending on your weather conditions, dust, and other pollutants that could accumulate on your solar panels, it’s important for you to at least regularly rinse off your panels, and if necessary, follow the tips above to carefully clean them, or hire professional cleaners. Done right, cleaning your solar panels will keep your system operating at maximum efficiency so you can reap the full benefits of going solar year after year.
2019. Irishellas.Com. Accessed March 6, 2019. https://www.irishellas.com/files/Analysis-of-dust-losses-in-photovoltaic-modules_2011.pdf.
"Renewable and Sustainable Energy Reviews | Vol 59, Pages 1-1688 (June 2016) | Sciencedirect.Com". 2019. Sciencedirect.Com. Accessed March 13, 2019. https://www.sciencedirect.com/journal/renewable-and-sustainable-energy-reviews/vol/59/suppl/C.
"I Have to Clean My Solar Panels, And You Probably Do Too | Green Built Alliance". 2016. Green Built Alliance. Accessed March 6, 2019. https://www.greenbuilt.org/i-have-to-clean-my-solar-panels-and-you-probably-do-too/.