Do solar panels need regular cleaning to maintain top efficiency or does the occasional rainstorm get the job done?

A car that’s well-oiled and serviced runs better, so there’s no surprise that solar panels do their job more efficiently when they’re given the same level of attention.

Beyond the set of wheels in our garages, we like to keep our windows crystal-clear and free of grime, too. So why should cleaning our solar panels be any exception? The question should more be focused on when you need to put in the hard yards, and how frequently.

So in this post, we’re covering all of your biggest questions around how to adopt a productive solar panel maintenance routine. We’ll look at all the requirements across what you need to clean them with and how, as well as the main sources of dirt, and when you need to call in the professionals.

Dust, leaves and water – common solar blockers.

Dust causes regular problems beyond the build-up of grime over the years. But your exact location also plays a big role in how much this can affect your system, and what triggers it.

A bit of dust might not have an effect, according to tests done by Ontario Solar Installers, because light can still get through. They recommend that you let nature take its course, as rain will accomplish most of the task of solar panels cleaning.

A test done by one company found the amount the efficiency is lowered is minute – maybe 5 per cent or less. And, with a typical 5 kW system, this might equate to about $20 of loss in your energy bill. Another company found that a thorough clean made the panels 3.5 per cent more efficient.

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:

  1. A place where dust makes up most of the buildup that forms on solar panels.
  2. A place where the makeup of the dust is such that rain will effectively wash it away.
  3. 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:

  1. Do your panels lie pretty flat—between zero and five degrees?                                        
  2. Do you live downwind from a highway, airport, or farmland?                                       
  3. Is rainfall sparse enough to allow heavy dust buildup?                                                       
  4. Do you live in an area prone to pollution from industrial smog or wildfire smoke?   
  5. Is your house surrounded by tall trees?                                                                                  
  6. Have you just come through a season of high pollen count?                                            
  7. Is your local climate humid enough for moss to grow around your home?                    

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.

  1. Does the buildup seem to be mostly dust or are there more sticky substances like bird droppings, pollen, and smoke in the mix?
  2. Is it possible to spray your panels off with a garden hose from the ground or will you need a ladder?
  3. Is there a safe way—either by ladder or otherwise—to climb onto your roof if necessary?
  4. 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?
  5. Do your roofing materials and roof pitch create a safe platform to work from? Or is it too high, steep, fragile, and/or slippery? 

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.

FINAL THOUGHTS

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.

SOURCES:   
  1. 2019. Irishellas.Com. Accessed March 6, 2019. https://www.irishellas.com/files/Analysis-of-dust-losses-in-photovoltaic-modules_2011.pdf.
  2. “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.
  3. “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/.