One thing learned during the coronavirus pandemic was the effectiveness of soap and water — regularly washing our hands was our best defense. While dirty solar panels do benefit from a regular washing to ward off reduced output and efficiency, soap isn’t the answer here.
California-based solar installer and maintenance provider Bland Company never uses a cleaning agent on solar panels, instead relying on deionized water and a rotating-brush system to wash solar panels.
“Soaps can leave a film or residue that not only shades panels like the dirt that was just washed off, but it can also encourage dirt to stick and build up faster,” said Daniel Green, Bland marketing director. “We use deionized water that is applied through our rotating-brush system. This is the best way to leave the solar panels with a spot-free shine that’s as beautiful as the first day they were installed.”
Rather than risk Bland employee safety or potential damage to the solar panels they’re cleaning, the company has been using Sola-Tecs brush cleaners since 2018. A rolling brush is attached to wheels that glide across the solar panels, allowing for an almost-hands-free deep clean. Bland also runs the customer’s water through a demineralizing and ionizing system.
“[Sola-Tecs] is the only cleaning system we use. We’ve found that in combination with our water treatment procedure, it’s the best way to clean solar panels,” Green said. “It requires less water, fewer passes and no harsh chemicals or detergents.”
Premier Solar Cleaning (PSC) in Southern California also finds that using deionized water through water-fed poles and brushes works just fine to clean solar projects.
“If you have ever smelled your hands after washing them with soap, what you smell is the soap left behind, even though you cannot see any soap afterwards,” said Adam Fuller, co-founder of PSC. “If we used soap to clean panels, the very small molecules of soap would leave something behind for dust and dirt to build upon.”
PSC offers a full maintenance suite, including infrared inspections to find damaged panels that need more than just a good wash. Fuller also stays busy doing year-round “pigeon evictions,” cleaning underneath panels and installing critter guards to ward off birds and other animals. He takes pride in giving customers honest answers and showing how production will increase after panels are cleaned.
“The homes and factories nearest the airport and highways gather smog or oil-based pollution, which resist running off with a normal rainfall,” Fuller said. “These make some of the older blue panels appear black at first glance. Dirt on the surface reflects light away from the panels. A clean panel remains cooler, allowing the flow of electrons to move more easily.”
National residential and commercial O&M provider SunSystem Technology also stays away from soap and uses filtered water and a rotating brush to clean panels, but director of marketing Jeff Struhm said the company uses a mixture of diluted vinegar and hydrogen peroxide to aide in scrubbing away dirt and grime.
“When rain happens, soil accumulates at the bottom edge of the solar panel, obstructing the lower PV cell row and hindering the production efficiency,” Struhm said. “It’s like a car getting hosed down — you still need to scrub it or use a soil-releasing mixture in order to avoid scrubbing.”
Sometimes just water isn’t enough, but everyone agrees that soap should never be used. That’s why lubricant manufacturer Polywater released its Solar Panel Wash five years ago. The highly concentrated additive isn’t a filmy soap; instead it enhances water’s ability to clean solar panels, said Charlie Cole, Polywater international VP.
“We’re giving the water the capacity to lift the soil off the panel as opposed to a solvent, which is basically surrounding the dirt particle and taking it off the panel,” Cole said. “[Solar Panel Wash] is safer for the components of the panel. It’s not going to affect anti-reflective films; it’s not going to corrode the aluminum rails. It’s biodegradable, meaning that it’s non-persistent, making it friendly with the environment. It’s not going to affect the groundwater.”
Solar Panel Wash modifies the surface tension of the water, so instead of water beading up, it will form a continuous film across the solar panels to lift dirt and debris. Cole said Solar Panel Wash is especially helpful in arid locations where dust is high and water is scarce, because the wash allows for less water to be used in cleaning.
“A lot of these installations are done in desert regions where the availability of water is really an issue. If we can reduce the use of water, it’s an environmental benefit,” Cole said.
Polywater works with panel manufacturers to get its wash approved for use to not void any warranties. Canadian Solar and other global brands have confirmed Solar Panel Wash is safe for use on their panels. It can be purchased through Polywater’s global network of distributors and from Amazon in North America.
Solar O&M providers are glad the industry is waking up to the need for periodic panel washing.
“At the beginning, panel managers were saying, ‘Don’t use anything but rain water.’ People were taking that to heart, and then three years after the panel installation they started to see a significant degradation of productivity,” Cole said. “For a large installation, if your efficiency goes down by 50%, that really cuts into the economic justification that was made in the first place.”
Even on residential projects, homeowners will benefit from paying some extra attention to the cleanliness of their few solar panels.
“We oftentimes hear customers say that the rain does just fine cleaning their panels, and while the rain does wash some dirt off, it doesn’t truly clean the panels. If the panels are already filthy, the rain just makes it worse by converting dust to thick layers of mud,” Bland’s Green said. “The perfect analogy is to consider your car. If your car hasn’t been washed in six months, does leaving it out in the rain make the dirt better or worse? The same is true with dirty solar panels.”
Just don’t use soap — a little elbow grease and water work fine.