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.
Courtesy: Premier Solar Cleaning
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.
Courtesy: Premier Solar Cleaning
“[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.
Courtesy: Premier Solar Cleaning
“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.
Non-soap Solar Panel Wash from Polywater
“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.
Courtesy: Polywater
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.”
Courtesy: Polywater
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.
When I was about 30 years old, I had made friends with a retired UPS supervisor, & his brother, in a fast growing town in central Kentucky, (this was back around 1980, just before the Chicago Bears got on a roll for the 1985 Superbowl, … they owned a carwash/full service gas station, with a oil change bay, … they were quite energetic, in coming up with ways to provide a number of services for the community, …
The one thing I remember JS, saying about that business, is that soap, does not clean cars, … and he showed me a barrel that provided the customers “seller”, … You see, the customers love to see suds, & believe that it is the soap which is cleaning their vehicle, … And JS, acknowledged that the soap only helps in providing a medium to carry the dirt away from the vehicle, … The real “magic behind the curtain” was sitting just to the side of it, & in a dry corner of the contents room sat several bags of water softener salt, … packed up 6 high on pallets, & covered with plastic so it did not get wet too early, … just in case a water leak sprang from somewhere amongst the equipment, …
Soft water was the key to cleaning, & hot “soft” water would degunk just about anything you could find on any automotive vehicles, … from heavy trucks that worked the coal mines, to old grannies, that only use the car on Sunday, to go to church, to the ingle guys who would “cruise” the malls, … there was a lot of traffic that got washed at the self-service/full service car wash, you could buy a carwash, fill up your car, get the oil changed, & I’d be there if you wanted to get your car waxed, … or to have the luster restored to the paint, then waxed, … I was too cheap, for the prices I was charging, but made enough to feed my family, barely, … but that is another story, … lol, … lets just say that I learned how to have, & keep a nice ride without a lot of expense, & very little upkeep, …
Airborne Hydrocarbons like to stick to glass, paint & metal and, much to the surprise of researchers, who were investigating the Lotus Effect of extreme hydrophobicity; Hydrocarbons also like surfaces that have been treated to shed water or are in some manner modified to be self cleaning. TiO2 coating may be an exception but they may interfere with photon transmission. The hydrocarbon build up attracts airborne particles.
Where I work in the SF Bay area, I’m sandwiched between 10 lanes of I-880 and one of the main off ramps to Tesla. Suffice to say, my car gets dirty. On occasion, I have noticed that a gentle but persistent rain, unaccompanied by wind and thus rapid evaporation, practically leaves my car and the windshield, streak free. My car is 20 years old, the paint has signs of bossing from the car wash and yet a gentle, persistent rain leaves it pristine.
I measured before and after cleaning my panels at the end of a dry summer in Portland and found 1% or less output increase only. Very dusty locations probably more.
Seven years after installing PV on my Chandler, AZ home, I have concluded that cleaning PV modules is unnecessary. After a full year of operation I cleaned my modules and compared before and after kWh production. The day before cleaning and the day after were identical cloudless days at the exact same temperature. I discovered there was absolutely no change in kWh performance. While cleaning modules may be worthwhile in heavy bird dropping area or Fresno with heavy soiling from agricultural activity, in my firm opinion, it does not pay to do this in the vast majority of residential PV applications.
Car windscreen cleaner solution would seem to fit the task. It removes road film, bird effluvia and squashed bugs…..
Use SWP Solar Wash Protect a concentrate Bio degradable solution mixed with water for better wash for long period. It is dust repellent cleaning solution for Solar Panels only.
Depends on the tilt of the modules as well. Panels at 30 degrees get cleaner with rain water better that 10 degrees tilt or less
You won’t get bird droppings off without detergent.
Getting it soaked with ordinary water (without soap) for a few minutes before washing is sufficient to remove it.
Rainx……..works for me ..about 10 years now
Unless you have lots of birds flying over the panels lol
I tried Rainx it works fine with rain, but in the winter snow tends to hang up more than on plain panels.
I don’t use soap because I drink the water off my roof.
Must taste pretty good I’d say…you’re drinking everything else that LEACHES off your roofing materials.
I would have to imagine that he runs it through some kind of filter, most people don’t drink rainwater directly
This article seems to be using the word “soap” rather broadly. Of course you aren’t going to rub your panels with a bar of Dial soap! Detergents and surfactants are another story. They really help to remove surface contaminants, rinse easily, and don’t leave a sticky film. You need to avoid consumer products that have other junk in them like skin softeners, and the final rinse should be D.I. water. D.I. water by itself is fine, but sometimes an oily contaminant needs more.
The best way to clean solar panels is with rotating brushes or robots that have rotating brushes mounted on them. In our extensive cleaning experience (our machines have cleaned 100s of GW) soap is not necessary, just de-ionized water!
I’ve had my 5KWh system for about 6yrs now and I’ve been keeping a detailed log on its energy production, I’ve never had a service done and never had anyone wash the panels, I let the rain clean the panels and to this day it’s producing the same it was when installed, when I say same I mean no great reduction in power, very happy with mine.
Relay soap is not recommended I as an instullar prefers a brush and water,and a soft tawel.
Long ago, when Sanyo made the HIT solar PV panels, their product sheet called out “cheap” dish washing liquid, not the stuff with skin softening aloe Vera or something like that. Warm water dish soap and a (towel) to wash down the panels. First step was spray down all the panels and let the water drain, second step wash down panels with dish soap, then spray off and squeegee with a soft rubber blade. I’d say most solar PV manufacturers will absolutely say not to use harsh chemicals like Windex or cleaners with any kind of cleaning “grit”. Panels can last for many years using this method. I have noticed that some bugs like to lay their egg cases on solar PV panels, these leave a waxy blob on the panel that is not always easy to remove. In those cases, warm soapy water, squeegee with a soft rubber blade, repeat until gone.