Fighting Dirty: Manual Washing vs. Automatic Cleaning of Solar Modules

If only a solar project was truly finished once you hooked it up to the grid. We now know better than to expect an array to function at peak production for 20 years without a little upkeep. O&M has grown into a huge business, and module washing is an important segment that shouldn’t be forgotten. Just as quickly as system owners have recognized a need for panel cleaning, new technologies have entered the market. No-touch robots offer an alternative to manual washing, and now some techniques avoid water altogether. Both sides say they’re better than the other—manual washing may be more precise and of a higher quality while automatic/robotic cleaning might be quicker and can be scheduled more frequently. What method works best for your system?

Manual Washing
Elite Module Washing, based out of Longmont, Colo., is a manual panel washing team that mobilizes to nearly any location in the United States and abroad. Rather than have Elite affiliates in various cities, CEO Bryan Dirkes said having one team allows him to make sure everyone is qualified and properly trained.

“We hire everyone locally here out of Colorado, and we travel to the sites with our set crews,” he said. “Everybody knows their job, everybody knows what they’re doing. There isn’t any training each day or worrying about if so-and-so can do this.”

Elite (1) Elite works mostly on utility-scale sites and usually won’t take on a new customer unless it’s at least 40,000 panels. Contracts are based on how dirty the geographic region is—arid and agricultural areas tend to be dirtier than others and require more frequent cleanings. Often, the beginning of summer is Elite’s busiest time because a lot of customers want panels cleaned at the height of the solar season to get maximum output.

Elite only uses water and a soft bristled brush to clean panels. Through local water hookups, the crew filters the water to make sure it’s at 0 TDS (total dissolved solids). Dirkes said that even though there are biodegradable soaps, the amount you would need to clean a large utility site with 1 million panels is too much to be comfortable with soaking into the ground. Water does a great job alone.

“Glass is already porous by nature. It has little divots you can’t see with your naked eye,” he said. “If you use any sort of soap or a squeegee for that matter, it’s going to end up filling those pores and you’ll get dirt, soap particles, anything stuck. Your glass is eventually going to haze over time.”

Elite prefers brushes over squeegees because they also help to clear gunk around the frame.

Elite (4)“Our brushes get in between the frames a bit. A lot of companies that use squeegees don’t have that capability,” he said. “They pull that squeegee down and it crams that dirt into that bottom rail. If it happens to flip to the other side on a single-axis tracker and it rains, then all that mud and grime is just going to be coming down the top of that panel. It totally defeated the purpose of cleaning. The brushes help push that stuff out of there and a rinse knocks it off completely.”

While Elite is contacted after owners notice production has slipped, Dirkes said most business comes during initial budget proposals before projects are even built. The company is currently bidding on projects that won’t begin construction for another year or two. This proves that everyone is taking panel washing more seriously.

“We’re always improving on our equipment and our procedures. By doing that, it can only make us better and faster,” Dirkes said. “We’re continuing to strive toward anything we can do to speed up the process or lower the price on something as vital as module washing.”

Automatic Cleaning
Heliotex has been manufacturing automatic cleaning systems since 2008 and has installations worldwide but focuses on California and Arizona. There are no moving parts or robotic elements; the Heliotex system looks like a sprinkler, with nozzles positioned every few panels. The system runs a wash (with soap) cycle and a rinse cycle, with adjustable frequency. No tools are used, and panels are cleaned just by gravity.

Heliotex (1)While the company suggests a one-minute wash and rinse cycle once a week, some installation areas may need more. Take a rooftop solar system next to a cement manufacturer. That constant cloud of dust should be cleaned weekly (if not daily). Heliotex owner Gene Hunt’s motto is to “clean it before it gets dirty.”

“Every day that you’re not cleaning the panels, it’s going to get dirtier,” he said. “There are two things with cleaning: You must use clean water, and don’t allow the panels to get dirty. Once they’re dirty, it’s harder to get clean.”
That’s why Heliotex persuades customers away from manual cleaning once or twice a year. With the Heliotex system, a quick and automatic spray on a weekly basis boosts production.

“Our system affords the opportunity to keep your panels clean every day, not just two to four days a year,” Hunt said.
The system operates in the overnight hours to 1) not interfere with the electricity-producing daytime, 2) prevent damage to the panels (you don’t want to spray water on hot glass at high noon) and 3) avoid soap and water drying prematurely. Heliotex has its own soap concentrate for use during the wash cycle that Hunt said complies with all EPA conditions and is biodegradable even over time and continual use.

Heliotex (2)Wash and rinse cycles do not always have to be run in succession. Hunt said that while washing doesn’t have to be done every week, rinsing more frequently does help keep panels clean without having to use the soap.

“The panels might not be too dirty so they’ll clean once a month but run just water cycles in between,” he said. “It ensures that you don’t get an accumulation of particulates on the panels.”

Frequent rinses takes away the concern of bird droppings and other debris baking on and really needing some elbow grease to remove.

Heliotex prices its systems by square-feet not kilowatts. The biggest requirement is access to water and water pressure. Heliotex will install various pipes and pumps if necessary to make sure the spray on the panels cleans them effectively. Rather than being an annual O&M cost, the Heliotex system can be looked at as a complementary installation to the solar array and take advantage of various tax rebates. SPW


Drought-stricken regions are usually the ones with the most solar installations. So why not use a waterless cleaning system? Here are two robots fresh to the market.

Ecoppia E4

Ecoppia E4

Ecoppia’s E4
The E4 water-free, robotic solution from Ecoppia cleans panels every day with a soft microfiber and gentle air flow. Floating over a frame that travels alongside each row of panels, Ecoppia claims the E4 removes 99% of dust during its daily cleanings. Each E4 robot has its own solar panel, so no power is taken from the solar row it’s cleaning. Headquartered in Israel, Ecoppia has cleaned more than 5.1 million panels since forming in 2013, mostly in the dusty, desert regions of the Middle East.


Ecovacs Robotics RAYBOT

Ecovacs Robotics RAYBOT

Ecovacs Robotics’ RAYBOT
Household robotic innovator Ecovacs Robotics just recently introduced the RAYBOT, a waterless solar panel cleaning robot. The small robot suctions to panels tilted up to 55° and sweeps, blows and vacuums dust and dirt. A detachable battery is easily replaced when power runs out. Ecovacs is currently conducting final tests for the solar robot in China and California and expects RAYBOT to launch later this year.




  1. Joseph DiMatteo, PE says:

    Interesting article but lacks important details like how many gallons per panel are used and the cost per panel in the different scenarios. My research and testing led us to untreated water and squeegees as the most cost and water effective. The idea that the panel glass suffers from the squeegee process is nonsense in our experience and I doubt any panel manufacturer would agree with that notion.