Dust Wars: Robot Cleans Solar Panels And Protects Efficiency

While utility-scale solar projects have transformed deserts into shimmering renewable-energy powerhouses,  a malevolent malefactor has risen with the wind. It collects in crevasses, and it sullies polycrystalline with reckless abandon …

Dust.

But a secret weapon to fight against this miniscule malefactor has arrived. It’s called Greenbotics, a robot-based cleaning service. The company has operated under what seems like a cloak of secrecy for more than a year while its technology is evaluated. Companies that have already used the dust-destroying service are unlikely to say so, even if they’re reaping the benefits.

Greenbotic’s CleanFleet robots at the McHenry Solar Plant in Modesto, Calif. The robots use a quarter of a cup to a half-cup of water per module cleaned.

“Everyone is trying to get a leg up on someone else, and no one wants to tell anyone what they’re doing,” says Marc Grossman, founder and CEO of Greenbotics. But, he says, the company has worked with all the big panel manufacturers.

The corporations have turned to this engineer and his robot because the technology — one that automatically cleans solar arrays for a lower cost than conventional methods such as pressure washing — is desperately needed.

Research shows that accumulation of dirt on solar panels, called soiling, can have a big impact on the performance of PV systems in regions where rainfall is limited. Google installed a solar array at its Mountain View, Calif., offices and found it could increase production by 12% with cleaning. Greenbotics has shown that systems lose anywhere from 5 to 15% worth of production annually across the county from dust and, as any weathered solar technician will affirm, bird droppings.

More solar farm operators are realizing, as their plants enter the second and third years of their lifespan, that dust has had a big impact. One operator says cleaning and vegetation management are the two most costly variables in plant O&M — even more expensive than equipment maintenance.

“A few plants did cleaning at the commissioning,” says Grossman, often because it’s in an EPCs contract to do so. “Then they ran the numbers and said, ‘It doesn’t make sense to clean again.’ Since we’ve been able to lower the price, now they’re interested.”

The company has focused its operation in the Southwest, which has a predictable summer with little precipitation. Greenbotics and its robot, dubbed CleanFleet, expect to undertake their first full summer of cleaning this year. So far, cleanings have been trial runs to prove the concept. Still, CleanFleet has successfully scrubbed plants as large as 30 MW.

The Robot

If you take the long view, the seeds for Greenbotics were planted early last decade in Chico, Calif., when Grossman and co-founder Kyle Cobb went to high school together. Later, at Caltech, Grossman met the third co-founder, Cedric Jeanty. Grossman and Jeanty excelled at engineering, and Cobb earned an MBA from the Anderson School of Management at UCLA.

Jeanty and Grossman both joined eSolar in 2008. Jeanty focused on power-plant design while Grossman worked on cleaning-system development. It was then that Grossman recognized the need for more economical cleaning and set a goal to achieve it through automation. In 2011, he started Greenbotics, bringing along colleagues Jeanty and Cobb for the journey. “The robot looks like I imagined it would a year and a half ago,” Grossman says.

Workers test Greenbotics’ CleanFleet robot on a solar array.

But realizing the vision, he says, took more than imagination. The robot seemed promising at first, but it developed an assortment of issues. One issue was the drive train. The engineers started off with wheels, but determined tracks were better, spreading the robot’s weight evenly over panels.

“Getting a task done robotically vs. doing it with a human is full of nitty-gritty details,” Grossman says. “It’s about getting just the right brush, just the right squeegee, with just the right amount of water, with just the right amount of force.”

They also put to work their background in aviation. Grossman and Jeanty build and fly light-weight aircraft, including their shared Van’s RV-6 — a two-seat, single-engine, low-wing airplane. Their knowledge of light-weight building materials let the engineers supply the robot with more water, which it uses in a conservative manner.

“Marc and Cedric are immensely talented,” Cobb says. “They have a great range of skills that, frankly, has helped us solve a lot of problems that would have taken a much bigger team a lot longer.”

At some plants, for example, water must be hauled from distant locations. A single cleaning with pressure washing at a large plant could consume 100,000 gallons of water — reverse osmosis water, at that. Grossman and Jeanty knew they had to find a way to reduce water usage. In the end, their system uses a quarter of a cup to a half-cup per module cleaned. The reduced water usage helps lower the overall cost of the cleaning.

Greenbotic’s CleanFleet robots wash away dust at the McHenry Solar Plant in Modesto, Calif. “The robot looks like I imagined it would a year and a half ago,” co-founder Marc Grossman says.

The Work

One plant benefitting from Greenbotics is the McHenry Solar Power Plant in Modesto, Calif., a 25-MW installation owned by K Road, an independent power developer. “We are proud to supply clean, renewable electricity to communities served by the Modesto Irrigation District,” said William Kriegel, K Road’s CEO, at the plant’s opening last October. But months later, to keep the plant producing at peak levels, the panels had to be cleaned.

Steve Hanawalt made the call to clean the plant and to do it with Greenbotics. He runs Power Factors, an independent O&M services company, which is charged with maintenance at McHenry. He first met the Greenbotics team at Solar Power International last year. Previously in charge of cleaning at SunPower Corp., Hanawalt had done a lot of thinking about how to best clean panels and had some ideas of his own.

“Cleaning is a high cost, so when I saw the Greenbotics idea, I thought, somebody took our idea and improved upon it by a factor of 10,” Hanawalt says.

The McHenry plant has seen “material improvement” since the cleaning, which ended in June, Hanawalt says. It was too early to obtain precise data. But Cobb says the robot will restore panels to “near-perfect” cleanliness. The increase in energy output is dependent on how dirty the plant was in the first place, he says, but severely dirty installations may see improvements around 15%.

For their part, the Greenbotics team hopes more people pay attention to the success.

“We’ve had a lot of inbound interest,” says Cobb. “Still, it takes time to develop relationships with customers.”

The founders say they hope to one day develop customers in other dust-heavy regions around the world, such as India and the Middle East. SPW

How did Greenbotics get it start? Here is a timeline to follow along: