Researchers find way to clean solar panels without using a single drop of water
Researchers in the US have developed a new technology they say can remove dust from solar panels installed as part of large-scale PV projects without using a single drop of water.
In research published in the journal Science Advances, a paper by MIT graduate student Sreedath Panat and professor of mechanical engineering Kripa Varanasi describes how their technology uses electrostatic repulsion to dusty clean panels, instead of water or brushes.
According to MIT, the system differs from other attempts at the technology by using a simple electrode passed just above the solar panel’s surface, which imparts an electrical charge to the dust particles, causing them to detach and virtually leap off the panel’s surface.
The researchers say system, which can be operated automatically using a simple electric motor and guide rails along the side of the panel, has the potential to displace the up to 10 billion gallons of water per year currently estimated to be used for panel cleaning.
Currently, all this water is used because the accumulation of dust on solar panels or mirrors (in the case of concentrating solar, as pictured in the video below) can reduce the output of PV by as much as one-third in just one month.
Lab tests conducted by Panat and Varanasi showed that the dropoff of energy output from dust-affected panels happens steeply at the very beginning of the process of accumulation and can easily reach 30 per cent reduction after just one month, without cleaning.
The team calculated that even a 1 per cent reduction in power, for a 150MW solar farm, could result in a $200,000 loss in annual revenue.
Water-based solar panel cleaning known as “dry-scrubbing” is also expensive, sometimes contributing about 10 per cent of the total operating costs of solar installations, the researchers say.
But previous attempts at waterless cleaning have focused on the use of automated brushes, which can cause irreversible scratching of the surfaces, which also can be expensive, labour-intensive and detriomental to a panel’s efficiency.
“There is so much work going on in solar materials,” Varanasi told MIT News. “They’re pushing the boundaries, trying to gain a few percent here and there in improving the efficiency, and here you have something that can obliterate all of that right away.”
That said, Varanasi describes the water footprint of the solar industry as “mind boggling,” and particularly impractical in some of the dry regions that large-scale solar is deployed.
“So, the industry has to be very careful and thoughtful about how to make this a sustainable solution,” he said.
Varansi says that other attempts at electrostatic-based solutions have often relied on a layer called an electrodynamic screen, using interdigitated electrodes, which can have defects that allow moisture in and cause them to fail.
These other systems might be useful on, say, Mars, where moisture is not an issue, but on Earth, even in the driest desert environments, water ingress can be a serious problem.
The MIT team’s solution, which had backing from Italian energy firm Eni, only requires an electrode, which can be a simple metal bar, to pass over the panel, producing an electric field that imparts a charge to the dust particles as it goes, MIT explains.
An opposite charge applied to a transparent conductive layer just a few nanometers thick deposited on the glass covering of the the solar panel then repels the particles, and by calculating the right voltage to apply, the researchers were able to find a voltage range sufficient to overcome the pull of gravity and adhesion forces, and cause the dust to lift away.
At this stage, the researchers have demonstrated the success of their system through a miniature lab setup, using samples of dust with a range of particle sizes. The next step is to scale it up and conduct actual field trials on solar farms.
What the lab tests showed, however, was that humidity in the air provided a thin coating of water on the particles, which turned out to be crucial to making the electrostatic effect work.
“We performed experiments at varying humidities from 5 percent to 95 percent,” Panat said. “As long as the ambient humidity is greater than 30 per cent, you can remove almost all of the particles from the surface, but as humidity decreases, it becomes harder.
But Varanasi says that most deserts fall into the 30 per cent humidity category, with even those that are typically drier than that tending to have higher humidity in the early morning hours, leading to dew formation – and allowing the cleaning to be timed accordingly.
“Moreover, unlike some of the prior work on electrodynamic screens, which actually do not work at high or even moderate humidity, our system can work at humidity even as high as 95 percent, indefinitely,” Panat said.
In practice, at scale, the team says that each solar panel could be fitted with railings on each side, with an electrode spanning across the panel. A small electric motor, perhaps using a tiny portion of the output from the panel itself, would drive a belt system to move the electrode from one end of the panel to the other, causing all the dust to fall away.
The whole process could be automated or controlled remotely. Alternatively, thin strips of conductive transparent material could be permanently arranged above the panel, eliminating the need for moving parts – and for water.
“We truly need a non contact way of removing dust from solar panels that consumes no water to make it sustainable,” said Panat in the video above.
“So what we have developed is a technology… that removes dust from solar panels without consuming a single drop of water.
“Electrostatic repulsion of dust from solar panels has the immense potential to completely eliminate the scratching damage due to dry scrubbing and also eliminate the usage of water to clean solar panels.”Sophie Vorrath
Sophie is editor of One Step Off The Grid and deputy editor of its sister site, Renew Economy. Sophie has been writing about clean energy for more than a decade.