The new system uses electrostatic repulsion to cause dust particles to detach without the need for water or brushes. To activate the system, an electrode passes just above the solar panel’s surface, imparting an electrical charge to the dust particles that are then repelled by a charge applied to the panel. The system can be operated automatically using an electric motor and guide rails along the side of the panel. The research is described in Science Advances in a paper by MIT graduate student Sreedath Panat and Kripa Varanasi, a professor of mechanical engineering.
Lab tests showed that the drop-off of energy output from the panels happens steeply at the start of dust accumulation, and can reach 30 per cent reduction after one month without cleaning. They calculated that a one per cent reduction in power, for a 150MW solar installation, could result in a $200,000 loss in annual revenue. The researchers said that globally, a three-to-four per cent reduction in power output from solar plants would amount to a loss of between $3.3bn and $5.5bn.
“There is so much work going on in solar materials,” Varanasi said in a statement. “They’re pushing the boundaries, trying to gain a few per cent here and there in improving the efficiency, and here you have something that can obliterate all of that right away.”
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Water cleaning makes up about 10 per cent of the operating costs of solar installations, some of which are in deserts and require water to be trucked in. The new system could potentially reduce these costs while improving the overall power output by allowing for more frequent automated cleanings.
“The water footprint of the solar industry is mind boggling,” Varanasi said. “So the industry has to be very careful and thoughtful about how to make this a sustainable solution.”
Previous electrostatic solutions have relied on a electrodynamic screen, using interdigitated electrodes. These screens can have defects that allow moisture in and cause them to fail, Varanasi said.
The new system requires an electrode to pass over the panel, producing an electric field that imparts a charge to the dust particles as it goes. An opposite charge applied to a transparent conductive layer just a few nanometres thick deposited on the glass covering of the solar panel then repels the particles. 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.
Using specially prepared laboratory samples of dust with a range of particle sizes, experiments proved that the process works effectively on a laboratory-scale test installation, Panat said. The tests showed that humidity in the air provided a thin coating of water on the particles, which turned out to be crucial to making the effect work.
“We performed experiments at varying humidities from five per cent to 95 per cent,” 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.”
“The good news is that when you get to 30 per cent humidity, most deserts actually fall in this regime, said Varanasi.” Those that are typically drier than that tend to have higher humidity in the early morning hours, leading to dew formation, so the cleaning could 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 per cent, indefinitely,” Panat said.
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