Developed by engineers at MIT, the new system uses electrostatic repulsion to cause dust particles to detach without the need for water or brushes. 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.
Lab tests have shown that the drop-off of energy output from solar panels happens steeply when dust begins to accumulate, reaching up 30 per cent reduction after one month without cleaning. It was calculated that a one per cent reduction in power for a 150MW solar installation could result in around $200,000 of lost revenue per year. 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,” said Kripa Varanasi, a professor of mechanical engineering at MIT. “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.”
It’s estimated that 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,” said Varanasi. “So the industry has to be very careful and thoughtful about how to make this a sustainable solution.”
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, according to MIT graduate student Sreedath Panat. 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 work is published in Science Advances.
