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Energy

Self-Cleaning Solar Panels

A technology intended for Mars missions may find use on solar installations in the deserts on Earth.

One of the best places to put a solar panel is in the desert, where it’s sunny. But deserts are also dusty, which means the panels have to be washed frequently so the dust doesn’t stop them from capturing sunlight. New technology could provide a solution–by letting solar panels clean themselves.

Desert storm: Dust clouds like this one in the Persian Gulf can cut solar power output if dust accumulates on the panels. New technology that cleans the dust off might help.

The technology was developed for future rover missions to Mars, but it could work here on Earth to keep solar panels operating at peak capacity. It uses electrostatic charge to repel dust and force it to the edges of the panels. It can remove 90 percent of the dust on a solar panel in a two-minute cycle, says Malay Mazumder, a research professor at Boston University who led the work. The technology was described this week at the American Chemical Society meeting in Boston.

Dust that accumulates on solar panels and blocks the light can cripple rovers on the moon or Mars. The Spirit and Opportunity Mars rovers lasted longer than expected because occasional gusts of wind have cleared off their panels. “But we may not be lucky all of the time,” says Rao Surampudi, a project monitor at NASA’s Jet Propulsion Laboratory. Indeed, the Mars Pathfinder rover mission in the 1990s didn’t benefit from such winds.

Dust has also bedeviled solar installations on Earth. For example, dust storms have cut power production by 40 percent at a large, 10-megawatt solar power plant in the United Arab Emirates. Washing the panels can be time-consuming or require costly automation–and it takes a lot of water, a precious resource in the desert. “With this new technology, solar panels can be automatically cleaned without water or labor,” Mazumder says.

The system takes advantage of the fact that most dust particles, particularly in dry environments, have an electric charge. A transparent electrode material such as indium tin oxide delivers an alternating current to the top surface of the panel. As it swings between being positively and negatively charged, it creates an electric field that repels positively and negatively charged particles. The electric field also helps to impart a charge to uncharged dust particles, allowing them to be quickly repelled as they come in contact with the panel. The researchers have designed the system so that the electric field works its way from one side of the solar panel to the other, gradually moving the dust along until it falls off.

The system doesn’t use much energy–electrical current is small and typically it only needs to be on between two and five minutes a day, Mazumder says. The system could include a sensor to determine when the panel needed cleaning. The technology doesn’t work if the dust gets wet and muddy, so it should be triggered to remove dust before it rains, Mazumder says.

Mazumder’s technology is one of two approaches NASA has funded for cleaning off solar panels. The other vibrates the entire panel to shake dust loose. It’s still not clear which will prove more practical for space missions, says Surampudi, who oversaw the research into both dust-clearing techniques. Using vibrations is simpler and requires fewer modifications to the solar panel, he says. But it does not remove fine particles as well as the electrical field approach. For terrestrial applications, Mazumder’s technology will have to compete with other potential approaches to cleaning off solar cells without using water, such as blowing air on them or adding a nonstick layer.

The electrical field technology could prove simple to produce, Mazumder says, because many solar manufacturers already have equipment for depositing transparent electrodes, which would generate the electrical fields, onto panels. He says the next step is to determine whether it will be possible to meet the researchers’ goal of keeping manufacturing costs below about 1 percent of the total cost of the solar panel. But the value of the system will depend on how dusty solar panels get in different locations. Conventional washing with water, for example, works well enough for a large collection of rooftop solar panel systems operated by Southern California Edison, the utility says.

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