Solar panel arrays are often built in deserts where sunlight is plentiful and property is cheap. Unfortunately, dust and winds are also common in deserts, and dust on solar PV panels can reduce their electrical output by 30% after just one month of exposure to the elements. Even a 1% drop in power for a 150 MW solar installation could result in a loss of $200,000 in annual revenue. The researchers say that globally, a 3-4% reduction in energy from solar power plants would result in a loss of $3.3-5.5 billion.
This makes regular cleaning essential.
But it’s estimated that cleaning solar panels currently requires around 10 billion gallons of water a year, enough to provide drinking water to one million people in developing countries. Keeping panels clean without water is labor intensive and can scratch and damage panel surfaces, which also reduces efficiency. To solve this dilemma, a team of researchers from MIT has devised a way to automatically clean solar panels, or the mirrors of solar thermal power plants, without water or contact.
The new system uses electrostatic repulsion to blast dust particles from panels without using water or brushes. To activate the system, an electrode passes just above the surface of the panel, giving the dust particles an electrical charge. They are then repelled by a similar charge applied to a transparent conductive layer a few nanometers thick, which is deposited on the glass coating of the solar panel. The researchers were able to find a range of voltage that could overcome the pull of gravity and the forces of adhesion and lift off the dust. The system can be automated using an electric motor and guide rails along the side of the panel.
Other engineers tried to develop electrostatic approaches to cleaning solar panels, but they generally relied on an electrodynamic screen and the use of interdigital electrodes. These screens may have defects that let moisture in and damage the electronics. So they might be useful in a place like Mars where humidity isn’t an issue, but on Earth, even in desert environments, it can be a serious problem.
In testing, the MIT team found that the humidity in the air created a thin layer of water on the dust particles, which proved crucial to making the cleaning effort effective. They found that as long as the humidity is above 30%, all the dust is removed, but as the humidity drops, it becomes more difficult.
“The good news,” says Kripa Varanasi, professor of mechanical engineering at MIT, “is that most deserts are in the 30 percent humidity range. higher in the early morning, causing dew to form, so cleaning could be timed accordingly.
When scaled, a small motor, using perhaps a tiny fraction of the panel output, could drive a belt system to move the electrode across the panel. The process could also be automated or remotely controlled. Alternatively, thin strips of a conductive, transparent material could be installed above the panels, eliminating the need for moving parts.
See the dust collection system in action below: