Solar panels are increasing in efficiency and hold great promise for generating power without carbon emissions. However, as with all exposed outdoor surfaces, your panels are going to gather dust and dirt, and even droppings from inconsiderate birds. These layers of dust and other airborne residues, such as pollen, can steal as much as 35% of the energy efficiency from your panels.
While manufacturers recommend occasional cleaning with warm water and a squeegee, not too many of us are going to climb up on our roofs for monthly cleaning duty, nor spend the money to hire the service people to do it. And if you are a solar farm with thousands of panels, or a floating solar farm? Forget it. So what is the industry to do?
One solution is robotic cleaning devices, which have been developed for large installations in countries such as Israel, but they are expensive, can scratch surfaces, and since they must move over the entire surface of each panel, are prone to mechanical problems and breakdown. And of course, they require their own smaller solar power source.
For the past few years teams have been working on self-cleaning surfaces for solar panels, including specialized coatings that both repel water and allow removal of particles without any moving parts. A Boston University team uses alternating voltages to create an electrostatic field that gently pulses the particles off the panel in waves.
Most recently, a team of researchers and students from the University of Washington’s Department of Electrical Engineering developed a system they call Aquapel. The group experimented not only with hydrophobic surfaces but also with micro-patterning of the surfaces using microfabrication techniques used in microelectronics etching.
The result is a juxtaposed combination of a water-conducive surface on a water repellent background. The technique uses minute vibrations to direct the water droplets through the grooves in a set pattern so they collect particles and clean the entire surface. The droplets can even move up the slope of the panel. Some of us are old enough to remember the old mechanical toy football game that vibrated a piece of sheet metal to make plastic players move around. The concept is similar, except with microgrooves to direct the players.
Di Sun, a Ph.D. student at the UW, says that the coating is both oil- and water-repellent, which makes it less prone to adhesion of dust or pollen. The surface is a single molecular layer in order to allow passage of a maximum amount of light to the solar cells.
Because the technology is designed for high-volume microetching, the team believes it can be highly scalable for large system use. They speculate that if implemented in a 100 MW solar farm the technique could save as much as $58 million as well as 420 million liters of water that would normally be used for cleaning panels throughout the project lifetime.
The team recently won the Alaska Airlines Environmental Innovation Challenge, a University of Washington student start-up competition.