MIT researchers have developed a way to automatically clean solar panels in a waterless, non-contact system that could significantly reduce problems caused by dust.
The new system uses electrostatic repulsion to release dust particles without the need for water or brushes. To activate the system, an electrode passes just above the surface of the solar panel, giving an electrical charge to the dust particles which 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 scientific progress in a paper by MIT graduate student Sreedath Panat and Kripa Varanasi, a mechanical engineering professor.
Laboratory tests showed that the decrease in the energy output of the panels occurs strongly with the onset of dust accumulation and can reach a 30 percent reduction after a month without cleaning. They calculated that a one percent reduction in power for a 150 MW solar installation could lead to a loss of $200,000 in annual revenue. The researchers said a three to four percent reduction in solar power plants worldwide would equate to a loss of between $3.3 billion and $5.5 billion.
“There is so much work going on in the field of solar materials,” Varanasi said in a statement. “They’re pushing the boundaries and trying to gain a few percent here and there in improving efficiency, and here’s something that can erase all of that right away.”
MORE FROM ENERGY & ENVIRONMENT
Water treatment accounts for about 10 percent of the operating costs of solar installations, some of which are located in deserts and require water to be supplied. The new system could potentially reduce these costs while improving overall power through more frequent automated cleaning.
“The water footprint of the solar industry is mind-boggling,” Varanasi said. “So the industry has to be very careful and thoughtful about how this can become a sustainable solution.”
Previous electrostatic solutions relied on an electrodynamic screen, using interlocking electrodes. These screens can have defects that let moisture in and cause them to fail, Varanasi said.
The new system requires an electrode to pass across the panel, creating an electric field that charges the dust particles along the way. An opposing charge applied to a transparent conductive layer only a few nanometers thick, deposited on the glass cladding of the solar panel, then repels the particles. By calculating the correct tension, the researchers were able to find a tension range sufficient to overcome gravity and adhesion forces and lift the dust.
Using specially prepared lab samples of dust with different particle sizes, experiments have shown the process works effectively on a lab-scale test rig, Panat said. The tests showed that humidity in the air provided a thin layer of water on the particles, which proved to be crucial for the effect to work.
“We conducted experiments at varying humidity from five percent to 95 percent,” Panat said. “As long as the humidity is above 30 percent, you can remove almost all particles from the surface, but as the humidity decreases, it gets harder.”
“The good news is that when you get to 30 percent humidity, most deserts fall under this regime,” Varanasi said. Those that tend to be drier tend to have higher humidity in the early morning hours leading to dew build-up, so the cleaning can be timed accordingly.
“In addition, unlike some of the previous work on electrodynamic screens, which actually don’t work in high or even moderate humidity, our system can operate indefinitely at humidity levels as high as 95 percent,” Panat said.
