Solar power is expected to reach 10% of global electricity production by 2030, and much of this will likely be located in desert areas, where sunlight is abundant. But the accumulation of dust on solar panels or mirrors is already a significant problem – it can reduce the production of photovoltaic panels by up to 30% in just one month – so regular cleaning is essential for such installations.
But cleaning solar panels is currently estimated to use about 10 billion gallons of water a year, enough to provide drinking water for 2 million people. Attempts to clean without water are labor intensive and tend to cause irreversible scratches on surfaces, which also reduce effectiveness. Now a team of MIT researchers has developed a way to automatically clean solar panels, or the mirrors of solar thermal power plants, in a waterless, contactless system that could significantly reduce the dust problem, they say. .
The new system uses electrostatic repulsion to cause dust particles to detach and virtually jump off the surface of the panel, without the need for water or brushes. To activate the system, a simple electrode passes just above the surface of the solar panel, imparting an electrical charge to the dust particles, which are then repelled by a charge applied to the panel itself. The system can be operated automatically using a simple electric motor and guide rails along the side of the panel. The research is described in the journal Scientists progressin an article by MIT graduate student Sreedath Panat and mechanical engineering professor Kripa Varanasi.
Despite concerted efforts around the world to develop ever more efficient solar panels, Varanasi says, “a mundane problem like dust can actually put a serious dent in the whole thing.” Laboratory tests conducted by Panat and Varanasi have shown that the drop in panel energy production occurs sharply at the very beginning of the dust accumulation process and can easily reach a 30% reduction after just one month without cleaning. . Even a 1% reduction in power, for a 150 megawatt solar installation, they calculated, could result in a loss of $200,000 in annual revenue. The researchers say that globally, a 3-4% reduction in electricity generation from solar power plants would equate to a loss of between $3.3 billion and $5.5 billion.
“There is so much work going on in solar materials,” says Varanasi. “They’re pushing the envelope, trying to gain a few percent here and there by improving efficiency, and here you have something that can erase all of that right away.”
Many of the largest solar energy installations in the world, including in China, India, the United Arab Emirates and the United States, are located in desert regions. The water used to clean these solar panels using pressurized water jets must be trucked in from a distance and must be very pure so as not to leave deposits on the surfaces. Dry scrubbing is sometimes used, but it is less effective at cleaning surfaces and can cause permanent scratches which also reduce light transmission.
Water cleaning accounts for around 10% of the operating costs of solar installations. The new system could potentially lower those costs while improving overall power output by enabling more frequent automated cleanings, the researchers say.
“The water footprint of the solar industry is staggering,” says Varanasi, and it will increase as these installations continue to expand around the world. “So the industry has to be very careful and thoughtful about how to make this a lasting solution.”
Other groups have attempted to develop electrostatic based solutions, but these have relied on a layer called an electrodynamic screen, using interdigital electrodes. These screens can have flaws that allow moisture to enter and cause them to fail, Varanasi says. While they can be useful somewhere like Mars, he says, where humidity isn’t an issue, even in desert environments on Earth it can be a serious problem.
The new system they have developed only requires an electrode, which can be a simple metal bar, to pass over the panel, producing an electric field that imparts a charge to the dust particles as they go. An opposing charge applied to a transparent conductive layer a few nanometers thick deposited on the glass coating of the solar panel then repel the particles, and by calculating the right voltage to apply, the researchers were able to find a voltage range sufficient to overcome the attraction of gravity and the forces of adhesion, and causes the lifting of dust.
Using specially prepared laboratory dust samples with a range of particle sizes, the experiments proved the process works effectively on a lab-scale test setup, Panat says. Tests showed that the humidity in the air provided a thin layer of water on the particles, which was crucial for the effect to work. “We performed experiments at varying humidities from 5% to 95%,” says Panat. “As long as the ambient humidity is above 30%, you can remove almost all particles from the surface, but as the humidity decreases, it becomes more difficult.”
Varanasi says “the good news is that when you hit 30% humidity, most deserts fall into that regime.” And even those that are generally drier than that tend to have higher humidity early in the morning, causing dew to form, so cleaning can be timed accordingly.
“Furthermore, unlike some of the previous work on electrodynamic displays, which do not operate at high or even moderate humidity, our system can operate at humidity as high as 95%, indefinitely,” says Panat.
In practice, on a large scale, each solar panel could be equipped with guardrails on each side, with an electrode extending across the entire panel. A small electric motor, perhaps using a tiny part of the output of the panel itself, would drive a belt system to move the electrode from one end of the panel to the other, causing all the dust to fall off. The whole process can be automated or controlled remotely. Alternatively, thin strips of conductive transparent material could be permanently disposed above the panel, eliminating the need for moving parts.
By eliminating reliance on trucked water, eliminating the accumulation of dust that may contain corrosive compounds, and reducing overall operating costs, such systems have the potential to dramatically improve efficiency and reliability. global solar installations, explains Varanasi.
Researchers develop new method to remove dust from solar panels
Sreedath Panat et al, Electrostatic Dedusting Using Adsorbed Moisture-Assisted Charging Induction for Sustainable Solar Panel Operation, Scientists progress (2022). DOI: 10.1126/sciadv.abm0078. www.science.org/doi/10.1126/sciadv.abm0078
Provided by Massachusetts Institute of Technology
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