In water-scarce areas, a new cleaning approach could help remove dust from solar panels, enhancing overall efficiency.
Solar power is predicted to account for 10% of worldwide electricity output by 2030, with much of it concentrated in desert areas where sunshine is abundant. However, dust collection on solar panels or mirrors is already a big concern — it may diminish the performance of photovoltaic panels by up to 30% in just one month — thus such installations require regular cleaning.
However, it is estimated that washing solar panels consumes roughly 10 billion gallons of water every year, which is enough to supply drinking water to up to 2 million people. Attempts at waterless cleaning are time-consuming and can result in irreparable surface scratching, which affects efficiency. Now, a group of MIT researchers has developed a waterless, no-contact technique for autonomously cleaning solar panels or solar thermal plant mirrors, which they claim might drastically minimize the dust problem.
Without the use of water or brushes, the innovative method employs electrostatic repulsion to induce dust particles to detach and almost leap off the panel’s surface. A simple electrode passes just above the solar panel’s surface to activate the system, imparting an electrical charge to the dust particles, which are subsequently repelled by a charge provided to the panel. A simple electric motor and guide rails along the edge of the panel can be used to automate the mechanism. Sreedath Panat, an MIT graduate student, and Kripa Varanasi, a professor of mechanical engineering, published a study in the journal Science Advances today.
A basic problem like the dust may actually put a major dent in the whole thing,” Varanasi says, despite intensive efforts throughout the world to produce ever more efficient solar panels. Panat and Varanasi’s lab studies revealed that the loss of energy production from the panels begins abruptly at the start of the dust buildup process and can easily approach a 30% reduction after just one month without cleaning. They projected that a 1% drop in power may result in a $200,000 loss in annual revenue for a 150-megawatt solar plant. According to the experts, a 3% to 4% decline in solar plant output would result in a loss of $3.3 billion to $5.5 billion globally.
Varanasi says, “There is so much development going on with solar materials.” “They’re pushing the envelope, trying to improve efficiency by a few percent here and there, and here you have something that can annihilate all of that straight away.”
Many of the world’s largest solar power plants are in desert areas, including those in China, India, the United Arab Emirates, and the United States. Water for cleaning these solar panels with pressurized water jets must be trucked in from afar, and it must be extremely pure to avoid leaving deposits on the surfaces. Dry scrubbing is occasionally employed, however, it is ineffective at cleaning the surfaces and might result in permanent scratches, which lowers light transmission.
Solar installations’ water cleaning costs account for around 10% of their total operating costs. According to the researchers, the novel approach might potentially lower these expenses while increasing overall power output by allowing for more frequent automatic cleanings.
“The solar industry’s water footprint is mind-boggling,” Varanasi adds, adding that it will continue to grow as these installations spread over the world. “As a result, the industry must be extremely cautious and thoughtful about how to make this a long-term solution.”
Other groups have attempted to develop electrostatic-based solutions, however, they have depended on an electrodynamic screen made up of interdigitated electrodes. According to Varanasi, these screens can have flaws that allow moisture to enter and lead them to break. While they would be advantageous on a planet like Mars, where moisture isn’t an issue, he thinks they can be a severe problem even in dry regions on Earth.
The new technology requires just that an electrode, which can be a simple metal bar, pass over the panel, creating an electric field that charges the dust particles as it passes. The particles are repelled by an opposite charge applied to a transparent conductive layer just a few nanometers thick deposited on the glass covering of the solar panel, and the researchers were able to find a voltage range sufficient to overcome gravity and adhesion forces and cause the dust to lift away by calculating the right voltage to apply.
Experiments on a laboratory-scale test installation confirmed that the technique works efficiently, according to Panat, using specially generated laboratory samples of dust with a range of particle sizes. The testing revealed that air humidity supplied a thin coating of water on the particles, which was vital to the effect’s success. “We did studies at different humidities ranging from 5% to 95%,” Panat explains. “You can remove practically all of the particles off the surface as long as the ambient humidity is greater than 30%, but as humidity drops, it gets more difficult.”
“The good news is that when you get to 30 percent humidity, most deserts actually fall into this regime,” Varanasi adds. Even those that are normally drier have increased humidity in the early morning hours, resulting in dew formation, thus cleaning could be scheduled accordingly.
“Moreover, unlike some previous electrodynamic screen research, which can not work at high or even moderate humidity, our device can work endlessly at humidity as high as 95 percent,” Panat explains.
In practice, each solar panel might have railings on both sides and an electrode spanning the entire panel at scale. A small electric motor may be powered by a small amount of the panel’s output, which would drive a belt system to move the electrode from one end of the panel to the other, clearing the dust. The entire procedure might be automated or managed from afar. Alternatively, instead of moving elements, small strips of conductive transparent material could be permanently positioned above the panel.
Such technologies have the potential to dramatically enhance the overall efficiency and reliability of solar installations by eliminating the need for trucked-in water, reducing dust buildup that can contain corrosive chemicals, and cutting overall operational expenses, according to Varanasi.
The MIT Energy Initiative received funding from Eni S.p.A., an Italian energy company.