MIT Researchers Develop a Method for Cleaning Solar Modules That Is Water-Free and Does Not Require
Researchers at the Massachusetts Institute of Technology (MIT) have devised a way for keeping solar panels dust-free using static electricity, obviating the need for water washing. According to the research, dust can impair solar panel operation by up to 30% in just one month without cleaning, equating to a revenue loss of between $3.3 billion and $5.5 billion.
The MIT team's waterless, no-contact method causes dust particles to efficiently bounce off the panel's surface via electrostatic repulsion. This is accomplished by passing an electrode in the form of a metal bar across the panel's surface, which charges the dust particles. The solar panel is then charged, which repels the dust particles, causing them to leap upward and away from the panel. The new method may be controlled automatically via a timer, thanks to an electric motor and guide rails on the panel's side that allow the electrode to move over the panel without contacting it directly.
In actuality, each solar panel might be equipped with side railings and an electrode covering the width of the panel. A small electric motor might be powered by a small percentage of the panel's output to move the electrode from one end of the panel to the other, removing all dust particles. The entire procedure might be mechanised or remotely controlled. Alternatively, tiny strips of transparent conductive material could be fixed above the display, obviating the requirement for moving parts. Experiments conducted on a laboratory-scale test installation using specially generated laboratory dust samples with a range of particle sizes demonstrated that the technique works successfully. The studies revealed that the humidity in the air provided a small layer of water on the particles, which was necessary for the effect to work. The researchers conducted studies at various humidity levels ranging from 5% to 95%. As long as the ambient humidity is greater than 30%, it is possible to remove practically all particles from the surface. As the humidity decreases, the process becomes more difficult.
Many of the world's largest solar energy facilities, including those in China, India, the United Arab Emirates, and the United States, are located in desert locations. Water must be trucked in from afar to be used to clean these solar panels with pressurised water jets, and it must be extremely pure to avoid leaving deposits on the surfaces. While dry scrubbing is occasionally done, it is less successful in cleaning the surfaces and might result in permanent scratches, reducing light transmission. By removing the need on water and dust accumulation, as well as cutting overall operating expenses, such systems can considerably increase the overall efficiency and dependability of solar installations. India's water resources have traditionally been a cause of contention. In a research, the World Wide Fund (WWF) stated that 30 Indian towns face impending water-related threats unless prompt measures to mitigate and control climate change are done.
In response to concerns about water use in solar projects, the Ministry of New and Renewable Energy (MNRE) published a letter suggesting optimal water use for module cleaning in utility-scale solar projects. According to the ministry, developers were wasting too much water cleaning solar modules and should strive to decrease wastage. In India, the use of waterless robotic cleaning technologies is gaining traction.
Solar energy is predicted to account for 10% of worldwide energy generation by 2030, with the majority of the capacity likely to be situated in desert locations with plentiful sunlight. 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 — and so requires regular cleaning.
However, it is estimated that washing solar panels consumes approximately 10 billion gallons of water every year – enough to supply drinking water to up to 2 million people. Waterless cleaning attempts are labour consuming and frequently result in irreparable damage of the surfaces, reducing efficiency. Now, a team of researchers at MIT has developed a method for automatically cleaning solar panels or solar thermal plant mirrors in a waterless, no-contact system that they claim might drastically minimise the dust problem.
Without the need of water or brushes, the innovative technique causes dust particles to detach and literally leap off the panel's surface by electrostatic repulsion. To activate the device, a simple electrode is passed just over the solar panel's surface, charging the dust particles, which are subsequently repelled by a charge provided to the panel. Automatic operation of the device is possible using a simple electric motor and guide rails along the panel's edge. The technique is presented in a paper published today in the journal Science Advances by MIT graduate student Sreedath Panat and mechanical engineering professor Kripa Varanasi.
Despite persistent global efforts to produce ever-more-efficient solar panels, Varanasi notes that "a seemingly insignificant issue like dust can actually put a huge dent in the whole thing." Panat and Varanasi laboratory experiments shown that the energy output of the panels drops precipitously at the start of the dust gathering process and can easily reach 30% reduction after just one month without cleaning. Even a 1% reduction in power may result in a $200,000 annual income loss for a 150-megawatt solar project, they concluded. According to the experts, a 3 to 4% decline in solar energy output globally would result in a loss of between $3.3 billion and $5.5 billion.
"There is a lot of activity in the field of solar materials," Varanasi says. "They're pushing the envelope, attempting to improve efficiency by a few percent here and there, and here you have something that can annihilate all of that immediately."
Many of the world's largest solar energy facilities, including those in China, India, the United Arab Emirates, and the United States, are located in desert locations. Water must be trucked in from afar to be used to clean these solar panels with pressurised water jets, and it must be extremely pure to avoid leaving deposits on the surfaces. Dry scrubbing is occasionally employed but is less successful at cleaning and can result in permanent scratches, which also reduces light transmission.
Water purification accounts for approximately 10% of the running costs of solar installations. The novel approach, the researchers claim, could 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 says, and it will continue to grow as these installations expand globally. "As a result, the industry must exercise extreme caution and foresight in determining how to make this a sustainable solution."
Other organisations have attempted to produce electrostatic solutions, but they have depended on an interdigitated electrode layer called an electrodynamic screen. These screens may contain flaws that allow moisture to enter and eventually lead them to fail, Varanasi explains. While they may be advantageous on a planet like Mars, where moisture is not an issue, he notes that they can be a severe concern even in dry situations on Earth.
They created a new device that requires only an electrode, which can be a simple metal bar, to move across the screen, creating an electric field that charges the dust particles as it passes. An opposite charge applied to a transparent conductive layer only a few nanometers thick deposited on the solar panel's glass covering repels the particles, and by calculating the appropriate voltage to apply, the researchers were able to find a range of voltages sufficient to overcome gravity's pull and adhesion forces and cause the dust to lift away.
Panat states that trials using specially generated laboratory samples of dust with a range of particle sizes demonstrated that the procedure works efficiently on a laboratory-scale test installation. The studies revealed that the humidity in the air provided a small layer of water on the particles, which was necessary for the effect to work. "We conducted studies at various humidity levels ranging from 5% to 95%," Panat explains. "As long as the ambient humidity is greater than 30%, you can remove practically all of the particles from the surface, but it becomes more difficult as the humidity falls."
According to Varanasi, "the good news is that when humidity reaches 30%, the majority of deserts actually fall into this regime." Even those that are generally drier than that tend to have higher humidity in the early morning hours, resulting in dew formation, allowing the cleaning to be timed appropriately.
"Moreover, unlike some previous work on electrodynamic screens, which fails to operate at high or even moderate humidity, our technology operates forever at humidity levels as high as 95%," Panat explains.
In actuality, each solar panel may be installed with railings on both sides and a single electrode covering the width of the panel. A small electric motor, maybe powered by a small amount of the panel's output, would drive a belt system to move the electrode from one end of the panel to the other, so removing all the dust. The entire procedure might be mechanised or remotely controlled. Alternatively, tiny strips of transparent conductive material could be fixed above the display, obviating the requirement for moving parts.
By removing the reliance on trucked-in water, preventing the accumulation of dust that may contain corrosive compounds, and cutting overall operating costs, such technologies have the potential to dramatically increase the overall efficiency and dependability of solar arrays, Varanasi adds.
The research was funded by Eni S.p.A., an Italian energy company, through the MIT Energy Initiative.
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