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New Method Could Remove Dust on Solar Installations in Water-Limited Regions

By 2030, solar power is anticipated to reach 10% of global power generation, and much of that is likely to be situated in desert areas, where sunlight is ample.

New Method Could Remove Dust on Solar Installations in Water-Limited Regions.

Image Credit: Massachusetts Institute of Technology.

However, the housing of dust on mirrors or solar panels is already a considerable problem — it can decrease the output of photovoltaic panels by as much as 30% in just one month — so regular cleaning is necessary for such installations.

At present, cleaning solar panels has been calculated to utilize around 10 billion gallons of water annually — sufficient to supply drinking water for up to 2 million people. Efforts at waterless cleaning are laborious and tend to make irreversible scratching of the surfaces, which also decreases efficiency.

Currently, a research group at the Massachusetts Institute of Technology (MIT) has engineered an approach that enables solar panels to be cleaned automatically, or the mirrors of solar thermal plants, in a waterless and no-contact system that could considerably decrease the prevalence of dust.

The latest system utilizes electrostatic repulsion so that dust particles detach and virtually jump off the surface of the panel, without the need for brushes or water. For the system to be triggered, a simple electrode flows just above the surface of the solar panel, which imparts an electrical charge to the dust particles, which are further repelled by a charge that has been employed to the panel itself.

The system could be made to function automatically with the help of a simple electric motor and guide rails along the side of the panel. The study has recently been published in the journal Science Advances, in a paper by MIT graduate student Sreedath Panat and professor of mechanical engineering Kripa Varanasi.

In spite of concerted efforts globally to design ever more efficient solar panels, Varanasi states, “a mundane problem like dust can actually put a serious dent in the whole thing.”

Laboratory tests performed by Panat and Varanasi illustrated that the dropoff of energy output from the panels occurs steeply at the start of the process of dust accumulation and can easily reach a 30% decrease following just one month without cleaning.

The researchers calculated that even a 1% reduction in power, for a 150-megawatt solar installation, could lead to a $200,000 loss in annual revenue. The scientists say that globally, a 3 to 4% reduction in power output from solar plants would come to a loss of between $3.3 billion and $5.5 billion.

There is so much work going on in solar materials. They’re pushing the boundaries, trying to gain a few percent here and there in improving the efficiency, and here you have something that can obliterate all of that right away.

Kripa Varanasi, Professor of Mechanical Engineering, Massachusetts Institute of Technology

Several of the largest solar power installations in the world, inclusive of what is in India, China, the United Arab Emirates, and the United States, are situated in desert regions. The water utilized for cleaning these solar panels with the help of pressurized water jets has to be carried in from a distance, and it has to be very pure to prevent deposits on the surfaces.

At times, dry scrubbing is employed, but it is less effective at cleaning the surfaces and can result in permanent scratching that also decreases transmission of light.

Water cleaning accounts for around 10% of the operating charges of solar installations. The new system could possibly help reduce these costs while improving the overall power output by enabling frequent automated cleanings, state the scientists.

The water footprint of the solar industry is mind boggling. So, the industry has to be very careful and thoughtful about how to make this a sustainable solution.

Kripa Varanasi, Professor of Mechanical Engineering, Massachusetts Institute of Technology

Varanasi says that the water footprint will be on the continuous rise as those installations keep expanding across the world.

Other research groups have attempted to develop electrostatic-based solutions, but these depend on a layer known as an electrodynamic screen, utilizing interdigitated electrodes.

Varanasi states such screens could have defects that let moisture in and causes them to fail. While they might find its use on a place like Mars, he says, where moisture is not a problem, even in desert environments on Earth this can be a crucial problem to be taken care of.

The newly-developed system just needs an electrode, which could be a simple metal bar, to pass over the panel, generating an electric field that imparts a charge to the dust particles as it goes.

An opposite charge applied to a transparent conductive layer measures a thickness of just a few nanometers. This is deposited on the glass covering of the solar panel which further repels the particles, and by estimating the right voltage to apply, the scientists were able to determine a voltage range sufficient enough to overcome the pull of gravity and adhesion forces, and cause the dust to lift away.

Panat states, by making use of specially prepared laboratory samples of dust with a range of particle sizes, experiments showed that the process works efficiently on a laboratory-scale test installation. The tests illustrated that humidity in the air supplied a thin coating of water on the particles, which became vital to making the effect work better.

We performed experiments at varying humidities from 5 percent to 95 percent. As long as the ambient humidity is greater than 30 percent, you can remove almost all of the particles from the surface, but as humidity decreases, it becomes harder.

Sreedath Panat, Graduate Student, Massachusetts Institute of Technology

Varanasi states that “the good news is that when you get to 30 percent humidity, most deserts actually fall in this regime.” Even those that are typically drier have higher humidity in the early morning hours, resulting in dew formation, so cleaning could be scheduled accordingly.

Panat stated, “Moreover, unlike some of the prior work on electrodynamic screens, which actually do not work at high or even moderate humidity, our system can work at humidity even as high as 95 percent, indefinitely.”

Practically, at scale, each solar panel could be embedded with railings on each side, with an electrode spanning throughout the panel. A small electric motor, probably using a small portion of the output from the panel itself, would push a belt system to shift the electrode from one end of the panel to the other. This makes all the dust fall away.

The entire process could be controlled or automated remotely. Instead, thin strips of conductive transparent material could be permanently arranged above the panel, thereby removing the need for moving parts.

By eliminating the dependency on trucked-in water, by reducing the dust buildup that can consist of corrosive compounds, and by lowering the overall operational costs, such systems exhibit the ability to considerably enhance the complete efficiency and reliability of solar installations, stated Varanasi.

This study was financially supported by Italian energy firm Eni. S.p.A. through the MIT Energy Initiative.

How to clean solar panels without water

Video Credit: Massachusetts Institute of Technology.

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