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DUST-REPELLENT SOLAR PANELS COULD SAVE BILLIONS OF GALLONS OF WATER

Solar farms have a significant clean water footprint. But new technologies could
help.

By Anuradha Varanasi | Published Mar 22, 2022 10:00 AM

 * Technology
 * Environment
 * Science

Deserts are perfect for solar farms—minus the dust. Antonio Garcia on Unsplash
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Most of the large-scale solar parks in the world are located in deserts. These
landscapes provide ample vacant land and year-round sunlight for solar power
production. Researchers have envisioned transforming the Sahara—the vastest
desert region on earth—into a massive solar park that might have the potential
of producing four times the world’s present energy demand. 

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But, there’s a major problem—dust. Gradual dust accumulation on solar panels can
reduce their efficiency by almost 30 percent within one month of operation. For
some context, solar power losses of only three to four percent on a global scale
could mean an economic loss of at least 3.3 to 5.5 billion dollars. As climate
change intensifies dust storms, there may be a rapid loss of solar panels’
efficiency unless they are cleaned several times a month.



Pressurized water jets and sprays are the most common method of cleaning solar
panels. To avoid the risk of staining and damaging the glass of solar panels,
only pure and demineralized water can be used. The need to transport clean water
to dry or remote desert regions with scarce water supplies accounts for 10
percent of solar parks’ operations and maintenance costs. 



While the global capacity of solar parks is currently above 500 gigawatts,
researchers estimate that up to 10 billion gallons of drinking water are used
every year just for cleaning solar panels. To put things in perspective, that
amount of water can fulfill the annual requirements of approximately 2 million
people living in developing countries. 

“I was amazed at the sheer amount of pure water that is required for cleaning
solar panels,” says Kripa Varanasi, a professor of mechanical engineering at MIT
(no relation to the author). “The water footprint of the solar industry is only
going to grow in the future. We need to figure out how to make solar farms more
sustainable.”


THE NEED FOR A WATERLESS AND CONTACT-FREE CLEANING METHOD



Attempts to get rid of dust accumulation on solar panels by using dry scrubbing
methods like brushes and air pressure risk damaging solar panels due to the
surface getting scratched over time. 



The inefficiency of current cleaning methods motivated Varanasi and his graduate
student, Sreedath Panat, to invent a contactless cleaning system that can
automatically repel dust from solar panels with zero water usage.

The new system uses electrostatic repulsion to zap dust particles off the
surface of solar panels. While dust by itself is not a conductor, they found
that applying an electric force or adequate voltage range through an
electrode—such as a metal bar—that passes right above the solar panel’s surface
charges the dust particles resting on the panel. Next, an opposite charge is
applied to a transparent film—similar to the ones used on phones and
laptops—which is then installed on the system, allowing the glass surface of the
panel to repel pesky dust particles.



[Related: Floating solar panels could be the next big thing in clean energy.]



This system can be used separately along with a solar panel cleaning robot.
Alternatively, it is retrofitted along each side of the panel and functions on a
small amount of solar energy. Varanasi and Panat wrote about their research in a
recent paper published in the journal Science Advances. 

In the past, NASA has used electrostatics for removing dust from solar panels on
Mars rovers with the help of electrodynamic screens. However, that technology
worked only because they were implemented in extremely dry conditions without
humidity impossible on Earth. “It also requires expensive interdigitated
electrodes that have a weaker force and cannot tolerate moisture,” explains
Varanasi.



That made the duo opt for a different method of using electrostatics for
Earth-bound solar panel cleaning. They began by conducting experiments with
different sizes of dust particles and discovered that the silica in dust
particles absorbs moisture from the atmosphere.



“A charge on the dust particles comes from a thin layer of absorbed water that
is only a few nanometers thick but still acts as a conductor. That enabled us to
estimate the electric force of dust particles and remove dust particles between
the sizes of 30 to 40 microns,” says Varanasi. 

This promising breakthrough for the researchers arrived after performing their
experiments at a wide range of humidity levels from five percent to 95 percent.
They then observed that humidity is the driving force behind making the system
work.



“As long as the relative humidity is above 30 percent, this system is robust and
works very well,” says Varanasi. “We can apply this to most geographical areas
and even the driest deserts because of dew formations in the mornings.” 



[Related: What you need to know about converting your home to solar.]

The duo has created a lab-scale prototype that consists of a solar panel, a
conductive surface, and a moving electrode attached to the top. But, this system
still can’t rid a solar panel of particles less than 10 microns in size. 



 “These tiny dust particles are the ones that create the shadowing effect on
solar panels,” he adds. “We are working on some more improvements to overcome
that issue.”




ALTERNATIVES FOR REDUCING SOLAR PANELS’ WATER FOOTPRINT

As the MIT engineers are preparing to make their new system scalable in the
future, other researchers are working towards developing a solar panel coating
technology to reduce dust accumulation. Inspired by the lotus leaf’s
self-cleaning properties, Germany-based researchers at Ben-Gurion University
attempted to develop silicon-based, hydrophobic coating for solar panels. This
could prevent dust from accumulating on the surface of solar panels and reduce
the amount of water required to clean them.

As of now, a UK-based company, Solar Sharc, has already launched a dust
repellent coating for solar panels. They use nanoparticle structures for
transparency that are only a few microns thick. According to the company’s
website, the coating is self-cleaning and enables the formation of water
droplets on the surface that can roll off the panels. 



But Varanasi says the problem with a coating of nanostructures is that it could
erode over time after withstanding dust storms and windy conditions. “The
texture of the anti-soil coating on the solar panels’ surfaces could then get
affected and lose its transparency,” he says.



Despite all the convoluted challenges involved in preventing dust accumulation
on solar panels, engineers like Varanasi remain optimistic about developing the
right technology for making the solar industry more environmentally
sustainable. 

“Water is a precious resource,” he says. “If the solar industry is proactive and
approaches this problem from a holistic view, it will not directly impact
communities’ access to clean water.”

climate change
renewable energy
solar energy
sustainability
Technology

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