Energy-Efficient Cleaning Robot for Maintaining Solar Panels

At a solar energy farm on the outskirts of Budapest in Hungary, a cleaning robot is diligently performing the day’s work. A great number of solar panels are waiting to be cleaned – as swiftly and effectively as possible without the use of chemicals or any undesirable discharges to the natural environment.

The robot is the work of a joint project between Norwegian Researchers and the Hungarian company ProDSP Technology.

Manual cleaning being carried out at Scatec Solar’s solar energy farm in Jordan. Photo: Mohammad Ba’ra.

“It’s a well-known fact that solar panels work more efficiently when they’re clean”, says SINTEF researcher and Project Manager Martin Bellmann who, in his routine work, develops what is referred to as sustainable energy technology. “But what‘s new here is that we’ve developed a robot to do the job. This means that the solar cells are cleaned both quickly and efficiently with as little as possible wear and tear or environmental impact”, he says.

There’s dirt and there’s dirt

Using a robot to clean solar cells may sound like a straightforward job – however there’s dirt and there’s dirt. A solar farm spanning several square kilometers is being cleaned, without any chemicals and without causing any damage to the natural environment. How is that achievable?

Solar cell Researcher Birgit Ryningen is probing a set of glass plates in SINTEF’s Daylight Laboratory.  They are all contaminated to order, but in varying degrees.

The motive is that the dirt in question has been specifically applied. These plates will now be examined in detail by Researchers so as to provide answers about how much the contamination blocks sunlight. This is the closing phase of the project.

The degree to which dust particles and contamination affects solar cells is very location-dependent.

Birgit Ryningen, Solar cell Researcher

When this project began, she conducted a literature study to find out how such dirt impacted its surroundings, only to discover that current research focusing on air pollution and dust particles mostly was directed on the human body. However, she did locate examples of research into the ways in which sand storms impact solar cells installed in the Middle East. Simply put, more research was required in order to provide Researchers with more details regarding this subject.

“We’ve seen that some dust particles absorb light while others reflect it”, says Ryningen.  “And small particles reflect more light than larger ones, whereas some scale contamination is biological and acts as a kind of ‘sun factor’”, she says. And certain scale coatings are thicker than others.

However, the common fact regarding all of them is that they must be removed in order for the solar cells to work optimally consistent with specifications. Therefore, the Researchers have developed a cleaning method that is both quick and sensitive, as well as being environmentally-friendly. Also it should be able to handle all the different types of contamination from the surroundings.

Cleaning is part of normal operations

The Norwegian company Scatec Solar owns, constructs, operates and maintains solar energy farms in a number of countries, including the Czech Republic, Rwanda, Honduras, South Africa and Jordan. Last year, the company’s sites yielded nearly 791 GWh.  This is comparable to the consumption of 200,000 average EU households.

Project Manager Caroline Sissener at Scatec Solar terms the Norwegian Researchers’ solution as interesting, particularly for solar energy farms situated in the Middle East.

Cleaning is part of standard operational procedures at our solar energy farms, where equipment is cleaned at least once or twice a year on order to avoid soiling. This involves the removal of everything from sand to bird droppings. But cleaning frequency is location-dependent. If a farm is located in a desert environment, the panels will require more frequent cleaning because the solar cells become covered with soil and sand.

Caroline Sissener, Project Manager, Scatec Solar

She adds that Scatec Solar repeatedly employ manual cleaning techniques because these are effective and economical, but that the company also employs automated systems.

Cleaning robots may offer a relevant and attractive solution for solar energy parks located in areas where frequent cleaning is required”, says Sissener.

She also mentions that manual techniques are vital to Scatec in some situations as they provide local jobs. The technique chosen is evaluated on a case-by-case basis, and environmental factors such as neighboring agricultural activity and water shortages are also taken into consideration.

Robot arm and micro-showers

The robot cleaner presently in SINTEF’s laboratory has gone through a variety of tests. Researchers have experimented with a range of chemicals, micro cleaning pads and air pressure application approaches – all tested, of course, on various types of soiling.

It is vitally important that we don’t discharge chemical pollutants into the environment. So we’ve rejected the use of traditional cleaning agents and have ended up using unbelievably small micro-droplets of water that are “sprayed“ onto the glass, almost as a vapour. Then the robot uses a micro cleaning pad that effectively removes the contaminant particles.

Birgit Ryningen, Solar cell Researcher

Since solar cells can be exposed to wear and tear, the Researchers have also been working hard to develop techniques of controlling the pressure exerted by the cleaning arm of the robot.

It is vital that the robot doesn’t scratch the sensitive glass surface. Even small scratches can reduce the efficiency of the solar cells,” explains Ryningen, adding that, “in theory, this should work on windows as well, which will open up a broader market for us!” she says.

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