Dancing dust – cleaning solar panels without water

It’s expected that solar power will provide 10% of worldwide power generation by the year 2030, and much of that will be produced from desert areas where sunlight is plentiful – but so is dust. The accumulation of dust on solar panels or mirrors is already a significant issue, reducing output by as much as 30% in just one month, so cleaning solar panels regularly is essential.

However, doing so with water would use almost 38 billion litres every year – enough to supply drinking water to 2 million people. Now, researchers have devised a new no-contact system to automatically clean solar panels, which could significantly reduce the amount of dust accumulating on them without using precious water resources to do so.

The system uses electrostatic repulsion to cause dust particles to detach and leap off the panel’s surface, according to the new study published in Science Advances. This is an exciting new avenue, as existing attempts at waterless cleaning are labour intensive and cause irreversible scratching of the surfaces, which permanently reduces efficiency.

The new technique works by passing a simple electrode – a conductor of electricity, which could be a simple metal bar – just above the surface of the solar panel. The electric field produced by the electrode causes the dust particles to become electrically charged as well.

The same charge the dust holds is then applied to the solar panel’s surface through a conductive layer a few nanometres thick. The researchers have calculated the voltage range to apply to overcome the pull of gravity and adhesion forces, so the dust particles are pushed from the surface until they fall off.

Experiments proved that this process currently works effectively on a laboratory-scale test installation, and that the humidity content of the air – which provides a thin coating of water on the particles – is crucial in doing so.

“We performed experiments at varying humidities from 5 percent to 95 percent,” says author Sreedath Panat, a graduate student at Massachusetts Institute of Technology, USA. “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.”

But aren’t these supposed to work in deserts? Not to worry, as according to senior author Kripa Varanasi, professor of mechanical engineering at MIT, “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 tend to have higher humidity in the early morning, leading to dew formation, so cleaning could be timed accordingly.

“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,” adds Panat.

In real-world scale and practice, the authors suggest that every solar panel could be fitted with railings on each side, with an electrode spanning across the panel. A small electric motor, perhaps even using electricity output from the panel itself, could then drive a belt system to move the electrode back and forth.

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