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Innovative research provides breakthrough in 'night-time solar' energy: 'We hope for rapid progress'

"This technology could potentially … remove the need for batteries in certain devices — or help to recharge them."

Night-time solar clean energy

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When we think of solar power, we usually think of energy harnessed from rays of sunlight. A recent breakthrough changes that by producing electricity from "night-time" solar power.

Researchers at the School of Photovoltaic and Renewable Energy Engineering at the University of New South Wales (UNSW Sydney) recently produced electricity using solar power emitted as infrared light. The solar power most of us are familiar with uses sunlight; rays of light hit a solar panel, and cells in the panel absorb the sun's energy and convert it to electricity. 

As it turns out, there is lingering solar energy available even at night. As the Earth cools each night, leftover solar power from the day radiates outwards in the form of infrared light — the kind of light night vision goggles detect to illuminate the dark. 

The researchers at UNSW Sydney created a semiconductor using similar materials to those used in night vision goggles. This semiconductor is called a thermoradiative diode, and it is able to capture lingering solar energy in the form of infrared light and convert it to electricity, confirming what was previously purely theoretical. 

The discovery provides researchers with the ability to tap into a whole new source of solar energy. 

"Using thermal imaging cameras you can see how much radiation there is at night, but just in the infrared rather than the visible wavelengths," Ned Ekins-Daukes, team lead of the research, said in a news release. "What we have done is make a device that can generate electrical power from the emission of infrared thermal radiation."

"Night-time" solar is in the earliest stages of development; the thermoradiative diode generates about 100,000 times less electricity than a solar panel. Still, the researchers are optimistic about their discovery. 

In the news release, Ekins-Daukes compared the breakthrough to the invention of the first silicon solar cell in 1954. According to the American Physical Society's APS News, those solar cells operated at 6% efficiency, meaning they could only harness 6% of the sun's energy. Today, the average solar cell is 15%-22% efficient.

The researchers believe their technology could harness energy emitted in the form of body heat, providing renewable energy for bionic devices. Artificial hearts and pacemakers, for example, currently require batteries that have to be replaced every five to seven years. By harnessing body heat, "This technology could potentially … remove the need for batteries in certain devices — or help to recharge them," Ekins-Daukes said.

The technology is a long way off from commercialization, but, as another co-author, Dr. Michael Nielsen, put it: "By leveraging our knowledge of how to design and optimise solar cells and borrowing materials from the existing mid-infrared photodetector community, we hope for rapid progress towards delivering the dream of solar power at night."

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