A new device can produce electricity from the cool air of the evening, according to University of California Los Angeles materials scientist Aaswath Raman and Stanford University engineers Wei Li and Shanhui Fan. In a prototype they created, the device generated around 0.8 milliwatts of power, enough to keep a hearing aid working. The prototype can operate at hours when solar cells cannot, making nighttime an optimal source of renewable power, as ScienceAlert detailed:
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Using a material called a thermocouple, engineers can convert a change in temperature into a difference in voltage. This demands something relatively toasty on one side and a place for that heat energy to escape to on the other.
They put together a cheap thermoelectric generator and linked it with a black aluminium disk to shed heat in the night air as it faced the sky. The generator was placed inside a polystyrene enclosure sealed with a window transparent to infrared light, and linked to a single tiny LED.
For six hours one evening, the box was left to cool on a roof-top in Stanford as the temperature fell just below freezing. As the heat flowed from the ground into the sky, the small generator produced just enough current to make the light flicker to life.
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