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This unit utilizes the cold night sky to generate electricity

A new unit is an anti-solar panel that harvests energy from the cold night sky.

By utilizing the temperature difference between Earth and outer space, a prototype of the unit produced enough electricity at night to power a small LED light. A larger version of this night generator can today light rooms, charge phones or operate other electronics in remote or low-resource areas that lack electricity at night when solar panels are not working, researchers report online September 12 in Joule .

The core of the new night light is a thermoelectric generator that produces electricity when one side of the generator is cooler than the other ( SN: 6/1/1

8 ). The sky-facing side of the generator is attached to an aluminum plate sealed under a transparent housing and surrounded by insulation to keep the heat out. This plate remains cooler than the ambient air by losing all heat it absorbs as infrared radiation ( SN: 9/28/18 ). That radiation can zip up through the transparent lid and atmosphere against the cold space.

At the same time, the bottom of the generator is attached to an exposed aluminum plate which is continuously heated by the ambient air. At night, when not baking under the sun, the top plate can be a few degrees Celsius colder than the generator bottom.

Stanford University engineer Wei Li and colleagues tested a 20-inch prototype of the unit on a clear December evening in Stanford, California. The generator produced up to about 25 milliwatts of power per square meter unit – enough to light a small LED or LED lamp. The team estimates that further design improvements, such as better insulation around the cool top plate, can increase production up to at least 0.5 watts per square meter.

  electrical device
A device that uses the night sky to generate electricity (image)) operated a small LED lamp in a ceiling test. Wei Li

"It's a very smart idea," said Yuan Yang, a materials researcher at Columbia University who is not involved in the work. "Electricity production is much smaller than solar panels," which generally produces at least 100 watts per square meter. But this night generator can be useful for emergency support, or energy for people living off the grid, Yang says.

A typical lamp might consume some watts of electricity, says Shanhui Fan, an electrical engineer at Stanford University who worked on the unit. So a unit that took up a few square meters of roof space could light a room with energy from the night sky.

Aaswath Raman, a materials scientist and engineer at UCLA, also imagines using the team's generator to help operate remote weather stations or other environmental sensors. This can be especially useful in polar regions that do not see sunlight for several months at a time, Raman says. "If you have a little low power and you have to drive it through three months of darkness, that could be one way."

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