A transformation device generates cold night sky energy, when solar energy does not work

A cheap thermoelectric device exploits the cold of space without the input of active heat, generating electricity that powers a LED at night, researchers report on September 12 in the newspaper. Joule.

"The device is able to generate electricity at night, when solar cells do not work," says lead author Aaswath Raman, an assistant professor of materials science and engineering at the University of California at Los Angeles . "Beyond lighting, we believe that this could be a broadly enabling approach to energy production suited to remote sites and any place where nighttime electricity production is required.

"Remarkably, the device is able to generate electricity at night, when the solar cells do not work." – Aaswath Raman

Solar cells are an effective source of renewable energy during the day, but there is currently no similar renewable approach to producing night energy. Solar lamps can be equipped with batteries to store the energy produced during the day for night use, but this increase increases costs.

The device developed by Wei Li and Shanhui Fan, scientists at Raman University and Stanford University, bypasses the limits of solar energy by taking advantage of the radiative cooling, according to which a surface exposed to the sky transmits its heat to the atmosphere in the form of thermal radiation, reaching a temperature colder than the ambient air. This phenomenon explains how frost forms on the grass during freezing nights, and the same principle can be used to produce electricity, exploiting temperature differences to produce renewable electricity. at night, when the demand for lighting is maximum.

Raman and his colleagues tested their low-cost thermoelectric generator on a roof in Stanford, California, under clear skies for the month of December. The device, consisting of a polystyrene enclosure covered with aluminized mylar to minimize thermal radiation and protected by a transparent infrared windshield, sits on a table one meter above the roof level, sucking the heat from the ambient air and releasing it into the night sky through a simple black transmitter. When the thermoelectric module was connected to a voltage booster and a white LED, the researchers found that it was feeding the light passively. They then measured their power output for six hours, concluding that it generated up to 25 milliwatts of energy per square meter.

"Our work highlights the many energy opportunities that remain by taking advantage of the cold of outer space as a source of renewable energy." – Aaswath Raman

Since the radiative cooler consists of a single, painted aluminum disc and all other components can be purchased in-store, Raman and the team believe the unit can be easily scaled for convenient use. . The amount of electricity it generates per unit area remains relatively low, which for the time being limits its widespread applications, but researchers estimate that it can be 20 times more powerful thanks to improved engineering, notably by removing the heat gain of the radiative cooling component to increase the heat. – efficiency of trade – and exploitation in a warmer and drier climate.

"Our work highlights the many energy opportunities that remain by exploiting the cold of space as a source of renewable energy," says Raman. "We believe this is the foundation of a complementary solar technology. While the output power will still be significantly lower, it can operate at times when solar cells can not. "

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This work is supported by the US Department of Energy, as well as the Mellon Family Foundation.

Reference: "Generating Light of Darkness" by Aaswath P. Raman, Wei Li and Shanhui Fan, September 12, 2019, Joule.
DOI: 10.1016 / j.joule.2019.08.009

For more information on this invention, see A low cost device generates electricity in the dark.