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Thursday, April 28, 2022

These Solar Cells Produce Electricity at Night

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These Solar Cells Produce Electricity at Night Researchers used radiative cooling to generate enough to power LEDs or charge a cellphone PRACHI PATEL11 APR 2022   In IEEE Spectrum

By taking advantage of the temperature difference between a solar panel and ambient air, engineers have made solar cells that can produce electricity at night.

Compared to the 100 to 200 watts per square meter that solar cells produce when the sun is shining, the nighttime production is a trickle at 50 mW/m2. “But it is already financially interesting for low-power-density applications like LED lights, charging a cellphone, or trying to power small sensors,” says Shanhui Fan, a professor of electrical engineering at Stanford University who published the work along with coauthors in Applied Physics Letters.

Fan and his colleagues harnessed the concept of radiative cooling, the phenomenon by which materials radiate heat into the sky at night after absorbing solar energy all day and that others have tapped before to make cooling paint and energy-efficient air-conditioning. Because of this effect, the temperature of a standard solar cell pointing at the sky at night falls below ambient air temperature. This generates a heat flow from the ambient air to the solar cell. “That heat flow can be harvested to generate power,” Fan says.

To do that, the researchers integrated a photovoltaic cell with a commercial thermoelectric generator (TEG) module, which converts temperature difference into electrical power. The TEG sits underneath the solar cell, and an aluminum sheet between the two conducts heat from the solar cell to the TEG. The other side of the TEG connects via a heat sink to ambient air .... ' 

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