These Solar Cells Produce Electricity at Night
hubie writes:
Researchers used radiative cooling to generate enough to power LEDs or charge a cellphone
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.
[...] The team tested their prototype TEG-integrated solar cell for three days in October 2021 on a rooftop in Stanford, Calif. The demonstration showed a nighttime power production of 50 mW/m2. The team estimates that in a hotter, drier climate, the same setup could generate up to 100 mW/m2.
[...] "In principle, it could be possible to engineer the thermal-emission property of the solar cell to optimize its radiative cooling performance without affecting solar performance," Fan says. "Our theoretical calculations point to the possibility of a few hundred milliwatts or maybe even 1 watt."
Journal Reference:
Sid Assawaworrarit, Zunaid Omair, and Shanhui Fan, Nighttime electric power generation at a density of 50 mW/m2 via radiative cooling of a photovoltaic cell [open], Appl. Phys. Lett. 120, 143901 (2022)
DOI: 10.1063/5.0085205
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