Instead of absorbing energy from the sun to produce electricity, a new class of devices generates power by absorbing heat from its surroundings instead and beaming it at outer space. Such devices, which do not require exotic materials as their predecessors did, could help ventilate greenhouses and homes, researchers say.
In 2014, scientists invented superthin materials that can cool buildings without using electricity by beaming heat into outer space. When these materials absorb warmth, their compositions and structures ensure they emit heat outward as very specific wavelengths of infrared radiation, ones that air does not absorb. Instead, the radiation is free to leave the atmosphere, carrying energy with it, and cooling the area around the material in a process called radiative cooling. The materials could help reduce demand for electricity. Air conditioning accounts for nearly 15 percent of the electricity consumed by buildings in the United States alone.
Researchers then began exploring whether they could harness radiative cooling to generate power. Whereas solar cells produce electricity from the flow of energy into them from the sun, thermoradiative devices could generate power from energy flowing out from them into space.
“Thermoradiative devices operate like solar cells in reverse,” says Jeremy Munday, professor of electrical and computer engineering at the University of California, Davis. “Rather than pointing them at a hot object like the sun, you point them at a cool object, like the sky.”
However, these devices were typically semiconductor electronics that needed rare or expensive materials to operate efficiently. In a new study, Munday and his colleagues investigated using Stirling engines, which “are mechanically simple and do not rely on exotic materials,” he says. “They also directly produce mechanical power—which is valuable for applications like air movement or water pumping—without needing intermediate electrical conversion.”
A Stirling engine meets a heat-emitting antenna
At the heart of a Stirling engine is a gas sealed in an airtight chamber. When the gas is heated, it expands and pressure increases within the chamber; when it is cooled, it contracts, reducing pressure. This creates a cycle of expansion and contraction that drives a piston, generating power.
Whereas internal combustion engines rely on large differences in temperature to generate power, a Stirling engine is very efficient when it comes to small differences in temperature.
“Stirling engines have been around since the early 1800s, but they always operated by touching some warm object and rejecting waste heat into the local, ambient environment,” Munday says. Instead, the new device is heated by its surroundings and cooled when it radiates energy into space.
The new device combines a Stirling engine with a panel that acts as a heat-radiating antenna. The researchers placed it on the ground outdoors at night.
A year of nighttime experiments…
Read full article: Radiative Cooling Powers Fans By Night
The post “Radiative Cooling Powers Fans By Night” by Charles Q. Choi was published on 12/07/2025 by spectrum.ieee.org