A team of engineers has developed an experimental engine that generates mechanical power at night by tapping into the temperature difference between the Earth and the freezing cold of deep space. The prototype, created at the University of California, Davis, demonstrates how natural heat radiation into the night sky can be harnessed to produce usable energy, according to new research reported by ScienceDaily.
The research, published in Science Advances, shows that the compact device can produce measurable mechanical power after sunset by radiating heat toward space while drawing warmth from the ground. The system is based on a Stirling engine, which converts temperature differences into mechanical motion.
Unlike combustion engines that require large heat gaps, Stirling engines can operate efficiently with relatively small temperature contrasts. In this setup, one side of the engine remains warmed by ambient ground temperatures, while the other side cools by radiating heat into the night sky. Because deep space acts as an extremely cold thermal sink, the temperature difference is enough to drive a piston connected to a flywheel.
The design places the engine atop a specially engineered panel that acts as a radiative cooling surface. On clear nights, objects naturally lose heat to space through infrared radiation. The researchers leveraged that effect, allowing one side of the engine to cool passively without fuel or electricity. The concept relies on radiative interaction rather than physical contact with space.
After a year of nighttime testing, the team found that the device could generate at least 400 milliwatts of mechanical power per square meter. In demonstrations, the engine powered a small fan and was also connected to a generator to produce electrical current. While the power output is modest, it is significant for a system that requires no fuel and operates after dark.
The approach works best in dry climates with clear skies, where radiative cooling is strongest. Potential applications include ventilating greenhouses, cooling buildings, or powering low-energy devices overnight without relying on batteries or grid electricity.
The university has filed a provisional patent for the technology. If scaled effectively, the concept could complement daytime solar systems by generating small amounts of mechanical or electrical power using the natural temperature contrast between Earth and space once the sun goes down.