Researchers have developed an engine that generates power from the night sky by exploiting the temperature difference between the cold air and warm ground. Unlike conventional Stirling engines, which typically generate power from a large heat gradient, this device can work based on a small difference in temperature.

Equipped with a heat-radiating antenna, the engine harnesses the temperature differential between the warm ground and the colder ambient air at night. The system is in direct thermal contact with the Earth via an aluminum mount installed at a depth of 5 cm and an infrared emissive paint ensures substantial radiative emission for the sky-facing surface. The bottom plate is thermally connected to the ground with an aluminum mount, which is pressed into the soil to a depth of 5 cm.

The experimental Stirling engine generates mechanical power from the temperature difference between the Earth and deep space when placed outdoors at night. Source: Mario Rodriguez, University of California Davis

Nighttime tests conducted by University of California Davis researchers demonstrated that by tapping the temperature gradient, the system can deliver 400 milliwatts/m². The emissive paint covering the top radiates heat into space, resulting in a hot reservoir below and a cold reservoir above with a variant in excess of 10° C.

The technology described in Science Advances effectively powered a fan and a small electrical motor to produce current and is envisioned for use in other low-power applications.