We all know about energy from light — the solar energy. But have you ever heard of energy from the absence of it, that is, darkness.

The device works by taking advantage of the temperature difference between Earth's warmth and the extreme chill of outer space. Paired with a radiative cooling panel, the small engine can produce mechanical power through the night without burning fuel or relying on batteries.

The Stirling engine is known for working efficiently even with small temperature differences. While internal combustion engines need large heat gradients, Stirling engines thrive on minor ones.

Professor Jeremy Munday, who led the research with graduate student Tristan Deppe, explained that this makes them ideal for tapping into the natural temperature drop after sunset.

The setup of the device includes a radiative panel facing the sky, losing heat to the cold of space, while the ground below acts as the warm side. The difference is enough to move the piston and spin the flywheel, producing steady mechanical power.

In a year of testing, the device generated about 400 milliwatts of power per square metre — enough to run small fans or light electrical motors. The researchers believe this approach could help ventilate greenhouses or cool buildings in areas with clear night skies.

UC Davis has filed a provisional patent and plans to refine the design for larger applications.

energy / research / innovation