Engineers at the University of California, Davis have developed a device capable of generating mechanical energy at night by harnessing the temperature difference between the warmth of the Earth and the cold of outer space. This technology could be used to ventilate greenhouses and other buildings without the need for fuel. The results of the study were published in the journal Science Advances.

How the Device Works

The device is based on a Stirling engine, which converts thermal energy into mechanical motion. Unlike internal combustion engines, the Stirling engine requires a much smaller temperature difference to operate efficiently. In a typical setup, one side of the engine remains warm while the other is cooled, causing the piston to move and generate mechanical energy.

Usually, the temperature difference is created by heating one side of the engine with fuel. In this development, outer space serves as the cold reservoir, eliminating the need to burn fuel. The device uses radiative cooling: at night, heat naturally escapes into the sky, and this process is utilized by the system.

Design and Testing

In the device's design, the Stirling engine is mounted on a panel that acts as a heat-radiating antenna. The system is placed outdoors at night: the ground warms one side of the engine, while the panel directs heat upward, connecting the other side to the cold of space.

During year-long nighttime tests, it was found that the compact device can generate at least 400 milliwatts of mechanical power per square meter. In demonstrations, the engine powered a small fan and was connected to an electric motor to produce electricity.

Potential Applications

The results show that a significant amount of energy can be harvested from the night sky. The highest efficiency is achieved in regions with low humidity and clear skies. In the future, this technology could be used to ventilate greenhouses and residential buildings without relying on traditional energy sources.