Abstract
Radiative cooling can be used to passively cool objects below ambient temperature by exhausting heat toward the sky. The emitted power flux may be used to generate electricity, but devices often require low-bandgap or rare-earth materials that are difficult to scale. Here, we demonstrate an alternative approach that generates mechanical power from Earth's ambient radiation using a Stirling engine. Outdoor experiments performed throughout the year show that temperature differences >10°C are sustained during most months, resulting in the generation of >400 milliwatts per square meter of mechanical power with a potential for >6 watts per square meter. We further apply this technique for air circulation, achieving >0.3 meters per second with a potential volumetric flow rate that exceeds 5 cubic feet per minute (cfm), which is sufficient for CO(2) circulation in greenhouses and for thermal comfort inside residential buildings.