Harvesting energy from the coldness of the universe

Whenever heat flows from a hotter to a colder body, there’s an opportunity to siphon off energy. In fact, most energy sources on earth depend on a temperature difference. As the extremely hot sun beams energy to the lukewarm earth, a solar panel converts some of it to electricity. The energy contained in oil similarly stems from the sun. Even wind power and hydroelectricity rely on the energy flow from hot to cold areas in the earth’s atmosphere.

As it turns out, though, we’ve been neglecting a temperature difference as a potential source of energy: that between the earth’s surface and cold outer space. While not as big a difference as between the sun and the earth, about 10¹⁷ J of infrared thermal radiation is beamed into space every second. And all of that goes to waste.