A team of researchers at Stanford have invented a new and weird type of material that cools when exposed to sunlight. It could be used to insulate buildings, and reduce the need for energy-consuming air conditioning.
The material, developed by Shanhui Fan, uses optical tricks to radiate heat whose frequency lies in our planet’s “thermal window” – a range of wavelenghts from 8 to 13 micrometers. At these frequencies, the heat passes through the atmosphere, doesn’t become trapped in it anymore, and gets in outer space, which acts as a heat sink.
Previously, other scientists have harvested this effect, called passive radiative cooling, but the materials they made were also black, so in addition to releasing the heat at night, they also captured a lot of during the day. Fan’s material behaves like a mirror that reflects 97% of heat back into space.
“Something that cools down rather than heating up in the sun is counterintuitive, but that’s what the device is designed to do,” he says.
His next step is to build a square-meter of this material. The proof of concept piece only had 8 square inches.