A team of researchers at Stanford University have developed a new type of solar structure that can provide cooling for buildings, even in direct sunlight, which could lead to air conditioning units that require no electricity.
The solar cooling device designed by the team reflects most of the sunlight hitting it, while also taking heat from the buildings or structures it is installed on and radiating it out into space, thereby improving the cooling efforts of those structures.
According to the team, the challenge of creating such a device is in developing a reflector capable of reflecting as much sun as possible, while also efficiently emitting thermal radiation within a specific range of wavelengths, so the heat energy can escape the Earth's atmosphere.
"People usually see space as a source of heat from the sun, but away from the sun outer space is really a cold, cold place. We've developed a new type of structure that reflects the vast majority of sunlight, while at the same time it sends heat into that coldness, which cools manmade structures even in the daytime." - Shanhui Fan, professor of electrical engineering
The solution came from using nanostructured photonic materials that can either enhance or suppress certain wavelengths of light, enabling the team to combine the reflector and thermal emitter in one device that has no moving parts and no external energy demands. The team engineered nanophotonic materials from quartz and silicon carbide, which are both weak in absorbing sunlight, to build their device.
According to the research results, the new panel can achieve a net cooling power of over 100 w per square meter, and that a typical single-family house with only 10% of its roof covered with the panels could see about 35% of its cooling needs in the summer offset by the device.
Because these radiative cooling panels use passive technology, there is no external energy input required, and the lack of moving parts to wear out or break on the panels would lead to a longer useful life and low maintenance costs.
"We can foresee applications for radiative cooling in off-the-grid areas of the developing world where air conditioning is not even possible at this time. There are large numbers of people who could benefit from such systems." - Fan
The results of the team's research are published in Nano Letters: Ultrabroadband Photonic Structures To Achieve High-Performance Daytime Radiative Cooling