The researchers show that devices for harvesting solar and space energy will not compete for land space and can actually help each other function more efficiently.
“It is widely recognized that the sun is a perfect heat source nature offers human beings on Earth,” said Zhen Chen, a former postdoctoral research associate at Stanford in the group of Shanhui Fan and is currently a professor at the Southeast University of China. “It is less widely recognized that nature also offers human beings outer space as a perfect heat sink.”
Chen and his colleagues developed a device combining radiative cooling with solar absorption technology. The device consists of a germanium solar absorber on top of a radiative cooler with silicon nitride, silicon, and aluminum layers enclosed in a vacuum to minimize unwanted heat loss.
Both the solar absorber and the atmosphere are transparent in the mid-infrared range of 8-13 microns, offering a channel for infrared radiation from the radiative cooler to pass through to outer space. The team demonstrated that the combined device can simultaneously provide 24ºC in solar heating and 29ºC in radiative cooling, with the solar absorber improving the radiative cooler’s performance by blocking heat from the sun.
The design has applicatins back on Earth. “On a rooftop, we imagine a photovoltaic cell can supply electricity while the radiative cooler can cool down the house on hot summer days,” said Chen.
However there is still plenty of work to do before it can be scaled up for commercial use. While the vacuum enveloping the device could be scaled up with relative ease, the infrared-transparent window made from zinc selenide is still too costly, and the solar absorber and radiative cooler could be designed from cheaper high-performing materials as well. Chen thinks it is also important to test the use of photovoltaic cells in the place of a solar absorber–an idea which has yet to be demonstrated.
“I think this technology could potentially revolutionize the current solar cell technology,” said Chen. “If our concept is demonstrated and scaled up, the future solar cell will have two functions in one: electricity and cooling.”