New device harvests energy from the Sun

 By Agata Boxe

A new device developed by scientists from Stanford University can capture heat from the sun and coldness from outer space, according to a recent study published in the journal Joule. The findings may pave the way to creating solar cells that will provide both electricity and cooling. Solar energy is one of the most widely known alternatives to fossil fuels, but it is not the only option…

“It is widely recognized that the sun is a perfect heat source nature offers human beings on Earth”, explained lead study author Zhen Chen, a former postdoctoral research associate at Stanford and currently a professor at the Southeast University of China in a statement. It is less widely recognized that nature also offers human beings outer space as a perfect “heat sink”.
Researchers have known that objects emit heat as infrared radiation, which is a form of light the human eye cannot actually see. A portion of this radiation trickles into space, which enables surfaces that give off enough radiation within the infrared space to reach a temperature that is lower than that of their surroundings.
So-called “radiative cooling technology” reflects an abundance of infrared light, offering an environment-friendly alternative to air conditioning. Scientists have also hoped the technology may boost the efficiency of solar cells, which normally decreases as solar cells get hotter.

Energy balance of a passive radiative cooling device. A special thermo-photonic material system needs to be able to radiate efficiently in the mid-infrared (Svetlana V Boriskina, arrow), and to repel sunlight and atmosphere’s radiation (wavy red arrows), as well as to resist the convection and conduction heat gain from air (straight red arrows) (

A device to combine them all

Now Chen and his colleagues have managed to combine radiative cooling technology with solar absorption technology in a single device. The device includes a solar absorber and a radiative cooler constituted by silicon nitride, amorphous silicon and aluminum layers captured in a vacuum to decrease heat loss. If used on a rooftop, “a photovoltaic cell can supply electricity while the radiative cooler can cool down the house on hot summer days”, Chen said. (A photovoltaic cell is another term for a solar cell).

An array of RadiCold cooling modules on the roof of a building on the University of Colorado Boulder campus (Yang Lab, University of Colorado Boulder)

More research needs to be done before the technology can be used commercially, he added. For example, some of the components are too costly and could be designed using more affordable yet equally effective materials. Chen also stressed the importance of testing photovoltaic cells in lieu of a solar absorber, which still needs to be demonstrated.
Despite these challenges, “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”.

READ MORE: How air conditioning changed the world by Nicholas Newman

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Agata Boxe