New Photovoltaic Cell Makes Electricity From Thermal Radiation

The electromagnetic spectrum is comprised of thousands upon thousands of frequencies. Sound and light are all part of the spectrum, as are the frequencies that make radio and television broadcasts possible. Today’s solar panels light waves from a small part of the EM spectrum and turn them into electricity, but there are many other frequencies like thermal radiation that could someday stimulate new kinds of photovoltaic cells to generate electricity as well.

Researchers at Stanford have recently published a study in the journal Applied Physics Letters that describes a new type of cell that converts thermal radiation into electricity. When the sun goes down, living organisms and physical structures like buildings, road, and sidewalks radiate heat back into the atmosphere. We call this radiational cooling and it is those electromagnetic waves the Stanford researchers say can be put to work making electricity.

Putting Thermal Radiation To Work

FIG. 1. Nighttime power generation from radiative cooling of a PV cell. (a) Schematic showing the energy balance of the PV cell and (b) thermal circuit model of the PV-TEG device. Image credit: Applied Physics Letters

Capturing thermal radiation is similar to how a hydroelectric dam captures energy from falling water and converts it into storable, usable electricity, Shanhui Fan, an electrical engineer at Stanford and leader of the research, tells The Daily Beast. Fan and his team tapped into an unseen reservoir — surrounding air through which thermal radiation is traveling — and attached an insulating material called a thermoelectric module. This material acts like a hydroelectric dam, taking heat flow and producing energy out of it.

The modest capability of the new PV cells is still remarkable for a thing that is only in the prototype stage, Peter Bermel, an electrical engineer at Purdue University, told The Daily Beast in an email. People may not recall that early solar panels were so inefficient, they were laughed at by many skeptics, or that LEDs not so long ago were so dim, no one could possibly imagine a commercial use for them. These new PV cells could extend the life of solar panels and provide a reliable source of electricity for the more than 750 million people who live without electricity worldwide.

“What [this PV cell] could be useful for is to provide you with a convenient light source, things like lighting up LEDs and charging cellphones or sensors, that kind of stuff,” Fan says. For many without access to the electrical grid, that would be a big improvement in their quality of life.

Another added bonus is that the energy collected from radiative cooling can boost a PV cell’s efficiency during the day, Fan and his team discovered. “During the daytime, when you use a solar panel, [the new PV cell] augmented the power generation of solar cells,” Fan said.

The researchers do have some hurdles up ahead in making their new PV cell more energy efficient and cost-effective. But Fan is hopeful that one day his team’s device could offer a source of electricity for people in developing countries and anywhere else reliable energy is hard to come by, especially at night.

The Takeaway

Don’t write this discovery off. Today’s solar panels use only a tiny portion of the electromagnetic spectrum. If research like this can find ways to use more of it to produce clean renewable energy, that would be a major win for the Earth.


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