‘Inverted’ solar panel can generate power even at night, experts say

Conventional solar technology absorbs light rays from the sun to increase voltage. As strange as it may seem, some materials are able to work in the opposite direction, that is, to generate energy by radiating heat back into the cold night sky. A team of engineers in Australia have already successfully demonstrated the theory in action, using the same kind of technology found in night vision goggles to generate power.

So far, the prototype generates only a small amount of energy and is unlikely to become a competitive source of renewable energy on its own – but in conjunction with existing photovoltaic technology, it can harness the small amount of energy provided by solar cells cooling after sunset.

“Photovoltaics, the direct conversion of sunlight into electricity, is an artificial process that humans have developed to convert solar energy into energy,” said Phoebe Pearce, a physicist at the University of New South Wales. . “In this sense, the thermoradiative process is similar; we divert energy flowing in the infrared from a warm Earth to the cold Universe.

By making atoms in any material swing with heat, you force its electrons to generate waves of low-energy electromagnetic radiation in the form of infrared light. As dull as this movement of electrons may be, it still has the potential to trigger a slow electrical current – all it takes is a one-way electron traffic signal called a diode.

Made up of the right combination of elements, a diode can mix electrons slowly losing its heat to a cooler environment. In this case, the diode is made of mercury cadmium telluride (MCT). Already used in devices that detect infrared light, the ability of MCT to absorb mid- and long-range infrared light and turn it into current is well understood.

However, the ability to be used effectively as a true power source is still unclear. When heated to around 20 degrees Celsius, one of the tested MCT photovoltaic detectors generated a power density of 2.26 milliwatts per square meter – a value that is not enough to heat water for coffee. You would probably need MCT panels covering a few blocks to accomplish this small task. But it is still in its infancy and there is potential for this technology to grow in the future. “Right now, the demonstration we have with the thermoradiative diode is of relatively very low power. One of the challenges was actually detecting it,” said lead researcher of the study, published in ACS Photonics, Ned Ekins-Daukes. “But the theory says it’s possible that this technology could produce about 1/10th the energy of a solar cell.”

With this kind of efficiency, it might be worth integrating MCT diodes into more typical photovoltaic arrays so that they continue to charge their batteries long after the sun goes down. “In the future, this technology could potentially harness that energy and eliminate the need for batteries in some devices — or help charge them,” Ekins-Daukes said.

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