Solar cells that work at night-time, doesn’t it sounds amazing? According to Jeremy Munday, professor in the Electrical and Computer Engineering Department at UC Davis, this is no farce.
In reality, according to a concept paper by Munday and graduate student Tristan Deppe, a specially designed photovoltaic cell could generate up to 50 watts of power per square meter under ideal conditions at night, which is about a quarter of what a traditional solar panel would produce during the daytime. Said article was published in the January 2020 issue of ACS Photonics, and featured on its cover.
Munday is designing prototypes of these night-time solar cells that can generate limited amounts of power. The experts hope to improve the devices ‘ power output and performance.
The process is similar to the workings of a regular solar cell, but in reverse, says Munday. An object that is hot in contrast with its surroundings radiates heat as infrared light. Compared to the sun a traditional solar cell is cool, so it absorbs light.
If you have a warm body and you point it to the sky, it’s going to radiate heat as space is by-default really cold. For centuries, people have been using that phenomenon for night-time cooling. Over the last five years, there has been a lot of interest over devices that can do it during the day (by filtering out sunlight or pointing away from the sun), added Munday.
Power generation by radiating heat?
Thermoradiative cell, another type of device that generates power by radiating heat to its surroundings is being researched over how to absorb waste heat from engines using them.
“We thought, what if we were to take one of these devices and put it in a warm area and directed to the sky”, says Murphy.
The thermoradiatic cell pointing to the night sky will emit infrared light, as it’s warmer than outer-space.
A typical solar cell produces energy by absorbing sunlight, which allows a voltage to appear across the device allowing current to flow. Alternatively, light is emitted in these new devices, and the current and voltage flow in the opposite direction, but you still generate energy. “One has to use different materials but the physics is the same. If you took steps to either block direct sunlight or point it out away from the sun, the device will operate during the day as well. Given that this new type of solar cell could potentially operate around the clock, balancing the power grid over the day-night cycle is a fascinating option” according to Munday.