The Reason Photovoltaic Solar Panels Can Now Work At Night

The increased productivity will make solar energy even more financially and operationally competitive. JL

Luke Dormehl reports in Digital Trends:

While this would only be around a quarter of what a regular solar panel is able to generate during daytime, that would nonetheless be a quarter more power than is currently generated at night. If you take a warmer object and point it someplace cold it will radiate heat toward it in the form of infrared light. Researchers have been directing their solar cells at the sky, where it will radiate infrared light because it is warmer than outer space.

For obvious reasons, today’s sun-powered solar cells don’t work at night. But researchers from the University of California, Davis believe that they may have come up with a solution. And it’s one that would allow specially designed photovoltaic cells to keep generating power even when it’s dark. While this would only be around a quarter of what a regular solar panel is able to generate during daytime, that would nonetheless be a quarter more power than is currently generated at night.

The approach works a bit like a regular solar cell in reverse. A conventional solar cell is cool compared to the sun, so it absorbs light. But if you take a warmer object and point it someplace cold it will radiate heat toward it in the form of infrared light. That’s what the UC Davis researchers have been doing, directing their solar cells at the sky, where it will radiate infrared light because it is warmer than outer space. Due to some smart physics and a device called a thermoradiative cell which generates power by radiating heat, they believe they may have come up with a breakthrough type of solar cell.

“As you know, in many places solar cells work great for about eight hours per day, but after the sun goes down we need other power sources or storage,” Jeremy Munday, professor in the Department of Electrical and Computer Engineering at UC Davis, told Digital Trends. “That is where this concept comes in. I like to think about solar cells as being kind of like heat engines without the moving parts. You take a semiconductor that is doped in a particular way, and you put it between a hot object and a cold object. For a normal solar cell, the hot object is the sun and the Earth is the cold object. For our devices, the Earth becomes the ‘hot’ object and deep space, with a temperature of 3 K (negative 454.27 Fahrenheit), becomes the cold object.”

In their latest piece of research, the investigators explore the theoretical and practical limits of such devices. In the lab, meanwhile, they have developed prototypes, although Munday says there’s still much to be done before they can be used to generate a significant amount of power. “So far, it is just proof-of-principle,” he noted.

Should all go according to plan, it will be possible to build solar cells which can be used to produce power during both the day and the night. These could be used on their own or in conjunction with traditional photovoltaics.

A paper describing the work, titled “Nighttime Photovoltaic Cells: Electrical Power Generation by Optically Coupling with Deep Space,” was recently published in the journal ACS Photonics.