Jan 30 2020
According to Jeremy Munday, a professor in the Department of Electrical and Computer Engineering at UC Davis, solar cells can function at night.
A conventional photovoltaic or solar cell (left) absorbs photons of light from the sun and generates an electrical current. A thermoradiative cell (right) generates electrical current as it radiates infrared light (heat) toward the extreme cold of deep space. UC Davis engineers propose that such cells could generate a significant amount of energy and help balance the power grid over the day-night cycle. Image Credit: Tristan Deppe/Jeremy Munday.
According to a concept article, published in and featured on the cover of the January 2020 issue of ACS Photonics, by Munday and Tristan Deppe (graduate student), an exclusively designed photovoltaic cell is indeed capable of producing up to 50 W/m2 under perfect conditions at night, which is about a quarter of what a typical solar panel can produce in the daytime.
Munday, who newly joined UC Davis from the University of Maryland, is involved in the development of prototypes of such nighttime solar cells that has the ability to produce low energy. It is hoped by the scientists that the efficiency and power output of the devices could be enhanced.
According to Munday, the process is the same as working of the normal solar cell but in other way round. An object hotter than its environment will radiate heat as infrared light. A traditional solar cell is cooler when compared to the sun; therefore, it tends to absorb light.
Space is very, very cold. Hence, when a warm object is pointed at the sky, heat from the object will be radiated toward it. Earlier, this phenomenon has been used by people for nighttime cooling. In the last 5 years, Munday stated, there has been a great interest in devices that are capable of performing this in the daytime (by pointing away from the sun or filtering out sunlight).
Generating Power by Radiating Heat
Thermoradiative cell is another type of device that can produce electricity by radiating heat to its environment. Scientists have explored using such a cell to absorb waste heat from engines.
“We were thinking, what if we took one of these devices and put it in a warm area and pointed it at the sky,” stated Munday.
When such a thermoradiative cell is pointed at the night sky, it would release infrared light since it is warmer than outer space.
A regular solar cell generates power by absorbing sunlight, which causes a voltage to appear across the device and for current to flow. In these new devices, light is instead emitted and the current and voltage go in the opposite direction, but you still generate power.
Jeremy Munday, Professor, Department of Electrical and Computer Engineering, UC Davis
Munday continued, “You have to use different materials, but the physics is the same.”
This can also work during the daytime, if direct sunlight is blocked or it is pointed away from the sun. This new kind of solar cell is an interesting alternative to balance the power grid over the day-night cycle due to its ability to work day and night.