Tatsat Chronicle Magazine

Scientists Find A New Way to Harvest Clean Solar Energy, Even at Night

The invention could potentially provide power to some of the 750 million people who lack access to electricity at night.
April 6, 2022
Solar Energy

Researchers at Stanford University have designed a photovoltaic cell that eliminates the need for batteries and collects energy from the environment during both the day and night. The device uses heat that leaks back from Earth to space. The researchers claim that the energy has the same levels as incoming solar radiation which is the primary source of solar. The latest invention could potentially provide power to some of the 750 million people who lack access to electricity at night.

At night, solar cells radiate and lose heat toward the sky, reaching temperatures a few degrees lower than the surrounding air. The device which is under development uses a thermoelectric module to generate voltage and current from the temperature gradient between the cell and the air. This process depends on the thermal design of the system, consisting of a hot side and a cold side.

“A large fraction of the world’s population lacks access to the electric grid. Standard photovoltaic (PV) cells can provide a renewable off-grid source of electricity but only produce power from daytime solar irradiance and do not produce power at night,” wrote the study authors.

“While there have been several theoretical proposals and experimental demonstrations of energy harvesting from the radiative cooling of a PV cell at night, the achieved power density is very low. Here, we construct a device, which incorporates a thermoelectric generator that harvests electricity from the temperature difference between the PV cell and the ambient surrounding.”

During the day, the system operates in a reverse mode which contributes additional power to the conventional solar cell. The experts report that their device is inexpensive and could theoretically be incorporated within existing solar cells.

Lighting requires a few watts of electricity for night use. Current equipment generates 50 milliwatts per square meter, which means a photovoltaic area of ​​about 20 square meters is required for the lighting system.

“None of these elements was specifically designed for this purpose,” says author Shanhui Fan. “So I think there’s room for improvement, in the sense that if anyone designs each of these components for our use, I think performance could be better.”

The team’s goal is to optimize the device’s thermal insulation and thermoelectric components. They are exploring technological advances in solar cells to improve radiation cooling efficiency without affecting solar energy collection efficiency.