New solar panels can generate electricity at night

A team of engineers from Stanford University has created a solar cell that generates electricity at night by exploiting the temperature differences between the cell and the air. Photovoltaic systems capable of harvesting energy in the dark could reduce the need for batteries that store electricity produced during the day, which could lead to better access to electricity for rural communities around the world.

Although solar cells have become more efficient and affordable over the past two decades, the technology still suffers from the obvious limitation of not being able to harvest energy from the sun after it has set. But there is another natural phenomenon that solar cell systems could exploit to generate power: radiative cooling.

Radiative cooling is the process by which objects lose heat through thermal radiation. At night, solar cells (and other objects on Earth) radiate heat to space, causing the solar cells to become slightly cooler than the air around them.

In an article published in Applied Physics Letters, the Stanford team described how they built a low-cost system that uses a thermoelectric generator to convert these slight temperature differences into electricity, a process described by the Seebeck effect. The configuration essentially reverses how the solar cells operate during the day, as Jeremy Munday, a professor in the Department of Electrical and Computer Engineering at UC Davis, told UC Davis News in 2020.

“A regular solar cell generates power by absorbing sunlight, which causes a voltage to appear across the device and current to flow,” Munday said.

“In these new devices, light is instead emitted and current and voltage go in the opposite direction, but you’re still generating power. You have to use different materials, but the physics are the same.

The new system can generate 50 milliwatts per square meter on a clear night. This output represents a significant improvement over similar previous systems, although the new configuration would still require around 20 square meters of solar cells to power conventional lamps. But given that the system was built with off-the-shelf components, it is likely that the incorporation of purpose-built parts would increase power generation.

Design and prototype of a PV-TEG device. (a) Design drawing and (b) constructed prototype. (Credit: Assawaworrarit et al., Applied Physics Letters, 2022)

Expand access to electricity

About 770 million people currently live without reliable access to electricity, mostly in Asia and Africa, according to the International Energy Agency. And while the costs of installing and operating renewables like solar have come down over the past decade, it’s still generally cheaper to build new fossil fuel power plants than new energy infrastructure. renewable, especially in developing countries. The purchase of batteries to store the energy produced by solar energy further increases these costs.

Finding affordable ways to extend the harvest time of solar cells could make solar power a more viable option for people who live far from major grids.

“In many rural areas dependent on mini-grids or off-grid systems, providing electricity overnight often requires a significant additional battery storage facility, which adds significant complexities to the system,” the authors wrote. . “Our approach can provide nighttime emergency lighting and power in off-grid and mini-grid applications, where [solar] cellular installations are growing in popularity.

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