Engineers develop solar panels that can produce electricity at night with no need for batteries 

Solar panels are an excellent alternative to traditional energy sources, but they come with a pitfall—they can only generate electricity during the day. A new development by Stanford engineers aims to solve this problem.

Researchers came up with a breakthrough solar panel that can serve as a “continuous renewable power source for both day- and nighttime,” according to the study recently published in the Applied Physics Letters journal.

The device can generate enough power to charge a phone or run an LED light even at night.

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Every solar panel has a set of solar cells made from layers of semi-conducting material. When the sun radiates energy toward one, it creates a flow of electricity, and solar energy is harvested.

Since traditional solar panels only produce power during the day, many rural areas that rely on solar off-grid systems need to install battery storage to collect energy during the daytime and store it to have enough at night. However, these batteries can be expensive.

Luckily, there may be a better and cheaper alternative.

solar panels on a roof
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When the sun is out, solar panels radiate heat to outer space with a temperature of around -270.15ºC while heat travels toward lower temperatures. This makes the solar panel cooler than the night air, and researchers speculate that this temperature difference can be used to produce solar power.

The device uses a thermoelectric generator, which can pull electricity from this slight difference in temperature between the cell and the air. This process depends on the system’s thermal design, which has a hot and cold side.

Nighttime power generation from radiative cooling of a PV cell.  (a) Schematic showing the energy balance of the PV cell and (b) thermal circuit model of the PV-TEG device.
Applied Physics Letters

“You want the thermoelectric to have very good contact with both the cold side, which is the solar cell, and the hot side, which is the ambient environment,” explained author Sid Assawaworrarit. “If you don’t have that, you’re not going to get much power out of it.”

The setup is cheap and could be incorporated into existing solar cells. In fact, the thermoelectric itself is the most expensive component in the system. It is also simple, so it is feasible to build them in remote locations with limited resources.

“Our approach can provide nighttime standby lighting and power in off-grid and mini-grid applications, where [solar] cell installations are gaining popularity,” said the study.

Mini-grid applications refer to independent electricity networks that can be used when a population is too small or far away to extend the grid.

Design and prototype of a PV-TEG device.  (a) Design drawing and (b) prototype constructed.
Applied Physics Letters

Using electricity at night for lighting requires only a few watts of power. The current device produces 50 milliwatts per square meter, which means lighting would need about 20 square meters of photovoltaic area.

“None of these components were specifically engineered for this purpose,” said author Shanhui Fan. “So, I think there’s room for improvement, in the sense that, if one really engineered each of these components for our purpose, I think the performance could be better.”

The researchers aim to improve the thermoelectric components and thermal insulation of the device. They are looking into engineering developments in the solar cell to enhance its radiative cooling performance without affecting its solar energy harvesting capability.

solar cells
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Recently, the price of solar energy has declined, making it more accessible to the public. Some companies have used solar energy, and California has even incentivized shifting to solar.

As the war persists in Ukraine, investing in alternative energy is necessary.

“In the face of global supply uncertainty, we must ramp up clean energy production and eliminate our reliance on hostile nations for our energy needs,” Abigail Ross Hopper, president and CEO of Solar Energy Industries Association, told CNBC.

With an estimated 770 million people around the world without electricity, these new solar cells could be a real game-changer.

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