Originally published October 29, 2019.

A “thermoelectric generator” is what scientists are calling it.

This new device is a similar technology to a solar panel, but it doesn’t channel energy from the sun. It harnesses energy from the night sky through a process called radiative cooling.

If you’ve ever gone outside on an early morning and noticed frost or dew on the grass, then you’ve witnessed radiative cooling. This occurs when the ground, still warm from the sun’s energy, emits heat back into the atmosphere, which makes the ground cooler than the air surrounding it.

Researchers at Stanford and UCLA, Aaswath Raman, Wei Li and Shanhui Fan have recently developed a prototype of the device that has generated enough electricity to power a small LED light bulb. A larger version of this technology may light up an entire room or even charge a cellphone.

But how does it work?

The technology behind this device is far from new. The concept was developed over 200 years ago. A thermoelectric generator uses temperature differences between two metal disks to generate electricity.

The prototype device was tested by researchers on a rooftop in Stanford, California under a frigid night sky. The device, made of polystyrene and reflective mylar is placed underneath a wind cover. Then, with the help of a black emitter, researchers had the device attract heat from the surrounding atmosphere and emit it back out into the atmosphere again.

Afterwards, the researchers measured the amount of power output over a span of six hours, and found that it generated about 25 milliwatts of energy per square meters, enough to power a small night light.

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In a statement released on Sept.12, 2019, researchers say that the device is fairly inexpensive and can be scaled for practical use.

Aaswath Raman, lead author of the research said, “Our work highlights the many remaining opportunities for energy by taking advantage of the cold of outer space as a renewable energy resource. We think this forms the basis of a complementary technology to solar. While the power output will always be substantially lower, it can operate at hours when solar cells cannot.”

Thermoelectric devices could play an important role in how we employ renewable energy someday. The device has the potential to be mass-produced at a low cost if its technology is refined. For example, manufacturers can change the coating of the disks to reach an even lower temperature than the surrounding atmosphere at night, leading to an even greater temperature difference that will raise the power output

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This new technology shows that science is moving in the right direction to solve energy problems on a global scale. Thermoelectric energy may not be solar energy’s other half, but with the right advancements, it could be a clean energy alternative.