Device generates light from the cold night sky

September 12, 2019

An inexpensive thermoelectric device harnesses the cold of space without active heat input, generating electricity that powers an LED at night, researchers report September 12 in the journal Joule.

"Remarkably, the device is able to generate electricity at night, when solar cells don't work," says lead author Aaswath Raman (@aaraman), an assistant professor of materials science and engineering at the University of California, Los Angeles. "Beyond lighting, we believe this could be a broadly enabling approach to power generation suitable for remote locations, and anywhere where power generation at night is needed."

While solar cells are an efficient source of renewable energy during the day, there is currently no similar renewable approach to generating power at night. Solar lights can be outfitted with batteries to store energy produced in daylight hours for night-time use, but the addition drives up costs.

The device developed by Raman and Stanford University scientists Wei Li and Shanhui Fan sidesteps the limitations of solar power by taking advantage of radiative cooling, in which a sky-facing surface passes its heat to the atmosphere as thermal radiation, losing some heat to space and reaching a cooler temperature than the surrounding air. This phenomenon explains how frost forms on grass during above-freezing nights, and the same principle can be used to generate electricity, harnessing temperature differences to produce renewable electricity at night, when lighting demand peaks.

Raman and colleagues tested their low-cost thermoelectric generator on a rooftop in Stanford, California, under a clear December sky. The device, which consists of a polystyrene enclosure covered in aluminized mylar to minimize thermal radiation and protected by an infrared-transparent wind cover, sat on a table one meter above roof level, drawing heat from the surrounding air and releasing it into the night sky through a simple black emitter. When the thermoelectric module was connected to a voltage boost convertor and a white LED, the researchers observed that it passively powered the light. They further measured its power output over six hours, finding that it generated as much as 25 milliwatts of energy per square meter.

Since the radiative cooler consists of a simple aluminum disk coated in paint, and all other components can be purchased off the shelf, Raman and the team believe the device can be easily scaled for practical use. The amount of electricity it generates per unit area remains relatively small, limiting its widespread applications for now, but the researchers predict it can be made twenty times more powerful with improved engineering--such as by suppressing heat gain in the radiative cooling component to increase heat-exchange efficiency--and operation in a hotter, drier climate.

"Our work highlights the many remaining opportunities for energy by taking advantage of the cold of outer space as a renewable energy resource," says Raman. "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."
This work is supported by the U.S. Department of Energy, as well as by the Mellon Family Foundation.

Joule, Raman et al.: "Generating Light from Darkness"

Joule (@Joule_CP) published monthly by Cell Press, is a new home for outstanding and insightful research, analysis and ideas addressing the need for more sustainable energy. A sister journal to Cell, Joule spans all scales of energy research, from fundamental laboratory research into energy conversion and storage up to impactful analysis at the global level. Visit: To receive Cell Press media alerts, contact

Cell Press

Related Solar Cells Articles from Brightsurf:

Solar cells of the future
Organic solar cells are cheaper to produce and more flexible than their counterparts made of crystalline silicon, but do not offer the same level of efficiency or stability.

A blast of gas for better solar cells
Treating silicon with carbon dioxide gas in plasma processing brings simplicity and control to a key step for making solar cells.

Record efficiency for printed solar cells
A new study reports the highest efficiency ever recorded for full roll-to-roll printed perovskite solar cells.

Next gen solar cells perform better when there's a camera around
A literal ''trick of the light'' can detect imperfections in next-gen solar cells, boosting their efficiency to match that of existing silicon-based versions, researchers have found.

On the trail of organic solar cells' efficiency
Scientists at TU Dresden and Hasselt University in Belgium investigated the physical causes that limit the efficiency of novel solar cells based on organic molecular materials.

Exciting tweaks for organic solar cells
A molecular tweak has improved organic solar cell performance, bringing us closer to cheaper, efficient, and more easily manufactured photovoltaics.

For cheaper solar cells, thinner really is better
Researchers at MIT and at the National Renewable Energy Laboratory (NREL) have outlined a pathway to slashing costs further, this time by slimming down the silicon cells themselves.

Flexible thinking on silicon solar cells
Combining silicon with a highly elastic polymer backing produces solar cells that have record-breaking stretchability and high efficiency.

Perovskite solar cells get an upgrade
Rice University materials scientists find inorganic compounds quench defects in perovskite-based solar cells and expand their tolerance of light, humidity and heat.

Can solar technology kill cancer cells?
Michigan State University scientists have revealed a new way to detect and attack cancer cells using technology traditionally reserved for solar power.

Read More: Solar Cells News and Solar Cells Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to