Transformative? New Device Harvests Energy in Darkness

Aaswath Raman was driving by way of a village in Sierra Leone in 2013 when an thought got here to him as all of a sudden as, maybe, a gentle bulb switching on.

The village was not geared up with electrical energy, and Dr. Raman, engineer at the University of California, Los Angeles, was unaware he was in a village till he heard the voices of shadowed human figures.

“It took us about five minutes to realize we were passing through a town, because it was completely dark,” Dr. Raman mentioned. “There wasn’t a single light on.”

Dr. Raman puzzled whether or not he may use all that darkness to make one thing to gentle it up, not in contrast to the way in which that photo voltaic panels generate electrical energy from the solar’s warmth and lightweight.

He did. In new analysis printed on Thursday in the journal Joule, Dr. Raman demonstrated a way to harness a dark night sky to power a light bulb.

His prototype device employs radiative cooling, the phenomenon that makes buildings and parks feel cooler than the surrounding air after sunset. As Dr. Raman’s device releases heat, it does so unevenly, the top side cooling more than the bottom. It then converts the difference in heat into electricity. In the paper, Dr. Raman described how the device, when connected to a voltage converter, was able to power a white LED.

“The core enabling feature of this device is that it can cool down,” Dr. Raman said.

Jeffrey C. Grossman, a materials scientist at the Massachusetts Institute of Technology who studies passive cooling and solar technology, said the work was “quite exciting” and showed promise for the development of low-power applications at night.

“They have suggested reasonable paths for increasing the performance of their device,” Dr. Grossman said. “But there is definitely a long way to go if they want to use it as an alternative to adding battery storage for solar cells.”

Everything emits heat, according to the laws of thermodynamics. At night, when one side of Earth turns away from the sun, its buildings, streets and jacket-less people cool off. If no clouds are present to trap warmth, objects on the Earth can lose so much heat that they reach a lower temperature than the air surrounding them. This is why blades of grass may be glazed in frost on clear fall mornings, even when the air temperature is above freezing. The cloudless atmosphere becomes a porthole to the void, through which warmth flows like air through a porch screen.

His puck-in-a-dish is elevated on aluminum legs, enabling air to flow around it. As the dark puck loses warmth to the night sky, the side facing the stars grows colder than the side facing the air-warmed tabletop. This slight difference in temperature generates a flow of electricity.

When paired with a voltage converter, the prototype produced 25 milliwatts of power per square meter. That is about three orders of magnitude lower than what a typical solar panel produces, and well short of even the roughly 4-watt maximum efficiency for such devices. Still, several experts said the prototype was an important contribution to a new and relatively unusual space in the renewable energy sector.

“I figured the amount of electricity we could get would be pretty small, and it was,” he said. “But walking around in Sierra Leone, I realized lighting remains a big problem, so it’s an opportunity as well.”

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