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September 13, 2019 02:10 am

New Device Harvests Energy In Darkness

In new research published on Thursday in the journal Joule, Dr. Raman, an electrical engineer at the University of California, Los Angeles, demonstrated a way to harness a dark night sky to power a light bulb. The New York Times reports: 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 prototype built by Dr. Raman resembles a hockey puck set inside a chafing dish. The puck is a polystyrene disk coated in black paint and covered with a wind shield. At its heart is an off-the shelf gadget called a thermoelectric generator, which uses the difference in temperature between opposite sides of the device to generate a current. A similar device powers NASA's Curiosity rover on Mars; its thermoelectric generator derives heat from plutonium radiation. Usually, the temperature difference in these generators is stark, and they are carefully engineered to separate hot and cold. Dr. Raman's device instead uses the atmosphere's ambient temperature as the heat source. The shift from warm to cool is very slight, meaning the device can't produce much power. 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.

Read more of this story at Slashdot.


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