It May Soon Be Possible To Generate Clean Energy From The Darkness Of The Night Sky

Aaswath Raman still recalls growing up and visiting his grandparents in Mumbai, India, where the daily temperature often reaches 100 degrees Fahrenheit and the humidity is stifling.

But what Raman recalls most is how hot the house his grandparents lived in was during the day, especially since they refused to buy an air conditioner:

“It’s not unusually different from Miami, I suppose — just a bit challenging without air conditioning.”

Years later, when he became a scientist, Raman would harken back to those visits to his grandparents, which eventually led him to learn more about a process known as “radiative cooling,” which EcoWatch defines as “when objects facing up shed heat into the sky after dark, cooling the surrounding area.”

As it turns out, the idea of radiative cooling has been around for centuries:

“Ancient Middle Eastern civilizations–especially the Persians–used radiative cooling to make ice, pouring water into a pool as the sun set, collecting the frozen chunks the next morning. Even though the ambient temperature stayed above freezing, the pool would grow more cold than the surrounding air as the water radiated heat into the sky. During the day, heat from the sun would have kept the water warm, but at night, it grew colder and colder until it froze over.”

If it worked in Persia, Raman speculated, it should work in modern times, too.

Raman, an assistant professor of materials science at engineering at UCLA, began speculating that perhaps it was possible to take advantage of radiative cooling and produce a device that would create clean energy. So he and some of his colleagues designed one that does exactly that:

“For now, the device is too costly and generates too little electricity to compete with other forms of clean energy. To power a 3-watt LED lightbulb, the generator would need to be 1300 square feet. Raman said he believes scientists could get that number down 60 square feet, and they could also lower costs enough to make it useful in remote areas disconnected from the power grid. A future iteration of the device could allow people without access to electricity to turn on a lightbulb, charge a cell phone, or power some other small device at night.”

The professor says there are many uses for radiative cooling:

“There are also low-power sensors: think monitoring oil pipelines, or weather and climate monitoring in the Arctic. The combination of remoteness and low-power needs make them a great fit for this device, especially in polar, northern regions where you have limited or no sunlight for a large fraction of the year.”

The device itself looks modest, and is simple to create:

“It looks like a small disc propped up on four legs. The side facing up radiates heat into the night sky, while the side facing down is warmed by the surrounding air. Sandwiched in between these two surfaces is a thermoelectric generator, which uses the difference in temperature to produce power.”

Another advocate for using radiative cooling to produce clean energy is Jeremy N. Munday, professor of electrical and computer engineering at the University of California Davis, who notes:

“This is an excellent demonstration of how the night sky can be used as a thermodynamic resource to do something useful.”

One of the main breakthroughs in the field of radiative cooling has been the creation of metamaterials — super thin, hair-like materials — that Raman and his colleagues perfected during their research. Those metamaterials work like a mirror, reflecting the sun and its heat back into the sky during the daytime and removing the heat.

And to think, all of this began because Professor Raman decided to look at a problem and consider a solution that drew on ideas that have been around for years. As Raman remarks:

“It always seemed like such a mature and well-developed field. Was there anything we could do to make it better? Turns out, yes!”

Featured Image Via Flickr



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Andrew Bradford

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