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Universe Conspires to Keep Us Cool with Photonics

Cool researchers from Stanford University Zhu, Fan and Raman
Cool researchers from Stanford University Zhu, Fan and Raman

Every cloud has a silver lining, or so they say. So these researchers from Stanford University took a cue from that and tried to make a paint to help keep buildings cool with photonics radiative cooling.

Say what? It’s basically a mirror that reflects heat from the sun away from buildings. But it doesn’t stop there, it actually takes the heat from INSIDE the buildings and sends it off into outer space. Professor Shanhui Fan and research associate Aaswath Raman published this energy-saving idea in the journal Nature.

“This is very novel and an extraordinarily simple idea,” according to Eli Yablonovitch, a photonics pioneer who teaches at UC Berkeley. “As a result of professor Fan’s work, we can now [use radiative cooling], not only at night but counter-intuitively in the daytime as well.”

This is made possible because the material is a highly efficient mirror, reflecting back 97 percent of sunlight into outer space, much like what clouds do. Also, it allows infrared light from under to pass through to the dark reaches of space as well. It’s a multilayered material that’s thinner than aluminum foil at 1.8 microns. It consists of seven layers of hafnium oxide and silicon dioxide atop a lining of silver. The material is engineered in order to reflect some light while allowing infrared light to pass through.

By applying this material on a surface, one can bring down the internal temperature of a building 9 degrees Fahrenheit (5 degrees Celsius) cooler than the ambient temperature.

The technology will some day be able to reduce energy use in the US by trebling the use of the A/C. In the US, up to 15 percent of the energy used in buildings goes to air conditioning. With things heating up, thanks to global warming, this idea is a breakthrough because it keeps us cool passively. Meaning, you don’t need energy, which mostly comes from fossil fuel burning, to keep you cool.

The team is now trying to overcome some technical hurdles so that the day of photonics radiative cooling comes out of the lab and onto your roof. First is in how to bring on the heat – from inside the building, that is, out to the coating. Second is how to produce the material in panels large enough to cover roofs from its current incarnation, which is as big as a personal pan pizza.

In the meantime, we can look to the stars for inspiration. Just as the sun provides an unlimited source of renewable energy with solar power, the universe provides an unlimited cache to which we can dump heat and cool down.

Now, that’s a cool idea, isn’t it?

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