Atop the Grocery Outlet located in Stockton, California, eight rows of neatly arranged rectangles sit shimmering under the bright sunlight. They may look like solar panels or mirrors, but the 32 rectangles have a job quite different than either of those two items. The rectangles protect this business from overheating.
Facing directly into the sun, the panels amazingly do not absorb the extreme heat beating down from above. Instead, they are actually sending some of it back into space. By doing so, they are helping to improve the performance of systems that are keeping things inside the business cold. The phenomenon allowing such a feat is known as radiative cooling.
Things on the earth all emit varying degrees of heat through infrared rays that invisibly rise skyward. After the sun goes down each day, this absence of sunlight surprisingly produces an environment that creates enough chill to even form ice. As an example, remember that a vehicle’s windshield can frost over whether or not the temperature has dropped below freezing. This is radiative cooling.
According to Aaswath Raman, a building’s roof, a person’s skin, and the ground around us are all cooling by releasing their heat upward. Mr. Raman works at the University of California at Los Angeles as a professor of materials science and engineering. He is among the masterminds behind the shiny tiles being used at Grocery Outlet, and he helped to found SkyCool Systems while attempting to upend the traditional technology used to create chill.
In our thirst for more and more refrigeration and air conditioning, current systems generate excessive heat themselves, and chemical compounds are released into the atmosphere. In the United Kingdom, Birmingham Energy Institute has estimated that approximately 11 percent of the globe’s 2018 greenhouse gas emissions were produced from these sources.
Estimates for the year 2050 say that 1.6 billion refrigerators and over 4.5 billion air conditioners will be consuming around 40 percent of the electricity produced. If SkyCool’s technology goes mainstream, and if other researchers and competitors succeed, the natural ability to lower a building’s temperature could drastically help to slow down the cycle and ease the burden on conventional energy methods.
After the rows of shiny panels were installed on Grocery Outlet’s 25,000-square-foot facility during the second half of 2019, a remarkable 15 percent drop in energy use was noted. The savings generated by this ease on the refrigeration system has saved the store nearly $6,000 yearly.
Of course, for radiative cooling to work on a wide scale, it would need to have affordable manufacturing and installation costs. The setup atop the supermarket’s building was financed through Lime Energy, a company that does retrofits and upgrades for boosting efficiency. If installation costs can pay for themselves in a short period of time, radiative cooling could quickly become a primary way to save power while reducing emissions.
The U.S. Department of Energy funded the early research done by Raman. Chris Atkinson was formerly the program director at the DOE’s Advanced Research Projects Agency-Energy. He stated, “I was somewhat skeptical that you could gain this significant amount of cooling even under direct sun.” Continuing, he further revealed, “But once it was explained to me, it sounded plausible, and the results are remarkably compelling.”
During the decades of 1970 and 1980, physicists and architects pondered the possibility of radiative cooling during daylight hours, but they remained very skeptical. Some tried putting water pools on rooftops. However, these structures attracted too much heat from the sun and were terribly difficult to maintain.
With nanotechnology at Raman’s disposal, he was able to use the ability to arrange atoms and molecules as needed in order to successfully develop the material now used by SkyCool Systems. A Stanford professor of physics and electrical engineering, Shanhui Fan, helped aid and guide Raman’s research and development. The thin film that was created in less than one year was finely tuned to radiate infrared rays within a narrow range that will escape into space. Additionally, 97 percent of sunbeams that hit the material are reflected. Per Raman, “It’s actually sending more heat out to the sky than the sky as a whole sends back.”
