The modern view, as demonstrated everywhere California supermarket rooftops To Japan’s Expo 2025 pavilionGo even further. Generally, if the sun is up and exerting heat, surfaces cannot be cooler than the ambient temperature. But in 2014, Raman and his colleagues obtained daytime radiative cooling. They adapted photonic films to absorb and then radiate heat at infrared wavelengths between eight and 13 micrometres-A range of electromagnetic wavelengths is called the “atmospheric window” because that radiation escapes into space rather than being absorbed. Those films can dissipate heat even under full sun, allowing the temperature inside the building to be up to 9 degrees Fahrenheit cooler than ambient temperature, with no AC or energy source required.
That was a proof of concept; Today, Raman says, the industry has mostly moved away from advanced photonics that use the atmospheric-window effect to simple sunlight-scattering materials. Ceramic cool roofs, nanostructured coatings, and reflective polymers all offer the possibility of bending more sunlight into wavelengths, and they are more durable and scalable.
Now the race is on. like startup skycool, planck energy, spacecoolAnd i2cool Commercial manufacturers are competing to make and sell coatings that reflect at least 94% of sunlight in most climates, and more than 97% in humid tropical climates. pilot project are already Provided significant cooling to residential buildings, reducing AC energy requirements by 15% to 20% in some cases.
The idea could go far beyond reflective roofs and roads. Researchers are developing reflective clothing that can be worn by people most at risk of heat exposure. “It’s personalized thermal management,” says Gan. “We can realize passive cooling in T-shirts, sportswear and apparel.”
Courtesy of Skycool Systems
Of course, these techniques and materials have limitations. Like solar power grids, they are sensitive to weather. Clouds block reflected sunlight from bouncing into space. Dust and air pollution cause the shiny surface of materials to become dull. Many coatings lose their reflectivity after a few years. And the cheapest and harshest materials used in radiation cooling rely on Teflon and other fluoropolymers, “forever chemicals” that do not biodegrade, posing environmental risks. “They are best-in-class products that hold up outdoors,” says Raman. “So for long-term scale-up, can you do it without those fluoropolymer-like materials and still maintain durability and get to this lower cost point?”
Like any other solution to climate change problems, one size will not fit all. “We can’t be overoptimistic and say that radiative cooling can meet all of our future needs,” says Gan. “We still need more efficient active air conditioning.” Glossy ceiling is not a panacea, but it is still good enough.
Becky Ferreira is a New York-based science reporter and author First Contact: The story of our obsession with aliens,
