Cooling the environment without electricity

Scientists at the University of Colorado Boulder (USA) have invented a metal membrane that can cool the surrounding environment without using electricity.

Composed of transparent microspheres, polymers, and silver, the material uses passive radiative cooling to dissipate heat from the object it encases. The film is capable of rejecting energy such as infrared radiation as well as reflecting sunlight.

While nighttime radiative cooling materials, including pigmented paints, have proven successful, daytime applications present challenges. The problem arises when such materials absorb sunlight, quickly exceeding the cooling power and burning the target surface.

This prompted researchers to create a material that both reflects sunlight and allows the emission of infrared rays.

Cooling membranes can be pressed in roll form, allowing for mass production.

They created a flexible thin film with two layers: a transparent polymer layer containing randomly dispersed 8-micrometer diameter silicon-dioxide (SiO2) microspheres and a 200-nanometer thick silver coating.

The randomly distributed polymer film is transparent to the solar spectrum but can radiate infrared rays, said Ronggui Yang, the author of the work. The collective resonance of the microspheres ensures that the film is effective in radiating infrared rays. At the same time, sunlight can pass through the material and be reflected back through the silver coating, preventing heating.

During the tests, the film produced an average cooling power output of more than 110 W/m2 over 72 hours, with an average power output of 93 W/m2 at noon. This is equivalent to the amount of electricity generated by a typical solar panel of the same size. The transparent polymer film can also be used to coat the surface of solar cells, not only to cool them but also to increase their efficiency.

Researcher Yang commented that the main advantage of this technology is that it can operate 24/7 without using electricity or water. This is also an opportunity to explore potential applications in the energy industry, aerospace, agriculture, etc.

However, the downside of this research is that wrapping the film around buildings will not be as simple as creating a layer on the roof. The film can cool the building in the hot summer, but at night or in the winter, the film will continue to reduce the temperature.

According to VNA