International. A team of researchers from the EPFL (swiss Federal Institute of Technologies) has developed a coating that is capable of absorbing heat as well as repelling it. Invisible to the eye, this particular process prevents excess energy production and overheating of facilities.
Solar thermal collectors are used to produce hot water and contribute to home heating. During the colder seasons all the energy they absorb is useful. In summer, however, thermal collectors overheat and deliver excess heat. Until recently, this overproduction remains an unsolved problem that can even damage facilities.
Researchers have developed an intelligent material that changes its properties based on temperature. In the case of overheating during the summer, this new material would allow the collector to get rid of excess energy by radiating from it.
The EPFL laboratory focuses on optimizing the transition temperature through "doping" that adapts to the material. The material must behave as a "good" semiconductor at lower temperatures and as a "bad" metal conductor at higher temperatures. "With a layer of this material on a metal substrate, you can obtain a surface that has a low thermal emissivity in a cold state and high thermal emissivity in a hot one," explains the researcher.
The team works specifically on materials that are absorbent in the solar spectrum and reflective in the infrared range, a distinction that can be made according to wavelength. This is called the selective effect. The innovation of this project is the successful combination of a selective effect with a thermochromic function - color reacts and changes with heat, a phase change that occurs at 68 °C. The new material developed in the laboratory allows the efficient absorption of solar energy while reducing the impact of overheating.
