Research group led by Prof. PEI Gang and Prof. ZOU Chongwen, from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences, proposed a new method to continuously harvest and utilize energy from the sun and outer space all day long. Taking the sun as heat source at 6000K, and outer space as heat sink at 3K, they skillfully used spectrally self-adaptive intelligent coating technique to reduce the energy consumption for heating and cooling of buildings in an environmentally friendly way.
This work was published in PNAS.
Concept of dynamic integration of PT and RC based on the SSA/E. (Image by AO Xiaoze et.al)
The sun and the universe are the ultimate heat source and the heat sink of earth's energy cycle. There are two main methods to capture the energy from the sun and universe: photothermal (PT) for thermal collection and radiative cooling (RC) for clean cooling with no energy consumption. High temperature heat energy is directly obtained from the solar thermal through PT. And RC can directly transmit residual heat energy through the atmospheric window (8-13μm) through infrared radiation to the cold outer space, realizing the direct utilization of outer space cryogenic temperature at a very long distance.
However, current PT and RC both rely on static spectral selective coatings. Infrared spectral conflict occurs during these processes. Given the single-target, single-function approach, researchers from USTC innovatively proposed a spectral adaptive regulation mechanism for continuous utilization of PT in daytime and RC during nighttime within a single device.
Researchers in this team developed a spectral selective adaptive multilayer coating based on vanadium dioxide (VO2). This coating stays at metallic state under daytime solar irradiation, which makes it capable to work as a PT absorber. The solar absorptivity of the overall coating is 0.89, and the infrared emissivity is only 0.25, performing greatly in energy absorption. Meanwhile, without irradiation at night, this coating stays at the insulating state with unity emissivity within the atmospheric window, working as a selective RC emitter.
The spectrally self-adaptive absorber/emitter (SSA/E) applying above-mentioned coatings performed excellent adaptive switchable functions of PT mode in daytime and RC mode at night. According to experiments, its surface temperature can be 170℃ higher than ambient temperature in the daytime and 20℃ lower at night.
SSA/E continuously operates with neither break nor energy waste, which greatly improved the overall efficiency of harvesting and utilizing cold and heat energy from the universe. This work provides a new approach to continuous energy capture, opening up the clean and cheap way for effective heating and cooling of buildings.
Written by LU Hongyu, edited by LIU Zige , USTC News Center