A research group led by Prof. PEI Gang and Prof. ZOU Chongwen of the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences has proposed a new method for continuously harvesting and utilizing the energy from the sun and outer space. all day. Taking the sun as a heat source at 6000K and space as a heat sink at 3K, they skillfully used a spectrally self-adaptive smart coating technique to reduce energy consumption for heating and cooling buildings in an environmentally friendly way.
The sun and the universe are the ultimate heat source and heat sink of the Earth’s energy cycle. There are two main methods for capturing energy from the sun and the universe: photothermal (PT) for thermal collection and radiative cooling (RC) for clean cooling without energy consumption. High temperature thermal energy is directly obtained from solar thermal via PT. And RC can directly transmit the residual thermal energy through the atmospheric window (8-13μm) by infrared radiation to the cold outer space, realizing the direct utilization of the cryogenic temperature of the outer space at a very long distance.
However, current PTs and RCs both rely on static spectral selective coatings. Infrared spectral conflict occurs during these processes. Considering the single-target, single-function approach, USTC researchers innovatively proposed an adaptive spectral regulation mechanism for the continuous use of PT during the day and RC during the night at the within a single device.
Researchers in this team have developed a spectrally selective adaptive multilayer coating based on vanadium dioxide (VO2). This coating remains in the metallic state under daytime solar irradiation, which makes it capable of functioning as a PT absorber. The solar absorptivity of the whole coating is 0.89, and the infrared emissivity is only 0.25, which can greatly absorb energy. Meanwhile, without irradiation at night, this coating remains in an insulating state with unity emissivity in the atmospheric window, functioning as a selective RC emitter.
The spectrally self-adaptive absorber/emitter (SSA/E) applying the above mentioned coatings has achieved excellent adaptive switchable functions of PT mode at daytime and RC mode at night. According to experiments, its surface temperature can be 170℃ higher than room temperature during the day and 20℃ lower at night.
SSA/E operates continuously without interruption or energy waste, which has greatly improved the overall efficiency of harvesting and utilizing cold and thermal energy from the universe. This work provides a new approach to continuous energy capture, paving the way for clean and inexpensive building efficient heating and cooling.