Radiative cooling as low-grade energy source: A literature review

Radiative cooling is a technology intended to provide cooling using the sky as a heat sink. This technology has been widely studied since 20th century but its research is scattered all over the literature, requiring of a review to gather all information and a state-of-the-art. In the present article, the research has been classified in: (1) radiative cooling background, (2) selective radiative cooling, (3) theoretical approach and numerical simulations, and (4) radiative cooling prototypes. Even though this is a low-grade technology it can dramatically reduce the energy consumption, since it is renewable and requires low energy for its operation. However, new functionalities of the device, apart from radiative cooling, are required for profitable reasons. Some recommendations extracted from the literature to improve the efficiency of radiative cooling are: to use a cover to achieve low temperatures, to use water instead of air as heat-carrier fluid, and to couple the device with heat storage. Finally, further research should be focused in the development of new materials with improved radiative properties, the measurement of incoming infrared atmospheric radiation and/or new technics to predict it, and the evaluation of new device concepts.