Emerging radiative materials and prospective applications of radiative sky cooling - A review

The enhanced cooling performance and the reduced operational cost of the integrated radiative sky coolers are essentially necessitated in a wide range of applications, such as cooling of buildings, electronic devices, solar cells, power plants and personal wears, etc. The radiative sky coolers are enabled by radiating heat into deep space and reflecting sunlight without external energy input, thereby providing passive cooling. Previously, radiative sky cooling was limited to nocturnal applications; however, recent advancements in nanotechnology and metamaterials have altogether led to achieve sub-ambient temperatures under direct solar irradiation, creating diurnal applications. In addition to elaborate radiative heat transfer mechanism and evaluate the corresponding limitations, this review puts forth an in-depth study on the structural characteristics of broadband and selective band radiative sky coolers, the latest advancements in radiative materials and emerging applications of the radiative sky coolers. Most importantly, valuable insights are discussed regarding the barriers and scalability of radiative sky coolers on the commercial scale. It is therefore anticipated that a broader picture of the recent progress about radiative sky cooling as presented herein provides a great potential to boost up energy-saving, resolve water-scarcity, maximize power generation, minimize urban heat effects and so forth.