Radiative sky cooling: Fundamental principles, materials, and applications

TLDR

Radiative sky cooling passively cools objects by emitting thermal infrared radiation through the 8–13 µm atmospheric window, requiring no electricity and offering potential for buildings, vehicles, solar cells, and power plants, though it has historically been limited to nighttime use. This review examines the fundamental principles of radiative sky cooling and recent advances in materials and system design. The authors analyze potential applications across scenarios, emphasizing technology viability and benefits, and discuss how nanophotonics and metamaterials enable daytime subambient cooling. Recent experiments demonstrate daytime radiative sky cooling achieving subambient temperatures under direct sunlight, and roll‑to‑roll fabrication makes large‑scale deployment feasible, positioning the technology to save energy in buildings and vehicles, reduce urban heat islands, address water and environmental challenges, improve power generation efficiency, and combat global warming.

Abstract

Radiative sky cooling cools an object on the earth by emitting thermal infrared radiation to the cold universe through the atmospheric window (8–13 μm). It consumes no electricity and has great potential to be explored for cooling of buildings, vehicles, solar cells, and even thermal power plants. Radiative sky cooling has been explored in the past few decades but limited to nighttime use only. Very recently, owing to the progress in nanophotonics and metamaterials, daytime radiative sky cooling to achieve subambient temperatures under direct sunlight has been experimentally demonstrated. More excitingly, the manufacturing of the daytime radiative sky cooling material by the roll-to-roll process makes large-scale deployment of the technology possible. This work reviews the fundamental principles of radiative sky cooling as well as the recent advances, from both materials and systems point of view. Potential applications in different scenarios are reviewed with special attention to technology viability and benefits. As the energy situation and environmental issues become more and more severe in the 21st century, radiative sky cooling can be explored for energy saving in buildings and vehicles, mitigating the urban heat island effect, resolving water and environmental issues, achieving more efficient power generation, and even fighting against the global warming problem.