Radiative sky cooling thermal concentration with cooling power exceeding one kW per square meter

Abstract

The world's first demonstration of passive radiative cooling under the sun in 2014 attracted substantial attention due to its ubiquitous and passive nature. Numerous nanophotonic and metamaterials capable of radiative sky cooling have been reported over the past decade. However, the cooling power density of such materials is approximately one magnitude lower (100 W m⁻²) compared to terrestrial solar irradiation. Furthermore, improved optical characteristics could yield a modest increase in cooling power density due to the blackbody radiation limit. We report a rationally designed AsymSkyCool method (Asymmetrically sized heat-source-on-radiative-Sky-Cooling-coated-substrate) for radiative sky cooling thermal concentration (tcRC). The tcRC concept yields over 2000 W m⁻² at night and close to 1000 W m⁻² at 493 W m⁻² solar irradiation. The nearly tenfold improvement over the state-of-the-art sky cooling-based concentrators is enabled by advanced thermal management utilizing radiative energy concentration and localization. As climate plays a crucial role in the radiative sky cooling material performance, the concept has been experimentally verified in three geolocations, including Ljubljana, Slovenia (46.04°N), Shanghai, China (31.02°N), and Kunming, China (24.86°N). This work provides new insights into the usability of radiative sky cooling materials for thermal energy-intensive applications, such as high-power electronics cooling, radiative cooling-assisted sorbent- and solely radiative cooling-based atmospheric water harvesting that will unlock substantial benefits for advancements in energy, water, and food nexus.