Radiative cooling for energy sustainability: Materials, systems, and applications

As a sustainable technology, radiative cooling has received considerable attention due to its potential in energy sustainability. Unlike conventional cooling techniques, radiative cooling does not consume electricity during its operation and is therefore particularly attractive in reducing the energy demand for cooling and addressing global warming by reducing carbon emissions. The general principle requires a radiative cooler to be thermally emissive to dissipate heat via thermal radiation. During the daytime, the cooler needs to minimize the solar heating effect to ensure subambient temperatures. Guided by these criteria, researchers have developed various materials with engineered optical, thermal, and mechanical features. In this review, we will first explore the fundamentals of heat transfer in radiative cooling processes. Subsequently, we will summarize the state-of-the-art progress on material synthesis and system designs. Building upon those recently developed features, we will review how this technology has been implemented in practical applications, ranging from thermal management of buildings, semiconductor cooling, personal comfort design, and atmospheric water harvesting. Finally, we will conclude this review by identifying and discussing some of the remaining challenges requiring future research and development.