Solar energy materials for thermal applications: A primer

Solar energy materials have properties that are tailored to the characteristics of the electromagnetic radiation in our natural surroundings, specifically its spectral distribution, angle of incidence and intensity. This tailoring can be made with regard to solar irradiation, thermal emission, atmospheric absorption, visible light, photosynthetic efficiency and more. Solar energy materials can be of many kinds, e.g., metallic, semiconducting, dielectric, glassy, polymeric, gaseous, etc. In particular, thin surface coatings of solar energy materials may exhibit the desired properties in their own right or may yield such properties when backed by an appropriate substrate. This article surveys a number of topics related to thermal applications such as solar thermal converters, transparent thermal insulators, devices for radiative cooling by exposure to the clear sky, and windows and glass facades with static or dynamic properties. The purpose of the present paper is to provide a bird's eye view over a wide class of materials of rising importance rather than giving detailed accounts of highly specialized topics.