As the entropy sink, the cold source is an integral part of a complete thermodynamic cycle in all heat-producing technologies. The unique challenge is to obtain coldness from renewable and sustainable sources. In this talk, I will discuss our recent efforts on radiative cooling in energy sustainability [e.g. Nature Sustainability (2019); PNAS (2021); Cell Rep. Phys. Sci. (2021)]. In particular, the potential to reduce the operational temperature of semiconductor solar panel using electricity-free cooling technology will be discussed.