As the world faces serious energy challenges, the development and implementation of renewable energy technologies become increasingly important. Solar energy resource dwarfs all other renewable and fossil-based energy resources combined. This special issue addresses the role of the development of solar energy. The themes include a photocatalytic process, a photoelectrochemical process, a photosynthesis process, solar cell technologies (photovoltaics (PV)), and solar PV/thermal systems, which resulted in a collection of twelve outstanding articles submitted by investigators representing eleven countries across Asia, Europe, and North America.