This book provides a comprehensive understanding of solar energy systems, with an emphasis on both photovoltaic (PV) and solar thermal technologies. It combines theoretical knowledge with practical skills required to design, analyze, and implement efficient solar energy systems. The content offers an in-depth exploration of solar radiation principles, PV cells and systems, solar thermal collectors, energy storage methods, cost analysis, and relevant policies. Special attention is given to practical design methodologies, including numerous solved numerical problems and case studies. Breaks down complex scientific principles—such as Snell’s law, Bouguer’s law, and Max Planck’s electromagnetic theory, including the physics of solar radiation. Emphasizes practical implementation and design of solar energy systems. Serves as a comprehensive resource for solar energy technologies, starting with collector design and applications for solar heaters with storage. Explores cutting-edge solar thermal and PV technologies, such as solar cooling, passive solar architecture, solar distillation, and building-integrated PV. Includes numerical problems and case studies to aid in system sizing and design. This book is aimed at graduate students, researchers in solar energy, and professionals in energy engineering and related fields.