The textbook book discusses the basics required to understand various application of solar energy. It covers basic mathematical tools required to analyze any solar thermal (ST), photo-voltaic (PV), and photo-voltaic thermal (PVT) system. The book provides a platform for undergraduate, postgraduate, researchers, and entrepreneurs to optimize the basic parameters for best performance of any system based on solar energy. The book includes about 500 examples that the reader can use to better understand the subject.