The energy sector will be shaped by comprehensive changes in the coming decades, taking into account aspects of supply security, economic efficiency, and climate and environmental protection. This textbook describes the fundamentals of selected technologies for utilizing renewable energy sources, which are globally considered to have the greatest long-term potential. The focus is on the conversion of solar radiation and wind energy. Both technologies are essential components of a sustainable energy supply. Additionally, the generation, storage, and transport of hydrogen, as well as the types and applications of fuel cells, are explained. Example problems and exercises facilitate and deepen understanding.