This book provides a comprehensive overview of the principal renewable energy sources: Solar thermal, tidal, photovoltaic, wind, biomass, wave, hydro, and geothermal. With the aid of 370 detailed illustrations, 50 tables of data and a wide range of case studies, it explains, for each source, the underlying physical and technological principles and examines the environmental impact and future prospects. Basic energy concepts and current energy systems are outlined, as are the key issues of economics how the energy systems of the 21st century may change in order to incorporate an increasing proportion of renewable power.