The provision of sustainable energy supplies for an expanding and increasingly productive world is one of the major issues facing civilisation today. Renewable Energy examines both the practical and economic potential of the renewable energy sources to meet this challenge. The underlying physical and technological principles behind deriving power from direct solar (solar thermal and photovoltaics), indirect solar (biomass, hydro, wind and wave) and non-solar (tidal and geothermal) energy sources are explained, within the context of their environmental impacts, their economics and their future prospects.