The present book deals with renewable and sustainable energy systems, technology and their applications in the developments of the energy sector. They describe energy and development, energy demand and availability, energy crisis, sources of energy, and its environmental impact. They incorporate solar energy, hydro energy, ocean energy, biomass energy and wind energy systems and their respective technologies and economics. Solar radiation is the most important renewable energy resource because it drives all environmental processes acting at the surface of the Earth. Biomass is one of the renewable energies abundantly present and not utilized well. At present time developing energy utilization technology and economic analysis is important. So, to use renewable energy it is mandatory to know three main things: resources available, systems to be developed and the energy potential to satisfy needs. Finally, this contributes much for the renewable energy conversions, sustainable and economical developments in the future energy technology.