Renewable energy is contributing significantly to fulfill the continuously increasing energy demand of the world. Research in the field of renewable energy has to play a vital role if the potential of renewable energy is to be fully exploited. This book is intended to explore some recent developments in the field of these renewable energy sources. This book is comprised of four chapters on solar energy, four chapters on wind energy, two chapters on bio energy and two chapters on renewable energy. Chapters on solar energy include the basic concepts of photovoltaic cells, modules, array, modeling PV cell operation under Matlab/Simulink, alternative materials to conventional silicon based solar cells, recent transparent thin film materials and their performance characteristics. Chapters on wind energy present two new methods to predict wind power, a methodological approach for performance evaluation of wind farms, dynamic behavior of a weak hybrid power system and a structural analysis of multi-story vertical axis wind turbines. It also includes the impact of physical properties such as density and viscosity of biodiesels, as well as an investigation of performance of a low heat rejection engine using neem kernel oil and its methyl ester as fuel. A renewable energy conversion and waste heat recovery using organic Rankine cycles and various challenges and opportunities for sustainable development for implementation of renewable energy technologies are described at the end.