This book is a compilation of chapters that discuss the most vital concepts and emerging trends in the field of sustainable energy. Due to the rise in pollution and depletion of natural resources renewable energy has emerged as the most credible alternative. It is being adopted worldwide as it has extremely low or no negative impact of the environment. This book is compiled in such a manner, that it will provide in-depth knowledge about the theory and practice of renewable energy. The objective of this text is to shed light on the techniques of renewable energy that could ensure energy saving and efficiency like geothermal power, solar photovoltaic and ocean energy to name few. Researchers and students in this field will be assisted by this book.