Energy is a major key to industrial development and the world's well-being. Constantly growing demand for energy that relies only on fossil fuels cannot continue indefinitely. The Earth's finite supply will eventually be exhausted. The awareness of the depletion of fossil fuel resources has challenged engineers and scientists to search for alternative energy sources that can meet the demands for the near and distant future. It has been recognized that attention should be given to resources that are continuous, renewable in their availability, and must be pollution free. This book is dedicated to an understanding of these sources. This book is not about wind, solar, or any other renewable energy the purpose is to bring together in one book a general knowledge, to a moderated level, about the ways and the devices that are used in power generation from some renewable energy sources.