There are increasing demands on energy supplies as they become an essential requirement to support modern life in most countries. Conventional resources for power generation that depend on fossil fuels become less reliable because of price fluctuations and long-term supply uncertainties. Furthermore, strong environmental awareness coupled with recent efforts to reduce greenhouse gas emissions has encouraged a shift from fossil fuels to renewable power generating resources. This has resulted in a significant investment in renewable energy technologies such as wind, solar, hydro and fuel cells. This book provides new research on performance, improvement strategies and the future directions on energy efficiency.