Renewable energy, also known as green energy, is obtained from renewable resources. Such natural resources include sunlight, rain, waves, geothermal heat and wind. It plays an important role in electricity generation, transportation, air and water heating or cooling, and off-grid energy services. Some of the different technologies which are used to produce renewable energy are wind turbines for converting wind power into electricity, water turbines for producing hydroelectricity and photovoltaic cells for harnessing solar energy. Various other renewable technologies, such as cellulosic ethanol, marine energy and hot-dry-rock geothermal power, are also being developed. There are numerous benefits of using renewable energy over fossil fuels such as reducing air pollution and improving public health. Different approaches, evaluations and methodologies and advanced studies on renewable energy have been included in this book. Such selected concepts that redefine this area have been presented herein. Those in search of information to further their knowledge will be greatly assisted by this book.