This book will be beneficial for students, researchers and scientists working in the field of green energy systems. In the last few decades, green energy technologies have gained significant interest. The increase of heat transfer in green energy technologies is one of the most important concerns in energy collection, energy storage, energy utilisation, energy conservation, and optimum design. Since nanofluids/nano-enhanced phase change materials are used to increase heat transfer characteristics and thermal properties compared to conventional fluids/phase change materials, the performance of green energy technologies can be improved. These novel strategies are gaining interest to researchers and authors in recent years. This book presents the various applications of nanofluids, hybrid nanofluids, and nano-enhanced phase change materials in green energy technologies such as solar thermal energy storage, photovoltaic/thermal systems, tracking and non-tracking solar collectors, solar thermal power plant, and wind turbine cooling systems. The thermophysical properties of the nanofluids and nano-enhanced phase change materials are also presented. This book also overviews the challenges and opportunities in implementing the nanofluids/nano-enhanced phase change materials application in green energy technologies.