This book is compiled jointly by the Tajikistan and Pakistani scientists based on the result of research and various designs of photovoltaics, wind-power systems, biogas digestors and micro-hydropower systems. The economics of these renewable energy installations that are widespread in different countries in the world for the last decade are described and highlighted. Authors believe that this book will provide understanding of the basic points of the economics of the renewable energy installations and will be a useful source for students, researchers and professionals. In particular, in this book the concept of life-cycle cost (LCC), calculations of present worth, annual life-cycle cost (ALCC) and unit electricity cost are described. For the various designs of photovoltaics, wind-power systems, biogas digestors and micro-hydropower systems the unit electricity costs are calculated. Taking into account that the renewable energy installations usually have less effect to the environment, the concept of total cost of the energy is also described.