The supply of energy from primary sources is not constant and rarely matches the pattern of demand from consumers. Electricity is also difficult to store in significant quantities. Therefore, secondary storage of energy is essential to increase generation capacity efficiency and to allow more substantial use of renewable energy sources that only provide energy intermittently. Lack of effective storage has often been cited as a major hurdle to substantial introduction of renewable energy sources into the electricity supply network. This 2nd edition, without changing the existing structure of the 1st edition, has expanded chapters that review different types of renewables and considers which of these requires storage. The book also discusses the limitation of renewables' usage without storage and considers more substantial possibilities that arise from integrating a combination of different storage devices into a system. This book will appeal to university teachers and students that are specialising in power systems development, renewables and other nonconventional electrical energy sources integration in the existing power systems, its economics and environmental impact. The first part of the book will also appeal to the general public.