Renewable energy sources with their growing importance represent the key element in the whole transformation process worldwide as well as in the national/global restructuring of the energy system. It is important for a sufficient energy system is to find a solution and key element to complete energy supply, that is, energy storage. Reasons and background, which make the energy storage so crucial, imply that exact, enduring development of energy storage is an indispensable part of the full energy supply. There are some necessary components for further development and implementation of renewable energy sources, and these components involve not only a flexible generation system but also network expansion, demand-side integration, and storage. As the energy storage is a much needed component that can facilitate a low carbon energy system, energy storage technologies find their applications in two major areas, and these are electricity network energy storage and transport/mobility. Interest toward energy storage has also grown due to technical and innovative progress in the field of energy storage technologies. Additionally, energy storage can be considered from different perspectives, which always give corresponding benefits, emphasizing the importance and attractiveness of energy storage.