Overriding goals of the comtemporary energy systems are to increase the deployment of renewable energy sources and reduce carbon dioxide emissions. In order to reach these goals as well as to achieve successful energy transition, it is necessary to develop energy storage technologies and to invest into new concepts and projects. Power-to-Gas seems to be promising storage technology in the long-term context. Nevertheless, despite the perfection of the idea, there are many issues linked with the impelementation of this energy alternative. This book reveals what kind of energy storage mix is the best suitable and economically efficient for Germany, comparing and assesing all well-known storage technologies.