The extended Wind-to-Gas concept, based on the concept of Sterner 2009 [3], presented in Fig. 1 can answer to the first and second problem considering the requirements of the future energy system. In this
study, we focus on the first issue. The concept is based on converting excess electricity by REU into hydrogen and subsequently into methane. CH4 is distributed and stored in the existing natural gas network. It is combusted at times of limited availability of REU electricity in a combined cycle plant (light grey shaded area in Fig. 1). Combined cycle plants are able to quickly change generation from partial to full load. The extension to the Wind-to-Gas system presented here is coupling the plant to a CO2 capture unit and subsequently to dynamic CH4and CO2 storage. Once the CO2storage reservoir is charged by means of availability of a cushion and working gas e.g. with CO2 produced by a biogas plant (which result in negative emissions) or from sources which cannot avoid producing CO2as steel or cement industry (which result in balanced emissions). The CO2can then be produced from the storage reservoir and used to generate CH4 which again can be stored locally in another storage reservoir as well as produced and combusted as required. CO2 generated during combustion is then captured and stored underground making it available for the next generation cycle (dark grey shaded area in Fig. 1).