Performance of a Power-to-Gas Energy Storage System based on Integrated High Temperature co-Electrolysis and Methanation

In this study, performance of a renewable energy storage system based on a Power-to-Gas conversion process, composed by high temperature co-electrolyzer of SOEC (Solid Oxide Electrolyte Cell) technology and a methanation section, are investigated, including all the thermal and electric energy needs. A parametric analysis of the feed stream composition and of the methanation section operating temperature is carried-out. Based on the first results, in order to reduce thermal energy consumption, a configuration with heat recovery is also considered. In order to evaluate performance results, efficiency indices (electric-to-fuel conversion index, first and second law efficiencies) are introduced. Results show that best set-up from the point of view of synthetic natural gas quality does not coincide with configuration with highest efficiency indices. Moreover, the configuration which includes heat recovery allows to achievesignificant increase of the first and second law efficiency indices, up to values around 70-75%.