Energy storage from renewable sources is one of the main current goals for the energy sector, and the production of a substitute of natural gas could be a good solution to solve the problem in the short term, helping the transition to hydrogen in the long term. Renewable energy sources usually generate variable electric power or medium/low energy content gas. This paper proposes a way to upgrade these products through the use of electrolytic hydrogen. By using electrolytic oxygen as an oxidant for biomass partial oxidation and for high temperature fuel cells, the exhaust gas after post-combustion is an almost pure mixture of water and carbon dioxide. Once such a gas is dehydrated, the carbon dioxide can be mixed with electrolytic hydrogen to obtain methane through the Sabatier process. Four layouts based on molten carbonate fuel cells and solid oxide fuel cells has been investigated. The results obtained are very similar: the conversion efficiency is close to 60% and the mix of energy output consist of fuel for about 75% and electric power for about 25%. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.