Comparison of synthetic natural gas production pathways for the storage of renewable energy

The production of synthetic natural gas (SNG) to store renewable energy in a chemical energy carrier can be accomplished basically through three main production pathways: the biochemical (biogas upgrade), thermochemical (gasification and synthesis gas upgrade) and electrochemical ('Power-to-Gas') pathway. The technologies applied in these concepts are described and the three pathways are compared in terms of their state of development, efficiencies, and economics. While the biochemical pathway is already established on a commercial scale, the thermochemical and electrochemical routes are still in the pilot-plant phase. Biochemical production of SNG reaches efficiencies in the range of 55-57% but with a potential of above 80%. In comparison, higher efficiencies of up to 70% for the thermochemical pathway are currently expected, with future improvement up to 75%. Electrochemical production achieves efficiencies in the range of 54-60% with expected potential up to 78%. Therefore at the moment the highest efficiencies are given for the thermochemical pathway followed by the electrochemical and biochemical pathways. Economic evaluation is done by comparing specific production costs as well as mean specific investment costs for SNG. Generally speaking, specific production and investment costs decrease with time horizon and increasing scale of the plant. Specific production cost levels in (sic)ct/kWh(SNG) vary between 5.9 and 13.7 (biochemical), 5.6 and 37 (thermochemical), and 8.2 and 93 (electrochemical). Thus, none of the concepts can compete with today's natural gas prices, but all options are able to provide valuable assistance for a sustainable transition of the energy system. (C) 2015 John Wiley & Sons, Ltd