Power-to-SNG technology for energy storage at large scales

Power to Synthetic-Natural-Gas (SNG) technology combining grid electrolysis, methanation and final energy use is assessed taking into account technical, economic and environmental aspects. This evaluation is based on electrolyzer performance during long-term operation at large-scales, with datasheets from previous studies where a specific framework for hydrogen energy storage and electric grid load balancing matching with the Spanish power system was thoroughly defined. To go further, mass and energy balances, preliminary design of main unit processes, as well as efficiencies, costs and impact potentials are investigated in this study. It proves the feasibility for power management using gas storage, while reducing conventional capacity, with high utilization of technologies and increasing the contributions of renewable energies, at the same time that producing clean fuels for the hydrogen economy. The cumulative efficiency is mainly caped by the electrolytic processes, whereas the methanation steps remove all material issues related to transport by pipelines or end-use applications. The production costs of hydrogen, methane and electricity are estimated in 0.5 €/kgH2, 0.26 €/Nm3SNG and 51 €/MWhe, considering a zero price for 'surplus energy' and future costs of the components; electrolysis accounts for 60% of total expenses, methanation 30% and re-electrification 10%, while the primary energy price becomes dominant (e.g., 25 €/MWhe translates to 133 €/MWhe of regenerated power) due to the low global energy yield (30.8%). Finally, the greenhouse gas (GHG) emissions (35 gCO2,eq/kWhe) are low as far as the primary input is mainly surplus renewable energy and processes are basically cyclic.