Techno-economic comparison of Power-to-Gas systems using solid oxide and anion exchange membrane carbon dioxide/water electrolysers

Carbon dioxide (CO2) electro-reduction is an alternative pathway to synthesize low-carbon fuels and chemicals from renewable electricity. However, comprehensive techno-economic evaluations on this technology are still relatively few in the scientific literature. In this work, novel Power-to-Gas systems have been structured into three main subsequent process steps: (1) CO2 separation by absorption with aqueous monoethanolamine from a waste incinerator flue gases; (2) co-electrolysis of CO2 and steam (H2O) to produce a syngas; (3) catalytic methanation to generate substitute natural gas (SNG) with a methane (CH4) purity exceeding 92 %. Two different electrolysis configurations have been analysed, involving: (1) two anion exchange membrane electrolysers in parallel performing CO2 and H2O electrolysis (1.8 and 7.5 MWel, respectively); a solid oxide electrolyser splitting CO2/H2O coupled with one anion exchange membrane H2O electrolyser (3.6 and 7.4 MWel, respectively) for additional hydrogen (H2) production. Because of the CO2 crossover of the anion exchange membrane electrolyser to the anode side and its lower energy efficiency (34 %) with respect to the SOEC, the combination of Solid Oxide and Anion Exchange Membrane Electrolysers achieves higher natural gas production rate (296 vs 455 kgSNG/h), higher global energy efficiency of SNG production (37 % vs 47 %), and lower specific energy consumption per captured CO2 (39 MJ/kgCO2 vs 50 MJ/kgCO2). Additionally, the high-temperature configuration provides a levelized cost of substitute natural gas of around 304 €/MWh with respect to 376 €/MWh of the low-temperature scenario assuming 80 % capacity factor and electricity cost of around 52 €/MWh. To achieve economic competitiveness with natural gas and biomethane, both systems will benefit from efficiency optimization, cost reductions by technological learning rate and scaling-up to hundreds of MWel, as well as incentives on renewable fuels production. The proposed configurations are easily adaptable to the production of other key chemical products, such as methanol and Fischer–Tropsch products.