Life cycle assessment of power-to-gas applications via co-electrolysis of CO₂ and H₂O

Abstract Solid-oxide electrolysis technology (SOEC) can efficiently convert electricity from renewable sources into H₂ via steam electrolysis, or syngas (a mixture of H₂ and CO₂) via co-electrolysis of steam and CO₂. Co-SOEC provides the advantage of better thermal integration for standalone applications or with other industrial processes. In this paper two promising cases are investigated from the perspective of life-cycle assessment to evaluate the potential of reducing carbon emissions: (1) coupling co-SOEC with a cement plant, and (2) integrating co-SOEC into a biomass gasification plant. Life cycle assessment was performed based on the collection of comprehensive information regarding the electricity sources for different scenarios and a sensitivity analysis was included to verify the consistency of the results. The results show that in both cases the co-electrolysis system can be beneficial in terms of reduction of global warming potential, although it depends heavily on the geographic location and on the share of renewable energy. The highest benefits among the cases reviewed were found in the case of a coal-fed cement plant, where annual CO₂ savings reached up to 2.39E + 05 tonnes CO₂-eq in France with 23.6% of the electricity provided by photovoltaics (PV). In Germany, on the other hand, both cases first show benefits when the renewable share reaches a very high percentage of the electricity input: 50% provided by PV for the case of the cement plant and 82% for the case of a biomass-gasification unit. Since electricity input is the main impact concerning power-to-gas applications, the carbon content of the electricity grid mix is very important. As grid mixes become ‘cleaner’ in the future with more renewable share in the electricity generation in every country, the investigated applications are expected to provide even higher benefits.