From Biogas to Grid: Co-Electrolysis and Methanation for High-Yield Biomethane

This paper presents a concept for increasing biomethane yields from biogas plants by combining solid oxide co-electrolysis with downstream methanation, thereby utilizing biogenic CO₂ instead of releasing it unused. A major opportunity for this concept is provided by Austria’s untapped biomethane potential together with existing gas infrastructure and storage capacities for seasonal balancing of renewable gases. A distribution grid case study illustrates how biomethane injection can exceed local demand during periods of low consumption, leading to indirect utilization via recompression, transfer, or storage, while winter demand enables higher direct substitution of fossil gas. To evaluate integration options, a modular system-level simulation framework is developed, linking detailed single-cell SOEC electrochemistry, mass transport, and thermal behaviour with balance-of-plant components and heat-integration strategies. Two application pathways are considered. In the reference plant, H₂ for conventional CO₂ methanation is supplied by a PEM electrolyser. Within this work, alternative concepts based on SOEC technology are investigated using simulation. In a simulations study, a SOEC steam electrolysis is evaluated to supply H₂ for conventional CO₂ methanation. Further, SOEC co-electrolysis is assessed in the simulation to produce tailored syngas for CO methanation with enhanced heat-recovery potential and reduced H₂ demand. Overall, the results indicate that coupling SOEC-based conversion with methanation can improve carbon utilisation, increase renewable methane output, and support flexible operation aligned with grid constraints and seasonal demand.