The role of solid oxide fuel cells in repowering agricultural biogas plants: A techno-economic assessment of electricity and biomethane pathways

Biogas plays a well-established role in the European energy system, particularly in countries with strong agricultural supply chains. Biogas can be valorised either through electricity generation via Internal Combustion Engines (ICEs) or through upgrading to biomethane for grid injection. Solid Oxide Fuel Cells (SOFCs) are emerging as a promising alternative to ICEs, owing to their higher electrical efficiency and reduced pollutant emissions. This study evaluates the energy and economic feasibility of integrating SOFCs into existing agricultural biogas plants in northern Italy approaching the end of their incentive period. Four representative acilities were analysed under four operating configurations: electricity generation via ICE or SOFC, and biomethane production with auxiliary power supplied by either technology. Results indicate that SOFCs offer significant advantages for electricity generation in small-scale plants (100–300 kWel), where their high efficiency, combined with capital incentives, makes them economically preferable to ICE repowering. In contrast, for large-scale plants (~1 MW), biomethane upgrading achieves the highest profitability. Medium-sized facilities represent a transition case, where the preferred strategy depends strongly on gas-grid distance and injection pressure requirements. Overall, the study demonstrates that SOFC integration can enhance the performance of existing biogas infrastructures. The optimal valorisation route ultimately depends on plant size, site-specific conditions, and the applicable incentive framework.