Headline: Combining Renewable Energy and Residual Carbon Sources for Biomethane Production: a Case Study for Sardinian Energy Supply

Synthetic fuels obtained from the recycling of waste and biological products using renewable energy (i.e., Power-to-X technologies) can be easily integrated into existing energy systems, with local smart grids acting as initial entry points. In this article the authors explore the feasibility of an optimized conceptual plant based on a Power-andResiduals-to-Methane system (PRtM) for the production of synthetic natural gas in Sardinia. This integrated system can store intermittent Renewable Energy Electricity (REE) production via batteries, or as CH 4 which can be directly pumped into the grid. In this article the authors present a process and a preliminary economic assessment (i.e., LCOE) of the PRtM in the Sardinia Region, together with a discussion on potential emissions reductions at plant and regional levels. The results show that PRtM energy output (electricity and CH 4 combined) currently costs 74 €/MWh LCOE and could fall further to 63 and 58 €/MWh by 2030 and 2050 respectively. Furthermore, estimations reveal that the potential to CO 2 emissions could exceed 10Kt/y for the presented scale of the plant, with a maximum contribution of more than 200 KtCO 2 /y if regional biogas production is taken into account.