Comprehensive analysis of renewable energy integration in decarbonised mobility: Leveraging power-to-X storage with biogenic carbon sources

In this study, the conceptual design of a system for delivering constant energy supply to a decarbonized urban mobility setting was conducted. Two systems were designed based on battery electric vehicles and fuel cell electric vehicles. The primary energy supply is renewable electricity, converted to H2 in an electrolyzer for fuel cell electric vehicles. Excess electricity is stored as methane or methanol, synthesized using CO2 from biogas upgrading. Technical performance indicators were calculated using data from the city of Zurich. Electrical mobility was found to be the most efficient option, considering engine efficiency and lower electricity conversion requirements for H2. The system operates in storage mode approximately 70% of the time, converting excess electricity into methane or methanol, and requires re-conversion of electricity for the remaining time. Methane was identified as the best storage molecule for electricity, with a 29% electricity-to-electricity efficiency, while methanol proved optimal for H2 storage, achieving 43% H2-to-H2 efficiency. The total system cost was evaluated using a biogas plant near Zurich, revealing that the cost of generated electricity and H2 ranges between 0.18–0.21 €/kWh. The low cost of renewable electricity, available 70% of the time, makes the proposed solution cost-competitive for decarbonizing mobility. Additionally, the system facilitates carbon capture by transferring CO2 from decentralized emitters to a centralized reforming plant, with a carbon capture penalty of only 0.01–0.02 €/kWh.