Comprehensive Analysis of Renewable Energy Integration in Decarbonised Mobility: Leveraging Power-to-X Storage with Biogenic CO2 Sources

In this study, we conducted the conceptual design of a system aimed at delivering constant energy supply for a decarbonised urban mobility setting. To this scope, we designed two systems based on battery electrical vehicles (BEV) and fuel cell electric vehicles (FCEV). The supply is primarily provided by renewable electricity, eventually converted to H2 in an electrolyser to feed FCEV. Excess electricity is stored in methane or methanol, synthesised using CO2 coming from biogas upgrading. We calculated technical performance indicators based on input values obtained for the city of Zurich. We observed that the electrical mobility is the most efficient option from various perspectives, including the efficiency of the engine and the lower amount of electricity required for conversion to H2. The study shows that for electrical mobility the system would work in storage mode for ca. 70 % of the time (i.e., converting the excess electricity in methane or methanol), requiring the re-conversion of electricity for the remaining time. Methane appears as the best storage molecule for electricity, due to the higher efficiency of the conversion processes, however limiting the electricity-to-electricity efficiency to 29 %. Methanol proves to be the best molecule for H2 storage, with 43 % H2-to-H2 efficiency. The total cost of the system is evaluated considering the case study of a biogas plant close to Zurich. It was found that the cost of the generated electricity and H2 would range between 0.18-0.21 €/kWh. Combined with the low cost of renewable electricity that is offered to customers for 70 % of the time, this makes the proposed solution a cost-competitive option for the decarbonisation of mobility. Additionally, we observed how the designed system would allow a simple option to integrate carbon capture, operating the transfer of CO2 from decentralised emitters to a centralised reforming plant. Thanks to this, we calculated that the carbon capture penalty would only range to 0.01-0.02 €/kWh.