Assessment of the seaborne supply chain costs of green hydrogen energy carriers with a focus on synthetic methane

This study evaluates the international seaborne supply chain costs of fully renewable-based hydrogen energy carriers delivered from the Middle East to Japan, with particular emphasis on comparing synthetic methane with liquefied hydrogen, methylcyclohexane, and ammonia. A two-region, single-year, temporally detailed hydrogen supply model is employed to determine cost-optimal capacity sizing and hourly operations across the entire supply chain, while explicitly accounting for the hourly intermittency of variable renewable energy. The results indicate that synthetic methane is the second most cost-competitive carrier, at 6.2 USD per kgH 2 , after the direct use of ammonia at 4.8 USD per kgH 2 . Both synthetic methane and direct ammonia use avoid reconversion processes in the importing region, thereby reducing energy losses and associated costs. Synthetic methane further benefits from its compatibility with existing liquefied natural gas transportation technologies, which moderates transportation-related capital costs. The analysis confirms that the estimated costs are broadly applicable to other importing regions. In addition, the results indicate that innovative methane synthesis technologies could reduce the supply chain cost to 5.1 USD per kgH 2 —nearly equivalent to the level of direct ammonia use. Nevertheless, the carrier faces institutional challenges related to CO 2 attribution, underscoring the need for internationally harmonized accounting rules for carbon capture and utilization.