Synthetic natural gas as a green hydrogen carrier – Technical, economic and environmental assessment of several supply chain concepts

•The assessed concepts enable hydrogen supply based on synthetic natural gas.•Electrified steam methane reforming reduces energy input over autothermal reforming.•Closed CO2 cycles allow energy and cost savings over supply via direct air capture.•For a distance of 10,000 km, CO2 cycling can be realized at around 60 €2020/tCO2.•Costs of hydrogen supply are estimated at 6.6 to 8.6€2020/kgH2 for 2030. Based on synthetic natural gas, existing natural gas markets and infrastructures can be used to make renewable sources of energy from sun- and/or wind-rich regions available on a global scale. To overcome the challenge of providing non-fossil CO2 for the production of this synthetic natural gas, a novel concept analyzed in this paper envisages to reform the synthetic natural gas in the importing country and transporting the captured CO2 back to the exporting country to be reused for the production of synthetic natural gas; i.e., the synthetic natural gas serves as a hydrogen carrier. This paper examines and compares the energy efficiency, cost and greenhouse gas emissions of different hydrogen supply chains using synthetic natural gas as a carrier related to the year 2030. To do so, all relevant components are taken into account to model the entire supply chains. A special focus is put on different options for providing the required CO2 and on different technologies for synthetic natural gas reforming. The assessment shows that the availability of a cheap source of biogenic CO2 at the point-of-export as well as electrified steam methane reforming result in the lowest hydrogen supply cost of 6.6 to 7.0€2020/kgH2, also achieving best results in terms of energy efficiency (around 44%). With regard to minimizing greenhouse gas emissions, autothermal reforming of methane appears to be advantageous. A closed CO2 cycle is favorable over sole onsite CO2 provision, if no cheap CO2 of non-fossil origin is available at the point-of-export and the costly direct air capture process would have to be used.