Abstract Power-to-gas (PtG) is widely expected to play a valuable role in future renewable energy systems. In addition to partly allowing a further utilization of the existing gas infrastructure for energy transport and storage, hydrogen or synthetic natural gas (SNG) from electric power represents a high-density energy carrier and important feedstock material for further processing. This premise leads to a significant demand for large-scale PtG plants, which was evaluated with an amount of up to 4530 GWel for electrolysis and up to 1360 GWSNG for methanation capacities at a global scale. Together with the upscaling of single-MW plants available today, this will enable to achieve appropriate cost reduction effects through technological learning. Under given scenarios, reduction potentials for CAPEX of >75% are expected for multi-MW PtG plants in the long-term, with significant advantages of PEM and solid oxide electrolysis over alkaline systems in the short- and mid-term. The resulting effects on PtG product costs were evaluated via a holistic techno-economic assessment, resulting in SNG production costs of 15 €-cent/kWh and below for large-scale appliances in 2050, depending on the renewable electricity supply.