The suitability of existing sources of CO2 in a region (Ireland) for use in power to gas systems was determined using multi criteria decision analysis. The main sources of CO2 were from the combustion of fossil fuels, cement production, alcohol production, and wastewater treatment plants. The criteria used to assess the suitability of CO2 sources were: annual quantity of CO2 emitted; concentration of CO2 in the gas; CO2 source; distance to the electricity network; and distance to the gas network. The most suitable sources of CO2 were found to be distilleries, and wastewater treatment plants with anaerobic digesters. The most suitable source of CO2, a large distillery, could be used to convert 461 GWh/a of electricity into 258 GWh/a of methane. The total electricity requirement of this system is larger than the 348 GWh of renewable electricity dispatched down in Ireland in 2015. This could allow for the conversion of electricity that would be curtailed into a valuable energy vector. The resulting methane could fuel 729 compressed natural gas fuelled buses per annum. Synergies in integrating power to gas at a wastewater treatment plant include use of oxygen in the wastewater treatment process.