Power to gas needs a source of carbon to produce methane. No, the carbon dioxide in the atmosphere is not a good candidate for this, since it's at very low concentration. Theoretically one could use biomass, but thats a very inefficient method of carbon collection.
Also, exist prototype power to gas facilities are ~50% efficient, just for the power-to-gas step. Even with a 66% efficient combined cycle gas turbine, which is the best we have, net efficiency is ~33%.
Also, exist prototype power to gas facilities are ~50% efficient, just for the power-to-gas step. Even with a 66% efficient combined cycle gas turbine, which is the best we have, net efficiency is ~33%.