Worse, there is some loss at each step.
TANSTAAF
Actually, this is really promising. It’s true that you need to add energy to convert the CO2 to hydrocarbons, but solar cells are certainly capable of providing the current necessary to facilitate the conversion. If this technology proves feasible, it would be a great step toward energy independence.
BTW, the oxygen to burn the hydrocarbons is simply recycled back to the atmosphere when the CO2 is converted to CH4.
This process also suggests a path to create natural gas inorganically in the earth’s crust: carbonate rocks, heat, and a little hydrogen could do the trick. The difficult part is creating the hydrogen efficiently.