Yes, exactly. There are/have been various small scale projects along those lines. Hydrogen and CO2 to methane, to longer-chain hydrocarbons that can be put into

Yes, exactly. There are/have been various small scale projects along those lines. Hydrogen and CO2 to methane, to longer-chain hydrocarbons that can be put into existing engines. As you say, the synthetic fuel is just an energy (and carbon) carrier, you have to put all of that energy into the system somewhere — ideally from solar or wind or nukes or something.