Round-trip electricity efficiency is what I was referring to, assuming you'd use electricity. If you have to synthesize fuel using electricity and then burn it to produce either movement (shaft-power) or electricity, the efficiency is on the order of 10%. Whereas for batteries, the efficiency is on the order of 80-90%.
Regardless, if any of the biological/algal methods of CO2 to fuel techniques become successful, why would we care if 5%, 50%, 100% of the solar energy received makes its way to the end product. It's basically free energy at that point. The only thing that would matter is real estate to house the facilities.