You're right. The point I was trying to make is that it takes a lot of energy to convert CO2 and H20 into a fuel, an energy storage medium. However, a lot of the energy stored in the fuel by breaking chemical bonds and rearranging them into fuel is lost when the fuel is converted back to CO2 and H2O by moving a vehicle down - or up - a road.
You gotta' take into account the Second Law of Thermodynamics. In a cyclic process entropy is created when work is performed like moving the pistons in an internal combustion engine to get the vehicle down the road so some of the energy content in the fuel will not be converted into motion. One consequence of this is the fact that vehicles have radiators to dissipate the heat that cannot be turned into motion. Even electric motors, which are very efficient, get warm. The power plant that produces electricity can't convert all the heat used to run turbines into electricity. Similar arguments can be made for wind powered turbines, though the wind is kind of "free" energy when it blows. The electric current used to charge batteries generates heat in the batteries. And discharging batteries to run electric motors in cars get warm. So, yes, the 1st law can be used to calculate the energy required to convert the combustion products back into fuel but more energy will be put into fuel manufacture than was converted into the work of motion. My guess is the total efficiency of the cycle (wind electricity, convert CO2 + H20 to fuel, burn fuel in vehicle, move vehicle) is somewhere near 15% or less.
According to a post above using wind generated electricity to make the conversion would require 40 acres for 200 liters of fuel. To give an estimate of scale: the USA consumes about 3.2 trillion liters of crude oil per day, so to make this fuel as a replacement using wind power would require 636 million acres. Not all the crude goes into fuel so the numbers may be off some. The land area of the continental US is about 1.9 billion acres, so somewhat less than 33% of the area of the US would be required to replace crude oil based hydrocarbon fuels. Considering wind doesn't blow well everywhere, a lot of land is used for agriculture, forests, national parks, deserts, etc., a significant contribution to a wind generated fuel source doesn't sound likely here. Nuclear fission or fusion generated electricity might do the trick considering the likely land area requirements for those plants. There are well known problems with nuclear fission electric production and nuclear fusion produced electricity hasn't been made commercially viable yet.
