alt Hacker News> Even during WWII Germany had to synthesize much of its hydrocarbon fuel.
Germany [0], as well as Apartheid South Africa (SASOL), and now China, synthesized that fuel from coal. Which is itself a fossil fuel.
[0] https://warhistory.org/@msw/article/synthetic-production-of-...
> Obviously, this will not be done as long as cheaper fossil hydrocarbons are offered. However the use of fossil hydrocarbons for plastic, asphalt or other applications that do not release CO2 is not harmful.
The issue with any fuel/feedstock production is not just the financial cost but the amount of energy returned on the energy invested. A modern civilization (like Japan) requires 10:1. Synfuels made using the method you described are 1:1 - they provide as much energy as it takes to make them.
Coal was the cheapest source of concentrated carbon monoxide, which is why it was used.
The same technology can be used with carbon monoxide made by reducing the carbon dioxide from air. This requires more energy, but when that is provided by solar energy, this is no longer a problem.
If the energy used to make synfuel is solar, it is an external input and it does not matter much which is the ratio between it and the energy stored in synfuel, except that it determines the profitability of a plant during the first years of operation, as it determines the ratio between the quantity of fuel produced in an interval of time and the installed power of solar panels.
While this ratio determines the time in which the initial investment can be recovered, it matters little for the ongoing expenses required for production, which will vary very little when the ratio varies in a large range, so it has little influence on the production cost after the assets are depreciated.