[DesertVarnish]

Difficult engineering problem but working from first principles suggests that the energy requirememts are not insurmountable. The roundtrip efficiency is worse than batteries but much better than photosynthesis.

Terraform Industries (and others, like Synhelion) has a plausible if slightly optimistic target to be price competitive with fossil fuels for methane in the early 2030s.

Some places with very cheap to extract hydrocarbons like Saudi Arabia may be able to compete for a very long time, but there are many futures where most of humanity's hydrocarbon consumption (including the ones used for the chemical industry, plastics, etc) derives from atmospheric carbon.

And this can happen fast, the world (mostly China) has developed a truly massive manufacturing capacity for PV.

[VBprogrammer]

Terraform Industries (and others); I'd seriously consider taking a long bet that these companies turn out to be better at converting investor capital into employee salaries, for a finite period of time, than they are at converting atmospheric CO2 into natural gas.

If such a technology was possible then it would be far better to start with carbon capture from existing emitters. The concentration of CO2 being easily 3 orders of magnitude higher.

[DesertVarnish]

For hydrocarbon synthesis, hydrogen production from electrolysis dominates the energy usage, along with driving the Sabatier process. DAC might be like 5-10%.

Higher CO2 concentration is better but certainly not needed, it doesn't make or break the economics.

[VBprogrammer]

I'm not going to argue over the numbers but any business which ignores such an obvious upside / upside scenario is not really serious about achieving economic criticality. It would allow a power plant, iron ore plant, cement producer, what have you, to make claims about their environmental credentials while simultaneously improving the efficiency of the process.