[tuatoru]

Hydrocarbons, especially medium-chain liquid hydrocarbons, can easily and safely be transported 10_000 kilometres and further.

Doing exactly that is presently about a quarter of total global international trade by value.

Their advantages of high energy density, safety, and undemanding environmental and handling requirements (distribution can be performed in temperatures from -40 to +40 celsius by almost untrained teenagers), and effectively unlimited storage duration and volume, far outweigh the energy inefficiency of producing them from atmospheric carbon. Especially once PV gets cheap enough.

Edit: I notice I didn't answer your question. For liquid hydrocarbons, I believe the answer is in the single digit percents, perhaps five percent. For LNG, the energy cost is much higher, perhaps as much as a third of the total energy value.

[ncmncm]

TFA is entirely about synthesizing transportable hydrocarbon energy storage.

But making methane is inferior to making ammonia, because extracting the diffuse carbon you need from air takes up energy. It does not displace any more CO2 emission, because somebody will burn it and dump the CO2 back into the atmosphere again.

So, the only reason to make hydrocarbons is for things like your chainsaw or A320 that are not worth replacing immediately.