[adrianN]

Thanks for doing the math. On a global scale it does look better than the math I did for Germany.

However, I think 50% process efficiency is too high. High temperature electrolysis is about 60% efficient, but then you only have hot uncompressed hydrogen. There are a number more steps involved to get to a liquid fuel, each of them with considerable losses. I can't find the sources right now but I believe I remember something like 15% end-to-end efficiency for getting to something you can fuel your car with.

[leoedin]

Yeah, it probably is. There's not really a nice process for making liquid fuel - hydrogen isn't a great fuel really. My understanding is that the biggest problem with making a practical liquid fuel is ironically getting the carbon. Hydrogen is in water, but carbon is only really in carbon dioxide - which is at very low atmospheric concentrations and so takes an incredible amount of energy to capture.

Ammonia would be easier (ubiquitous nitrogen everywhere), but isn't a particularly nice fuel either. At least it's easier to store than hydrogen.