[marktwain]

John has assumed that electrolysers work at 52% efficiency, and that burning hydrogen in a thermal generator works at 40% efficiency. Both assumptions seem reasonable.

Just a quibble. 52% efficiency seems a mite low for electrolysis. You might be able to do a bit better than 40% efficiency with fuel cells, which are not bound by the Carnot cycle limits.

Of course, higher efficiencies might cost more, so the total economics have to be considered.

[MtnClimber]

You might be able to do a bit better than 40% efficiency with fuel cells, which are not bound by the Carnot cycle limits.

Brings back memories of my college engineering thermodynamics class and working with steam tables.