[ballooney]

The electrical efficiency of breaking water to hydrogen, then combusting hydrogen through a turbine to generate electricity, compares extremely disfavourably to most other forms of storage - it takes about 50kWh of electricity to produce 1kg of Hydrogen, and if you propagate that back through a turbine and make some conservative assumptions about electrolyser costs and so on and so on, you're sort of approaching 5x the cost of others forms of renewable electricity to make electricity from stored hydrogen.

Of course, if we're building enough renewable capacity that electricity is basically free when it's sunny or windy, that changes the eceonomics and maybe we should all be making hydrogen in that sort of [bumpily]-abundant future.

However, storing hydrogen is also a pain - the density is crap even as a liquid and very technically challenging, and the density is mind-bogglingly crap as a gas - you'd want to find some vast geological underground reservoir in which to store it economically.

None of these are insurmountable, it's just not an especially attractive option as things stand.

[adrianN]

Total system cost is what matters, efficiency is only a small part of the equation. As far as I know a mixture of batteries and hydrogen in a renewable grid looks like the cheapest solution.

Storing hydrogen is trivially done in salt caverns. We already do it that way today.