How do you generate the hydrogen in the first place? Hydrogen is only a battery. An inefficient and cumbersome battery.

I was thinking of hydrocarbon fuel cells, to be honest.

Whether you're looking at hydrogen or hydrocarbons, you need some chemical energy carrier mechanism. In the long run, either will have to be formulated, and yes, there's about a 50% efficiency hit straight off the top in elecrolysing hydrogen.

But if you're trading an abundant, variable energy source (say, peak solar which is otherwise wasted) for a scarce but valuable and useful store, that's a net win.

Note that whether you're formulating H2 or hydrocarbons, the energy cost is about the same (the carbon sequestration from seawater mentioned above is low energy cost), though it requires fairly substantial capital investments.

Yes.

One other alternative is the Li-Ion batteries that we already have.

In any case, I am just reacting to the hype we sometimes see about an `H2 energy future', as if hydrogen was a source of energy.