This would be green hydrogen. Sure, it has low density, but underground storage is pretty cheap at scale. Yes, it's flammable, but that can be handled, and is handled routinely -- the world currently produces and consumes 700 cubic kilometers (at STP) of hydrogen per year.

The huge advantage of hydrogen here is that a gas turbine power plant might cost $600/kW, a tiny fraction of the cost of a nuclear power plant. So if you have a need for a backup plant whose cost will be dominated by amortization of its fixed cost, hydrogen beats nuclear.