So the efficiency of hydrogen split-store-generate needs to beat the efficiency of store-release of the battery and the costs of the equipment.
But it isn't yet competitive with "store energy collected in the summer for use in the winter".
For that usecase, far more energy must be stored for far fewer dollars to make it competitive vs just having a big fuel tank and a winter-only diesel generator.
Keeping lakes of water for a few months for hydropower are also competitive - the storage capacity of a big lake on a mountain top is immense.
I've heard pumped water is like 90% efficient, but you need a gradient and space.
Does wind power decrease in winter? I also remember schemes for making a huge solar farm in the Sahara and a superconducting conduit to Europe, and that was several paradigm shifts in solar cell performance ago (15 years). But almost all large countries seem to have a sufficiently sized desert to do this with (US, Russia, China).
If solar gets good enough, and it is still on some prime parts of the economies of scale price drops, you don't care as much about long-distance transmission loss.
What we need is a proper international standard for cars to be able to interact with the grid, to be able to charge and discharge based on grid conditions and pricing.
Its stupid to have everyone coming home from work at 6pm and plugging in their cars to charge right at the existing afternoon demand peak, when solar is waning. Just getting those cars to delay charging until around midnight (allowing user override) would shift a huge amount of peak demand.
Same concept if you don't use your car during the day - it should be able to discharge right into the morning and afternoon peaks, at your control. The user should be credited for this onto their car account.
It might even make sense to have dedicated high-voltage circuitry in houses and apartment blocks, to be used for EVs, solar, etc.
And we should really figure that out immediately since EV production is ramping up right now. We can't just rely on single automakers (Tesla) to work out these societal problems.
The greenest time to charge here in Northern CA is between 11AM and 1PM, when solar production is maximum.