Building gigantic storage with 1 year cycle is a gigantic waste of resources and even if you assume electricity to be totally free to make it pay for itself the invest most per storage would have to be like 100x cheaper then current grid storage.
Hydrogen in no shape or form will every be used as seasonal storage.
Hydrogen is just another form of battery that would practically have to have a 6h to a few day cycle. And in that case there are better options.
Or think in context of this liquid air (or compressed air) battery.
If you can get liquid air or compressed air batteries to cost $300/kWh or so, hydrogen in the same container compressed to the same degree can store about 100 times the energy (especially if sub-cooled). So the storage cost (if dominated by the container structure) drops by a factor of ~100. That’s $3/kWh for storage, if you don’t use salt caverns. Not great if only amortized over 20 years (plus the bad round-trip efficiency), but also not terrible if it’s only used for like 5% of the electricity needs.
And that’s the real issue with seasonal storage: no one needs it really until you get to 95-100% decarbonization of the grid. Otherwise, best to use like a few gas turbines or something as backup/seasonal power. So investing a bunch of storage when you haven’t even built out a bunch of solar or wind, yet, is kind of suboptimal. Good to do demo plants, though, so you can get ready with the tech for when you DO need to decarbonize that last 5% or so.
