[kimmk]

For seasonal grid-level storage, I wonder if simple compressed hydrogen storage (around 350 bar) is the most reasonable solution. AFAIK doesnt require any high-tech materials, avoids most embrittlement caused by LH2 and boil-off rates are reasonable.

[msandford]

The most efficient seasonal battery is probably synthetic hydrocarbons. By the time you get to propane (3 carbons) the pressures for liquid are super super reasonable (400psi including a giant safety factor) and there's zero embrittlement.

Further is that vehicles can use propane so you don't even have to idle the plants during the winter so long as there's some PV from the southern states. They might be running at 100% capacity in summer and 40% capacity in winter but that's way better than 0%. It's a lot easier to keep people employed to operate the plants if they're needed year round.