[salamandars]

Could hydrogen electrolysis be viable as grid or building level energy storage? Round trip efficiency is bad of course, but I (naively) wonder if it wouldn't have a lot of the downsides fuel cells have for vehicles?

You could bury a huge volume of tanks beneath new buildings and store the gas at a lower pressure than we see in hydrogen car tanks - wouldn't that make the whole system simpler and more economical?

[pfdietz]

Yes, grid is a big use case. Hydrogen can be stored in salt domes for maybe $1/kWh (energy capacity cost). This is two orders of magnitude cheaper than batteries, and could be used for seasonal load leveling.