maybe hydrogen
Definitely hydrogen. We need, as in require, it for various things form steel smelting to chemical feedstock, either hydrolysed on-shore or brought in via ammonia tankers, in the country it's going to be transported via pipelines (part of the network already are getting switched over from natural gas... fun fact Germany's network started out as a hydrogen network), and those pipelines can store three months of total energy storage (not just electricity). That's not even including dedicated storage, that's just high operating pressure vs. low operating pressure. Fraunhofer thinks it's the best idea since bottled beer.