This is really thinking it backwards. You don't build the storage before you have the renewables to store. And almost no country is at a point where they need storage in large amounts (as long as that's an option it's cheaper to add flexibility by exchanging with neighboring countries).

E.g. hydrogen electrolyseurs + gas plants that can use H2 exist and aren't particularly challenging. The reason you don't see that yet is that we don't have the huge amounts of renewables that would need this infrastructure yet.