In general, from my own efforts to try to understand the answer to that question, pumped hydro storage is probably the most promising but it'll only work in pla

In general, from my own efforts to try to understand the answer to that question, pumped hydro storage is probably the most promising but it'll only work in places that have the geography for it. There are a couple of excellent examples in Scotland, https://en.wikipedia.org/wiki/Cruachan_Power_Station https://en.wikipedia.org/wiki/Cruachan_Power_Station is one. The trick is that there's a 400m drop; lots of places won't have the geography to get that much head.