I can see this makes sense especially for medium term storage. A lot full of batteries is great for the next ten seconds, next ten minutes, even to some extent the next ten hours, but it surely doesn't make much sense to store ten days of electricity that way compared to just keeping the water behind a dam. We know that many of the world's large dams are capturing snow melt or other seasonal flows, running them only when solar or wind can't provide the power you need lets you make more effective use of the same resource.