Hi I have been reading this thread with interest, not that we have solar but just the way things are going, I remember on a visit to the barrage not fat from us hearing that when France had a surplus of electricity the would pump water into the river Rance to store extra energy have a look at
Rance tidal power plant - Wikipedia, the free encyclopedia.
It’s a very interesting area, however the people running the plant control the tides inside the river Rance and a few times the dingy has been well high and dry!!!!
Its quite interesting also because this was all built a long time ago and still well used!!