I always have been fascinated with free/cheap energy. They actually do a version of your pool thing with the lake I am buying property on in Virginia. They generate power when Smith Mountain Lake (dammed) goes into a smaller lake at times of peak demand, then pump back water at times of low demand. So it is almost a form of a battery. Of course there is loss, but it apparently is worth it to meet the demand.
I think one day they will master fusion in some form hopefully.
That's great! I'm glad to hear that this type of thing is being done. Once the investment in new clean energy technologies is done, I think efficiencies in all kinds of things will go up. Greater efficiencies should translate into more time to do the things you want and less time to do the things you don't. (So long as you retain some self autonomy in your financial dealings.)
Clean fusion, room temperature super conductivity and advanced nano-technology has always been the subject of my wet dreams, lol. We can hope that people will use them for the benefit of everyone if they are developed.
However, decentralized systems that build cooperation could be a better method of creating abundance for more people until we learn how better to play peacefully together. Centralized fusion power generation still keeps the control in monopoly type hands who many not like the thought of reducing the marginal cost of energy to near zero.