You're not going to get a wholesale contract for the electricity from a swimming pool full of water moved once a day. I have no idea where you even go to get the contract, but if you remember that lobby "meeting" scene from "The Big Short" you've got the idea. https://www.youtube.com/watch?v=LUC1BuH_Gdo
By the time you're moving enough water to get a wholesale contract to sell your power, you're also going to need to buy enough electricity that you had to sign a wholesale contract for that and now you're just another small energy storage company, you are competing with the hollow mountain and all the startups who've bought a lot of batteries and a building on an industrial estate near a big transformer. You could doubtless make some money, this is a growing industry and enthusiasm goes some distance but you aren't going to get away with having a capped consumer supply contract and then selling that as wholesale electricity.
By the time you're moving enough water to get a wholesale contract to sell your power, you're also going to need to buy enough electricity that you had to sign a wholesale contract for that and now you're just another small energy storage company, you are competing with the hollow mountain and all the startups who've bought a lot of batteries and a building on an industrial estate near a big transformer. You could doubtless make some money, this is a growing industry and enthusiasm goes some distance but you aren't going to get away with having a capped consumer supply contract and then selling that as wholesale electricity.