Most power needs can be supplied by OTEC - ocean thermal energy conversion. And there's also solar, which is cheap enough already to probably be enough all by itself. Energy storage, I've always felt that we overcomplicate... On land, a large weight could be lifted to store energy, then let down to use the energy. Tall buildings should have this... At sea, a water tank at the top of each piling could do the same job. It might synergize with otec quite well - idk, just a suspicion.

Likewise, fresh water accumulation needn't be as complicated as we make it currently. I've often imagined a sort of floating alembic to gather fresh water via evaporation. There's all sorts of unexplored directions for that.

The potential money makers at sea are potentially (am I over using this word?) huge. Algae farms making diesel and methane can power the solar system. Like, the whole thing... Methane for methalox fuel and diesel for heavy machinery. OTEC offers enough energy to be competitive mining bitcoin. Much more than enough. Mariculture can easily produce enough food for the entire world, even a world with multiple times current population. Really, its a crime that we aren't using our oceans. Its absurd...