OTECs are amazing, and step 1 of "The Millennial Project: Colonizing the galaxy in eight easy steps"[0]
[0]: https://en.wikipedia.org/wiki/The_Millennial_Project
There's a shore-based research OTEC in Hawaii, but the best is a floating, closed-loop OTEC in the ocean.
wiki article states "Up to 10,000 TWh/yr of power could be generated from OTEC without affecting the ocean's thermal structure". which converts to about 500GW which... isn't that much
Interesting link. I would think step 7 would come before step 6 though. I thought about this for a few minutes and can't come with a reason otherwise.