OTEC has been "coming" forever, I went to a presentation that reads astonishingly like that Wikipedia article 40 years ago when I started college. The mechanisms were the same, the idea of using the energy to generate chemicals rather than send electricity through long cables was the same (back then they were suggested ammonia rather than hydrogen, but that's in the Wikipedia article too.)
Curious that the efficiency could be up to 6% -- now, granted, we're not using that temperature difference at all now, but still -- 6%? Solar panels can be up to 30% or more now.
If we were going to use OTEC for hydrogen to power, say, 10% of the cars in the world -- wouldn't we need tens of thousands of plants, each costing millions of dollars?