This is such an abundant energy resource that has been ignored for so long.  It is described as such from their company:

OTEC is “a process that can produce electricity by using the temperature difference between deep cold ocean water and warm tropical surface waters,” Makai Ocean Engineering, the company that built the plant, explains on its website. “OTEC plants pump large quantities of deep cold seawater and surface seawater to run a power cycle and produce electricity.” Makai touts OTEC as a constant, clean energy source that is “capable of providing massive levels of energy.”

And here is a commenter on the video thread who makes an unusual analogy to the process:

Reverse the Refrigerator, or the Air Conditioner, closed cycle process. Water at 4 deg C is densest and sinks in the ocean; while the surface ocean water follows the thermal energy absorption pattern..

I hope to see more of these plants being built in the future.

thanks to ecowatch.com for the great info