Until about 15 years ago, before the levelized cost of energy (LCOE) associated with solar and wind began to plummet, the world had high hopes for the renewable energy technologies collectively knows as hydrokinetics, i.e., extracting the kinetic energy out of moving water.  Nowadays, however, at least as far as I’m aware, no one other than hobbyists are working in this area.

Of course, there is no rule that says you can’t spend your own money in any way you wish.  However, what you’re going to run into in ocean current or any of the other flavors of hydrokinetics, e.g., wave, tidal, or run-of-river, is the old adage, “If you don’t care how you pay per kilowatt of electricity, I’ll get you all renewable energy you could possibly imagine.”

I’m fairly certain that the story here about the Japanese is false.  Either that or it’s 15 years old.

Japan and Ocean Current Energy