There are pilot applications being tested in Europe, and I support continuing that research, even though it would probably involve direct Government subsidies and risk of another Solyndra. I just do not believe any utility today could take the bet that this is practical yet.
Every renewable except traditional hydro and geo is very heavily subsidized, often with either interest free loans, feed in tarrifs, direct handouts, or some combination of all three. That creates a hugely inflated market that is skewed by flushing tax dollars down the drain. This is not sustainable.
Which is why wave and tidal are an even bigger joke than wind and solar. Despite its limitations solar actually does have some very real niche applications where it is useful, but that thing? A symbol of insanity and waste.At 10 cents/kw hr, the plant will produce $1000 worth of electricity twice a day.
Looking at the scale of the structure and the engineering required for massive spinning blades with apparently variable pitch, the economics seem challenging.
Rance also uses turbines, but adds a tidal barrier to create a race for a longer interval. The barrier is of course an additional cost.