Ocean Renewable Power Company.
Tidal power is scarcely a new idea. People in the Middle Ages who lived by the sea sometimes used tidal power to turn water wheels, which ground grain into flour.
According to the U.S. Dept. of Energy, "It doesn't cost much to operate tidal power plants, but their
construction costs are high and lengthen payback periods. As a result,
the cost per kilowatt-hour of tidal power is not competitive with
conventional fossil fuel power."
Guess it all depends on what you consider the "cost" of fossil fuel.
Photo from Peter Kaminski's photostream at Flickr.