Of these, the three most well-developed technologies are tidal power, wave power and ocean thermal energy conversion.
Tidal power requires large tidal differences which, in the U.S., occur only in Maine and Alaska.
Ocean thermal energy conversion is limited to tropical regions, such as Hawaii, and to a portion of the Atlantic coast. Wave energy has a more general application, with potential along the California coast. Wave energy conversion takes advantage of the ocean waves caused primarily by interaction of winds with the ocean surface. Although many wave energy devices have been invented, only a small proportion have been tested and evaluated. Furthermore, only a few have been tested at sea, in ocean waves, rather than in artificial wave tanks.