Ocean energy is divided into in-stream, tidal, and wave energy. In-stream and tidal energy technology consists of many designs, but all convert the kinetic energy of the flowing water into electricity, most using some type of turbine.
Turbine designs range from underwater wind turbine-style to vertical- or horizontal-axis cross-flow turbines. As an emerging technology, wave energy conversion devices exist in a wide array of designs aiming to convert wave energy into electricity. While not as consistent as the tides, the amount of potential wave energy is frequently predictable days in advance.
River in-stream energy conversion (RISEC) devices work in a similar manner to tidal devices, but generally on a smaller scale.