Wave Tidal Energy
The ocean produces two types of energy: thermal energy from the sun's heat, and mechanical energy from the tides and waves. Oceans cover more than 70 percent of Earth's surface. This aspect makes them the world's largest solar collectors.
The sun's heat warms the surface of the ocean and this temperature difference creates thermal energy. Relatively speaking, a very small percentage of the heat trapped in the ocean (energy) could power the entire planet.
Ocean mechanical energy is quite different from ocean thermal energy. Tides and waves are intermittent sources of energy but ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices.
There are also differences between tidal and wave conversion to energy. Waves are created by the action of wind over water; the winds in turn being the result of the differential heating of different parts of the land and sea by the sun. Waves are really just forms of stored wind power.
However, tidal energy is something else completely and should not be confused with wave power. Tidal energy is that which comes from gravitational pull of the moon, which drags water around the globe to create tidal rises and falls. Tidal barrages make use of the vertical rise and fall of the tides by creating a head of water to drive turbines. However, one can also drive turbines by the horizontal movement of tidal flows. Keeping in mind that the speed of the tidal currents may be low but the mass of water is very large. There are a number of devices that are under development to try to capture this energy.