All renewable energy obtained from the sea such as wave energy, ocean current, river current, tidal energy, salinity gradient energy, offshore wind and the ocean thermal gradient energies falls under “Ocean energy”. The river energy responds and are derived from the moving river water’s hydrokinetic energy. From where a river flows into the ocean you can see tidal signature down to a hundred miles in the river. Whether called a river site or tidal site is of no difference and the river current’s velocity is functioning from the result of effect of gravity, slope of reach, riverbed’s roughness and the slowing of the current from frictional forces.
Tidal energy comes from the mass of water’s movement as well as the moon and sun’s gravitational forces and the direction it takes. Also the earth’s waters inertial and centrifugal forces. Because of the moon’s proximity to earth it has twice the sun’s force of tide raising as the earth’s rotation causes Bulges to form in the ocean and one will always be closer to the moon and the other one on the other side or the earth.
Waves doing its work create the wave energy and the wind’s influence generates the ocean waves by the cause of ripples on the surface. Continuous blowing and stronger wind causes the developed seas and then the swells. When water is very deep the wave energy travels thousands of miles until it is dissipated on faraway shores.