The energy contained in the tidal power of our seas is a major resource of energy. Tides are generated by the gravitational and rotational forces on the earth, involving the sun and the moon.
Tidal energy is one of the oldest forms of energy used by humans.
Indeed, tide mills, in use on the Spanish, French and British coasts, date back to the 11th century. The modern version of a tide mill is a barrage constructed over an estuary. Tidal power stations operate by capturing the tidal water, behind a barrage, and releasing the water at low tide through turbines generating electricity. More sophisticated systems generate both on the ebb and the flood tides. A large tidal range is essential, which only occurs in certain estuaries where the length and depth create water movement in resonance with the natural tidal periods.