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Tidal & Currents
Tidal range energy is potential energy derived by height changes in sea level, caused by the gravitational attraction of the moon, the sun and other astronomical bodies on oceanic water bodies. The effects of these tides are complex and most major oceans and seas have internal tidal systems.
The rise and fall of the tide (range) offers the opportunity to trap a high tide, delay its fall behind a barrage or fence, and then exhaust the potential energy before the next tidal cycle. The worldwide theoretical power of tidal power (including tidal currents) has been estimated at around 7,800 TWh / year.
The movement of ocean water volumes, caused by the changing tides, creates tidal current energy. Kinetic energy can be harnessed, usually nearshore and particularly where there are constrictions, such as straits, islands and passes.
Tidal current energy results from local regular diurnal (24 hours) or semi-diurnal (12+ hours) flows caused by the tidal cycle. Tides cause kinetic movements, which can be accelerated near coasts, where there is constraining topography, such as straits between islands.
Open ocean surface currents are driven by latitudinal distributions of winds (clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere). They tend to operate at shallow depths (<800 m) and are slower but more continuous flows than tidal currents.