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Potential of Tidal power generation
The potential behind tidal power and tidal barrages in the UK should theoretically meet all the country's demand three times over. Many other countries with a shorter coast line (in proportion to area or population) will also have considerable potential.
Tidal power therefore has advantages over wind power, 1) predictability so engineers can make adjustments to grid power flows in advance of tide changes; 2) the load factor of 75% instead of around 30% (wind) and 3) water being 800 times denser than air there is more power for given size of turbine.
Tidal power, barrages, dams, making use of tidal 'range.' (ref 186)
In a barrage system, use is made of the 'potential' energy in the tide. Water is captured at high tide behind a dam in an estuary and flows to the lower level as the tide recedes driving turbines which in turn drive electric generators. The system could work both ways. A typical tidal power 'barrage' set up may look like this:-
Examples are the Severn Barrage project proposal in the UK to generate 8.600 MW with a 14 metre tide (ref 123 & 234) depending on barrage location; or La Rance in France, finished in 1967, 240 MW, with a 8 metre tide.
20 places have been identified around the world as potential barrage sites, eight being around the UK, including the Humber, Dee, Solway estuaries.
Tidal lagoon
A further possibility in a tidal and shallow area such as the European continental shelf is to construct a vast lagoon which fills up at high tide and drives turbines while emptying and from low tide when refilling. A study by Atkins consultants of a 5km sq area off Swansea UK concludes feasibiliy for 60 MW generation, tides 4.1 to 8.5m 36% load factor. Walls are designed for a 11.1 m rise in future.
Tidal turbine farms, making use of tidal flow- predictable tidal flows 18-20 hours a day.
Tidal turbines make use of the kinetic energy in tides where many are mounted in the path of the tidal flow. The energy in a tidal current is proportional to the cube of the water velocity and there is thus 8 times the tidal stream power in 'spring tides' compared to 'neap tides'(a two week cycle) and of course no power in periods of 'slack water, when the tide is turning. There are several different approaches being tested.
Sea Gen (above) are supplying 3 X 1.2MW turbines at Campbell River, West Canada; total potential in area 4000MW.
Blue Energy manufacture Vertical mounted tidal turbines. Several would be locked together in the path of the tide:-
Gorlov vertical helical turbines are planned in Korea generating 1 MW each; eventually a group of 3600 MW are projected.
Hydrofoils
The Sea Snail is an alternative concept being developed by CRE+E consists of hydrofoils which induce a down force from the stream flow and counteract the overturning moment of the tidal current. Devices oscillate to generate electricity.