Tidal power is a form of marine power. The power of the rise and fall of the sea level can be harnessed to generate electricity. There are only a few commercial tidal power plants operating in the world. The oldest one is located in La Rance, France and the largest one is the Sihwa Lake Tidal Power Station in South Korea. The technology for the production of tidal energy is still in its early moments, and there is room for big improvements.There are different methods to generate tidal power, the 4 top and most relevant are the following: tidal streams or currents (also called tidal turbines), tidal barrages, tidal lagoons, and Dynamic Tidal Power.
Tidal currents (or tidal turbines)
The method of generating energy using the tidal currents or tidal streams is the most commonly used. A tidal stream is a fast-flowing water created by tides which is made pass through a turbine to generate energy in a similar way to wind turbines that use wind to power turbines. Unlike wind, tides are predictable and stable. Where tidal generators are used, they produce a steady, reliable current of electricity. Some tidal generators can be built into the structures of existing bridges, minimising environmental impacts.
The upfront cost of the tidal stream stations is high and installation and maintenance is difficult as well. But it is still less expensive and has less environmental impact than other tidal system like barrages.
Tidal Barrages
A barrage is a dam constructed to harness the energy of the stored water. When the tide is high the water fills the dam creating a pool or tidal lagoon. When the tide is low the water is released into the river passing through a turbine and generating electricity.
Barrages can be constructed across tidal rivers, bays and estuaries. The environmental impact of a tidal barrage may be quite significant for the plant and animal life, as well as for the landscape of the territory. A tidal barrage is a much more expensive tidal energy generator than turbines. The tidal power plant at the Rance River in France, uses a tidal barrage.
Tidal Lagoons
This method of tidal power generation involves the construction of tidal lagoons, normally using already natural lagoons, bays or estuaries so that the environmental impact is reduced compared to the tidal barrages, reducing as well its cost. It works in pretty much the same way as a tidal barrage as when the tide rises the lagoon fills and when it falls the water is then released through the turbines.
But the energy output from generators using tidal lagoons is likely to be low. There are no functioning examples yet worldwide, only China is constructing a tidal lagoon power plant at the Yalu River, near its border with North Korea.
Dynamic Tidal Power (or DTP)
There is another method dedicated to generate tidal energy very promising but still untried, called Dynamic Tidal Power (or DTP). The basis of these new technology consists in harnessing the significant water-level differential in shallow coastal seas after the creation of artificial waves, featuring strong coast-parallel oscillating tidal currents.
Tidal power station can have environmental impacts so it is important to study in depth before the construction which is the impact and how is possible to minimise it.
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