Tidal power
A tidal power plant is a hydroelectric power plant, the potential and kinetic energy is transformed from the tides of the sea into electricity.
Tidal power plants derive their energy ultimately the Earth's rotation using the gravitational pull of the moon and the sun to the earth (see also tides ). They slow down the flow of the sea by tidal movement from minimal. The braking is done by damming the up and running flow and, consequently, by the use of the potential energy contained in the retained water through turbines, which then transform the generated by them rotational energy into electrical generators useful energy. In relation to the total braking by the natural tidal friction, this is of no consequence, the earth has because of its high mass a very high rotational energy.
Dam construction
So far, tidal power stations were always realized with a dam in bays or estuaries.
Operation
Tidal power plants operate according to the principle and dam to be built in bays and estuaries in ( estuaries ), which have a particularly high tidal range (difference between high and low water level ). In order for this to be effective, the corresponding bay is dammed with a dike. In the dike are water turbines, which are operated at high tide from flowing water, at low tide from the effluent water, which is why the turbines operate in both flow directions. This is done by setting one changes the rotor blades. Since even a low water gradient can be used to generate electricity, so-called tubular turbines are used, the most well known is the Kaplan turbine.
Such a tidal power plant can also use excess electricity from other power plants to pump sea water into the storage space. So that in the subsequent return in addition an electric current can be generated. In this case, the tidal power station also acts as a pump storage power plant.
Economy and ecology
If one requires a minimum tidal range of 5 m, so there are about a hundred suitable bays on the ground, which could be used for a tidal power station. Only half of these could be an economical use. Since tides every 12 hours and 24 minutes intervals, the power can not be dispensed evenly. This problem of uneven energy is strengthened also by high jumping and weak neap tides. Operation with salt water causes severe corrosion of the turbines; This means considerable maintenance, which in turn lowers the cost efficiency.
They are also environmentally problematic as they affect the flora and fauna of coastal waters. The coastal ecosystems have been created with the natural twelve-hour cycle, but behind such a tidal power plant, the phases are shifted. The migration of aquatic animals from and into the bay, and there opens out into rivers is impeded.
Such tidal power plants with a dam in the future because of the limited possible locations and the high environmental impact can only make a small contribution to cover electricity demand (see links).
Facilities
The first and long -time largest tidal power plant, the Rance tidal power plant was built in 1961 on the Atlantic coast at the mouth of the Rance River in France and opened in 1966. The tidal range is in the bay at St. Malo normally 12, sometimes 16 meters. The concrete dam is 750 m long, which created a reservoir with a surface area of 22 km ² and a net capacity of 184 million m³. The dam has 24 passages, in each of which a turbine is installed with a capacity of 10 MW. The entire plant has a capacity of 240 MW and supplies around 600 GWh of electrical energy. This power plant also works as a pump storage power plant.
In 2011 the tidal power plant Sihwa -ho in South Korea 40 km southwest of Seoul with ten turbines to 25.4 MW each (total 254 MW) was completed. It is part of a 13 km long dam which separates a natural inlet from the Yellow Sea and was originally intended to store water for the surrounding communities. Since the stored water began to rot, planned to be. The now installed low-pressure turbines of the Austrian company Andritz Hydro 22 meters mounted below the water level and use the ongoing costs of power from the effluent at low tide the sea water.
By Sihwa La Rance was replaced as the largest tidal power station in the world.
Another tidal power plant, the tidal power plant Annapolis, albeit with only 20 MW is located in Annapolis Royal on a side bay of the Bay of Fundy in Nova Scotia, Canada. It was commissioned in 1984 and served primarily of research and development. It operates in one-way mode and uses only the outgoing tide.
An even smaller experimental device, Kislaja Guba tidal power plant with only about 400 kW, since 1968 the fjord Kislaja Guba (sour Bay ) exists in the Russian Barents Sea.
Other smaller tidal power plants in Russia there are at Murmansk with 0.4 MW and China. The largest Chinese tidal power plant is located at Jiangxia in Zhejiang Province. It was completed in 1986 and has 10 MW.
For some time a large tidal power plant of 5,000 MW capacity is planned at the Bay of Fundy, the level of investment it but have not been realized. In addition there are also concerns about the impact of such a project; only ecological consequences ( the Bay of Fundy is an important fishing area) is also feared that the tidal range would be changed to the opposite side of the bay by a power plant dam and in cities such as Boston could be flooded.
Meanwhile, it has taken on a dam project in the Bay of Fundy distance and plans instead of standing on the seabed turbines. According to the exhibition shown at the power plant of Annapolis (as of September 2011 ) was the data transfer for test purposes established 2009 12 meter diameter turbine from a few days duration. A study of underwater cameras was unsuccessful, you could examine only two of the existing turbine blades made of composite materials due to the flow. This showed this significant damage. Since the data connection to plant could no longer be produced in 2010 it was decided to recover the turbine. As it turned out after the evaluation of the stored data, the flow at the bottom of the bay was so strong that the turbine had lost all leaves within three weeks.
In the UK it is planned under the name Severn Barrage construction of a particularly large tidal power station. At the mouth of the Severn between Cardiff and Bristol, a 16 km long barrier is to be built by the Bristol Channel. The planned 216 turbines there should achieve an overall capacity of 8500 MW, covering five percent of Britain's electricity consumption. The location is convenient for a tidal power plant due to the high tidal range of up to 15 meters. So far, costs in the amount of 15 billion pounds ( 19 billion euros ) are estimated for the project. In the UK this major project is controversial. Various environmental groups call because of the anticipated environmental damage against the construction of the Severn Barrage. The follow-up of the project was halted in late 2010 by the British government after a feasibility study had calculated costs of up to 34 billion British pounds.
Other types
Nowadays, tidal power plants are hardly built according to the above principle, as the ecological effects are too strong. It is based on so-called in -flow tidal power plants, in which by means incorporated in the water turbine electricity is generated. These can be helical or pinwheel similar or other shapes.
They are described in the article ocean current power plant in more detail.
History
The force of the tidal range was used on the Channel coast in England and France in the 17th century. Even today you can see tide mills from earlier centuries there at some coastal sections.