Tidal energy is a sustainable source of energy that has been used for many years worldwide. The principle of tidal energy is based on capturing the movement produced in the water by the tides. This is achieved by using turbines which converts the movement into electricity. There are many examples in history of such application, for instance, the tidal mills built in UK, France, Spain and Portugal as early as the twelfth century near the coasts and big rivers.
Bay of Fundy, between the Canadian provinces of New Brunswick and Nova Scotia, a place well know for its high tides. Picture from kasio69 (Flickr) (CC BY 2.0)
Tidal energy can only be obtained in special locations where the tides are high and regular enough to produce large amounts of electricity, then the installation of such turbines is considered acceptable from the economical point of view. Prior to the installation of any tidal power plant a thorough study is done in order to calculate the number and intensity of tides and have an accurate prediction of the electricity to be produced by the power plant.
Presently, tidal energy is exploited in locations near oceans and seas, as well as rivers mouths. Natural narrow channels with high tidal flow rates can also take the advantage of capturing the tidal power. In order to increase the efficiency of the tidal plants, in some places, the energy is stored in dams, nearby the coast or river mouths.
Another of the considerations for the tidal power plants is the environmental impact that can cause. This situation limits its installation to spots where the impact on the location is low or negligible. If the technology is developed further in the future, it will also mitigate the environmental impact.
Tidal power projects are generally expensive due to the equipment necessary to install, for that reason only locations with sufficiently high tides are nowadays considered. All this limitations can change in the future if the technology used to harness the tidal power resource is developed and used in large-scale. It is expected that in the near future this type of renewable energy increases its presence worldwide due to the further developement of the associated technology. There are many studies showing the potential of tidal energy in Europe and America, and this would lead to supply a substantial share of future electricity demand.
Currently tidal power plants are located in the Atlantic coastal areas of North America and France and in the Irish Sea in the case of UK. The East China Sea is where the Sihwa Lake tidal power station is located. The countries using most the tidal energy are South Korea (Sihwa Lake 254MW), France (Rance 240MW), Canada (Annapolis Royal 20MW), China, Russia and UK.