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Tidal energy is a form of green energy that harnesses the natural motion of the tide.
Compared with wind, which is intermittent and variable, tidal current energy has some distinct advantages such as high predictability and regularity, which make the exploitation of tidal current energy more attractive. Along those same lines, tidal current energy is compatible with the environment.
Tidal power is non-polluting, reliable and predictable.Changing tidal flows by damming a bay or estuary could, however, result in negative impacts on aquatic and shoreline ecosystems, as well as navigation and recreation.Each specific site is different and the impacts depend greatly upon local geography, meaning that solid environmental impact data is almost impossible.In the Bay of Fundy, tidal power plants could decrease local tides by 15 cm. This does not seem like much when one considers that natural variations such as winds can change the level of the tides by several metres.The main barrier to increased use of the tides is that of construction costs. There is a high capital cost for a tidal energy project, with possibly a 10-year construction period.Source
The major factors in determining the cost effectiveness of a tidal power site are the size (length and height) of the barrage required, and the difference in height between high and low tide. These factors can be expressed in what is called a site's "Gibrat" ratio. The Gibrat ratio is the ratio of the length of the barrage in metres to the annual energy production in kilowatt hours (1 kilowatt hour = 1 KWH = 1000 watts used for 1 hour). The smaller the Gibrat site ratio, the more desireable the site. Examples of Gibrat ratios are La Rance at 0.36, Severn at 0.87 and Passamaquoddy in the Bay of Fundy at 0.92.Source
“Once deployed, marine and wave power technologies change water flow and turbulence, and scientists want to know how these changes impact marine wildlife, namely whether their environment impact is minimal or not.These sonars will give scientists precious info on how fish and birds act around different marine renewable energy devices, and will give them an answer about the possible risk of collision between marine wildlife and installed turbines (tidal power is renewable energy that comes from tidal currents and is generated by using turbines in the tidal flow).Tidal and wave resources have great potential to become important renewable energy sources in years to come. These two sources are predictable and this gives them an important advantage over solar and wind. However, before widely deploying wave and tidal energy technologies it is important to study their environmental impact.”
Tidal Streams are common in remote areas. This means that careful consideration of the wishes of the local community is required to ensure the scheme can work to its potential. Being under water avoids aesthetic problems and shipping and navigation should not be affected provided it is taken into consideration when planning. The scheme can provide employment during construction and operation, which will add to the local economic prosperity. Also, these schemes are unique at present and would help to put the area on the map.Source
Construction was actually started on a large-scale tidal power project proposed for Passamaquoddy Bay in the 1930's, but the project was later abandoned for economic reasons...However, much of the required technology is still in the research and development stage, and the economic viability and environmental impacts of these technologies are largely unknown.Source
The world's largest tidal barrage is the Lake Shiwa in South Korea. It has a peak capacity of 254MW and yearly production of 552.7 GWh. Currently, the Koreans are looking into the possibility of building and expanding seven more facilities, including the second largest tidal barrage, the Icheron, with potential of 700-1000MW. They are also looking into expanding the Uldolmock plant from 1 MW to 90 MW by 2013.
The world's oldest and second largest operating facility, at La Rance, France, exhibits a peak rate of 240 MW capacity. With tidal ranges of about 8 meters, the facility generates about half a billion kWh annually using 24 low-head Kaplan turbines.
The third largest power plant, and the only one in North America, is Canada's Annapolis Royal tidal power plant. Located in Nova Scotia's famous Bay of Fundy, the plant exhibits a peak generating capacity of 20 MW with annual yield of 30Gwh/y. Built in 1984 as a pilot project to test the effects of such a plant, Annapolis Royal will be not be alone in the bay for much longer. Recent test programs and government incentives have boosted development, and proposals for tidal current turbines have been announced.
The Jiangxia Tidal power station in China emits 3,200 kW from five experimental units. This is the only tidal power plant in China. China has raised several other small test plants, though about half of them are now shut down.Source
Tidal Energy is non-polluting and uses inexhaustible, renewable, and untapped energy resources.With Biorock technology, Tidal Energy can be used to protect low-lying islands and coasts, and restore coral reefs and fisheries damaged by global warming(It is currently being used in the Amazon, South Korea, Ireland, Wales, Denmark (shortly if not now), France, Annapolis (North America), China, and other places). It does not create any emissions that may contribute to global warming. Tidal power is not entirely the most consistent source of electricity though, as it does not adhere to peak usage schedules, due to daily tidal cycles (differing energy harnessing potential between Ebb and Flood tides). Tidal energy is most sustainable and beneficial as a tool in a larger tool belt of renewable energy sources needed to meet our energy demands. Source
As an energy source, tidal power is one of the greener options because it does not emit harmful greenhouse gases or contribute to the accumulation of acid rain. Questions remain, however, on the long-term impact of underwater turbines and barrages on ecosystems, as well as on recreation and tourism.The steep construction and maintenance costs associated with undertaking massive projects in challenging physical environments also are a potential deterrent to the use of tidal power. (This is saying that it is really expensive to build and maintain these).Source