As the world searches for alternatives to oil, the use of tidal energy may be a viable solution. Tidal energy or tidal power is a form of hydropower. It converts the energy of tides into electricity and other forms of power. However, not everyone believes tidal energy is a cost and environmentally efficient answer to the energy crisis.

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How Tidal Energy Works

Tidal energy is produced with the changing levels of the sea; the tide moving in and out. There are three ways to harness the power of the tides.

Tidal turbines are much like underwater windmills. They use the same technology as windmills, but the blades are stronger and shorter. The water current turns the blades which activate a generator which produces electricity. This type of system works best in strong tidal zones.

Tidal barrages, the second method of how tidal energy works, are similar to dams, but are much bigger as they are built across a bay or estuary. The range between low and high tide must exceed five meters (16.4 feet) for the barrage to work. As the tides come in, the water is collected into the basin through the dam. When the tide stops, the gates close and trap the water. As the tide goes back out, turbines in the gates open and as the water flows through them, generates energy.

Tidal lagoons are the third method of how tidal energy works. They are similar to barrages but are lower in cost and environmental impact. Tidal lagoons are self contained structures sectioned off from the sea. They work the same as the tidal barrage; as the tide rises, the lagoon fills and as the tide falls, the water turns the turbines which generate energy.

History of the Use of Tidal Energy

Hydropower is nothing new. For centuries people have used water to produce energy, from mills for processing grains to irrigation systems for crops. The use of waterpower can be traced back to ancient Egypt and Mesopotamia, the Turpan water system in ancient China and the Qanat system in ancient Persia.

Early methods of the use of tidal energy were dams with a sluice spanning a tidal inlet. The water flowed into the reservoir through a one-way gate which automatically closed. As the tide fell, the stored water was released to turn a water wheel. The Woodbridge Tide Mill built in 1170 in Suffolk, England is an example of this type of mill. These early systems are early methods of how tidal energy works.

Waterwheels and similar devices eventually gave way to the more efficient bulb-type hydroelectric turbine-generator combination. The first actual tidal wave hydropower facility was built in Brittany, France on the estuary of the Rance River. It opened in 1966 and is the largest tidal power station in the world in terms of installed capacity. It has 24 turbines reaching a peak rating of 240 Megawatts of power; enough power to supply .012% of France’s power demands.

The second large tidal barrage was built in 1982 and is located at Annapolis Royale, Nova Scotia, Canada. This tidal barrage boasts a 20 megawatt turbine and is the only commercial tidal barrage in North America. Currently, European and Asian countries are constructing hydroelectric tidal barrage plants of varying capacities.

Pros and Cons of the Use of Tidal Energy

The use of tidal energy has both advantages and disadvantages. Those opposed to constructing tidal barrages site the following reasons:

• Barrages impede fish migration; fish are instinctively obliged to swim through the turbines of the barrages at least twice in the migrating route and the mortality rate is about six percent.

• Barrages block navigation; even when locks are installed; it is slow and more costly;• Barrages change the intertidal zone; plant and animal life must adapt or move to a new location which impacts the ecosystem of the area.

• Barrages change the tidal regime downstream; numerous studies show coastal concerns hundreds of miles from proposed hydroplant sites.

• Tidal turbines have a high upfront cost and are difficult to install and maintain; and• Barrages have high infrastructure cost and are lengthy projects.

Those in favor of the use of tidal energy stations site these advantages:

• Tides are predictable and go in and out twice a day, making it easy to manage positive spikes.

• Its predictability makes it easy to integrate into existing power grids.

• Tidal energy is completely renewable.

• Tidal energy produces no emissions.

• Tidal energy reduces dependency on oil reserves from other countries.

• Dams built can double as protective cover for coastline during rough weather.

While the use of tidal energy must be considered as a future source of energy, environmental and cost concerns will have to be addressed. As technology advances, there is no reason not to believe that engineers, scientists, biologists and other related professionals will develop a way to harness the tide more effectively.