Tidal energy works by using special generators to convert the energy produced by the rise and fall of ocean tides into electrical power. The force of the water drives turbines placed in tidal streams or installed in dams called barrages.
One method of using tidal energy involves placing turbines directly into fast-flowing tidal streams. These streams are more stable and predictable than wind, and because of the density of water, they are more powerful. These work best in shallow coastal currents in areas such as inlets or straits where tides move at high velocity. They can be built into bridge structures or lined up in rows or fences similar to windmills at wind farms. Barrages are dams constructed across estuaries, bays or tidal rivers. When the tide rises, the gates are open, but when high tide is reached, they close. When the captured water is released, it flows through turbines in the dam to generate electricity.
Although the cost of operating tidal power plants is low, they are expensive to build. To prevent corrosion, special materials must be used such as stainless steel, titanium and various alloys. Lubricants and chemicals in the structures potentially can pollute ocean water. Additionally, there is risk of damage to marine life and habitats through silt build-up, generator noise and fish or marine mammals getting struck by the rotating blades.