Tidal Power and Tidal Energy

Tidal energy is power obtained from the regular rise and fall of the sea. Tides are caused mainly by the gravitational pull of the Moon, and to a lesser extent the Sun, on the world's oceans. Because these movements follow predictable cycles, tidal energy is more reliable to forecast than wind or sunlight, even though it is available only at certain times of day. It is a renewable resource, since the tidal motion is continuously driven by gravity and is not depleted by use.

Several methods are used to capture this energy. A tidal barrage works much like a hydroelectric dam: a barrier is built across an estuary or bay, trapping water at high tide and releasing it through turbines as the tide falls, so that the moving water spins the turbines and drives generators. Tidal stream systems instead place turbines directly in fast-flowing tidal currents, where the moving water turns the blades in a manner similar to an underwater wind turbine. In both cases, the kinetic energy of moving water is converted into rotational motion and then into electricity.

Tidal power belongs to the same family as hydropower, since both rely on the energy of moving water and the conversion of potential and kinetic energy into useful work. Historically, the predictable flow of tides was also harnessed by tide mills, which used the incoming and outgoing water to drive machinery in a way related to traditional water wheels. Tidal installations require suitable coastal sites with a large tidal range or strong currents, which limits where they can be built.

Frequently asked questions

What causes the tides that tidal power uses?

Tides result chiefly from the gravitational pull of the Moon, and to a smaller degree the Sun, on the oceans, producing a regular rise and fall of sea level.

How does a tidal barrage generate electricity?

It traps water behind a barrier at high tide and releases it through turbines as the tide falls, so the flowing water spins the turbines that drive generators.

Why is tidal energy considered predictable?

Tides follow regular astronomical cycles, so their timing and size can be calculated far in advance, unlike wind or sunlight.