Tidal power converts the rise and fall or movement of ocean water into electricity.
Tides are driven mainly by the gravitational forces of the Moon and Sun, combined with Earth’s rotation. Tidal-range projects use the difference in water level between a basin and the sea. Barrages or lagoons can hold water and release it through turbines as the tide changes. Tidal-stream systems instead place underwater turbines in fast-moving channels.
Tidal energy is highly predictable compared with wind and solar because astronomical cycles can be calculated far in advance. However, suitable sites are limited, and construction can affect sediment movement, habitats, navigation, and fish populations.
Tidal power is distinct from wave power. Waves are created mainly by wind acting on the ocean surface, whereas tides result from gravitational interactions. It is also different from ocean thermal energy conversion, which uses temperature differences between warm surface water and cold deep water.