Tidal and ocean-current power
Barrages, lagoons and underwater turbines driven by tides and steady ocean currents.
Capture · Water and ocean · No. 32
- Capture
- Output: Electricity
The La Rance barrage has made tidal power since 1966 and carries a road for up to 60,000 vehicles a day.
Chart: Illustration: Tidal and ocean-current power
Where it comes from
The pull of the Moon and Sun lifts and drops the sea every day. Barrages trap water behind a dam, while stream turbines sit in fast channels like underwater windmills.
Two barrages, Sihwa at 254 MW and La Rance at 240 MW, make up most of the roughly 513 MW of ocean power operating at the end of 2024.
Three things to know
- Tides can be predicted years ahead, but a barrage that generates only on the ebb runs for about four hours a day.
- Power rises with the cube of current speed, so only channels flowing faster than about 1.5-2 m/s are worth harnessing.
- When La Rance closed its estuary, most marine life vanished; a new and different balance took about ten years to form.
The journey
- 1 Moon and SunGravity raises and lowers the sea
- 2 TidesWater floods and drains estuaries
- 3 Barrage or rotorTraps a head, or sits in current
- 4 TurbineBulb turbines or underwater blades spin
- 5 Subsea cablePredictable power delivered to shore