Tidal range power
Electricity generated from the height difference between high and low tide, by impounding water behind a barrage or lagoon and releasing it through low-head turbines.
Tidal range power uses the same principle as low-head hydro, with head created by the tide. A barrage across an estuary or an artificial lagoon traps water at high tide; as the sea falls, water is released through bulb turbines. Plants can generate on the ebb only, the flood only, or both directions.
The theoretical energy per tidal cycle for a basin of area A and range R is:
Energy scales with the square of range, so only sites with mean ranges above roughly 5 m are considered viable: the Severn Estuary (UK, up to about 14 m), Bay of Fundy (Canada, up to 16 m), the Rance (France), Gulf of Khambhat (India) and parts of Korea and Russia.
Operating examples:
- Sihwa Lake (South Korea, 2011): 254 MW, the largest, flood generation only
- La Rance (France, 1966): 240 MW, about 500 GWh per year, 24 bulb turbines
- Smaller plants at Annapolis Royal (Canada, now closed) and Jiangxia (China)
Tidal output is highly predictable years ahead, but it shifts about 50 minutes per day and varies over the spring-neap cycle, giving capacity factors of about 20–30%. Very high capital costs, long build times and estuarine ecological impacts on sediments, birds and fish have blocked large projects such as the Severn Barrage and Swansea Bay lagoon. Long asset lives of 100 years or more can lower lifetime cost, but only with low discount rates.
Related terms
All terms →- Tidal stream power
Electricity generated by underwater turbines placed in fast tidal currents, analogous to wind turbines but driven by water about 800 times denser than air.
- Kaplan turbine
A propeller-type reaction hydro turbine with adjustable runner blades and wicket gates, suited to low heads of about 2 to 40 m and large flows.
- Wave energy
Energy captured from the motion of ocean surface waves using devices such as point absorbers, oscillating water columns and attenuators; still at pre-commercial stage.
- Capacity factor
The ratio of the energy a power plant actually produces over a period to the energy it would produce running at full nameplate capacity for the whole period.
- Hydraulic head
The vertical height difference between the water surface at a hydropower intake and the turbine outlet or tailwater, which together with flow determines available power.