How tidal stream turbines make electricity
Tidal energy uses the rise and fall of the sea, caused by the Moon and Sun. Tidal stream turbines work like underwater wind turbines.
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Seabed-mounted tidal-stream turbine. The pressure housing is sectioned. Reversal is compressed in time to illustrate changing tidal flow. Motion is slowed for inspection. Coloured overlays reveal flow through enclosed equipment; gold pulses show net electrical energy transfer, not individual electrons.
How it works
- Predictable tidal motion
- Water moves through rotor
- Shaft rotation
- Generator and power conversion
- Subsea cable and grid
Tidal energy uses the movement of seawater associated with the tides. A tidal-stream turbine, like the one in this model, extracts kinetic energy from a current flowing past its blades. The rotor drives a generator, power-conversion equipment conditions the output, and a subsea cable carries electricity ashore. In the illustrated arrangement the nacelle turns to face a reversing current; other designs accommodate reversal differently.
The astronomical drivers of tides make their timing predictable, but predictable does not mean constant output. Current speed changes through the tidal cycle, and a stream turbine produces little or no electricity during slack water. Site measurements are needed to understand the usable flow at rotor depth. Tidal-range schemes work differently: a barrier holds water back so a difference in water level can drive turbines. Wave energy uses surface-wave motion and is a separate marine-energy technology, not a tidal-turbine variation.
Inside the engineering
Follow the machinery, the working fluids and the electrical connection.
Mechanical
Hydrofoil blades turn the rotor in moving seawater. Bearings, a drivetrain and shaft seals transmit torque into the pressure housing. The structure and foundation carry current-induced loads; rotation slows around slack water before the next tidal direction.
Thermal & chemical
The resource is moving water, without combustion. Seals, coatings and corrosion protection matter in seawater. Heat from drivetrain and electrical losses must be rejected through a closed cooling arrangement without admitting seawater to the machinery.
Electrical
A generator feeds a cable that descends through a protected support tube and continues along the seabed. Shore-side power electronics, switchgear and transformation connect the turbine to the grid. Generation follows tidal conditions rather than a constant rated output.
Main types and variations
The animation represents a seabed-mounted horizontal-axis tidal-stream turbine. Mounting method, rotor orientation and tidal-range generation are different design choices; the examples below explain how each changes the route from moving water to electricity.
Seabed-mounted tidal-stream turbine
A support structure on the seabed holds a submerged rotor in the current. The foundation transfers the rotor’s thrust into the seabed, while the nacelle houses the drivetrain. Pitch and, in some designs, yaw control help the turbine work through changing flow directions and speeds.
What changes in practice
A fixed foundation keeps the rotor positioned, but installation, retrieval and cable routing must all be planned around the underwater site and tidal conditions.
Floating tidal-stream turbine
A moored floating structure supports submerged rotors in the passing tidal current. On Orbital’s arrangement, hinged legs can lift the turbine assemblies to the surface for access. Moorings hold the platform on station, and an export cable connects the moving structure to the seabed connection.
What changes in practice
Surface access can simplify some maintenance tasks. The design must also accommodate platform movement, mooring loads and the flexible electrical connection.
Vertical-axis tidal-stream turbine
Blades rotate around a vertical shaft as tidal flow passes across the rotor. This changes the blade motion and drivetrain arrangement from the propeller-like horizontal-axis machine. It remains a current-energy device: no basin or dam is needed to create a difference in water level.
What changes in practice
Rotor orientation is a separate choice from whether the supporting structure floats or rests on the seabed. “Tidal turbine” does not identify one universal geometry.
Tidal barrage
A barrier across a tidal basin uses gates to control filling and emptying. As the sea level changes, a level difference develops across the barrier. Water then passes through turbines. Depending on the equipment and operating strategy, generation can use the outgoing tide, the incoming tide or both.
What changes in practice
The resource is a changing water-level difference, not just a fast current. Altered water levels, sediment and estuary habitats are central design considerations.
Tidal lagoon
A seawall encloses an area of water rather than necessarily spanning an entire estuary. Gates and turbines control exchange with the sea as the tide rises and falls. A difference between the enclosed and external water levels supplies the hydraulic head for generation.
What changes in practice
A lagoon is another tidal-range layout. Its output remains tied to tidal cycles, and the enclosing wall and local coastal effects require project-specific assessment.
Worth knowing
- Tidal power is predictable, but only a few sites have strong enough currents.
- Tidal barrages, like La Rance in France, instead trap water behind a dam.
- Wave energy converters capture the motion of surface waves rather than currents.
See real examples
The atlas includes 10 wave and tidal records worldwide.
Show on the mapRelated answers
Textbook references
The science on this page follows these standard engineering textbooks. See the full bibliography.
- Ocean Energy: Tide and Tidal PowerTidal range and tidal stream technologies, history and projects.
- Sustainable Energy — Without the Hot AirHow much energy tides can realistically provide (free to read online).
Sources
Cutaways reveal enclosed equipment. Layouts, dimensions, materials and animation speeds are illustrative; this is an educational model, not a plant design or a thermodynamic simulation.