7.1 Tidal Barrage Systems and Components

Tidal barrages harness the power of ocean tides to generate electricity. These massive structures span estuaries, using sluice gates and turbines to control water flow and produce power. Understanding their components and operation is key to grasping tidal energy potential.

La Rance Tidal Power Station in France showcases tidal barrage technology in action. Operating since 1966, it generates enough electricity to power 225,000 homes annually. This real-world example highlights the long-term viability of tidal energy systems.

Tidal Barrage Components

Main Structural Elements

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• Tidal barrage spans the width of an estuary or bay to create a basin for capturing tidal water
• Embankments are constructed on either side of the barrage to prevent water from flowing around the structure
  • Typically made of concrete or earth-fill materials
  • Provides structural support and protection against erosion
• Basin is the enclosed area behind the barrage where water is stored during high tide and released during low tide
  • Size and shape of the basin affects the amount of energy that can be generated

Water Control and Power Generation

• Sluice gates are large openings in the barrage that can be opened or closed to control the flow of water
  • Allow water to enter the basin during high tide and exit during low tide
  • Typically made of steel and operated by hydraulic or electric motors
• Turbine caissons house the turbines and generators used for power generation
  • Water flowing through the turbines rotates the blades, which drives the generators to produce electricity
  • Caissons are prefabricated concrete structures that are floated into place and sunk onto the barrage foundation
  • Multiple caissons are installed along the length of the barrage to maximize power output (24 at La Rance Tidal Power Station)

Tidal Barrage Operation

Single-Direction Generation Modes

• Ebb generation involves allowing the basin to fill during high tide, then releasing the water through the turbines during low tide
  • Water flows from the basin to the sea, rotating the turbines to generate electricity
  • Most common mode of operation for tidal barrages (used at La Rance Tidal Power Station)
• Flood generation involves allowing water to flow through the turbines into the basin during high tide, then closing the sluice gates to retain the water
  • Less efficient than ebb generation due to the reduced head difference between the basin and the sea

Bi-Directional Generation Mode

• Two-way generation utilizes both ebb and flood tides to generate electricity
  • Turbines are designed to operate in both directions, allowing power to be generated during both filling and emptying of the basin
  • Increases the overall energy output but requires more complex and expensive turbine designs (bulb turbines used at La Rance)

Importance of Head Difference

• Head difference refers to the difference in water level between the basin and the sea
  • Directly affects the amount of energy that can be generated
  • Higher head differences result in greater water flow through the turbines and more power output
  • Tidal range (difference between high and low tide levels) determines the maximum head difference achievable at a given site

Tidal Barrage Example

La Rance Tidal Power Station

• Located on the Rance River estuary in Brittany, France
• World's first large-scale tidal power plant, operational since 1966
• Barrage is 750 meters long and 13 meters high, with a basin area of 22.5 square kilometers
• Equipped with 24 reversible bulb turbines, each rated at 10 MW, for a total installed capacity of 240 MW
• Generates approximately 500 GWh of electricity annually, supplying power to around 225,000 homes
• Demonstrates the feasibility and long-term reliability of tidal barrage technology
  • Has been in continuous operation for over 50 years with minimal environmental impact
  • Serves as a model for future tidal barrage projects worldwide (Swansea Bay Tidal Lagoon proposed in Wales, UK)