A tidal barrage is a dam-like renewable energy machine built across an estuary or bay where the ocean tide rises and falls predictably. It captures water at high tide, stores it in a tidal basin, and later releases it through turbines to make electricity. Tidal power matters because tides are driven mainly by the Moon and Sun, so their timing can be predicted far in advance.
This makes tidal barrages a reliable renewable source compared with weather-dependent energy sources.
Key Facts
- Tidal range is the height difference between high tide and low tide.
- Stored gravitational energy depends on water height: E = mgh.
- Power is the rate of energy transfer: P = E/t.
- Water flow through a turbine can be estimated by Q = A v, where Q is flow rate, A is area, and v is water speed.
- Electrical energy output depends on efficiency: Eout = efficiency x Ein.
- A tidal barrage usually generates most power when there is a large water level difference across the dam.
Vocabulary
- Tidal barrage
- A tidal barrage is a dam built across a tidal inlet or estuary to control water flow and generate electricity from tides.
- Tidal basin
- A tidal basin is the enclosed body of water behind the barrage where water is stored during part of the tide cycle.
- Turbine
- A turbine is a rotating machine that converts moving water energy into mechanical energy.
- Generator
- A generator converts the mechanical rotation of a turbine into electrical energy.
- Tidal range
- Tidal range is the vertical difference between the high tide water level and the low tide water level.
Common Mistakes to Avoid
- Confusing tidal barrages with wave energy devices, because barrages use the rise and fall of tides rather than the surface motion of waves.
- Assuming a barrage generates constant power all day, because power changes with the water level difference and the timing of the tide cycle.
- Ignoring efficiency losses, because turbines, generators, and water flow resistance mean not all stored gravitational energy becomes electricity.
- Using the ocean depth instead of the tidal range in E = mgh, because the useful height difference is the level difference across the barrage.
Practice Questions
- 1 A tidal basin stores 2.0 x 10^8 kg of water at an average height difference of 4.0 m. Estimate the stored gravitational energy using E = mgh with g = 9.8 m/s^2.
- 2 A barrage releases 6.0 x 10^7 J of useful electrical energy over 30 minutes. What is the average electrical power output in watts?
- 3 Explain why a tidal barrage may produce electricity at predictable times but still not produce the same amount of power at every moment.