A new tidal barrage is proposed for a coastal region to generate electricity as a renewable energy resource. Describe how the tidal barrage generates electricity and explain one advantage and one disadvantage of using tidal energy compared with using fossil fuels.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A coastal council is considering replacing a small coal-fired power station with a tidal barrage. The coal-fired power station burns coal to release thermal energy, which heats water to produce steam that turns turbines connected to generators.
Model answer (4 marks)
A tidal barrage uses the rise and fall of sea level to drive water through turbines.
1. During high tide water flows into the barrage and is stored behind a dam.
2. When the tide recedes the stored water is released through sluice gates, passing through turbines.
3. The turbines spin a generator, producing electricity.
Advantage: Because the energy comes from the sea’s motion, no carbon dioxide or other greenhouse gases are released during generation, unlike burning coal.
Disadvantage: Tidal power can only be produced when the tide is moving; it is not available continuously, whereas a coal plant can generate electricity on demand.
1. During high tide water flows into the barrage and is stored behind a dam.
2. When the tide recedes the stored water is released through sluice gates, passing through turbines.
3. The turbines spin a generator, producing electricity.
Advantage: Because the energy comes from the sea’s motion, no carbon dioxide or other greenhouse gases are released during generation, unlike burning coal.
Disadvantage: Tidal power can only be produced when the tide is moving; it is not available continuously, whereas a coal plant can generate electricity on demand.
Examiner tips
- Use the word ‘turbine’ and ‘generator’ to show the conversion of kinetic to electrical energy.
- Mention the cycle of high/low tide to explain intermittency.
- Show the environmental benefit of zero CO₂ emissions.
- Highlight the lack of continuous availability as the main drawback.
Common mistakes
- Confusing tidal energy with wave energy or describing only a single turbine without the storage step.
- Claiming tidal power is continuous or that it emits CO₂.
- Using vague terms like ‘renewable’ without linking to the tidal cycle.
Mark scheme (4 marks)
- Wave/tidal action directly turns turbines (in the barrage) to generate electricity
- Tidal energy is a renewable energy resource / can be replenished whilst it is being used (whereas fossil fuels are non-renewable / finite)
- Advantage: tidal energy does not produce carbon dioxide / greenhouse gases / does not cause air pollution when generating electricity (whereas burning fossil fuels does)
- Disadvantage: tidal energy is not always available / depends on tides so electricity cannot be generated continuously / at all times (whereas a fossil fuel power station can generate on demand)
Key terms in this question
renewable energy resource · tidal
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
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- Decode the mark scheme abbreviations →
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