A hydroelectric power (HEP) station is built in a mountainous region where a large reservoir stores water at a high elevation. Describe the sequence of energy transfers that occur from the stored water until electrical energy is produced, and state one advantage and one disadvantage of using hydroelectricity compared with burning fossil fuels.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Water stored at a high elevation in a reservoir is released and flows down through pipes to drive turbines connected to generators at the base of a dam.
Model answer (4 marks)
Gravitational potential energy of the water in the reservoir is converted into kinetic energy as the water flows down the penstock.
The kinetic energy of the moving water turns the turbine blades.
The turbine rotation drives the generator, which converts mechanical energy into electrical energy.
Advantage: hydroelectricity is a renewable source and produces no greenhouse‑gas emissions.
Disadvantage: the power output is less reliable because it depends on rainfall and water availability.
The kinetic energy of the moving water turns the turbine blades.
The turbine rotation drives the generator, which converts mechanical energy into electrical energy.
Advantage: hydroelectricity is a renewable source and produces no greenhouse‑gas emissions.
Disadvantage: the power output is less reliable because it depends on rainfall and water availability.
Examiner tips
- Use the exact sequence: GPE → kinetic → turbine → generator → electricity. Mention renewable and zero emissions as the advantage. State a single disadvantage such as reliability or dependence on rainfall. Keep the answer concise and use UK spelling.
Common mistakes
- Confusing potential energy with kinetic energy. Including unrelated details such as water treatment. Failing to mention the renewable nature or emissions advantage.
Mark scheme (4 marks)
- Gravitational potential energy (GPE) of the stored water is transferred to kinetic energy as the water flows down
- Kinetic energy of the moving water turns the turbine, which drives the generator to produce electrical energy
- One advantage: hydroelectricity is a renewable energy resource / does not release greenhouse gases / does not contribute to global warming / no fuel costs once built
- One disadvantage: hydroelectricity is less reliable / depends on rainfall levels / flooding of land to create reservoir causes habitat destruction / high initial construction cost
Related
- All Pearson Edexcel International GCSE Physics (4PH1) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
More Energy resources and electricity generation questions
- A coastal town is planning to install a tidal energy power station to generate e…
- A school is deciding whether to install solar panels or a small wind turbine to …
- A remote mountain village currently uses a diesel generator to produce electrici…
- A country currently generates most of its electricity by burning fossil fuels. T…