A hydroelectric power station uses water held in a reservoir at the top of a hill to generate electricity. Explain how energy is transferred from the water in the reservoir to produce electricity, and state one reason why hydroelectric power is considered a renewable energy resource.

WJEC GCSE Physics (Wales) — 1.2 Generating electricity · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The water in the reservoir has gravitational potential energy because it is held at a height. When the water is released it falls, converting its potential energy into kinetic energy. The flowing water drives a turbine, which is connected to a generator that produces electricity. Hydroelectric power is renewable because the water supply can be replenished by rainfall or other natural processes while it is being used.

Examiner tips

  • Use the word ‘potential energy’ for the water at height and ‘kinetic energy’ for the falling water.
  • Show the sequence: potential → kinetic → turbine → generator.
  • Mention that the water cycle replenishes the reservoir to justify renewability.
  • Keep the answer concise – 4 marks only.

Common mistakes

  • Confusing potential energy with kinetic energy for the water in the reservoir.
  • Failing to mention the turbine or generator as the conversion step.
  • Not stating the reason for renewability (e.g. water cycle).

Mark scheme (4 marks)

  1. The water in the reservoir has gravitational potential energy (because it is raised/at height)
  2. As the water falls/flows down, gravitational potential energy is transferred to kinetic energy
  3. The moving/flowing water turns a turbine (which drives/is connected to a generator)
  4. Hydroelectric power is renewable because the water supply can be replenished (e.g. by rainfall) whilst it is being used / it is not a finite resource

Key terms in this question

renewable energy resource

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