A wind turbine transfers energy from the wind to electrical energy. Explain why the wind turbine cannot be 100% efficient, and describe what happens to the energy that is not usefully transferred.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A wind turbine is connected to the National Grid. Its power rating is 2 MW. Engineers note that a significant proportion of the input energy is lost during operation.
Model answer (4 marks)
A wind turbine cannot be 100% efficient because the efficiency of any real system is limited by the conservation of energy – energy cannot be created, only transferred.
Only part of the kinetic energy of the wind is converted into useful electrical energy; the rest is lost as waste energy.
The waste energy is mainly converted into thermal energy (heat) by friction in the moving parts and by aerodynamic drag.
This heat is then dissipated into the surroundings, so the energy is no longer useful for the system.
Only part of the kinetic energy of the wind is converted into useful electrical energy; the rest is lost as waste energy.
The waste energy is mainly converted into thermal energy (heat) by friction in the moving parts and by aerodynamic drag.
This heat is then dissipated into the surroundings, so the energy is no longer useful for the system.
Examiner tips
- Use the term ‘efficiency cannot exceed 100% because of the conservation of energy’.
- Mention that the lost energy becomes heat due to friction and drag.
- Explain that this heat is dissipated to the surroundings and is no longer useful.
Common mistakes
- Claiming the turbine can be 100% efficient, ignoring the conservation of energy.
- Saying the energy is ‘lost’ without specifying it becomes heat or is dissipated.
- Using vague terms like ‘other energy’ instead of ‘thermal energy’.
Mark scheme (4 marks)
- The efficiency can never exceed 100% / 1 due to the conservation of energy — energy cannot be created
- Some energy is transferred as waste energy / not all energy transfer serves the purpose of the system
- Waste energy is transferred as thermal energy / heat due to friction in the moving parts
- Waste energy is dissipated / spread out to the surroundings and is no longer useful
Related
- All WJEC GCSE Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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