Supply and demand
2 marks · NormalHydroelectric power stations are considered useful for balancing supply and demand in a national grid.
Describe two reasons why they are particularly effective for this purpose.
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(1) They can be started almost instantly to meet sudden increases in demand. (2) Excess electricity can be used to pump water back into reservoirs, allowing energy to be stored for later use.
Must show: instant starting, energy storage/pumping
Common mistakes: Mentioning environmental effects instead of supply/demand reasons
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Marking points
B1 · 1 mark · Explains fast start/response to demand.
B1 · 1 mark · Describes pumped storage for storing or reusing energy.
Worked solution
They are effective because (1) they can start generating almost immediately, and (2) they store energy by pumping water back to high reservoirs when demand is low, releasing it when demand rises.