Energy Resources and Electricity Generation
6 marks · NormalA large country currently relies mostly on coal-fired and hydroelectric power stations. It is considering increasing its use of wind turbines. The graph below shows a typical day's changes in national electricity demand.
At what time of day is electricity demand at its highest? Give your answer in hours.
Which type of power station (coal-fired, hydroelectric, or wind turbine) is best suited to deal with sudden increases in demand shown on the graph? Explain your answer.
Describe one environmental disadvantage of relying on coal-fired power stations and one disadvantage of relying on wind turbines.
Suggest one reason why hydroelectric or wind power alone cannot always meet all the demand shown in the graph.
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(a) 16 hours (4:00 pm)
(b) Hydroelectric power stations are best suited, because they can be started and stopped quickly to respond to sudden changes in demand.
(c) Coal-fired stations: release greenhouse gases and contribute to global warming. Wind turbines: can spoil the landscape and cause noise pollution.
(d) Hydroelectric or wind power depend on weather and water levels, which may not match demand at all times.
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · States peak demand at 16 hours (accept 4 pm).
B1 (b) · 1 mark · Identifies hydroelectric as most responsive.
M1 (b) · 1 mark · Explains hydroelectric stations' quick response or start-up.
A2 (c) · 1 mark · Correctly states one environmental disadvantage for coal.
A3 (c) · 1 mark · Correctly states one environmental disadvantage for wind.
B2 (d) · 1 mark · Gives one valid reason (e.g., dependence on weather, water availability) why renewables cannot always meet demand.
Worked solution
a) Electricity demand is highest at 16 hours (4 pm).
b) Hydroelectric power stations are best because they can be turned on or off very quickly and respond rapidly to changes in demand, unlike coal which takes hours to start up, and wind turbines which depend on wind.
c) Coal-fired stations emit CO2, a greenhouse gas, which contributes to global warming. Wind turbines may spoil the view, create noise, and may be dangerous to birds.
d) The availability of water (for hydro) or wind (for wind turbines) may not be high enough at all times to supply the needed electricity.