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3.5 Big Energy Issues

GCSE Physics · AQA · Chapter 3: Energy Resources

A free GCSE Physics lesson for AQA (8463) from OBA School: matching supply to demand, comparing costs, trends in energy use, and the wider issues in choosing energy resources. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

  • Explain how power stations and pumped storage are used together to meet changing demand for electricity
  • Compare the capital, running and decommissioning costs of different energy resources
  • Describe and explain trends in the use of energy resources
  • Discuss the social, economic, environmental and ethical issues in choosing energy resources, and the limits of what science can solve

Key words

  • Demand: The total power that consumers need from the grid at a given time.
  • Base load: The minimum demand that is always there, day and night; supplied by stations that run all the time.
  • Start-up time: The time a power station needs to go from switched off to generating at full power.
  • Capital cost: The cost of building a power station (and, at the end, of decommissioning it).
  • Running cost: The cost of fuel, staff and maintenance while the station is generating.
  • Payback time: The time for the money saved by an energy-saving measure to equal what it cost.

Supply and demand

Electricity has to be generated at the moment it is used, so supply must match demand all the time. Demand changes:

  • during the day – lowest in the early hours of the morning, rising as people wake up, with a peak in the late afternoon and early evening (cooking, lighting, heating).
  • through the year – higher in winter, because it is colder and darker, so more heating and lighting are used.

Meeting the demand: start-up times

Different power stations take very different times to start up, so they are used in different ways:

  • Nuclear (and, in the past, coal); How it is used runs all the time to supply the base load; too slow to follow quick changes
  • Gas-fired; How it is used switched on and off to meet daily peaks and extra winter demand
  • Pumped storage; How it is used pumps water up when demand is low; generates within seconds for sudden rises
  • Wind and solar; How it is used used whenever conditions allow; spare output can be stored (e.g. pumped storage, batteries)

Renewable resources are unreliable: wind and waves drop on calm days, solar gives nothing at night and less in winter, tides vary with a monthly cycle, and reservoirs can run low in a drought. So a mix of resources and some energy storage is needed.

Comparing costs

The total cost of a power station includes the capital cost to build it, the running costs (fuel and maintenance) over its lifetime, and the cost of decommissioning it at the end. Building costs are often compared per kW of power; running costs per kWh of energy.

  • Gas; Build cost (£ per kW) 800; Running cost (p per kWh) 7.0; Comments cheap to build, but fuel is expensive; more with CCS
  • Nuclear; Build cost (£ per kW) 7000; Running cost (p per kWh) 1.5; Comments very costly to build and to decommission
  • Offshore wind; Build cost (£ per kW) 3000; Running cost (p per kWh) 0.8; Comments no fuel; maintenance at sea
  • Solar farm; Build cost (£ per kW) 700; Running cost (p per kWh) 0.4; Comments cheap to run; low output in winter
  • Hydroelectric; Build cost (£ per kW) 3500; Running cost (p per kWh) 0.3; Comments dam is costly, but lasts a very long time

Illustrative figures only – real costs change from year to year.

Worked example: build costs for 1200 MW of power

1200 MW = 1 200 000 kW
gas-fired: 1 200 000 × £800 = £960 000 000 (£0.96 billion)
offshore wind: 1 200 000 × £3000 = £3 600 000 000 (£3.6 billion)

Answer: wind costs about 3.75 times as much to build, but has no fuel costs

Saving energy reduces how many power stations are needed. Home insulation, efficient boilers and LED lamps cost money at first but cut fuel bills.

Worked example: payback time of cavity wall insulation

Insulation costs £720 to fit and saves £240 a year on heating bills.
payback time = cost ÷ saving per year = 720 ÷ 240 = 3 years

Answer: 3 years

Trends and wider issues

  • UK trends (see graph): coal fell from about a third of UK electricity to almost nothing; the last UK coal-fired power station closed in 2024. Reasons: CO₂ and acid-rain gases, carbon pricing, cheaper gas.
  • Renewables (mostly wind, plus solar and biomass) grew to about half, as costs fell and governments set targets to cut CO₂.
  • Worldwide, fossil fuels still supply most energy, and demand is rising as populations grow and countries develop.

Choosing energy resources involves more than physics. Science can measure emissions, costs and reliability, but it cannot decide on its own what we should do. Decisions also depend on:

  • Economic; Examples building and running costs; jobs; energy bills; cost of decommissioning and storing waste
  • Environmental; Examples greenhouse gases, acid rain, habitats, radioactive waste
  • Social; Examples noise and views near wind farms; homes lost to reservoirs; local opposition
  • Ethical and political; Examples effects on future generations; fairness to poorer countries; relying on imported fuel (energy security)

Exam tip: In “evaluate” or “discuss” questions, give points on both sides – reliability, cost, environment, social effects – then make a justified conclusion.

Common mistakes

  • Saying nuclear power stations are used for peaks. They are slow to start, so they supply the base load.
  • Calling pumped storage a renewable energy resource. It only stores energy from other stations.
  • Comparing only build costs. A station that is cheap to build (gas) can be expensive to run because of fuel.
  • Payback time: dividing the saving by the cost instead of the cost by the yearly saving.

Revision questions

Try these, then check your answers below each one.

Question 1. Which type of power station has the shortest start-up time? (Choose from: pumped storage, gas-fired, coal-fired, nuclear.)

Answer: pumped storage

Working: Pumped storage can generate within seconds to a minute. Gas-fired stations take minutes to hours, coal several hours and nuclear days.

Question 2. What name is given to the minimum demand for electricity that has to be supplied all day and all night?

Answer: base load

Working: The base load is the constant minimum demand. It is usually met by nuclear power stations, which run all the time.

Question 3. New double glazing costs £3600 and saves £240 a year on heating bills. Calculate the payback time.

Answer: 15 years

Working: 3600 ÷ 240 = 15 years.

Related lessons

Continue in the full course

This lesson is section 3.5 (AGCPH0305) of our free GCSE Physics course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Physics course.

 

 

 

 

 

 

 

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