1.2.2 Comparing Energy Resources — AQA GCSE Combined Science Trilogy 8464 - Physics Revision Notes & Topical Questions

Section 1 of 9Criteria for comparison

No energy resource is perfect. To compare them fairly we use a set of criteria: reliability (can it supply power whenever needed?), running cost and set-up cost, environmental impact (emissions, land use, waste, effect on wildlife), power output and lifetime, start-up time and geographical suitability. A good answer picks the criteria that matter in the situation described.

Section 2 of 9Reliability and flexibility

Fossil fuel, nuclear, geothermal and biofuel stations can run continuously; their output is controllable.

1

Gas stations can start within minutes, coal stations take hours,

and nuclear stations are best left running continuously because reactors are slow to adjust.

2

Hydroelectric and pumped storage stations can start in seconds to minutes and so cover sudden peaks.

3

Wind, solar, tidal and wave are variable.

4

Tides are predictable (twice a day, with spring tides stronger than neap), whereas wind and clouds are not.

5

Solar cells give no night output.

Section 3 of 9Costs

Wind and solar have no fuel costs and low running costs but their output per unit of area is modest, so many units are needed.

1

Nuclear stations have very high build and decommissioning costs but low fuel cost.

2

Fossil fuel stations are cheaper to build, but pay for fuel throughout their lives, and may need to pay for carbon-capture or emission rules.

3

Hydroelectric dams are expensive to build but cheap to run for many decades.

4

In calculation questions you may need to compare the total cost over the lifetime: total cost = set-up cost + running cost per year × years.

Section 4 of 9Environmental impact

Burning fossil fuels causes carbon dioxide emissions (enhanced greenhouse effect and climate change), and sulfur dioxide (acid rain) from coal.

1

Mining and drilling can damage land and seas.

2

Nuclear produces radioactive waste, but no carbon dioxide in operation.

3

Wind turbines are visually intrusive and can harm birds; hydroelectric dams flood valleys and alter river ecosystems; tidal barrages affect estuary habitats; biofuel crops compete with food production for land.

4

Solar cells need materials and energy to make and must be disposed of or recycled.

When you evaluate, give one benefit and one cost in each case and then state a justified decision. For an island nation with strong winds, wind plus pumped storage could fit. For a remote village with sunshine but no grid, solar cells with batteries are sensible because there are no fuel transport costs.

Section 5 of 9Making a justified choice

To justify a choice, state the situation, pick the most relevant criteria, and compare.

Making a justified choice

For example: "A small mountain village with a fast river and no grid would use a hydroelectric turbine because it provides continuous power, has low running cost and no fuel supply is needed." Use data when available,

such as output in MW, area needed, cost per kWh or emissions per kWh.

Also recognise that a mix of resources balances reliability, cost and emissions, and that energy saving reduces the need for any supply.

Section 6 of 9Evaluating data and trade-offs

When asked to evaluate, combine facts, numbers and reasons.

Evaluating data and trade-offs

If a table gives costs per kWh, emissions per kWh and start-up times, quote at least two values from it.

A resource with the lowest emissions might also be the most expensive to build; a cheap resource may produce a lot of CO₂.

Your conclusion should state which trade-off you consider most important and why, for instance: "Because the island has no coal or gas and imports are costly, wind power with batteries is the better option despite its variable output".

Energy saving is also part of the comparison: reducing demand through insulation, efficient lamps and better machines lowers the number of power stations needed.

Evaluating data and trade-offs

Combining several resources (a mix) avoids dependence on a single type.

For example, wind power may be backed up by gas stations that respond rapidly when the wind drops, with pumped hydro soaking up surplus.

The best answers recognise that no single choice is perfect and justify a compromise based on the situation.

Section 7 of 9Worked examples

A wind farm of 40 turbines each has a rated output of 2.5 MW but, on average, produces 30% of the rated value. Find the average output.
Station A costs £500 million to build and £20 million per year to run; station B costs £200 million and £60 million per year. Compare total cost after 10 years and after 30 years.
A town needs a power supply that can respond within minutes to sudden demand. Suggest a suitable resource with a reason.

Section 8 of 9Key terms

Term	Meaning
Reliability	The ability to supply power whenever it is needed.
Set-up cost	Cost of building and commissioning a power station.
Running cost	Ongoing costs such as fuel and maintenance.
Start-up time	Time taken to bring a power station to full output.
Greenhouse gas	Gas such as carbon dioxide that traps infrared radiation in the atmosphere.
Decommissioning	Safely shutting down and dismantling a station at the end of its life.

Section 9 of 9Exam technique

1

Concluding that "renewable is always better" without mentioning reliability or cost.

2

Comparing only one aspect (such as cost) and ignoring the situation described.

3

Forgetting that rated output is not the same as average output.

4

Assuming nuclear power releases CO₂ from fission; the emissions come from construction and fuel processing.

5

Stating "it's cheaper" without saying whether set-up or running cost is meant.