Lesson focus: Energy resources must be compared using several measurable criteria rather than a single label.
Compare reliabilityHow dependable something is: results you can trust when repeated, or an energy supply that is there when needed., response, emissions, land use, cost and environmental effects using evidence.
Build on earlier learning
Energy resourcesAfter classifying resources, this lesson compares their performance and impacts.
You will be successful when you can…
- Use several comparison criteria.
- Distinguish power from total energy.
- Explain intermittency and dispatchability.
- Recognise life-cycle impacts.
Words that carry the science
- reliability
- Ability to provide the required supply when needed.
- intermittent
- Not continuously available because the driving condition varies.
- dispatchable
- Able to increase or decrease output in response to demand.
- capacity factor
- Actual output over time compared with maximum possible output.
- life-cycle impact
- Effect across extraction, construction, operation and decommissioning.
Comparison needs common criteria
01Comparison needs common criteria
A fair comparison considers output, reliabilityHow dependable something is: results you can trust when repeated, or an energy supply that is there when needed., response time, cost, construction time, land or water use, pollution and greenhouse-gas emissions.
No resource ranks best on every criterion. A conclusion must match a stated location and demand.
02Availability and control differ
Wind and solar output depend on weather and daylight. Storage, interconnection and a varied supply mix can help match demand.
Gas, hydroelectric reservoirs and some stored fuels are dispatchableCan be switched on or turned up quickly when more electricity is needed., but response speed and constraints differ. Nuclear plants generally supply steady large output rather than rapid balancing.
03Operational and life-cycle evidence differ
Wind, solar and nuclear have low direct operational carbon emissions, but construction and fuel cycles still have impacts.
Fossil fuels release carbon dioxide during operation and can produce air pollutants. Life-cycle comparisons must use consistent boundaries and units.
Choose supply for an island clinic
The clinic needs dependable night power. The island has strong sun, limited fuel deliveries and space for batteries.
- Define the need: continuous critical supply, including night.
- Solar alone cannot meet night demand without storage or backup.
- Battery storage can shift daytime generation but has capacity and life-cycle limits.
- A justified design combines solar, suitable storage and an emergency backup rather than relying on one criterion.
How to make the reasoning visible: The decision follows local evidence and the reliability requirement.
Compare resource evidence
Scores are illustrative from 1 low to 5 high and require context.
| Resource | Dispatchability | Direct CO₂ | Local land effect |
|---|---|---|---|
| wind | 1 | 1 | 3 |
| gas | 5 | 5 | 2 |
| solar | 1 | 1 | 3 |
| reservoir hydro | 4 | 1 | 5 |
Why can the table not select a universal winner?
Which additional evidence would improve the comparison?
Check your understanding
Answer from memory, then check against the suggested answer.
What does intermittent mean?
What does dispatchable mean?
What is a life-cycle impact?
Why is installed power capacity alone a weak comparison?
Why can a low-carbon technology still have environmental impacts?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Electricity demand changes during the day.
Compare how well wind power and gas power meet changing demand.
(2)Compare their environmental effects, and suggest how both can be used.
(3)Total for this question: 5 marks
Command word: For compareA command word: say how two or more things are similar and how they are different., address both resources under the same criteria and give a contextual conclusion.