Work, Power & Energy Resources
Energy Resources & Energy Transfers
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 9% of your exam marks.
W = Fd, P = W/t and comparisons of renewable vs non-renewable energy sources tested regularly.
Two axes for comparison
- Renewable or not: will it eventually run out?
- Reliable or not: can it generate on demand? A reliable resource produces energy whenever it is needed; an unreliable one depends on the weather or the time of day
- These two axes do not line up cleanly: some renewables (geothermal, tidal, hydro) are reliable, while others (wind, wave, solar) are not
Trade-offs at a glance
| Resource | Renewable | Reliable | Main advantages | Main disadvantages |
|---|---|---|---|---|
| Fossil fuels | No | Yes | Large, steady output; output can be ramped to match demand; well-established technology | Burn produces carbon dioxide (greenhouse gas → global warming) and sulfur dioxide (contributes to acid rain); finite reserves |
| Nuclear | No | Yes | Very large output from a small mass of fuel; no CO₂ at the power station | Produces long-lived radioactive waste that must be stored safely for thousands of years; very expensive and slow to build; cannot quickly respond to demand changes; rare but serious accident risk |
| Biofuels | Yes | Yes | CO₂ released on burning is roughly balanced by CO₂ absorbed when the plant grew (near-carbon-neutral) | Crops grown for fuel compete with food crops for land and water |
| Wind | Yes | No | No fuel cost; no greenhouse gases in operation; cheap to install and maintain | Stops generating when the wind drops; can be seen as visually intrusive; can affect bird populations |
| Hydroelectric | Yes | Yes | Large output; output can be increased on demand by opening more gates; no greenhouse gases in operation | Building a reservoir floods a large area, destroying habitats and displacing people; few new sites left in the UK |
| Tidal | Yes | Yes (predictable) | Tides are perfectly predictable months in advance; no fuel | Few suitable estuaries; tidal barrages disturb shipping and damage estuarine wildlife |
| Wave | Yes | No | No fuel; no greenhouse gases | Output varies with the sea state; ocean devices are expensive to install and survive in harsh conditions |
| Geothermal | Yes | Yes | Steady year-round output; no fuel | Limited to volcanically active regions or sites with very deep boreholes; can release trapped greenhouse gases such as methane |
| Solar (PV) | Yes | No | No moving parts; ideal for remote or off-grid locations; cheap and quick to install on existing roofs | Generates nothing at night and far less in cloudy weather; each cell produces only a small amount of power |
| Solar (heating) | Yes | No | Cheap supplementary hot water; no greenhouse gases | Produces heat, not electricity; less effective in winter sunlight |
Comparing advantages and disadvantages of energy resources
What comes up: the exam pairs two energy sources (e.g. natural gas vs wave power, or nuclear vs wind) and asks you to discuss or state advantages and disadvantages of each — typically 4 marks, one mark per credited point.
Write (four marks): (1) Advantage of a fossil fuel or nuclear source: output can be varied rapidly to meet changing demand / the supply is reliable and not weather-dependent. (2) Disadvantage of a fossil fuel: burning it releases carbon dioxide, contributing to global warming, and the fuel is non-renewable so it will eventually run out. (3) Advantage of a renewable source (e.g. wave, wind, solar): it is renewable and produces no polluting gases during operation. (4) Disadvantage of a renewable source: output depends on weather conditions so generation may stop when demand is high; wave devices can also suffer storm damage.
Watch out: the mark scheme ignores references to visual pollution for wave power, and ignores unqualified "high cost" arguments for nuclear — you must specify setup or decommissioning cost to gain that mark.
Why a real grid uses a mix
- No single resource is perfect on both axes. The UK's National Grid therefore runs many resources in parallel:
- Steady-output sources (nuclear, gas, biofuel, geothermal) provide the base load, the minimum demand that exists 24 hours a day
- Fast-ramping sources (gas turbines, hydroelectric) handle peaks in demand, switching on or off within minutes
- Renewables (wind, solar, wave) feed in whenever conditions allow, displacing fossil-fuel use
- Reducing total greenhouse-gas emissions means pushing the mix away from fossil fuels and towards renewables and nuclear, while accepting that some non-renewable backup is still needed when the wind is calm and the sun is down