Work, Power & Energy Resources
Energy Resources & Energy Transfers
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 |
Common exam question
Advantages and disadvantages of a generating method
Question: Discuss the advantages and disadvantages of two ways of generating electricity, or give one advantage or disadvantage of a method (1–4 marks, one per point).
Asked in 3 of the 24 papers. A four-mark comparison wants an advantage and a disadvantage of each method. Gas or hydroelectric: output changes quickly to meet demand, and supply does not depend on the weather. Against gas: non-renewable, so it runs out, and burning it releases carbon dioxide, a greenhouse gas. Wave or wind: renewable, no polluting gases. Against them: waves or wind may be absent when needed, storms damage the equipment, wildlife is harmed. Hydroelectric floods land and habitats and needs a mountainous site. Nuclear: radioactive waste needing long-term storage, accident risk, non-renewable.
Cost is ignored in all three schemes unless it is nuclear's higher setup or decommissioning cost, named as such, and both comparison questions ignore visual pollution.
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