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 |
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