Renewable vs non-renewable definitions
Renewable: replenished naturally at or faster than it is used, so it will not run out on a human timescale (solar, wind, hydro, tidal, geothermal, biomass). Renewable does NOT mean "always available" (wind/solar are intermittent). Non-renewable: took millions of years to form and is used faster than replaced, so it will run out — coal, oil, gas (fossil fuels) and nuclear (uranium). Each definition needs two elements: replenishment/finiteness AND the timescale.
Energy chains for each generation method
Trace source → electrical output. Fossil/biomass: chemical → thermal (burning) → KE (steam/turbine) → electrical. Nuclear: nuclear → thermal → KE → electrical. Hydro/tidal: gravitational PE → KE (water) → KE (turbine) → electrical. Wind: KE (air) → KE (blades) → electrical. Solar PV: radiation → electrical directly (no thermal stage). Solar heating: radiation → thermal (water). Geothermal: thermal (hot rocks) → KE (steam) → electrical.
Reliability: baseload vs intermittent
Baseload (reliable, dispatchable): fossil fuels, nuclear, geothermal, hydroelectric (with reservoir), biomass — generate continuously and adjust to demand. Intermittent (unreliable): wind, solar, tidal — only generate when the resource is available and cannot be dispatched on demand. Reliability is the main comparison axis: wind is renewable and CO₂-free during generation but intermittent, while fossil fuels are reliable but emit CO₂ and are finite.
Drawn from real examiner reports.
"Renewable" defined as "always available"
The top trap: defining "renewable" as "always available / never runs out / unlimited". Wrong — wind is renewable but not always available (needs wind); solar fails at night. Mark-scheme form: "replenished naturally, so it will not run out on a human timescale" — two elements: replenished naturally AND not finite. "Always available" captures neither and scores zero.
June 2024 Paper 2P Q7(a): the examiner explicitly noted that candidates who wrote "always available" did not score, because this is incorrect for wind and solar. This was the most common wrong answer for the definition mark.
Classifying nuclear as renewable
Nuclear produces no CO₂ in the reactor, so many wrongly call it "renewable" or "green". It is non-renewable: uranium ore is finite and cannot be replenished naturally. "No CO₂" is also only true of the generation stage — mining, processing and construction do emit CO₂. Correct phrasing: nuclear produces no CO₂ during electricity generation, but the fuel is finite.
"It is renewable" given as an advantage
When the stem already says a resource is renewable, writing "an advantage is that it is renewable" just repeats given information and scores nothing. Give a physical advantage instead: no CO₂ during generation, no fuel cost, low maintenance, or (for geothermal) reliable 24-hour output. June 2024 Paper 2PR Q6(a) refused credit for "renewable" and for subjective points.
June 2024 Paper 2PR Q6(a): a large number of responses cited "renewable" as an advantage despite it being clearly given in the stem; these were not credited.
Geothermal treated as clean fossil fuel
Two geothermal traps: (1) treating a geothermal station like a fossil-fuel plant that "burns" fuel — its heat comes from hot underground rocks, with no combustion; (2) claiming it releases no greenhouse gases — the underground steam can carry natural CO₂ and H₂S. June 2024 Paper 2PR Q6(a) penalised both.
June 2024 Paper 2PR Q6(a): common errors included treating geothermal as a fossil-fuel plant and claiming it releases no greenhouse gases (it can release CO₂/H₂S).
Subjective points (cost, "ugly")
Subjective or vague points are not credited: "costs more", "looks ugly / visual pollution", "better for the environment", "cleaner". Replace them with specific, physical statements — "no CO₂ during generation", "only generates when the wind blows", "produces radioactive waste". Opinions without a mechanism score nothing.
(general exam technique)
Muddling the turbine-to-generator stage
In a "describe the energy transfers" answer, the turbine→generator stage is where candidates muddle the chain. State it precisely: the KE store of the turbine decreases and energy is transferred electrically (electromagnetic induction) to consumers. In June 2024 Paper 2P Q7(b) this stage lost the most marks; name the store and pathway, not just "makes electricity".
June 2024 Paper 2P Q7(b): candidates frequently muddled the hydroelectric chain at the turbine-to-generator stage — name the turbine KE store decreasing and the electrical pathway.
Read the stem, do not repeat it
Read the stem: if it states a resource is renewable, do not offer "renewable" as an advantage — it scores nothing. Give a fresh physical point beyond the definition (emissions, reliability, cost structure, waste, land use, geography).
Pick a clear comparison axis
Pick a clear comparison axis and contrast both sources on it: CO₂/pollution, reliability (baseload vs intermittent), land use, capital vs running cost, finite vs replenished fuel, waste products, geographical constraints. One well-chosen axis beats a list of vague claims.
Use technical language, not opinion
Use technical language, not opinion: "produces no CO₂ during generation" scores, "better for the environment" does not; "only generates when the wind blows" scores, "unreliable" alone may not. State the mechanism behind every advantage or disadvantage.
Separate advantages and disadvantages
Lay out advantages and disadvantages under clear sub-headings or bullets so each creditworthy point is easy to award. For "describe the chain" questions, trace Store → pathway → Store at every stage and name the pathway at the generator.
Mostly qualitative. The one numeric relationship needed is efficiency (spec point 4.4, applied to power stations):
No unit — express as a percentage (%).
Define "renewable energy resource". Give two elements that the mark scheme requires.
A gas-fired power station burns fuel with a total chemical energy input of 1200 MJ per hour. It generates 420 MJ of electrical energy per hour.
(a) Calculate the efficiency of the power station. Give the unit of your answer. (2 marks)
(b) State what happens to the energy that is not delivered as useful electrical energy. (1 mark)
