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What are the main renewable energy resources, and what are the trade-offs between them?

The main renewable energy resources (solar, wind, hydroelectric, tidal, wave, geothermal and biomass), how each generates energy, and the advantages and limitations of each.

A focused answer to AQA A-Level Environmental Science 3.3.3, covering the main renewable energy resources, how each generates energy, and the advantages and limitations of solar, wind, hydroelectric, tidal, wave, geothermal and biomass power.

Generated by Claude Opus 4.812 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. What makes a resource renewable
  3. The main renewable resources
  4. Comparing the resources and the system problem

What this dot point is asking

AQA wants you to describe the main renewable energy resources, explain how each generates energy, and evaluate the advantages and limitations of each, including reliability and environmental impact. Command words are Describe, Explain, Compare and Calculate, so expect both comparison and a numerical output or capacity-factor question.

What makes a resource renewable

The main renewable resources

  • Solar. Photovoltaic cells convert sunlight directly to electricity; solar thermal panels heat water; concentrating solar plants focus sunlight to drive turbines. Clean and now cheap, but intermittent (no output at night, reduced when cloudy) and lower output at high latitudes.
  • Wind. Turbines convert the kinetic energy of moving air to electricity; the power available rises steeply with wind speed. Clean and increasingly the cheapest new generation, but intermittent, and onshore turbines draw visual and noise objections.
  • Hydroelectric. Falling or flowing water turns turbines; reservoirs can store energy and be released on demand, and pumped storage acts as a giant battery. Reliable and dispatchable, but dams flood land, displace people, block fish migration and trap sediment.
  • Tidal. Barrages or underwater turbines use the predictable rise and fall of tides. Very predictable, but few suitable sites, high cost, and impacts on estuary ecosystems.
  • Wave. Devices capture the energy of ocean waves. A large resource but still developing and vulnerable to storm damage.
  • Geothermal. Heat from hot rocks underground heats water or generates electricity. Reliable and continuous, but limited to areas with suitable geology (volcanic or tectonically active regions).
  • Biomass. Burning wood, energy crops or waste, or producing biogas by anaerobic digestion. Roughly carbon-neutral if the crop is replanted to reabsorb the carbon released, but it competes with food production for land and still releases air pollutants.

Comparing the resources and the system problem

The capacity factor, the fraction of a plant's maximum possible output it actually delivers over a year, is the key concept for comparing reliability: it is high for geothermal and hydro and much lower for wind and solar, which is why headline capacity figures overstate the energy intermittent sources actually supply.

Exam-style practice questions

Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

AQA 20186 marksCompare the advantages and limitations of wind power and hydroelectric power for generating electricity.
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A compare needs paired points naming both resources, not two separate lists. Markers reward at least three contrasts.

Reliability: hydroelectric is reliable and can be switched on and off quickly to meet demand, including pumped storage, whereas wind is intermittent and depends on wind speed.

Cost and siting: wind farms are relatively quick and cheap to build and can be sited offshore, whereas large hydro needs a suitable valley and river, high capital cost and long construction.

Environmental impact: wind has low operational impact but visual and noise objections and some bird strike, whereas hydro dams flood large areas, displace people, block fish migration and disrupt sediment flow.

A strong answer concludes that both are low carbon but suit different roles, hydro for reliable dispatchable supply and storage, wind for cheap bulk generation that needs backup.

AQA 20215 marksA wind turbine has a power output of 2.0 MW and a capacity factor of 30 percent. Calculate the energy it generates in a year and explain why its capacity factor is well below 100 percent.
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A quantitative item. Markers reward the energy calculation and a correct explanation of capacity factor.

Calculation: hours in a year are 24×365=8760 h24 \times 365 = 8760 \text{ h}. At full output the turbine would generate 2.0 MW×8760 h=17520 MWh2.0 \text{ MW} \times 8760 \text{ h} = 17520 \text{ MWh}. With a capacity factor of 30%30\%: 17520×0.30=5256 MWh17520 \times 0.30 = 5256 \text{ MWh} per year.

Explanation: the capacity factor is below 100 percent because the wind does not always blow at the rated speed; output is zero in calm conditions, reduced in light winds, and capped or shut down in very high winds, so over a year the turbine averages only a fraction of its rated power. Award the time conversion, the multiplication by capacity factor, and the intermittency reasoning.

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