Energy resources

Revision notes

Energy resources used for electricity and heating include fossil fuels, nuclear fuel and renewable resources such as wind, solar, hydroelectricity, tidal, wave, geothermal and biofuels. Renewable resources are replenished on human timescales; fossil fuels and nuclear fuels are finite.

Many power stations transfer energy to rotate a turbine connected to a generator. Fossil-fuel and nuclear stations commonly use thermal energy to produce steam, while hydroelectric, wind and tidal systems use moving water or air more directly. Solar photovoltaic cells transfer energy from sunlight directly to electrical energy without a turbine.

No resource is impact-free. Comparisons should consider greenhouse-gas emissions, air pollution, habitat and land use, radioactive waste, construction materials, visual/noise effects, reliability, response to changing demand and cost. Wind and solar output vary with conditions, so grids using large fractions of variable generation require ways to balance supply and demand, such as storage, interconnection, flexible generation or demand management.

Renewable and non-renewable resources

A renewable resource is replenished naturally on a human timescale. Examples include wind, solar, hydroelectric, tidal, wave, geothermal and sustainably managed biofuel. Non-renewable resources such as coal, oil, natural gas and nuclear fuels are finite on human timescales.

Renewable does not mean impact-free. Every large energy system has effects associated with materials, construction, land use, habitats, reliability, cost or waste. Likewise, non-renewable resources differ substantially from one another: fossil fuels release carbon dioxide during combustion, while nuclear generation has low operational carbon emissions but creates radioactive waste and requires careful safety management.

Reliability and matching demand

Electricity supply must match demand continuously. Some resources are dispatchable, meaning output can be controlled when required; others are variable because they depend on weather or natural cycles. A fair comparison therefore considers not only average energy output but also predictability, storage, backup, interconnection and response time.

Wind and solar output can vary. Hydroelectric storage can respond quickly where suitable geography exists. Fossil-fuel and some biomass stations can be controlled but emit combustion products. Nuclear stations provide large continuous outputs but are less suited to rapid short-term changes in demand.

Environmental and economic evaluation

Good evaluation uses several criteria rather than declaring one resource simply 'best'. Consider greenhouse-gas emissions, air pollution, land and habitat effects, visual/noise impacts, fuel availability, waste, construction time, lifetime, operating cost and reliability. The importance of each factor depends on context.

Life-cycle thinking matters. A solar panel produces no combustion gases while operating, but manufacturing and installation still require materials and energy. Similarly, an electric technology may shift emissions away from the point of use rather than eliminate them if the electricity is generated from fossil fuels.

Power, energy and efficiency

Power is the rate of energy transfer, whereas total energy depends on power and operating time. Capacity or maximum output should not be confused with actual energy generated over a day or year. When comparing devices or generation methods, identify whether the question concerns power, energy, efficiency or environmental impact.

Exam technique

For six-mark comparison questions, organise the answer by criteria and make linked comparisons. Avoid one-sided lists. State an advantage, explain why it matters, then contrast it with a limitation or alternative resource.