1.7.3 Energy resources
- Syllabus
- 0625–2026–2027
- Topic
- 1.7.3
- Level
- —
Learning objectives
1.7.3.1Energy/electrical power sources: (a)• Describe useful energy/electrical power sources: (a) fossil fuels (b) biofuels (c) water: waves, tides and hydroelectric dams (d) geothermal resources (e) nuclear fuel (f) sunlight for solar cells (g) infrared/other EM waves for solar water heating and wind energy, including boilers, turbines and generators where used1.7.3.2Advantages and disadvantages of each• Describe advantages and disadvantages of each method in terms of renewability, availability, reliability, scale and environmental impact1.7.3.3Understand, qualitatively, the concept• Understand, qualitatively, the concept of efficiency of energy transfer1.7.3.4Radiation from the Sun is the main• Know: radiation from the Sun is the main source of energy for all our energy resources except geothermal, nuclear and tidal1.7.3.5Energy is released by nuclear fusion• Know: energy is released by nuclear fusion in the Sun1.7.3.6Research is being carried out to• Know: research is being carried out to investigate how energy released by nuclear fusion can be used to produce electrical energy on a large scale1.7.3.7Efficiency: (a) efficiency = useful• Define and use efficiency: (a) efficiency = useful energy output / total energy input × 100% (b) efficiency = useful power output / total power input × 100%
Trace how energy resources provide useful energy
An energy resource is used through a transfer pathway. Follow the pathway from the resource to the useful output, and include a boiler, turbine and generator only where they are actually used.
| Resource | First useful transfer | Route to useful output |
|---|---|---|
| fossil fuel or biofuel | chemical energy is released by combustion | heating in a boiler produces steam; steam turns a turbine; the turbine drives a generator |
| nuclear fuel | nuclear energy heats the reactor and water circuit | steam turns a turbine; the turbine drives a generator |
| geothermal | thermal energy from hot rocks heats water | hot water or steam supplies heating, or steam turns a turbine that drives a generator |
| hydroelectric, tidal or wave | moving or falling water turns machinery | a water turbine drives a generator |
| wind | moving air turns blades | the turbine drives a generator |
| solar cell | radiation transfers energy to the cell | electrical energy is produced directly, without a turbine |
| solar water heating | infrared and other electromagnetic radiation heats water | the useful output is thermal energy, not electrical energy |
A turbine is turned by moving fluid: steam, water or air. A generator is driven by the turbine and produces electrical power. A boiler supplies steam by transferring thermal energy to water; it is not needed by solar cells, wind turbines or hydroelectric schemes.
Renewable describes whether a resource is replenished; it does not tell you the transfer pathway. Nuclear fuel and fossil fuels are non-renewable even though their power stations can both use steam turbines and generators.
Compare energy resources using five criteria
No energy resource is best in every situation. Compare like with like using renewability, availability, reliability, scale and environmental impact.
| Criterion | Question to ask | Typical trade-off |
|---|---|---|
| renewability | Is the resource replenished as it is used? | fossil and nuclear fuels are finite; sunlight, wind, water, geothermal and sustainably replaced biofuel are renewable |
| availability | Is the resource present at this site or time? | sunlight and wind vary; geothermal and hydroelectric sites are geographically limited |
| reliability | Can output be supplied when demanded? | fuelled stations are controllable; wind, solar and waves are weather-dependent; tides are predictable but intermittent |
| scale | Can it provide the required power? | large stations and dams can supply large outputs; small local systems may need many units or storage |
| environmental impact | What changes occur during construction and operation? | combustion releases carbon dioxide and pollutants; dams flood habitats; wind and solar require land; nuclear produces radioactive waste |
For a justified decision, name the criterion, connect it to the named resource and the stated location or demand, then explain the consequence. A feature such as 'renewable' is not by itself a complete advantage unless its effect is stated.
Low carbon dioxide emissions during operation do not mean zero environmental impact. Keep greenhouse-gas effects, pollution, habitat change, waste, visual/noise effects and reliability as separate comparisons.
Recognise efficient energy transfer
An efficient device transfers a large fraction of its input energy into the intended useful output, so only a small fraction is dissipated in unwanted forms.
| Observation | What it says about efficiency |
|---|---|
| more useful output for the same input | efficiency is greater |
| less input for the same useful output | efficiency is greater |
| less wasted energy for the same input | efficiency is greater |
| a larger wasted output | efficiency is lower |
Energy is conserved: total input energy equals useful output energy plus wasted output energy. Wasted energy is usually dissipated to the surroundings and becomes less available for useful transfer.
Efficient does not mean powerful, fast or able to produce a large total output. Efficiency is a fraction of the input that becomes useful output; the numerical formula is introduced in the final card.
Trace most energy resources back to the Sun
Radiation from the Sun is the main original source for most energy resources used on Earth. Trace the intermediate process instead of assuming every resource receives sunlight directly.
| Resource | Link back to solar radiation |
|---|---|
| solar cells and solar heating | radiation is transferred directly from the Sun |
| biofuels | plants store transferred solar energy through photosynthesis |
| fossil fuels | ancient biomass originally stored transferred solar energy |
| wind | uneven solar heating of the atmosphere produces pressure differences and moving air |
| waves | wind transfers energy to the water surface |
| hydroelectric | solar heating drives the water cycle, raising water to higher gravitational potential stores |
The syllabus exceptions are geothermal, nuclear and tidal energy. Geothermal comes from Earth's internal thermal energy; nuclear comes from changes in atomic nuclei; tides arise from gravitational interactions, principally with the Moon.
A resource can be indirectly solar. Wind, waves, hydroelectric power, fossil fuels and biofuels all depend on earlier transfers of solar energy even though no solar cell is involved.
Explain fusion as the Sun's energy source
In the Sun, nuclear fusion joins light nuclei and releases energy. This is the process that supplies the Sun's energy—not combustion, radioactive decay or nuclear fission.
| Stage | Description |
|---|---|
| source | light nuclei fuse in the Sun |
| release | nuclear energy is released |
| transfer to Earth | energy crosses space as electromagnetic radiation |
| storage on Earth | plants can store some transferred energy chemically in biomass |
Fusion combines light nuclei. Fission splits a heavy nucleus. Both are nuclear processes, but the Sun's energy in this syllabus is attributed to fusion.
Do not describe the Sun as burning fuel by ordinary chemical combustion. Its energy release is nuclear fusion; detailed nuclear equations and mass-defect calculations are outside this objective.
Recognise the fusion-power research frontier
Research is being carried out to investigate how energy released by nuclear fusion could be used to produce electrical energy on a large scale.
| Research requirement | Why it is difficult |
|---|---|
| make hydrogen nuclei approach closely enough to fuse | the positively charged nuclei repel one another |
| provide conditions in which collisions can overcome this repulsion | an extremely high temperature is needed |
| maintain enough reacting nuclei under those conditions | the hot material must be kept dense and confined without damaging its surroundings |
The key syllabus claim is the research status: fusion is being investigated as a possible route to large-scale electrical energy. This is different from saying it is already a routine commercial source.
This card does not require reactor designs, fuel-cycle detail or predictions about deployment dates. It identifies why controlled fusion is difficult and why investigation continues.
Calculate efficiency from energy or power
Efficiency compares the useful output with the total input. Use either energy values measured over the same transfer or power values measured for the same process.
efficiency=total energy inputuseful energy output×100%
efficiency=total power inputuseful power output×100%
| Step | Check |
|---|---|
| 1 | identify the intended useful output |
| 2 | use useful output over total input, never wasted output over input |
| 3 | use energy with energy or power with power, in consistent units |
| 4 | multiply the ratio by 100 for a percentage |
| 5 | check that the answer is between 0% and 100% |
For a decimal efficiency η, useful output =ηimes total input and total input = useful output /η. Convert a percentage to a decimal before these rearrangements: for example, 20% is 0.20.
If wasted output is given, first find useful output from total input minus wasted output. A value above 100% signals that the ratio was inverted or that useful and total quantities were confused.