Energy Resources and Electricity Generation

Renewable resource. A resource that is NOT depleted by use over a human timescale, or is naturally replenished as fast as it is consumed. Examples on the 4PH1 spec:

• Wind — moving air (ultimately driven by solar heating of the atmosphere).
• Water — hydroelectric (dammed water flows downhill), tidal (rise/fall of sea level).
• Geothermal — heat in the Earth's crust (from radioactive decay).
• Solar heating systems — direct heating of water by absorbed sunlight.
• Solar cells (photovoltaic) — direct conversion of light to electricity.
• (Spec also implicitly recognises biomass — burning wood / crops grown specifically for fuel.)

Non-renewable resource. A finite resource being used faster than it is replenished:

• Coal, oil, natural gas — fossil fuels formed over millions of years from ancient biomass.
• Uranium / plutonium — used in nuclear fission reactors; mined and finite.

Important distinction. 'Renewable' refers to the FUEL SUPPLY, not the cleanliness. Nuclear is a LOW-CARBON resource but it is NON-RENEWABLE (uranium runs out). Edexcel mark schemes are strict about this.

Energy chain.

1. Solar radiation (the ultimate source) heats parts of Earth's surface unequally.
2. Pressure differences in the atmosphere → masses of air flow → kinetic energy of air (wind).
3. Wind exerts a force on turbine blades → kinetic energy of blades.
4. Rotating shaft drives a generator → electrical energy.

Advantages.

• Renewable, sustainable.
• Zero greenhouse-gas emissions during operation.
• Low running cost once installed.

Disadvantages.

• Intermittent — no output on calm days.
• Visual impact / noise — opposition near homes.
• Can harm birds and bats.
• Each turbine has a relatively low MW rating → many needed to match a fossil-fuel plant.

Hydroelectric.

1. Water collected behind a dam (high reservoir) — GPE store.
2. Water released through pipes → GPE → KE.
3. KE drives turbines → KE of blades.
4. Generators convert KE → electrical.

Ultimate source: SOLAR — sunshine evaporates water → falls as rain in the hills → fills reservoir.

Tidal.

• A BARRAGE is built across an estuary.
• At high tide, water flows IN, then is trapped.
• At low tide, the trapped water is released through turbines.
• Twice-daily generation (reliable; predictable from tide tables).

Ultimate source: gravitational interaction of the MOON (and Sun) with Earth's oceans.

Advantages of water power.

• Renewable, no greenhouse gases.
• Hydroelectric is responsive — can ramp up output quickly (pumped storage as a 'battery' for the grid).
• Tidal output is predictable.

Disadvantages.

• Hydroelectric reservoirs flood valleys → habitat loss, displaced communities.
• Tidal barrages alter estuary ecosystems and may block shipping/fish.
• Both require large capital investment and very specific geography.

Energy chain.

1. Heat in the Earth's crust (mostly from radioactive decay of natural isotopes such as U, Th, K) — thermal energy of rocks.
2. Cold water pumped down deep boreholes.
3. Water absorbs heat from the rocks → becomes high-pressure steam — thermal energy + KE of steam.
4. Steam drives a turbine → KE of blades.
5. Generator → electrical energy.

Advantages.

• Renewable (heat continually generated by ongoing radioactive decay).
• Continuous, NOT intermittent (unlike wind/solar).
• No greenhouse-gas emissions during operation.

Disadvantages.

• Only viable where hot rocks lie close to the surface (volcanic regions — Iceland, New Zealand, parts of Japan, USA).
• High drilling and infrastructure cost.
• Risk of releasing trapped underground gases.

Two DIFFERENT technologies — make sure to distinguish them.

Solar heating system (also called solar thermal panel).

1. A black absorber panel mounted on the roof absorbs solar radiation → THERMAL energy of the panel.
2. Water in pipes through the panel absorbs the thermal energy (by conduction) → hot water.
3. Useful output = HOT WATER for domestic use or building heating.

Typical efficiency: 50-70% of incident solar energy → usable hot water.

Solar cells (photovoltaic, PV).

1. Light photons strike the silicon semiconductor cell.
2. Photons excite electrons → electrons flow → ELECTRICAL energy directly.

Typical efficiency: 15-25% of incident solar energy → electrical.

Advantages (both technologies).

• Renewable, no emissions during operation.
• No moving parts (PV) → low maintenance.
• Suitable for distributed installation (rooftops).

Disadvantages (both technologies).

• No output at NIGHT; low output on cloudy days.
• Large area required to generate significant power.
• Manufacturing of PV cells uses energy and materials (overall life-cycle emissions are not zero).

Energy chain.

1. Chemical store of coal, oil or natural gas.
2. Combustion → THERMAL energy of hot gases.
3. Thermal energy boils water → high-pressure STEAM (thermal + KE).
4. Steam drives a turbine → KE of blades.
5. Generator → electrical energy.

Advantages.

• High energy density (fuel can be transported in concentrated form).
• Available where local geography doesn't suit renewables.
• Can supply continuous BASELOAD power.
• Existing infrastructure already built.

Disadvantages.

• Non-renewable → will eventually run out.
• Burning releases CO₂ → contributes to global warming and climate change.
• Burning also releases SO₂ (acid rain), NOₓ, and particulates → air pollution and respiratory disease.
• Coal mining and oil extraction can damage landscapes.

Efficiency. A typical fossil-fuel power station is about 35-45% efficient (rest is wasted as thermal energy of cooling water/cooling towers).

Energy chain.

1. Nuclear store in U-235 fuel rods.
2. Slow neutrons induce fission → KE of fission products.
3. KE of fission products → THERMAL energy of reactor core (by collisions).
4. Coolant carries heat to a heat exchanger; water boils → high-pressure STEAM.
5. Steam drives a turbine → KE of blades.
6. Generator → electrical energy.

Advantages.

• No CO₂ during operation → low-carbon electricity.
• Very high energy density: 1 kg of U-235 yields ~10⁶× the energy of 1 kg of coal.
• Continuous BASELOAD output (high capacity factor).

Disadvantages.

• Non-renewable (uranium is mined and finite).
• Radioactive waste needs safe long-term storage (thousands of years for some isotopes).
• High capital cost and very long construction time.
• Decommissioning is expensive and slow.
• Risk of accidents (Chernobyl 1986, Fukushima 2011) — even if statistically rare, consequences are severe.

Detailed reactor physics (spec 7.18-7.22) is covered in MR 5 (Topic 7). For 4.18P just describe the energy transfers.

Resource	Renewable?	CO₂ during operation?	Continuous?	Geography needed
Wind	Yes	None	Intermittent	Windy sites (often coastal/uplands)
Hydroelectric	Yes	None	Yes (responsive)	Valleys with rainfall
Tidal	Yes	None	Predictable (2× daily)	Estuaries with large tidal range
Geothermal	Yes	None	Yes	Volcanic regions
Solar heating	Yes	None	Day only	Sunny climate
Solar cells	Yes	None	Day only	Sunny climate
Fossil fuels	No	YES (CO₂, SO₂)	Yes	Anywhere with infrastructure
Nuclear	No	None	Yes (baseload)	Stable geology + cooling water

Edexcel question style for spec 4.19P. Often a 6-mark question asking for THREE advantages and THREE disadvantages of renewables vs non-renewables. Memorise the three key advantages (sustainable, low CO₂, fuel-secure) and three disadvantages (intermittent, capital-intensive, local environmental impact).