GCSE · Chapter 4
Energy resources and the global energy supply
By the end of this chapter you will be able to
- Say whether a resource is renewable or non-renewable, and give an example
- Explain how a power station or renewable device makes electricity
- Compare two resources in a table, using reliability, cost and environmental impact
- Use a percentage energy mix to calculate the energy from each source
- Evaluate a choice of energy resource for a town, and say why conserving energy matters
You should already know
- Energy stores and transfers (Chapter 1)
- Efficiency and percentages (Chapter 2)
Where this leads
- Nuclear fission and fusion (Chapter 12)
- Electromagnetic induction and generators (Chapter 20)
GCSE Physics. Content follows the GCSE (9-1) subject content for England (Edexcel and AQA). Content references: Distinguish renewable and non-renewable energy resources, Describe fossil fuels, nuclear fission and biofuels as energy resources, Describe wind, hydroelectric, solar, geothermal, tidal and wave energy and how each produces electricity, Compare energy resources on reliability, cost and environmental impact, Read and calculate from the energy mix of a town or a country, and discuss energy security and conservation.
Exercise P Do you remember?
1
FWhat is 40% of 5000? Write the number.
2000
Method. Find 10% and multiply by 4.
- Find 10%. 10% of 5000 is 500.5000 / 10 = 500
- Multiply. 40% is 4 x 500 = 2000.4 x 500 = 2000
- Write the answer. 2000
Check. 2000 / 5000 = 0.4 = 40%. ✓
2
FWhich store holds energy in the food we eat? Write the word.
chemical
Method. Recall the energy stores from Chapter 1.
- Recall. Food stores energy in its chemical bonds.chemical
- Write the answer. chemical
Check. ✓
3
FName the transfer when a solar panel gives out electricity to a lamp. Write the word.
electrical
Method. Think about what carries the energy to the lamp.
- Recall. A current carries the energy to the lamp, which is electrical.current: electrical
- Write the answer. electrical
Check. ✓
4
FA machine has 200 J in and 150 J useful. What is its efficiency as a percentage? Write the number.
75
Method. Efficiency = useful / input, then x 100.
- Divide. 150 / 200 = 0.75.150 / 200 = 0.75
- Percentage. 0.75 x 100 = 75%.0.75 x 100 = 75
- Write the answer. 75
Check. ✓
5
FWhat word means a resource that can be replaced in a human lifetime? Write the word.
renewable
Method. Think about the opposite of running out.
- Recall. A resource that is replenished naturally is renewable.renewable
- Write the answer. renewable
Check. ✓
4.1
Renewable and non-renewable resources
Video lesson: Renewable and non-renewable resourcesComing soon
Context. Priya’s school is discussing where the town’s electricity should come from in ten years. “Some sources will run out,” says her teacher. “Others will not.” To decide, we need to know the difference between a renewable and a non-renewable energy resource.
An energy resource is a source of energy that we can use. A non-renewable resource is used up faster than it is made, so it will run out. A renewable resource is replaced naturally and will not run out in a human lifetime, such as sunlight, wind and water. Renewable resources do not run out, but they may not be available all the time.
| Resource | Renewable? | How it makes energy (short) | Main drawback |
|---|---|---|---|
| coal | no | burn coal to heat water and make steam | releases carbon dioxide and pollutes the air |
| oil and gas | no | burn fuel to heat water or to power engines | releases carbon dioxide; supplies can run out |
| nuclear fission | no | fission of uranium heats water to make steam | radioactive waste; high build cost |
| biofuels | yes | burn or process plant material | uses land; can compete with food crops |
| wind | yes | turbines turn wind energy into electricity | depends on the weather; visual impact |
| hydroelectric | yes | falling water turns turbines | needs suitable sites; can harm habitats |
| solar | yes | panels turn light or heat into electricity or hot water | only works in daylight; panels are costly |
| geothermal | yes | heat from hot rocks warms water | only in places with hot rocks near the surface |
| tidal | yes | tides turn turbines | few suitable sites; affects wildlife |
| wave | yes | waves move machines that make electricity | rough sea damages devices; few sites |
Some energy resources, whether they are renewable, and their main drawback
Key ideas
- Non-renewable: coal, oil, gas, nuclear fuel (uranium). They will run out.
- Renewable: wind, water, solar, geothermal, tides, waves and biofuels. They are replaced naturally.
- A renewable resource is not always reliable, even though it does not run out.
- Biofuels come from plants, which are grown again, so they count as renewable.
Worked example 4.1.1
Which of these is a non-renewable resource: wind, coal or solar? Write the word.
Method. Check each resource against the definition.
- Wind. Wind is replaced by the weather, so it is renewable.renewable
- Coal. Coal takes millions of years to form, so it is used faster than it is made.non-renewable
- Solar. Sunlight is replaced every day, so it is renewable.renewable
- Write the answer. coal
Check. Only coal is non-renewable of the three. ✓
Worked example 4.1.2
Is a hydroelectric dam powered by a renewable resource? Write yes or no.
Method. Think about where the energy comes from.
- Source. The energy comes from water flowing downhill, which is replenished by rain.water replenished
- Decide. Water is replaced naturally, so the resource is renewable.renewable
- Write the answer. yes
Check. The rain comes from the Sun’s energy. ✓
Worked example 4.1.3
Name one renewable resource that depends on the Sun, and one that depends on the Moon. Write two words.
Method. Think about what each resource depends on.
- Sun. Solar energy depends on the Sun, and wind depends on the Sun heating the air.solar
- Moon. Tidal energy depends mainly on the pull of the Moon.tidal, Moon
- Write the answer. solar, tidal
Check. Other answers are possible, such as wind for the Sun. ✓
Watch out
Watch out: “renewable” does not mean “always available”. Wind and solar are renewable, but they depend on the weather and the time of day.
Exam tip
Exam tip. When asked to define renewable, use the words “replaced naturally” or “will not run out”.
Exercise 4A Renewable and non-renewable
1
FName a non-renewable fossil fuel. Write the word.
coal
Method. Recall a fossil fuel.
- Recall. Coal, oil and natural gas are fossil fuels and are non-renewable.coal
- Write the answer. coal
Check. Oil and gas are also fossil fuels. ✓
2
FName a renewable resource that uses flowing water. Write the word.
hydroelectric
Method. Think about a power source that uses water flow.
- Recall. Hydroelectric power uses falling water to turn turbines.hydroelectric
- Write the answer. hydroelectric
Check. ✓
3
FName a non-renewable resource that releases energy by fission. Write the word.
uranium
Method. Recall the fuel used in nuclear power stations.
- Recall. Uranium is the fuel used in fission reactors.uranium
- Write the answer. uranium
Check. Uranium is a non-renewable resource. ✓
4
FIs solar energy renewable? Write yes or no.
yes
Method. Check the definition.
- Check. Sunlight is replaced every day, so solar energy is renewable.replaced daily
- Write the answer. yes
Check. ✓
5
FIs coal renewable? Write yes or no.
no
Method. Check the definition.
- Check. Coal takes millions of years to form, so it is used faster than it is made.non-renewable
- Write the answer. no
Check. ✓
6
FWhich resource is replenished by the water cycle? Write the word.
hydroelectric
Method. Think about where the water comes from.
- Recall. Rain falls and refills the rivers, so the water that drives a dam is replaced.rain refills
- Write the answer. hydroelectric
Check. ✓
7
PSWrite two renewable resources in the table that do not depend on the weather. Write two names.
geothermal, tidal
Method. Look for resources that are not affected by weather.
- Think. Geothermal heat comes from the Earth, and tidal energy comes from the Moon.not weather
- Check. Wind and solar depend on the weather and the time of day.depend on weather
- Write the answer. geothermal, tidal
Check. Other answers are possible, such as hydroelectric from a reservoir. ✓
8
RExplain why biofuels are called renewable, in one sentence. Accept any sentence that says plants are grown again, so the fuel is replaced.
Accept any sentence that says plants are grown again, so the fuel is replaced.
Method. Think about where the biofuel comes from.
- Source. Biofuels come from plant material.plant material
- Replace. New plants can be grown to replace the ones used.replaced
- Write the answer. Accept any sentence that says plants are grown again, so the fuel is replaced.
Check. ✓
9
RA pupil says “all renewable energy is always available.” Explain why this is wrong. Accept any answer that says renewable energy depends on weather or time of day, so it is not always available.
Accept any answer that says renewable energy depends on weather or time of day, so it is not always available.
Method. Think about wind and solar.
- Think. Wind depends on the weather, and solar depends on daylight.weather and daylight
- Link. So renewable does not mean always available.not always available
- Write the answer. Accept any answer that says renewable energy depends on weather or time of day, so it is not always available.
Check. ✓
10
PSSort these into renewable and non-renewable: wind, gas, tidal, uranium. Write the two lists as words separated by commas: renewable first, then non-renewable.
wind, tidal, gas, uranium
Method. Check each one against the definition.
- Renewable. Wind and tidal are replaced naturally.wind, tidal
- Non-renewable. Gas and uranium are used up.gas, uranium
- Write the answer. wind, tidal, gas, uranium
Check. Two of each. ✓
11
PSHow many of the ten resources in the table are renewable? Write the number. (Count the rows marked yes.)
7
Method. Count the rows with yes in the Renewable column.
- Count. Biofuels, wind, hydroelectric, solar, geothermal, tidal and wave are marked yes. That is 7 rows.7 rows yes
- Write the answer. 7
Check. The table has 3 non-renewable rows (coal, oil and gas, nuclear fission). ✓
12
RIn one sentence, explain why a country should use a mix of renewable and non-renewable resources. Accept any sentence that says a mix gives security of supply and lets renewables cover gaps when the weather is poor.
Accept any sentence that says a mix gives security of supply and lets renewables cover gaps when the weather is poor.
Method. Think about reliability.
- Reliability. Renewables are not always available.not always
- Mix. A mix means that other sources can supply energy when renewables are low.mix
- Write the answer. Accept any sentence that says a mix gives security of supply and lets renewables cover gaps when the weather is poor.
Check. ✓
13
PSWhich non-renewable fossil fuel is commonly burned in power stations to heat water to make steam? Write the word.
gas
Method. Think about the fuels in common use in power stations.
- Recall. Gas is widely used in power stations to heat water for steam.gas
- Write the answer. gas
Check. Coal and gas are both fossil fuels. ✓
14
RExplain why uranium is said to be non-renewable, in one sentence. Accept any sentence that says uranium is mined from the Earth and cannot be replaced at the rate it is used.
Accept any sentence that says uranium is mined from the Earth and cannot be replaced at the rate it is used.
Method. Think about where it comes from.
- Source. Uranium is mined from rocks in the Earth.mined
- Replace. It cannot be replaced at the rate it is used.not replaced
- Write the answer. Accept any sentence that says uranium is mined from the Earth and cannot be replaced at the rate it is used.
Check. ✓
4.2
Fossil fuels, nuclear fission and biofuels
Video lesson: Fossil fuels, nuclear fission and biofuelsComing soon
Context. Tom visits a power station with a cooling tower. “What is the fuel?” he asks. The guide explains that the fuel heats water to make steam, and the steam turns a turbine. The fuel may be a fossil fuel, a nuclear fuel or a biofuel, but the basic process of turning a turbine is the same.
Fossil fuels (coal, oil and natural gas) formed from the remains of ancient plants and animals over millions of years. When they burn, they release energy, and carbon dioxide, which adds to global warming. Nuclear fission splits large uranium nuclei and releases energy as heat; it produces very little carbon dioxide but leaves radioactive waste. Biofuels come from plant or animal material, which can be grown again.
Key ideas
- A power station heats water to make steam; the steam turns a turbine, which turns a generator.
- Fossil fuels release carbon dioxide when burned, which adds to global warming.
- Nuclear fission releases heat with very little carbon dioxide, but produces radioactive waste.
- Biofuels are renewable, but growing them can use land needed for food.
Worked example 4.2.1
A coal power station uses coal to heat water. Name the energy transfer from the coal to the water. Write the word.
Method. Think about how the coal heats the water.
- Fuel. The coal is burned, releasing energy from its chemical store.chemical store
- Look. The burning coal transfers energy to the water, which becomes hot.heating
- Name. Energy moving by heating is heating.heating
- Write the answer. heating
Check. The steam then moves the turbine by a mechanical transfer. ✓
Worked example 4.2.2
Which of these releases carbon dioxide when burned: coal, nuclear fuel or wood from a managed forest? Write the two words that release carbon dioxide, separated by a comma: fossil fuel first, then the biofuel.
Method. Think about which resources release carbon dioxide on burning.
- Fossil. Coal releases carbon dioxide when burned.coal: CO2
- Biofuel. Wood from a managed forest also releases carbon dioxide, but the trees are grown again.wood: CO2 but replaced
- Write the answer. coal, wood
Check. Nuclear fission produces very little carbon dioxide. ✓
Worked example 4.2.3
Name the process in a nuclear power station that releases heat, when a large uranium nucleus splits. Write the word.
Method. Recall the name of the process.
- Look. A large uranium nucleus is hit by a neutron and splits into smaller nuclei.splits
- Recall. When a large nucleus splits into smaller nuclei, it is called fission.fission
- Write the answer. fission
Check. Fusion is the joining of small nuclei, and is not used in power stations yet. ✓
Watch out
Watch out: a nuclear power station does not burn uranium. It splits uranium atoms by fission, and the heat is used to make steam.
Exam tip
Exam tip. When you compare fossil fuels and nuclear, mention carbon dioxide and radioactive waste. These are the two key points.
Exercise 4B Fossil fuels, nuclear fission and biofuels
1
FWhich fossil fuel is a gas? Write the word.
natural gas
Method. Recall the three fossil fuels.
- Recall. Coal and oil are solid and liquid. Natural gas is the gas.natural gas
- Write the answer. natural gas
Check. ✓
2
FWhat is released when a fossil fuel burns that adds to global warming? Write the name of the gas.
carbon dioxide
Method. Recall the main greenhouse gas from burning.
- Recall. Burning fossil fuels releases carbon dioxide.carbon dioxide
- Write the answer. carbon dioxide
Check. ✓
3
FWhat is left over from nuclear power that is dangerous for many years? Write the word.
radioactive waste
Method. Think about the problem that nuclear power leaves.
- Recall. Nuclear power leaves radioactive waste that must be stored safely.radioactive waste
- Write the answer. radioactive waste
Check. ✓
4
FWhat do nuclear power stations use to heat water to make steam? Write the word.
fission
Method. Recall the process.
- Recall. Fission of uranium releases heat, which makes steam.fission
- Write the answer. fission
Check. ✓
5
FName a renewable fuel made from plant material. Write the word.
biofuel
Method. Recall the word for fuels from plants.
- Recall. A fuel made from plant or animal material is a biofuel.biofuel
- Write the answer. biofuel
Check. ✓
6
RExplain why fossil fuels are described as non-renewable, in one sentence. Accept any sentence that says they took millions of years to form and are used much faster than they are made.
Accept any sentence that says they took millions of years to form and are used much faster than they are made.
Method. Think about how long they took to form.
- Form. Fossil fuels formed from ancient plants and animals over millions of years.millions of years
- Use. We use them much faster than they are made.faster
- Write the answer. Accept any sentence that says they took millions of years to form and are used much faster than they are made.
Check. ✓
7
PSIn a coal power station the steam turns a turbine. Name the device that the turbine turns to make electricity. Write the word.
generator
Method. Think about what makes electricity from motion.
- Recall. A turbine turns a generator, which makes electricity.generator
- Write the answer. generator
Check. ✓
8
PSA power station uses fossil fuels. Give the chain of energy transfers from the chemical store of the fuel to the electricity. Write the transfers in order, as words separated by commas.
heating, mechanical, electrical
Method. Follow the energy through the power station.
- Heat. The fuel heats the water to make steam, which is heating.heating
- Turn. The steam turns the turbine, which is mechanical.mechanical
- Electricity. The generator makes electricity, which is an electrical transfer.electrical
- Write the answer. heating, mechanical, electrical
Check. ✓
9
RExplain why burning wood from a managed forest is often said to be carbon neutral. Accept any answer that says the trees take in carbon dioxide as they grow, to replace the carbon dioxide released.
Accept any answer that says the trees take in carbon dioxide as they grow, to replace the carbon dioxide released.
Method. Think about what the trees do while they grow.
- Grow. The trees take in carbon dioxide from the air as they grow.takes in CO2
- Balance. So the carbon dioxide released when they burn is taken back in by new growth.balance
- Write the answer. Accept any answer that says the trees take in carbon dioxide as they grow, to replace the carbon dioxide released.
Check. ✓
10
RGive one disadvantage of using biofuels, in one sentence. Accept any sentence that says biofuels can use land that is needed to grow food.
Accept any sentence that says biofuels can use land that is needed to grow food.
Method. Think about what biofuel crops need.
- Land. Growing biofuel crops needs land.land
- Food. That land may be needed to grow food.food
- Write the answer. Accept any sentence that says biofuels can use land that is needed to grow food.
Check. ✓
11
PSWhich two resources produce carbon dioxide when they are burned? Write two words, separated by a comma: a fossil fuel and a biofuel.
coal, wood
Method. Both burn and release carbon dioxide.
- Fossil. Coal is a fossil fuel that releases carbon dioxide.coal
- Biofuel. Wood is a biofuel that releases carbon dioxide when burned.wood
- Write the answer. coal, wood
Check. Nuclear fission does not burn fuel. ✓
12
RA nuclear power station produces 1000 MWh of electricity, and a coal power station produces the same amount, but the coal station gives out 800 tonnes of carbon dioxide. Explain why the nuclear station is considered to give less carbon dioxide. Accept any answer that says nuclear fission releases very little carbon dioxide.
Accept any answer that says nuclear fission releases very little carbon dioxide.
Method. Compare the sources of the energy.
- Coal. Coal releases carbon dioxide when it burns.burning
- Nuclear. Nuclear fission releases very little carbon dioxide during its operation.very little
- Write the answer. Accept any answer that says nuclear fission releases very little carbon dioxide.
Check. ✓
4.3
Renewable sources that make electricity
Video lesson: Renewable sources that make electricityComing soon
Context. On a windy day, a field of turbines turns steadily. Next to it, a hydroelectric dam holds back a lake. Both make electricity, but they use very different energy sources.
Each renewable source turns a turbine or drives a generator: wind turbines are turned by moving air; hydroelectric stations are turned by falling water; tidal turbines are turned by moving tides; wave devices are moved by waves. Solar panels turn light into electricity (photovoltaic), or heat water (solar thermal). Geothermal systems pump water into hot rock, and use the steam or hot water to make electricity or heat buildings.
Example figures for the share of electricity from renewable sources
Key ideas
- Wind: kinetic energy of moving air turns turbines.
- Hydroelectric: the gravitational potential store of water turns turbines.
- Solar: light (photovoltaic) or heat (solar thermal) from the Sun.
- Geothermal: thermal energy from hot rocks inside the Earth.
- Tidal and wave: the movement of the sea is converted to electricity.
Worked example 4.3.1
In a hydroelectric station, water is stored high in a reservoir. Name the energy store of the water before it flows. Write the word.
Method. Think about the height of the water.
- Where. The water is held in a reservoir high above the turbine.reservoir
- Look. The water is high above the turbine, so it has energy from its height.height
- Name. Energy stored because of height is the gravitational potential store.gravitational potential
- Write the answer. gravitational potential
Check. As it falls, the store becomes kinetic. ✓
Worked example 4.3.2
Name the energy store that a wind turbine takes its energy from. Write the word.
Method. Think about what the wind does.
- Look. Moving air has energy because it is moving.moving air
- Name. Energy in a moving object is the kinetic store.kinetic
- Write the answer. kinetic
Check. The turbine transfers the kinetic energy mechanically. ✓
Worked example 4.3.3
Which renewable resource uses the heat from rocks deep underground? Write the word.
Method. Recall the renewable source that uses the Earth’s heat.
- Look. The heat is stored in hot rocks below the ground, not at the surface.below ground
- Recall. Geothermal energy uses heat from hot rocks below the ground.geothermal
- Write the answer. geothermal
Check. Geothermal heat comes from radioactive decay and the Earth’s original heat. ✓
Watch out
Watch out: solar panels do not turn heat into electricity directly in a photovoltaic panel; they turn light into electricity. Solar thermal panels heat water, not electricity.
Exam tip
Exam tip. For each renewable source, name the store it comes from (kinetic, gravitational potential, light, thermal) and the device that turns it into electricity.
Exercise 4C How renewable sources make electricity
1
FWhich renewable source uses moving air to turn a turbine? Write the word.
wind
Method. Recall the source that uses moving air.
- Recall. Wind turbines are turned by moving air.wind
- Write the answer. wind
Check. ✓
2
FWhich renewable source uses water stored in a reservoir? Write the word.
hydroelectric
Method. Recall the source that uses a dam.
- Recall. Hydroelectric power uses water falling from a reservoir.hydroelectric
- Write the answer. hydroelectric
Check. ✓
3
FWhich renewable source uses the rise and fall of the sea to make electricity? Write the word.
tidal
Method. Think about the rise and fall of the sea.
- Recall. Tidal energy uses the rise and fall of the tides.tidal
- Write the answer. tidal
Check. ✓
4
FWhich renewable source uses light to make electricity? Write the word.
solar
Method. Think about what a photovoltaic panel uses.
- Recall. Photovoltaic panels turn light into electricity.light: solar
- Write the answer. solar
Check. ✓
5
FWhich renewable source uses hot water or steam from underground? Write the word.
geothermal
Method. Think about the heat inside the Earth.
- Recall. Geothermal systems use hot water or steam from rocks below the ground.geothermal
- Write the answer. geothermal
Check. ✓
6
FName the energy store of the water in a reservoir, before it flows through a turbine. Write the word.
gravitational potential
Method. The water is high up.
- Recall. Water stored high above the turbine has gravitational potential energy.high: gravitational potential
- Write the answer. gravitational potential
Check. ✓
7
RIn a wave device, the energy transfer to the device is mechanical. Explain why, in one sentence. Accept any sentence that says the waves push and move the device, which is a force doing work.
Accept any sentence that says the waves push and move the device, which is a force doing work.
Method. Think about what moves the device.
- Force. The waves push the device with a force.force
- Work. The force moves the device, doing work, so the transfer is mechanical.mechanical
- Write the answer. Accept any sentence that says the waves push and move the device, which is a force doing work.
Check. ✓
8
PSA solar thermal panel warms water. Name the transfer from the Sun to the water. Write the word.
radiation
Method. The Sun sends energy as waves to the panel.
- Sun to panel. The energy arrives at the panel as radiation.radiation
- Panel to water. The panel warms the water by heating.heating
- Write the answer. radiation
Check. Two transfers, radiation then heating. ✓
9
RGive one reason why geothermal energy is not used everywhere. Accept any answer that says hot rocks are needed close to the surface, which is only in some places.
Accept any answer that says hot rocks are needed close to the surface, which is only in some places.
Method. Think about where the heat is.
- Location. The heat must be close to the surface.close
- Place. That is only true in some places.some places
- Write the answer. Accept any answer that says hot rocks are needed close to the surface, which is only in some places.
Check. ✓
10
PSA hydroelectric dam holds water 40 m above the turbine. Using E = m g h for 1 kg of water, calculate the gravitational potential energy of 1 kg of water. Write the number of joules.
392
Method. Use E = m x g x h with g = 9.8 N/kg.
- Multiply. E = 1 x 9.8 x 40 = 392 J.1 x 9.8 x 40 = 392
- Write the answer. 392 J
Check. 392 / (9.8 x 40) = 1 kg. ✓
11
RA wind turbine turns the kinetic energy of the air into electricity. Describe the energy transfers from moving air to the electricity, in order. Accept any answer that says the air transfers energy mechanically to the blades, which turn a generator, which makes electricity.
Accept any answer that says the air transfers energy mechanically to the blades, which turn a generator, which makes electricity.
Method. Follow the energy from the air.
- Air to blades. The moving air does work on the blades, so the transfer is mechanical.mechanical
- Blades to generator. The turning blades turn a generator.generator
- Generator to electricity. The generator transfers energy to the electricity by an electrical transfer.electrical
- Write the answer. Accept any answer that says the air transfers energy mechanically to the blades, which turn a generator, which makes electricity.
Check. ✓
12
PSWhich source in this list depends mainly on the pull of the Moon: wind, tidal, geothermal or hydroelectric? Write the word.
tidal
Method. Think about which source is caused by the Moon.
- Tidal. Tides are caused mainly by the pull of the Moon.Moon
- Others. Wind comes from the Sun heating the air; geothermal from the Earth; hydroelectric from rain.not Moon
- Write the answer. tidal
Check. Hydroelectric depends on rain, which comes from the Sun. ✓
13
RExplain why a wave energy device needs to be strong, in one sentence. Accept any sentence that says the sea can damage the device, so it must be strong to survive.
Accept any sentence that says the sea can damage the device, so it must be strong to survive.
Method. Think about the conditions at sea.
- Sea. Storms and waves can be very strong.strong waves
- Device. The device must survive these conditions.survive
- Write the answer. Accept any sentence that says the sea can damage the device, so it must be strong to survive.
Check. ✓
4.4
Comparing resources and calculating the energy mix
Video lesson: Comparing resources and calculating the energy mixComing soon
Context. Mr Hughes is on the town council. The council must choose how to make the town’s electricity. He has a table of options and a pie chart of the current mix. To decide, he compares reliability, cost and environmental impact, and he calculates how much electricity each source gives.
When we compare energy resources, we consider: reliability (can it supply energy when needed?), cost (to build and run), and environmental impact (carbon dioxide, waste, land and habitats). An energy mix uses several sources, so that a shortage of one can be made up by another.
| Quality | Wind | Solar (panels) | Gas power station | Nuclear |
|---|---|---|---|---|
| reliable all the time? | no (weather) | no (night, cloud) | yes | yes |
| carbon dioxide while running | none | none | some | very little |
| build cost | medium | medium | low to medium | very high |
| radioactive waste | no | no | no | yes |
| can be switched on quickly | no | no | yes | no |
Comparing four ways of making electricity (general comparison)
| Source | Share of the town | Energy in MWh (total 5000 MWh) |
|---|---|---|
| Wind | 40% | 2000 MWh |
| Solar | 10% | 500 MWh |
| Gas | 35% | 1750 MWh |
| Coal | 5% | 250 MWh |
| Nuclear | 10% | 500 MWh |
Example energy mix for a town that uses 5000 MWh in a year: 1 MWh = 1 megawatt-hour
Key ideas
- Energy from a source = percentage share x total energy / 100.
- Reliability: can the source be switched on when needed?
- Environmental impact includes carbon dioxide, waste, land use and habitats.
- A good energy mix balances reliability, cost and impact.
Worked example 4.4.1
The town uses 5000 MWh. Wind provides 40%. Calculate the energy from wind. Write the number of MWh.
Method. Find 40% of 5000.
- Convert. 40% = 0.4.0.4
- Multiply. Energy = 0.4 x 5000 = 2000 MWh.0.4 x 5000 = 2000
- Write the answer. 2000 MWh
Check. 2000 / 5000 = 0.4 = 40%. ✓
Worked example 4.4.2
The gas share of the town is 35%. Calculate the energy from gas. Write the number of MWh.
Method. Find 35% of 5000.
- Convert. 35% = 0.35.0.35
- Multiply. Energy = 0.35 x 5000 = 1750 MWh.0.35 x 5000 = 1750
- Write the answer. 1750 MWh
Check. 1750 / 5000 = 0.35. ✓
Worked example 4.4.3
Which is more reliable: a wind farm or a gas power station? Write wind or gas.
Method. Think about when each can make electricity.
- Wind. A wind farm depends on the weather, so it is not always available.depends on weather
- Gas. A gas power station can be switched on when needed.switched on
- Write the answer. gas
Check. Reliability is about supply on demand. ✓
Watch out
Watch out: percentages must be applied to the total, not to another source. Use the total energy in the question each time.
Exam tip
Exam tip. When you compare two sources, use the three headings: reliability, cost and environmental impact. Use one sentence for each.
Exercise 4D Comparing and calculating
1
FCalculate the energy from solar in the example town, which provides 10%. Write the number of MWh.
500
Method. Find 10% of 5000.
- Multiply. 0.1 x 5000 = 500 MWh.0.1 x 5000 = 500
- Write the answer. 500 MWh
Check. 500 / 5000 = 0.1. ✓
2
FCalculate the energy from coal in the example town, which provides 5%. Write the number of MWh.
250
Method. Find 5% of 5000.
- Multiply. 0.05 x 5000 = 250 MWh.0.05 x 5000 = 250
- Write the answer. 250 MWh
Check. 250 / 5000 = 0.05. ✓
3
FCalculate the energy from nuclear in the example town, which provides 10%. Write the number of MWh.
500
Method. Find 10% of 5000.
- Multiply. 0.1 x 5000 = 500 MWh.0.1 x 5000 = 500
- Write the answer. 500 MWh
Check. 500 / 5000 = 0.1. ✓
4
FAdd the percentages in the example town mix. Write the total as a number.
100
Method. Add the five percentages.
- Add. 40 + 10 + 35 + 5 + 10 = 100.100
- Write the answer. 100
Check. The total is 100%, which means all the energy is included. ✓
5
FIn the example mix, which source gives the largest share? Write the word.
wind
Method. Compare the percentages.
- Compare. Wind is 40%, which is more than gas at 35%.40%
- Write the answer. wind
Check. Wind is the largest share here. ✓
6
PSIn the example mix, how much energy comes from renewable sources (wind and solar together)? Write the number of MWh.
2500
Method. Add the renewable percentages, then find that share.
- Add. Wind and solar together = 40% + 10% = 50%.50%
- Multiply. 0.5 x 5000 = 2500 MWh.0.5 x 5000 = 2500
- Write the answer. 2500 MWh
Check. 2500 / 5000 = 0.5. ✓
7
PSIn the example mix, the town needs more electricity on a still, cloudy night. Which source in the mix is least affected by this? Write the word.
gas
Method. Think about which sources depend on weather or daylight.
- Look. Wind and solar need wind or sun, so they are affected. Gas can be run at any time.gas not affected
- Write the answer. gas
Check. Nuclear is also available at night. ✓
8
PSA town uses 800 MWh of electricity in a month and gets 25% of it from wind. How much does the wind provide? Write the number of MWh.
200
Method. Find 25% of 800.
- Multiply. 0.25 x 800 = 200 MWh.0.25 x 800 = 200
- Write the answer. 200 MWh
Check. 200 / 800 = 0.25. ✓
9
PSCompare wind and gas on carbon dioxide while they are running. Write which one gives out more carbon dioxide: wind or gas.
gas
Method. Use the comparison table.
- Compare. Wind gives out no carbon dioxide while running; gas gives out some.gas gives CO2
- Write the answer. gas
Check. ✓
10
RNuclear is the most expensive to build in the table, but it gives out very little carbon dioxide. Explain why a council might still choose nuclear. Accept any answer that says it is reliable all the time and has low carbon dioxide emissions.
Accept any answer that says it is reliable all the time and has low carbon dioxide emissions.
Method. Think about reliability and emissions.
- Reliable. Nuclear is reliable all the time.reliable
- Emissions. It gives out very little carbon dioxide.low CO2
- Write the answer. Accept any answer that says it is reliable all the time and has low carbon dioxide emissions.
Check. It has a drawback: radioactive waste. ✓
11
REvaluate the claim: “wind is the best choice for a town because it is free to run.” Give one point for and one against. Accept any answer that says wind has no fuel cost, but it depends on the weather so it is not reliable on its own.
Accept any answer that says wind has no fuel cost, but it depends on the weather so it is not reliable on its own.
Method. Weigh the cost and reliability.
- For. Wind needs no fuel, so running costs are low.no fuel
- Against. It is not reliable, because the weather changes, so the town also needs another source.not reliable
- Write the answer. Accept any answer that says wind has no fuel cost, but it depends on the weather so it is not reliable on its own.
Check. ✓
12
RA town chooses an energy mix with a larger share of wind and a smaller share of gas. Give the environmental advantage in one sentence. Accept any sentence that says the mix gives out less carbon dioxide.
Accept any sentence that says the mix gives out less carbon dioxide.
Method. Compare the emissions of wind and gas.
- Compare. Wind gives out no carbon dioxide while running, and gas does.wind: none, gas: some
- Effect. So a bigger wind share gives out less carbon dioxide.less CO2
- Write the answer. Accept any sentence that says the mix gives out less carbon dioxide.
Check. ✓
4.5
Energy security and conserving energy
Video lesson: Energy security and conserving energyComing soon
Context. A country buys most of its gas from another country. When prices rise, electricity bills go up. “Can we rely on that?” a pupil asks. This is a question about energy security: a country needs a reliable supply that it can afford.
Energy security means having a reliable supply of energy that the country can afford, without depending on a single source or a single country. A varied mix of sources, and home-grown renewables, help to improve energy security. Conserving energy means using less energy, for example by insulating houses, using efficient appliances and turning off lights, so that less energy needs to be supplied.
Key ideas
- Energy security: a reliable, affordable supply.
- A varied mix of sources reduces the risk if one source fails.
- Conserving energy means using less, for example with insulation and efficient appliances.
- Using less energy reduces the need for new power stations and reduces emissions.
Worked example 4.5.1
Give one way a household can conserve energy, in one sentence. Accept any sentence that names a method, such as insulating the loft or turning off lights.
Method. Think about a change in the home.
- Where. Most of the heat in a house is lost through the roof and walls.roof and walls
- Method. Loft insulation reduces the heat lost through the roof.insulation
- Write the answer. Accept any sentence that names a method, such as insulating the loft or turning off lights.
Check. Any method that reduces energy use is correct. ✓
Worked example 4.5.2
A country gets 60% of its electricity from one fuel. Explain why this is a risk to energy security, in one sentence. Accept any sentence that says the country would be badly affected if that fuel became expensive or hard to get.
Method. Think about a single source.
- Risk. If that fuel becomes expensive or the supply is cut, the electricity supply is affected.risk
- Link. A varied mix reduces this risk.varied mix
- Write the answer. Accept any sentence that says the country would be badly affected if that fuel became expensive or hard to get.
Check. ✓
Worked example 4.5.3
Give one reason why a range of energy sources improves a country’s energy security, in one sentence. Accept any sentence that says it reduces the risk if one supply is cut or its price rises.
Method. Think about what happens if one source fails.
- Risk. If one source fails, the others can keep supplying energy.others
- Security. So the range of sources reduces the risk to the country.reduces risk
- Write the answer. Accept any sentence that says it reduces the risk if one supply is cut or its price rises.
Check. ✓
Watch out
Watch out: conserving energy and energy security are not the same. Conservation means using less; security means a reliable supply. Both help a country.
Exam tip
Exam tip. For an evaluation question, give a benefit and a drawback, then a conclusion that says which is better and why.
Exercise 4E Security, conservation and evaluation
1
FWhat word means having a reliable, affordable supply of energy? Write the phrase.
energy security
Method. Recall the phrase.
- Recall. Energy security means a reliable and affordable supply.energy security
- Write the answer. energy security
Check. ✓
2
FName a way to conserve energy in the home. Write the word or phrase.
insulation
Method. Think about a way to reduce energy use.
- Recall. Insulation reduces the energy wasted by heating.insulation
- Write the answer. insulation
Check. Turning off lights also conserves energy. ✓
3
FWhich is a benefit of using a varied mix of energy sources? Write one word: reliable or expensive.
reliable
Method. Think about what a mix does when one source fails.
- Recall. If one source fails, the others can keep supplying energy.reliable
- Write the answer. reliable
Check. ✓
4
FName a device that uses less energy for the same job. Write the name.
efficient appliance
Method. Think about appliances with a high efficiency.
- Recall. An efficient appliance wastes less energy for the same job.efficient appliance
- Write the answer. efficient appliance
Check. ✓
5
RExplain why using less energy can reduce the need for new power stations, in one sentence. Accept any sentence that says less energy demand means less new capacity is needed.
Accept any sentence that says less energy demand means less new capacity is needed.
Method. Think about how much energy a country needs.
- Demand. If demand falls, the existing supply is enough.demand falls
- Link. So fewer new power stations are needed.fewer power stations
- Write the answer. Accept any sentence that says less energy demand means less new capacity is needed.
Check. ✓
6
PSA country uses 1000 units of energy. It reduces use by 15% through insulation. How many units does it save? Write the number.
150
Method. Find 15% of 1000.
- Multiply. 0.15 x 1000 = 150 units.0.15 x 1000 = 150
- Write the answer. 150
Check. 1000 - 150 = 850. ✓
7
PSA country has 1000 units of energy use and 60% comes from one fuel. How many units come from this fuel? Write the number.
600
Method. Find 60% of 1000.
- Multiply. 0.6 x 1000 = 600 units.0.6 x 1000 = 600
- Write the answer. 600 units
Check. 600 / 1000 = 0.6. ✓
8
PSTwo countries have the same total energy use. Country A gets 60% from one fuel. Country B gets 25% from one fuel. Which has the greater risk to energy security? Write A or B.
A
Method. The bigger share from one fuel is the bigger risk.
- Compare. A depends more on one fuel (60%) than B (25%).60% > 25%
- Write the answer. A
Check. ✓
9
REvaluate: “a country should build only renewable power stations to be secure.” Give one reason for and one reason against. Accept any answer that gives a reason for, such as no emissions, and one against, such as the lack of reliability when the weather is poor.
Accept any answer that gives a reason for, such as no emissions, and one against, such as the lack of reliability when the weather is poor.
Method. Weigh the benefits and drawbacks.
- For. Renewables produce little carbon dioxide and use home-grown resources.for
- Against. Renewables depend on the weather, so they need backup or storage.against
- Write the answer. Accept any answer that gives a reason for, such as no emissions, and one against, such as the lack of reliability when the weather is poor.
Check. ✓
10
RGive one reason why a country might import its energy, and one risk of doing so. Accept any answer that gives a reason such as cheaper fuel, and a risk such as prices or supply being controlled by others.
Accept any answer that gives a reason such as cheaper fuel, and a risk such as prices or supply being controlled by others.
Method. Think about the cost and the control of supply.
- Reason. Imported fuel may be cheaper or easier to get.cheaper
- Risk. The supply and prices depend on other countries.depends on others
- Write the answer. Accept any answer that gives a reason such as cheaper fuel, and a risk such as prices or supply being controlled by others.
Check. ✓
11
PSIn a town, the energy use falls from 5000 MWh to 4000 MWh after an insulation scheme. Calculate the percentage reduction. Write the number of percent.
20%
Method. Find the reduction, then divide by the original.
- Reduction. Reduction = 5000 - 4000 = 1000 MWh.1000 MWh
- Percentage. Percentage = 1000 / 5000 = 0.2, which is 20%.1000 / 5000 = 0.2
- Write the answer. 20%
Check. 20% of 5000 = 1000. ✓
12
RExplain in one sentence how a town can improve energy security and reduce emissions at the same time. Accept any sentence that says it can use renewables and conserve energy, which both reduce the need for fossil fuel.
Accept any sentence that says it can use renewables and conserve energy, which both reduce the need for fossil fuel.
Method. Think about what both aims need.
- Renewables. Renewable sources reduce fossil fuel use and home-grown supply improves security.renewables
- Conserve. Conserving energy reduces the total needed.conserve
- Write the answer. Accept any sentence that says it can use renewables and conserve energy, which both reduce the need for fossil fuel.
Check. ✓
Chapter summary
| Skill | Method |
|---|---|
| Classify a resource | Renewable: replaced naturally; non-renewable: used up faster than made |
| Name how a source makes electricity | Turbines turned by wind, water, tides, waves, steam from fuel or heat |
| Compare resources | Use reliability, cost and environmental impact, one sentence each |
| Calculate the energy mix | Energy = percentage / 100 x total |
| Discuss security and conservation | A varied mix improves security; conservation reduces demand |
Can you…?
- I can say whether a resource is renewable or non-renewable
- I can describe how a source makes electricity
- I can compare two resources using three headings
- I can calculate a share of an energy mix
- I can explain energy security and how conservation helps
Key terms
- renewable
- a resource that is replaced naturally and will not run out in a human lifetime
- non-renewable
- a resource that is used up faster than it is made
- fossil fuel
- coal, oil or natural gas, formed from ancient plants and animals
- biofuel
- a fuel made from plant or animal material
- energy mix
- the different sources used to supply the energy needed
- energy security
- a reliable and affordable supply of energy
- reliability
- whether a source can supply energy when it is needed
Exercise 4Z Check-up
1
Name a renewable source that uses the heat of rocks underground. Write the word.
geothermal
Method. Recall the source.
- Recall. Geothermal energy uses heat from rocks.geothermal
- Write the answer. geothermal
Check. ✓
2
Name a non-renewable fuel that releases energy by fission. Write the word.
uranium
Method. Recall the fuel.
- Recall. Uranium is split by fission in nuclear power stations.uranium
- Write the answer. uranium
Check. ✓
3
What gas is released when fossil fuels burn, adding to global warming? Write the name.
carbon dioxide
Method. Recall the gas.
- Recall. Burning fossil fuels releases carbon dioxide.carbon dioxide
- Write the answer. carbon dioxide
Check. ✓
4
Which resource is renewable and uses the movement of the sea? Write the word.
tidal
Method. Recall the source.
- Recall. Tidal energy uses the movement of the tides.tidal
- Write the answer. tidal
Check. ✓
5
Calculate 30% of 2000. Write the number.
600
Method. Multiply by 0.3.
- Multiply. 0.3 x 2000 = 600.0.3 x 2000 = 600
- Write the answer. 600
Check. ✓
6
A town uses 4000 MWh. Wind gives 25%. How much does the wind give? Write the number of MWh.
1000
Method. Find 25% of 4000.
- Multiply. 0.25 x 4000 = 1000 MWh.0.25 x 4000 = 1000
- Write the answer. 1000 MWh
Check. ✓
7
Name the energy store of water held high in a reservoir. Write the words.
gravitational potential
Method. Recall the store.
- Recall. Water held high has gravitational potential energy.gravitational potential
- Write the answer. gravitational potential
Check. ✓
8
Explain why wind is not always reliable. Write one reason in one sentence. Accept any sentence that says the wind changes with the weather.
Accept any sentence that says the wind changes with the weather.
Method. Think about the wind.
- Reason. Wind speed changes with the weather, so it is not always available.changes
- Write the answer. Accept any sentence that says the wind changes with the weather.
Check. ✓
9
Give one benefit of conserving energy. Accept any sentence that says it reduces the energy bill or the emissions or the need for new power stations.
Accept any sentence that says it reduces the energy bill or the emissions or the need for new power stations.
Method. Think about the effect of using less energy.
- Benefit. Using less energy lowers bills and emissions.lower bills
- Write the answer. Accept any sentence that says it reduces the energy bill or the emissions or the need for new power stations.
Check. ✓
10
Write the word that describes a resource replaced naturally in a human lifetime. Write the word.
renewable
Method. Recall the word.
- Recall. A renewable resource is replaced naturally.renewable
- Write the answer. renewable
Check. ✓
Total 29 marks. Allow about 29 minutes.
Exercise 4X Exam-style questions
1
FName one renewable source and one non-renewable source of electricity. Write two words, separated by a comma: renewable first.[2 marks]
wind, coal
Method. Pick one of each type.
- Renewable. Wind is replaced by the weather.wind
- Non-renewable. Coal takes millions of years to form.coal
- Write the answer. wind, coal
Check. ✓
2
FA town uses 5000 MWh. Solar gives 10%. Calculate the energy from solar. Write the number of MWh.[2 marks]
500
Method. Find 10% of 5000.
- Multiply. 0.1 x 5000 = 500 MWh.0.1 x 5000 = 500
- Write the answer. 500 MWh
Check. ✓
3
RExplain why hydroelectric power is renewable. Accept any answer that says rain replaces the water, which is replenished by the water cycle.[2 marks]
Accept any answer that says rain replaces the water, which is replenished by the water cycle.
Method. Think about the water.
- Source. The water in a reservoir is replenished by rain.rain
- Link. The water cycle means the resource is replaced naturally.water cycle
- Write the answer. Accept any answer that says rain replaces the water, which is replenished by the water cycle.
Check. ✓
4
RGive two disadvantages of burning fossil fuels for electricity. Accept any two of: carbon dioxide emissions, global warming, air pollution, and fuel running out.[2 marks]
Accept any two of: carbon dioxide emissions, global warming, air pollution, and fuel running out.
Method. Think about the effects of burning.
- First. Burning releases carbon dioxide, which adds to global warming.CO2
- Second. Fuels are non-renewable and will run out.run out
- Write the answer. Accept any two of: carbon dioxide emissions, global warming, air pollution, and fuel running out.
Check. ✓
5
RDescribe how a tidal barrage makes electricity, in order. Accept any answer that says the tide fills and empties a basin, water flows through a turbine, and the turbine turns a generator.[3 marks]
Accept any answer that says the tide fills and empties a basin, water flows through a turbine, and the turbine turns a generator.
Method. Follow the water.
- Fill. The rising tide fills a basin behind the barrage.fills
- Flow. Water flows back through a turbine when the tide falls.flows through turbine
- Turn. The turbine turns a generator to make electricity.generator
- Write the answer. Accept any answer that says the tide fills and empties a basin, water flows through a turbine, and the turbine turns a generator.
Check. ✓
6
PSA town uses 8000 MWh. The mix is 35% gas, 25% wind, 30% nuclear and 10% solar. Calculate the energy from nuclear and the energy from solar together. Write the number of MWh.[3 marks]
3200
Method. Find the percentage for nuclear and solar, then the energy.
- Add. Nuclear and solar together = 30% + 10% = 40%.40%
- Multiply. 0.4 x 8000 = 3200 MWh.0.4 x 8000 = 3200
- Write the answer. 3200 MWh
Check. 3200 / 8000 = 0.4. ✓
7
RCompare wind power and nuclear power on reliability, carbon dioxide and waste. Accept any answer that says wind is less reliable, gives no carbon dioxide while running, and produces no radioactive waste; nuclear is reliable, gives very little carbon dioxide and produces radioactive waste.[4 marks]
Accept any answer that says wind is less reliable, gives no carbon dioxide while running, and produces no radioactive waste; nuclear is reliable, gives very little carbon dioxide and produces radioactive waste.
Method. Compare each point in turn.
- Reliability. Wind depends on the weather; nuclear runs all the time.reliability
- Carbon dioxide. Wind gives none while running; nuclear gives very little.CO2
- Waste. Wind produces no radioactive waste; nuclear does.waste
- Conclusion. Each has advantages, so a mix is often chosen.mix
- Write the answer. Accept any answer that says wind is less reliable, gives no carbon dioxide while running, and produces no radioactive waste; nuclear is reliable, gives very little carbon dioxide and produces radioactive waste.
Check. ✓
8
REvaluate the claim that a country should move all its electricity to solar power. Give one strength and one weakness, and a conclusion. Accept any answer that gives low emissions as a strength, and night-time and winter supply as a weakness, with a conclusion that backup or a mix is needed.[4 marks]
Accept any answer that gives low emissions as a strength, and night-time and winter supply as a weakness, with a conclusion that backup or a mix is needed.
Method. Weigh the points.
- Strength. Solar gives out no carbon dioxide while running.strength
- Weakness. Solar produces no power at night and less in winter.weakness
- Conclusion. A mix with storage or backup is more secure.mix and backup
- Write the answer. Accept any answer that gives low emissions as a strength, and night-time and winter supply as a weakness, with a conclusion that backup or a mix is needed.
Check. ✓
9
RA council wants to reduce its energy use by 25% and become more secure. Describe two actions it could take and explain how each helps. Accept any two sensible actions, such as insulation or efficient lighting, and renewable sources, each with a link to security or saving.[5 marks]
Accept any two sensible actions, such as insulation or efficient lighting, and renewable sources, each with a link to security or saving.
Method. Choose two actions and link each to the aim.
- Action 1. Insulate public buildings to reduce heat loss.insulate
- Link 1. Less energy is needed, so the 25% reduction is more achievable.less needed
- Action 2. Install renewable generation, such as solar on council roofs.solar
- Link 2. A home-grown supply improves energy security.security
- Check. Both actions help the council meet its aim.both help
- Write the answer. Accept any two sensible actions, such as insulation or efficient lighting, and renewable sources, each with a link to security or saving.
Check. ✓
10
RDescribe one advantage and one disadvantage of geothermal energy. Accept any answer: advantage, it is renewable and needs no fuel; disadvantage, it only works where hot rocks are near the surface.[2 marks]
Accept any answer: advantage, it is renewable and needs no fuel; disadvantage, it only works where hot rocks are near the surface.
Method. Give one advantage and one disadvantage.
- Advantage. It is renewable and needs no fuel.renewable
- Disadvantage. It only works where hot rocks are close to the surface.hot rocks
- Write the answer. Accept any answer: advantage, it is renewable and needs no fuel; disadvantage, it only works where hot rocks are near the surface.
Check. ✓