✅ Shared advantages
They will not run out. There is no fuel to buy, so the running costs are usually low. Nothing is burned, so no carbon dioxide is released while they generate electricity, and they do not add to global warming or pollute the air.
Energy Resources and Electricity Generation » Comparing Renewable Energy Resources
What you'll learn this session
Study time: 30 minutes
Edexcel spec: 4.19P
- What makes an energy resource renewable
- The advantages and disadvantages of wind, hydroelectric, tidal, wave, geothermal and solar power
- How to compare them for reliability, cost, land use, pollution and location
- How to write a balanced answer to a discuss or evaluate question
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Unlock This CourseWhat does renewable mean?
This content is examined in Paper 2 only.
You already know how wind, water, hot rocks and the Sun are used to generate electricity. This lesson is about judging them. No energy resource is perfect, and the exam asks for the good and bad points of each one when it is used on a large scale, to supply whole towns and cities.
The six resources in this lesson are all renewable. The wind keeps blowing, rain keeps refilling reservoirs and the Sun keeps shining, however much electricity we generate.
Key terms:
- Renewable energy resource: an energy resource that will not run out, because it is replaced naturally as it is used.
- Reliable: able to generate electricity whenever it is needed, whatever the weather or the time of day.
- Habitat: the place where a plant or animal lives.
What all renewable resources share
❌ Shared disadvantages
Most cost a lot to build. Several depend on the weather, so they are not reliable. Each one only suits certain places. Large-scale generation often needs a lot of equipment spread over a large area, such as a wind farm, a solar farm or a reservoir, and that can damage habitats or spoil the view.
The six resources, one by one
🌬 Wind
Wind turbines are quite quick to build and cheap to run. But they generate nothing on a calm day, and they are shut down in very strong winds, so wind power is unreliable. One turbine has a small output, so a wind farm needs many turbines. They can spoil the view, make some noise and kill birds. They suit hills, coasts and shallow seas.
💧 Hydroelectric
Water is kept in the reservoir until it is needed, so hydroelectric power is reliable and can be started quickly when demand rises. A long drought can lower the output. The dam is very expensive to build. Making the reservoir floods a whole valley, which destroys habitats and can force people to leave their homes. It needs mountains and plenty of rain.
🌊 Tidal
The times of the tides can be worked out years ahead, so tidal power is very predictable. It does not depend on the weather. But it is not constant: nothing is generated at the turn of the tide, when the water levels are equal. A barrage is very expensive. It changes the mudflats where wading birds feed and blocks the way for fish and boats. Few river mouths are suitable.
🏄 Wave
Waves are made by the wind, so wave power is unreliable: a calm sea generates very little. Each wave generator has a small output, so many are needed along a coast. They must be strong enough to survive storms, which makes them costly to build and repair. They can be a hazard to boats. They suit coasts that face the open ocean.
🌋 Geothermal
The rocks stay hot day and night, in all weathers, so geothermal power is reliable. A geothermal power station takes up little land and causes very little pollution. The big limit is location. It only works well where hot rocks lie close to the surface, in volcanic areas. Drilling deep holes into rock is expensive.
🌞 Solar
Solar cells generate nothing at night and less on cloudy days and in winter, so solar power is unreliable. They cost little to run. A large solar farm covers a lot of land, but solar cells can also sit on roofs, which uses no extra land. Solar power suits sunny countries best.
The comparison table
| Resource | Reliable? | Cost | Land and habitats | Places it suits |
|---|---|---|---|---|
| Wind | No: needs wind, but not too much | medium to build, low to run | many turbines; view, noise, birds | hills, coasts, shallow seas |
| Hydroelectric | Yes: water is stored until needed | very high to build, low to run | floods a valley | mountains with high rainfall |
| Tidal | Predictable, but not constant | very high to build, low to run | changes river mouth habitats | river mouths with a big rise and fall of the tide |
| Wave | No: needs waves | high to build and repair | little land; hazard to boats | coasts facing the open ocean |
| Geothermal | Yes: day and night, any weather | high to build (deep drilling), low to run | small area | volcanic areas |
| Solar | No: needs daylight, best in strong sunshine | medium to build, low to run | solar farms need a large area; roofs need none | sunny countries |
For all six, no fuel is burned, so no carbon dioxide is released while electricity is generated.
Writing a balanced answer
Questions on this topic often use the command words discuss or evaluate. Both want more than a list of good points.
- Give at least one advantage and at least one disadvantage of each resource in the question.
- Use the information in the question. If it says the place is flat, cloudy or on the coast, use that fact.
- Compare with words like "but", "whereas" and "however".
- For evaluate, finish with a conclusion and give a reason for it.
Worked example
A small island has strong winds. Evaluate the use of wind turbines to generate the island's electricity.
Step 1, an advantage linked to the place: the island has strong winds, so wind turbines would often generate a lot of electricity.
Step 2, another advantage: there is no fuel to buy and no carbon dioxide is released when the turbines run.
Step 3, a disadvantage: wind is unreliable. On calm days the turbines generate nothing, so the island would need another resource as a back-up.
Step 4, a conclusion with a reason: wind turbines are a good choice for most of the island's electricity because the wind there is strong and free, but only if there is a back-up for calm days.
Common mistakes
- Writing "renewable means it can be used again". Electricity is not reused. Renewable means the resource is replaced naturally, so it will not run out.
- Writing that renewable resources are "free". There is no fuel cost, but the equipment is expensive to build and has to be repaired.
- Calling tidal power unreliable in the same way as wind. Its output changes during the day, but we know exactly when. Call it predictable but not constant.
- Writing "it is bad for the environment". Say what the damage is, such as "the reservoir floods a valley and destroys habitats".
- Giving only advantages in an evaluate question, or leaving out the conclusion.
Exam-style question
A country has high mountains with heavy rainfall. It is cloudy for much of the year. The government wants to generate more electricity from renewable resources.
(a) State what is meant by a renewable energy resource. [1 mark]
(b) Give two advantages that are shared by all renewable methods of generating electricity. [2 marks]
(c) Explain why tidal power is described as predictable but wind power is described as unreliable. [2 marks]
(d) The government must choose between a hydroelectric power station and a large solar farm. Evaluate these two choices for this country. [5 marks]
Model answer
(a) A resource that will not run out because it is replaced naturally as it is used. (1)
(b) Any two from: there is no fuel to pay for (1), no carbon dioxide is released when generating electricity (1), the resource will not run out (1).
(c) The times of the tides can be worked out in advance, so we know when a tidal power station will generate electricity. (1) Wind depends on the weather, so we cannot be sure when a wind turbine will generate electricity. (1)
(d) The country has mountains and heavy rainfall, so it is well suited to hydroelectric power. (1) Hydroelectric power is reliable because water is stored in the reservoir until it is needed. (1) However, the dam is very expensive to build and the reservoir floods a valley, destroying habitats. (1) A solar farm does not flood a valley, but it generates nothing at night and little in cloudy weather, and this country is cloudy for much of the year. (1) Conclusion: hydroelectric power is the better choice here because it is reliable and suits the country, whereas solar cells would often generate little electricity. (1)
Exam tip
In part (d), the mountains, the rainfall and the clouds were put in the question for you to use. An answer that could be about any country will not reach full marks. End with one clear choice and the reason for it.