Cambridge IELTS 12 Test 4 Writing Task 1: Geothermal Power Plant
Cambridge IELTS 12 · Test 4 · Academic Writing Task 1Process diagram
The diagram shows how a geothermal power plant uses heat from underground hot rocks to generate electricity. It is a man-made process with five numbered stages, from cold water being pumped 4.5 km underground to electricity being produced by a generator and carried away by pylons.
The question
You should spend about 20 minutes on this task. The diagram below shows how geothermal energy is used to produce electricity. Summarise the information by selecting and reporting the main features, and make comparisons where relevant. Write at least 150 words.
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Key features to report
- The process has five numbered stages and is cyclical in part: cold water goes down one well, is heated underground and comes back up another well as hot water.
- Stage 1 and 2: cold water is pumped down the injection well to a depth of 4.5 km, where it reaches the geothermal zone of hot rocks.
- Stage 3: the water is heated as it flows through the hot rocks and is then pumped up the production well as hot water.
- Stage 4: at the surface the hot water enters a condenser, from which steam is produced and sent to the turbine.
- Stage 5: the steam powers the turbine, which in turn drives the generator, and the generator produces electricity that is carried away via a pylon.
- This is a man-made process, so the passive voice (is pumped, is heated, is converted) is essential, together with sequencing language.
Model overview
Overall, the process involves five main stages, beginning with cold water being pumped deep underground and ending with the generation of electricity. In essence, heat from hot rocks below the surface is used to turn water into steam, which then drives a turbine and generator.
Paragraph plan
- 1
Introduction
Paraphrase the task in one sentence: the diagram illustrates how a geothermal power station uses the heat of underground rocks to produce electricity.
- 2
Overview
Say how many stages there are, where the process starts and ends, and the core idea that underground heat turns water into steam that drives a turbine and generator. No details of the equipment here.
- 3
Body paragraph 1: underground stages
Describe stages 1 to 3: cold water pumped 4.5 km down the injection well, heated as it passes through the geothermal zone of hot rocks, and pumped back up the production well as hot water.
- 4
Body paragraph 2: surface stages
Describe stages 4 and 5: the hot water enters the condenser and steam is produced, the steam powers the turbine, the turbine drives the generator, and the electricity produced is transmitted through pylons.
Useful comparisons
- Divide the process into an underground phase (stages 1 to 3) and a surface phase (stages 4 and 5).
- Contrast the two wells: the injection well takes cold water down, the production well brings hot water up.
- Show the energy chain clearly: heat from rocks, hot water, steam, turbine movement, electricity.
- Mention the depth of 4.5 km, the only figure on the diagram.
- Explain the relationship shown in the labels: the turbine is powered by steam, and the generator is powered by the turbine and produces electricity.
- Finish with the electricity being carried away by the pylon to show the end point of the process.
Band 8+ model answer
179 words · An original model answer written for ieltswrites, not an official answer. It stays in English, as in the exam.
The diagram illustrates how a geothermal power station uses heat from underground rocks to generate electricity.
Overall, there are five main stages in the process, beginning with cold water being pumped deep below the surface and ending with the production of electricity. Essentially, heat from hot rocks is used to turn water into steam, which then drives a turbine and a generator.
First, cold water is pumped down a shaft known as the injection well to a depth of 4.5 kilometres. At this point, it reaches the geothermal zone, an area of hot rocks, and as it flows through these rocks it is heated. The hot water is then pumped back to the surface through a second shaft, the production well.
Once it reaches ground level, the hot water passes into a condenser, from which steam is produced and directed into a turbine. The force of the steam makes the turbine spin, and this movement in turn powers a generator, where electricity is produced. Finally, the electricity is transmitted away from the plant along power lines supported by pylons.
Why this answer scores highly
- Task Achievement
- Every stage in the diagram is covered in the correct order, the 4.5 km depth is included, and the overview summarises the whole process from cold water to electricity without adding outside information.
- Coherence and Cohesion
- Dividing the process into underground and surface stages gives a logical structure, and sequencers such as first, once, at this point and finally are used naturally rather than mechanically.
- Lexical Resource
- Technical labels are used accurately and then varied with paraphrases such as power station, shaft, drive and transmitted, showing control of process vocabulary.
- Grammatical Range and Accuracy
- The passive voice dominates appropriately, and it is combined with relative clauses, participle clauses and time clauses beginning with once and as.
Useful vocabulary
- geothermal energy
- heat energy from inside the earth
- power plant
- a facility that generates electricity; also called a power station
- injection well
- the shaft through which cold water is sent underground
- production well
- the shaft through which heated water is brought back to the surface
- the geothermal zone
- the underground area of hot rocks where the water is heated
- be pumped down
- be forced downwards by a pump
- condenser
- the unit at the surface where the hot water is handled and steam is produced for the turbine
- turbine
- a machine with blades that is turned by steam to create movement
- generator
- a machine that turns movement into electricity
- drive
- provide the power that makes a machine work
- transmitted
- sent along power lines to where it is needed
- pylon
- a tall metal tower that carries electricity cables
- subsequently
- after that; a useful sequencing word
Common mistakes
- Writing in the active voice with invented subjects, such as workers pump the water, instead of the passive voice suited to a man-made process.
- Leaving out the depth of 4.5 km, the only measurement given in the diagram.
- Mixing up the two wells, for example saying hot water goes down the injection well.
- Getting the order wrong at the surface: the steam powers the turbine first, and the turbine then powers the generator.
- Adding outside knowledge about how geothermal energy works or its environmental benefits, which is not in the diagram.
- Omitting an overview that states the number of stages and the beginning and end of the process.
Frequently asked questions
- Which Cambridge book is this question from?
- The geothermal power plant diagram is Writing Task 1 of Test 4 in Cambridge IELTS 12 Academic, published in 2017.
- Should I use the passive voice for this process?
- Yes. It is a man-made process, so the passive (is pumped, is heated, is produced) is the natural choice, although some active verbs such as the steam drives the turbine are also correct.
- Can I explain how geothermal energy works in general?
- No. Describe only what the diagram shows. Explanations from outside knowledge do not earn marks and can introduce errors.
- How many words should I write?
- Write at least 150 words; around 170 to 200 words covers all five stages and an overview comfortably.
Free and timed, with a live word count, just like the computer-delivered test. Then get an instant AI band score.
The exam simulator runs on a computer. Open this page on a laptop or desktop to practise.