The process of transforming geothermal energy from cold water into electricity

The diagram illustrates the process of generating electricity from geothermal energy by using cold water and underground heat sources.

Overall, the system involves five main stages, beginning with the pumping of cold water deep underground and culminating in the production of electricity for consumer use. The process makes use of underground hot rocks in the geothermal zone to convert water into steam, which ultimately drives a turbine connected to a generator.

At the first stage, cold water from a storage tank is pumped down through an injection well to a depth of approximately 4.5 kilometres beneath the earth’s surface. Once underground, the water passes through the geothermal zone, which consists of intensely heated rocks. The heat from these rocks raises the temperature of the water, transforming it into hot water.

Next, the hot water is channelled upward via the production well and delivered to a condenser. Inside the condenser, the hot water is converted into steam. This steam is then directed towards a turbine, causing it to spin. The rotation of the turbine subsequently activates the generator, which produces electricity. In the final stage, the generated electricity is transmitted to a power grid, making it available for household and industrial consumption.

1. Task Achievement (TA) – Band 8.0

Strengths:

• All stages of the process are covered in a logical order. ✅
• Uses precise vocabulary for the process: “injection well,” “production well,” “condenser,” “turbine,” “generator.” ✅
• Provides an overview: “The system involves five main stages…” ✅
• Clear cause-effect relationships are established: heat → steam → turbine → generator.

Weaknesses:

• Minor omission of exact percentages or quantitative detail (not always required for process diagrams).
• Could include a final note on environmental impact or efficiency for a slightly more advanced answer.

Example Improvement:

• Add linking phrase: “Finally, the electricity generated is distributed via the national power grid, ensuring a continuous supply to consumers.”

2. Coherence and Cohesion (CC) – Band 7.5–8.0

Strengths:

• Logical sequence from start to finish: pumping → heating → steam → turbine → electricity. ✅
• Effective use of cohesive devices: “once underground,” “next,” “then,” “subsequently,” “in the final stage.” ✅

Weaknesses:

• Some sentences could be combined for smoother flow.
• Repetition of “is converted” can be varied.

Example Improvement:

• Original: “Inside the condenser, the hot water is converted into steam. This steam is then directed towards a turbine…”
• Revised: “Inside the condenser, the hot water transforms into steam, which is subsequently directed towards a turbine…”

3. Lexical Resource (LR) – Band 8.0

Strengths:

• Excellent use of technical vocabulary: “geothermal zone,” “intensely heated rocks,” “rotates,” “activates.” ✅
• Precise verbs: “channelled,” “transmitted,” “pumped,” “delivered.”

Weaknesses:

• Minor repetition of “hot water” could be replaced with synonyms like “heated fluid” or “thermal water.”
• Could add formal academic phrases like “facilitates the generation of electricity” or “subsequently drives the turbine mechanism.”

4. Grammatical Range and Accuracy (GRA) – Band 7.5–8.0

Strengths:

• Accurate use of passive and active voice: “water is pumped,” “turbine causes it to spin.” ✅
• Variety of sentence structures: relative clauses (“which consists of intensely heated rocks”), participle phrases (“causing it to spin”). ✅

Weaknesses:

• Some sentences are long and could be split for clarity.
• Could incorporate more complex conditional structures or linking adverbs for high-level cohesion.

Example Improvement:

• Original: “The rotation of the turbine subsequently activates the generator, which produces electricity.”
• Revised: “As the turbine rotates, it activates the generator, thereby producing electricity for consumer use.”

Estimated Band Scores:

Criterion	Band	Notes
Task Achievement	8.0	Covers all stages, clear overview, logical sequence.
Coherence & Cohesion	7.5–8.0	Good sequence, effective connectors, minor repetition.
Lexical Resource	8.0	Excellent technical vocabulary, minor synonym variety issues.
Grammatical Range & Accuracy	7.5–8.0	Accurate, variety of structures, slight room for more complex sentences.

Overall Band Estimate: 7.5–8.0