Band 8+: The diagram below shows how electricity is generated in a hydroelectric station. Summarise the information by selecting and reporting the main features, and make comparisons where relevant. Write at least 150 words.

The image illustrates the process of converting water to electricity using a hydroelectric power station.

On the whole, water from a river is converted by a generator in the power station that eventually powers the national grid. Water moves from the high-level reservoir to the low-level reservoir during the day, and in the opposite direction at night, powered by the reversible turbines in the power station.

During the day, water from the river flows into a high-level reservoir which is controlled by a dam. Water then moves into the hydroelectric power station where the generator turns it into electricity. The electricity generated then goes to power lines and ultimately into the national grid. At the same time, the water moves into a low-level reservoir beside the power station.

At night, the flow of water is reversed. The water from the low-level reservoir goes back into the power station, then gets pumped back to the high-level reservoir by way of the reversible turbines.