The diagram below shows how electricity is generated in a hydroelectric power station.

The diagram below shows how electricity is generated in a hydroelectric power station. 

Sample answer:

The diagram illustrates the process of electricity generation in a hydroelectric power station. The entire process revolves around the cyclical movement of water between a high-level reservoir and a low-level reservoir, using a dam and reversible turbines.

During the day, the intake at the high-level reservoir is open, allowing water to flow down through the dam. As the water descends, it passes through turbines, which activate a generator to produce electricity. This generated electricity is then transmitted to the national grid via power lines. The downward flow of water is crucial as it harnesses the potential energy stored in the elevated water to drive the turbines and generate power efficiently.

At night, the process is reversed. The intake at the high-level reservoir is closed, and the turbines are used in reverse to pump water back up from the low-level reservoir to the high-level reservoir. This is facilitated by using the same turbines and generator setup, but the direction of water flow is inverted. This pumped storage system ensures that water is available at the higher elevation for use during the next day.

The reversible nature of the turbines allows for dual functionality: generating electricity during the day and pumping water at night. This method of using stored water to generate power and then replenishing it ensures a sustainable and continuous cycle of energy production.

In summary, the hydroelectric power station operates on a cycle of water movement facilitated by a dam, with electricity generation occurring during the day and water pumping at night. This efficient system leverages the potential and kinetic energy of water, providing a renewable and reliable source of electricity.