Please review my IELTS essay

The diagram below shows how electricity is generated in a hydroelectric power station. Summarise the information by selecting and reporting the main features, and make comparisons where relevant.

My essay:

The diagram illustrates the various stages involved in the production of electricity by using hydropower. Overall, the process mainly relies on the flow of water between two reservoirs, a high-level and a low-level one.

The first stage of the process begins when water from the river flows into the high-level reservoir. During the day, the dam blocking water will be opened, which enables it to be released into the low-level reservoir. As this happens, a turbine is rotated and activates the generator, producing electricity. Subsequently, the power generated will be transferred to the national grid via power lines. In the nighttime, the reversible turbine switches its function and pumps the water in the low-level reservoir back into its original place. The dam is then closed so that water is stored there and ready to be used again the next day.