The illustration demonstrates the process of electricity generation in a hydroelectric power plant.
Overall, it is noticeable that it is a 4 stages, man-made, linear process. It begins with keeping the water in the reservoir and ends with generating electricity.
First of all, a dam maintains the river water behind it in the high-level reservoir. During the day, the dam’s intake opens to let water flow toward the power station. As the water moves to the low-level reservoir, reversible turbines start to rotate, which causes the generators to rotate also. After that, the electricity is produced and then it is moved to the national grid through power lines.
During the night, the process happens in the reversal direction. At this stage, the reversible turbines are worked as pumpers, that pump water in the opposite direction, from the low-level reservoir to the higher ones. Finally, the intake is closed to keep the water in the upper-level reservoir to be used during the next day.