The hydroelectric power plants are classified in various ways like quantity of water available in the dam, total head of water in the reservoir and the nature of electrical load on them. In this series of articles all three classifications of the hydroelectric power plants have been covered. Let us start with the classification of hydroelectric power plants based on the quantity of water available in the dam or reservoir.
There are three types of the hydroelectric power plants based on the quantity of water available in the dam. These are:
1) Run-off river hydroelectric plants without pond
In the run-off river type of hydroelectric power plants the running water of the river is used for the generation of electricity. There is no facility for storing the water. Whenever the water is available the hydroelectric power plant generates electricity and when there is no water no power is generated. During rainy seasons when there is maximum flow of water available in the rivers, they produce maximum power. These types of hydroelectric power plants produce the power continuously only as long as flowing water is available.
2) Run-off river hydroelectric plants with pond
These types of run-off river hydroelectric power plants usually produce the power during peak loads. During the day-time and off-peak periods they don’t produce power and the water is stored in large pond. At night-times and during peak load the stored water is used to generate electricity. This has been possible because it is easy to start and stop the hydroelectric power plants, hence they can be used as peak load power plants. Starting and stopping thermal and nuclear power plants is very time consuming, hence they cannot be used for the peak loads rather they are used for the base loads. The pond in the run-off river plants facilitates the production of electricity at any time since it does not depend on the continuous flow of water. Stored water is as good as stored energy that can be used at any time.
3) Reservoir hydroelectric power plants
The reservoir in the hydroelectric power plants has the capacity to store extremely large quantities of water that can be used throughout the whole season. The reservoir usually gets filled during the raining season and the water lasts for the whole year till the next summer season. In these hydroelectric power plants large reservoir is constructed behind the dam wall. Water from the reservoir is released to the power generation unit via penstock. The flow of water to penstock is controlled by the gates. The reservoir hydroelectric power plants can be used as peak load plant or base load plant. They produce electricity throughout the year. Most of the hydroelectric power plants are the reservoir type of plants.