In the series of articles on the classification the hydroelectric power plants, in this article classification of hydroelectric power plants based on the head of available water in dam have been described. There are three types of hydroelectric power plants based on the height of water available in the reservoir, these are:
1) Low head hydroelectric power plants
The low head hydroelectric power plants are the ones in which the available water head is less than 30 meters. The dam in this type of power plants is of very small head may be even of few meters only. In certain cases weir is used and in other cases there is no dam at all and merely flowing water in the river is used for generation of electricity. The low head types of hydroelectric power plants cannot store water and electricity is produced only when sufficient flow of water is available in the river. Thus they produce electricity only during particular seasons when abundant flow of water is available. Since the head of water is very small in these hydroelectric power plants, they have lesser power producing capacity.
2) Medium head hydroelectric power plants
The hydroelectric power plants in which the working head of water is more than 30 meters but less than 300 meters are called medium head hydroelectric power plants. These hydroelectric power plant are usually located in the mountainous regions where the rivers flows at high heights, thus obtaining the high head of the water in dam becomes possible. In medium head hydroelectric plants dams are constructed behind which there can be large reservoir of water. Water from the reservoir can be taken to the power generation system where electricity is generated.
3) High head hydroelectric power plants
In the high head hydroelectric power plants the head of water available for producing electricity is more than 300 meters and it can extend even up to 1000 meters. These are the most commonly constructed hydroelectric power plants. In the high head hydroelectric power plants huge dams are constructed across the rivers. There is large reservoir of water in the dams that can store water at very high heads. Water is mainly stored during the rainy seasons and it can be used throughout the year. Thus the high head hydroelectric power plants can generate electricity throughout the year. The high head hydroelectric power plants are very important in the national grid because they can be adjusted easily to produce the power as per the required loads.
When constructing the high head types of hydroelectric power plants a number of factors especially those related to the environment and natural ecosystem of the land and water should be considered. The total height of the dam depends upon a number of factors like quantity of available water, power to be generated, surrounding areas, natural ecosystem etc.