Classification of Hydroelectric Power Plants
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Hydro energy is one of the renewable forms of energy. Hydro electric power plants have very high efficiency when compare to any other power plant. They have very long life, lesser impact over the environment, low production cost, lesser maintenance and flexibility in operation and control. The main drawbacks of these power plants are higher cost during construction and the land requirement for construction of reservoir.
Hydro electric power plants can be classified based on their location, the presence and absence of storage, range of operation, operational features etc.
Layout of Hydro electric power plants
Have your ever visited a hydro electric power plant?
Classification based on the hydraulic features
Based on the hydraulic features hydro electric power plants can be classified into the four types:
conventional hydro electric plants:
These plants utilize the hydraulic energy of the flowing water of the rivers. Dams are constructed to collect the water in the reservoir and is used to run the turbines.
Pumped storage plants
In this type of hydroelectric power plants the same water is utilized again and again by pumping back during the off peak hours. They are mainly used to meet the peak demand.
Tidal power plant
These power plant produces electric energy from the tides of the seas.
Depression power plants:
In this type of power plant water is diverted into a natural topological depression which provides head for the plant. Water is diverted from ample resources such as seas. It is a rare type of power plant. This type of power plants exists in Egypt.
Classification based on the operation
Base load plants
This type of plants involves in continuous power generation. Simply speaking conventional hydroelectric power plants are base load plants.
Peak load plants
If the power plant is operated only to meet the peak demand then it is called peak load plants. In general, pumped storage power plants are peak load plants. In this type of hydroelectric power plants the same water is utilized again and again by pumping back during the off peak hours.
Classification based on storage
By considering the availability of storage reservoirs, hydro electric power plants can be classified into power plants having storage reservoir and without storage reservoir. If the availability of the water is uneven over the year, storage reservoirs are essential. If there is a natural normal flow throughout they year then it is not essential to have a reservoir. Under such conditions a mini reservoir or pond that takes care of day to day fluctuations is enough.
Classification based on plant capacity
Very low capacity hydro electric plants
Up to 0.1 MW
Low capacity hydro electric plants
Up to 1.0 MW
Medium capacity hydro electric plants
Up to 10 MW
High capacity hydro electric plants
More than 10 MW
They can also be classified as follows
Micro hydro electric plants
< 100 kW
Mini hydro electric plants
100kW to 1MW
Small hydro electric plants
1 MW to a few MW
Medium hydro electric plants
More than a few MW
Super hydro electric plants
More than 1000 MW
Classification based on head
Based on the available head hydro power plants are classified into the following:
Low head plants
< 15 m
Medium head plants
15 – 70 m
High head plants
70 – 250 m
Very high head plants
More than 250 m
High head power plants
High head plants
Due to high head, small amount of water can produce large amount of power. Therefore these types of plants are very economical. The reservoir is found at the top of the mountain and the power house is found at the foot. For high head plants catchment area of small capacity is sufficient. If the water from one stream is not sufficient, more than water can be diverted from the neighboring streams. For heads above 500 m, Pelton turbine is used and for low heads Francis turbines are used.
Medium head plants
Larger volume of water is required in this type if power plant. The reservoir capacity will be large. In these power plant water is carried from the reservoir is carried to the penstock through the forebay. There is no need of surge tank as forebay itself acts as a surge tank. Francis, Kaplan and Propeller turbines are commonly used for the medium head plants.
Low head plants.
Low head plants require larger volume of water than high and medium head plants to produce same amount of power. The reservoir capacity will be large. Francis, Kaplan and Propeller turbines are commonly used for the low head plants.