How are hydro-power plants classified?


It’s no new news that a hydroelectric power plant is a clean-green renewable source of energy, India became the home for its first (although the first ever hydro-power plant is known to be commissioned in the US, somewhere around 1882) hydro-power plant in the year 1902 having a capacity of 4.5 MW named as Sivasamudram Scheme in Mysore followed by a power plant named Khopali having a capacity of 50 MW commissioned in Maharashtra. By 1947 we had already achieved a capacity of 500 MW. 

In today’s world we all have a common and basic knowledge of a dam or in particular hydropower plants but do we know enough?

A hydropower plant can have classifications based on the availability of the head, nature of the load, or the quantity of water available.

So people let’s dive in.

Hydro-power plants classified according to the availability of head:

  1. High Head Power Plants-

These plants usually work under the head of 100 to 2000 m, water is stored in such a way that it can be used to last throughout the year. The water is stored up in lakes on high mountains during the rainy season or when the snow melts.

A Pelton wheel is commonly used to operate the plant.

  • Medium Head Power Plants-  

Plants usually operate under heads ranging from 30 to 100 m. A Francis turbine is used to generate electricity. A forebay is provided at the beginning of the penstock that serves as a reservoir, in these plants the water is drawn from canals and carried to the forebay eventually reaching the power-house through the penstock, the forebay itself works as a surge tank.

  • Low Head Power Plants-

A dam across a river is constructed to utilize the diverging stream from the river at the dam, a dam is constructed on this stream creating a channel that joins the river further downstream, the commonly used turbine to generate electricity is Kaplan or Francis turbine.

Although sometimes due to the similarity of the concept the classification based on the head becomes a confusing task so in that case the classification is done based on the specific speed of the turbine used.

Hydro-power plants classification according to nature of load:

  1. Base Load Plants-

These plants cater to the baseload of the system. Baseload plants should supply constant power when connected to a grid, hence it cannot stop, often these plants are remotely controlled hence reducing the dependency on the staff. Run-off river plants with the absence of pondage might work as baseload plants but the capacity is quite low.

  • Peak Load Plants-

Peak load plants are the plants that can supply power during the peak loads. Some plants supply the power supply during the average load also but majorly these plants supply electricity during peak load hours only. A pondage can be provided to facilitate river-run-off plants for peak load hours.

Hydro-power plants classified according to the quantity of water available:

  1. Run-of-river Plants without Pondage-

This type of plants don’t store water and operate on the water as and when it is available, due to this erratic availability of water the capacity of the plant is comparatively less than other plants, these plants work under variable heads although the efficiency of this plant can be increased by storing water in a storage tank to cater the hourly fluctuations.

  • Run-of river Plants with Pondage-

The water that is collected behind a dam at a plant is known as pondage, it helps in increasing the stream capacity for a short period. These plants are much more reliable than the run-of-river Plants without pondage.

  • Storage Type Plants-

As the name suggests, the keyword is storage, a large reservoir is constructed to carry-over storage from the wet reason to the dry reason and provides a steady (firm) flow that is observed to be more than the minimum natural flow, these type of plants can be used either as baseload plants or peak load plants because of the ability to control the water availability, majority of hydro-electric plants are based on this type.

  • Pumped Storage Plants-

These plants are usually installed at places or sites where the availability of water is inadequate. The water passing through the turbines is stored in a tailrace pond, the water stored in this pond may be utilized for generating power at the peak loads by pumping the water back to the head reservoir using the extra energy available. These types of plants are interconnected with a steam or diesel power plant to use the off-peak capacity of interconnecting stations in pumping the water. The same water can be used during peak load periods.

  • Mini and Micro hydel Plants-

A mini hydel power plant operates under the head of 5 to 20 m and the micro hydel power plant operates under the head of 5 m or less the current energy crisis is allowing us to increase the capacity of mini and micro-hydel power plants, the total estimated potential of these plants is around 20,000 MW, a micro or mini power plant of the capacity of 5 MW can be constructed in a year or two but the large capacity power plants can take years, sometimes decades to construct and operate at maximum potential.

Source and Reference:
R.K Rajput, Non-conventional Energy Sources and Utilization

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