Humans have been harnessing the power of water for thousands of years. The potential energy of water has been used to drive mills, rotate pumps, and for numerous other applications. However, converting the potential energy of water to electrical energy, is a relatively new concept. 

To generate electricity using a hydroelectric dam, you need two things:

  1. An abundance of water.
  2. An elevation difference between the outlet and inlet sides of the dam; this difference in elevation is referred to as the ‘head’.

The headwater is located upstream of the dam and the tailwater downstream; the dam physically separates the headwater and tailwater. The headwater consists of a large body of water, this ensures a constant supply of water can be used for power generation. A water conductor -known as a penstock- connects the headwater to the powerhouse at the base of the dam. The powerhouse contains all the equipment needed to turn the potential energy of the water into electrical energy.

How Hydroelectric Dams Work

The below video is an extract from our Introduction to Hydroelectric Power Plants course.


Water enters the penstocks through one of the main inlets. The water then travels down through the penstocks until reaching the hydroelectric turbines located within the powerhouse. As the water passes over each turbine runner, the runners rotate, and we obtain mechanical energy. The mechanical energy from the turbine runners is passed to an electrical generator, which is connected on a common shaft. We have now converted the water’s potential energy into electrical energy and can distribute this through a transformer and high voltage national grid. To end the process, the water flows from the powerhouse through the draft tubes until reaching the tailwater. The entire process is continuous, which leads to a constant and reliable form of power generation.

Advantages and Disadvantages

Hydroelectric Dam Advantages

  1. Offer a constant and reliable form of power generation providing enough headwater is present.
  2. Represent a renewable (green) form of energy and produce no waste products. 
  3. Are very efficient compared to other power generation means.
  4. Cheap to operate.
  5. Have a long working service life (some hydroelectric plants are over 100 years old!).

Hydroelectric Dam Disadvantages

  1. Can disrupt local habitats considerably due to the large topological changes needed to create the operational conditions required by the dam. These adverse effects are felt by both plants and animals alike; this is by far the largest disadvantage associated with hydro dams. 
  2. Expensive to construct (high initial costs).
  3. Catastrophic consequences if the dam fails (with potential loss of life).
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