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Power generated by the motion of running water extracted by waterwheels or turbines is called hydroelectric power or hydropower. Hydropower has long established itself and developed over time. Today, as a renewable resource, hydroelectricity is obtaining more attention as environmental concerns arise.

Types of Hydroelectric Power Plants

A hydroelectric plant is basically a structure where water flows through causing a turbine and generator to rotate, generating electricity. By harnessing the force of running water, hydroelectric plants are capable of generating vast amounts of energy.

There are two main types of hydroelectric power plants:

Conventional Hydroplants: the most common type of plant. Using a dam on a river to store water in a reservoir, it uses released water (from the reservoir) to spin a turbine which in turn activates a generator, producing electricity.

Pumped Storage Plant: Unlike conventional hydroplants, pumped storage plants have two reservoirs: an upper reservoir and a lower reservoir. With the aid of generators, reversible turbines are able to spin backwards, causing water from the lower reservoir to be sent to the upper reservoir. From the upper reservoir, the water can be released back into the lower reservoir, thus spinning the turbines forward and generating electricity.

How Hydroelectric Power Plants Work

Hydroelectric power plants have the following components:

Dam: Holds back water, forming a reservoir. This reservoir may be used for recreational purposes, like Lake Roosevelt is to the Grand Coulee Dam.
Intake: Gates on the dam that allows the water into the penstock, a thin passage that carries the water to the turbine. It is within the penstock that water builds pressure. Turbine: the force of falling water causes the turbine's large blades to turn, which turns an attached generator
Transformer: converts the current from the generator into more useable voltages.
Transmission lines: conducts electricity from the plant for distribution.

A hydroelectric power plant generates electricity by releasing a controlled flow of water from the reservoir. Water travels down a channel called the penstock. Through the law of conservation of energy, potential energy is converted to kinetic energy as the water causes the turbine, connected to a generator, to rotate and produce an electric current.

The current is then passed onto the transformer, converting it to a small current at a high voltage, and through the transmission lines to substations where the voltage will be reduced and the electricity distributed to customers. High voltage is needed because a large amount of energy is needed to transport electricity over long distances.

Click here to a hydroelectric dam animation

Factors affecting electricity generation

The amount of electricity a hydroelectric plant generates depends on several factors. The two main ones include:

Amount of hydraulic head: hydraulic head refers to the distance between the water surface and the turbines. The greater the distance from the water surface to the turbine, the more electricity that can be generated. Generally, the distance the water falls correlates with the height of the dam.

Hydraulic head correlates to potential energy.

Ep = mgh

Ep= potential energy

m = mass

g = acceleration due to gravity (9.81 m/s2)

h = height

Because potential energy is dependant on height, the difference in distance between the water surface and turbine is an important factor in how much electricity can be produced.

Volume of water: more falling water will generate more power. Thus, large rivers have the potential to produce more electricity. Again, the volume of water has a correlation to potential energy. As the volume of water increases, so does the mass of the water, increasing the amount of potential energy.

Hydroelectricity Advantages and Disadvantages
  • Cheap and efficient
  • Very little emissions
  • Reservoirs of dams can be used irrigation, flood control and recreation
  • Tends to last longer than fossil-fuelled plants
  • May cause flooding in surrounding areas
  • May divert water and alter normal water flow
  • May inhibit the migration of fish
  • Can trap or kill fish within its turbines
  • May affect water quality downstream
  • Pollutants may build up in reservoirs
  • Long construction time (10 to 15 years)
  • Expensive to construct
  • Public opposition to building dams may slow down development


Hydroelectricity currently accounts for 20% of the world's electricity. It is particularly important in Canada within the provinces of British Columbia, Manitoba, Ontario, Quebec and Newfoundland and Labrador, where it is used extensively. In fact, Quebec has the world's largest hydroelectric generating system, The La Grande complex.

Hydropower has been an important source of energy and will continue to be developed in the future. With its unique environmental impacts, we will have to find a balance between our energy needs and the preservation of the environment.

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