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Water is used to generate electricity by harnessing the energy in moving water. The basic process is to take water from a river or lake and pass it through a tunnel or tube that includes a drop in elevation. The moving water then spins a turbine connected to a generator that produces electricity.
 
Large-scale projects will use a dam to capture and store the water. The major drawback of a dam is its effects on the surrounding natural environment as a result of flooding.

Small-scale projects have fewer effects on the surrounding evironment. Small-capacity waterpower plants or "run-of-the-river" projects use a weir or channel some of the water away from the river rather than a dam. Drawbacks to small-scale projects include less consistent power output and the inability to store water for future use.

Important factors when considering waterpower projects include:

  1. the distance the water will fall, otherwise known as the head. A higher head means a shorter penstock, which will reduce project costs.
  2. the flow of water throughout the year
  3. the proximity to transmission or distribution lines.


"Run-of-the-River" Waterpower Plant

The Umbata Falls hydro project is an example of a run-of-the-river facility.

The following interactive tool helps explain waterpower energy. Click here to use the tool.

 

Weir A weir is usually a low barrier, lower than a dam, that allows excess water to flow over it. It is used to direct the water into a canal and/or penstock. A weir will keep the water level marginally higher upstream.
Reservoir In larger waterpower facilities, a reservoir of dammed-up water provides potential reserves of water to be released should demand increase in the future.
Intake or sluice gate Gravity causes water to enter the penstock through the intake since it is located beneath the water’s surface. It is covered with a trash rack to collect debris.
Penstock Water flows under pressure through a pipe called the penstock, often located underground.
Turbine Located at the bottom of the penstock where water pressure is the greatest. The blades of the turbine turn from the force of the water.
Generator The generator converts energy from the rotating turbine shaft into electrical energy.
Transformer Electricity is conducted through a transformer, which changes the voltage or current, then sends it out to transmission lines that carry the electricity to the grid.
Tailrace This is the outflow of water back to the river downstream.