Figure 1. A hydroelectric dam where hydroelectricity is generated.[1]

Hydroelectricity is the electricity that is generated by converting the kinetic and potential energy of flowing water into electrical energy. Today, hydroelectricity supplies the world with about 16% of total electric power generation, while values in the earlier twentieth century were much higher - making up as much as 40% of the United States' total electricity.[2] In some countries around the world, hydroelectricity is the main type of electricity that is used.

Countries such as China, Canada, and Brazil are the leaders in total hydroelectricity generation with capacities of 200 GW, 89 GW, and 70GW respectively.[3] Other notible producers include Russia, India, Norway, Japan, and Venezuela (which is almost completely dependent on hydropower).[3] See the data visualization below for more statistics on hydroelectricity in the world.

One of the benefits of hydroelectricity is that it is less polluting than using the combustion fossil fuels for electricity. Although not free from emissions and other environmental impacts, they are significantly less polluting than other options. As well, hydroelectricity is relatively inexpensive once dams and reservoirs are built and these facilities can operate at very high efficiencies.[3] For more information on the ecological impacts of hydropower facilities, see: water quality degradation and environmental impacts of hydropower.


Hydroelectricity is generated at a hydroelectric facility - generally for large-scale generation this includes a hydroelectric dam. At these facilities, a dam holds back a large quantity of water, creating a reservoir. This reservoir holds water at a higher elevation than the rest of the original body of water (generally a river). This means that compared to the water in the river, the water in the reservoir has more potential energy. When a gate is opened at the top of the dam, the water flows through channels called penstocks down to the turbines. When the water reaches the turbines, its kinetic energy gained from falling is transferred to the rotational motion of the turbines. As the turbines spin, they move a generator and generate electricity. This is how hydropower (the power of water) creates hydroelectricity.

Although hydroelectric facilities that have large outputs generally use dams, there are some types of systems that do not utilize dams and have very little water storage (meaning there is no real reservoir of water). These types of systems are known as run-of-the-river systems, and are gaining popularity recently as alternatives to large scale reservoir dams.


Conventional hydroelectric generation relies on a head difference created by man-made dams and obstructions. The majority of current generation is conventional. Two types of systems that are considered conventional are hydroelectric dams and tidal dam. Unconventional generation techniques generally rely on flow rate or on a small head differential. These platforms produce less energy than conventional methods however they also have less impact on the surrounding environment. Some examples of unconventional hydropower platforms are low head hydro, run-of-the-river systems, instream hydro, and kinetic tidal.

Each type of hydroelectric generation method has an associated output classification based on its capacity. They are outlined in the table below.[4]

Classification Capacity
Large > 100 MW
Medium 15 - 100 MW
Small 1 - 15 MW
Mini 100 kW - 1 MW
Micro 5 - 100 kW
Pico ~ 200 W - 5 kW

World Electricity Generation: Hydroelectricity

The map below shows which primary energy different countries get the energy to generate their electricity from. Hydroelectricity is seen in blue. Click on the region to zoom into a group of countries, then click on the country to see where its electricity comes from. Some notable countries include China, Canada, Brazil, Russia, India, Norway, and Venezuela.


  1. Wikimedia Commons. (August 31, 2015). Ingur Hydroelectric Facility [Online]. Available: https://commons.wikimedia.org/wiki/File:Ingur_Hydroelectric_Power_Station.jpg
  2. R. Wolfson. Energy, Environment and Climate, 2nd ed. New York, U.S.A.: Norton, 2012
  3. 3.0 3.1 3.2 Abhishek Shah. (September 2, 2015). List of World’s Largest Hydroelectricity Plants and Countries – China Leading in building Hydroelectric Stations [Online]. Available: http://www.greenworldinvestor.com/2011/03/29/list-of-worlds-largest-hydroelectricity-plants-and-countries-china-leading-in-building-hydroelectric-stations/
  4. IPCC. (September 2, 2015). Chapter 5 - Hydropower [Online]. Available: www.ipcc.ch/pdf/special-reports/srren/drafts/SRREN-FOD-Ch05.pdf

Authors and Editors

Edwin Cey, Jordan Hanania, James Jenden, Kailyn Stenhouse, Jason Donev