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Leading the Way in Renewable Power

For over 2,000 years water has been used as an energy source and continues to power through the centuries, leading the way in renewable power.

Hydropower is the largest source of renewable power in the United States, accounting for about 7% of all electricity generated and 56% of the nation’s renewable generation (more information at  It is used in every state and avoids as much carbon pollution as removing 38 million passenger cars each year. Not only is it an available source of clean energy, but hydropower facilities are also reliable sources of energy that can meet rapidly changing demands for electricity.

Hydropower refers to electricity generated using the energy of moving water (hydroelectricity) and is most commonly associated with the use of dams to generate electricity. Ocean Energy is the term used to describe different forms of renewable energy that is harnessed from the ocean.  Ocean Energy and Hydropower have been separated into two different renewable energy sections to organize the renewable energy sources available through the ocean, from renewable energy sources available through other water sources.

There are three types of hydropower facilities that range in sizes from micro to large. The three types include impoundment, diversion, and pumped storage.

History of Hydro

Water wheel used at an old mill

Just like many of the different types of renewable energy sources, water has been used as an energy source for over 2,000 years, dating back to the Ancient Greeks.  Through the use of water wheels, the Greeks were able to grind their wheat into flour. Over the years, water wheels built up their resumes to include producing power to saw through wood and power textile mills and manufacturing plants.  Breakthroughs in hydroelectricity started to appear around the mid-1700s, and by the late 1800s, plants began to operate in the United States.

For a more detailed history of hydropower, please visit History of Hydropower.   

For more information on any of the hydropower technologies or hydropower in general, please visit the U.S. Department of Energy’s page on Types of Hydropower Plants.

Hydroelectric power plantAn impoundment facility is the most common type of hydroelectric power plant and is probably what most people think of when they hear hydropower. An impoundment facility uses a dam built across a river to block water’s progress from downstream. The river water above the dam is stored in a reservoir until it is needed. Electricity is created when underwater gates, or intakes, are opened in the dam. The weight of the reservoir forces water through a penstock, a pressurized pipeline that carries water to a turbine. The water flows through the turbine causing its blades to turn, which spins a shaft connected to a generator. The spinning activates the generator which produces electricity. The water continues on and flows out of the dam and downstream. The amount of water flowing through the penstock determines the amount of electricity generated and is controlled through opening and closing the intakes. This makes hydroelectric dams, or impoundment facilities, a rather reliable source of renewable energy.

For more information on how impoundment works, please visit EDF Energy - How electricity is generated through hydropower.

Collinsville DamA diversion, often called run-of-river, is very similar to an impoundment facility, except there is no dam or reservoir and tends to be on a smaller scale. Run-of-river systems cannot exceed storage of 48 hours of water supply by definition. The systems rely on naturally flowing rivers that have a steady and consistent flow. The pitch of the river is also an important factor as the greater the distance that the water falls, then the greater the amount of energy.

Run-of-river facilities divert a portion of a river through a canal or penstock and lead it to a generating house. The generating house, or powerhouse, is home to turbines and the power generation unit. The river water flows through the penstock and forcefully passes through the blades of one or more turbines causing them to turn. Just like impoundment, the spinning turbines essentially run the generator which generates electricity. The water is then fed back into the river further downstream.

Pump storage hydropower is very much like it sounds- it pumps water uphill and stores it like a battery. Pumped storage involves two reservoirs- one at a high elevation and one at a low elevation. During periods of high electrical demand the water that is stored in the upper reservoir is released into penstocks, flows downhill, spins the turbine(s) and generates electricity just like the other methods of hydropower. When the demand for electricity is low (usually at night and on weekends) water from the lower reservoir is pumped back up to refill the higher reservoir using excess energy or by other power sources like solar, wind, and nuclear. The water is once again stored in the upper reservoir and acts like a battery, holding energy until it is needed during future periods of high demand.
Pumped Storage Diagram
Of the nation’s 80,000 dams, only about 3% generate electricity. It is possible to turn non-powered dams into ones that generate hydroelectricity by installing electricity generation equipment. It is also possible to install this equipment on other manmade structures that carry water such as tunnels, canals, pipelines, and aqueducts. This is referred to as conduit hydropower.

Want to learn more? Check out National Hydropower Association’s pages on Conduit Hydropower and Converting Non-Powered Dams.

Hydropower does exist in Connecticut, one example being the Kirby Mill in Mansfield.  It is a run-of-river system with a highly efficient turbine and a “fish friendly” propeller. 

If you are interested in learning more about hydropower technology or would like to look into installing a hydropower system, please visit the Clean Energy Finance and Investment Authority

Hydropower is listed as a Class I renewable energy source as defined in the Connecticut General Statutes (CGS) Section 16-1(a)(26)(x).