How Do Hydroelectric Energy & Hydropower Work

hydroelectric power plant dam

How Does Hydroelectric Energy Work

While not the most common form of energy production when compared to coal, the concept of harnessing the energy of flowing water, such as river currents, has been around for centuries.

Today, hydropower accounts for 71 percent of all renewable energy and supplies approximately 16 percent of the world’s energy. According to the Department of Energy, every state uses hydroelectric energy. Furthermore, for states that get the majority of their electricity from hydroelectric power, their energy bills are lower than the rest of the country!

What is Hydroelectric Power?

Hydroelectric power is a type of renewable energy that harnesses the power of flowing water. In a hydroelectric plant, water is forced through a dam and takes advantage of gravity to turn the blades of the plant’s turbines, thereby generating electricity.

Hydroelectric power plants rely heavily on the work of gravity by using natural drops in elevation. This drop occurs naturally in mighty rivers and streams. As a result, this type of energy is a stark contrast to coal-fired power plants that burn fossil fuels to generate steam to create electricity.

Origin of Hydroelectric Power

In the past, ancient Romans built turbines for grinding grains to produce flour and bread. Later, water mills were common before the Industrial Revolution. These water mills served as energy generators that could provide enough power to grind grain, cut lumber, or create hot fires to produce steel.

One of the most critical years in the history of hydroelectric power was 1831, where Michael Faraday invented the first electric generator. In 1882, the first hydroelectric power plant began generating electricity in Appleton, Wisconsin. The first power plant generated about 12.5 kW.

As hydropower electricity gained in popularity, the Hoover Dam, which became known as the largest hydroelectric power plant, was built in 1936. China’s Three Gorges Dam was built in 2008, taking the name as the largest power plant in 2012. As of 2018, the Three Gorges Dam generates a capacity of 22,500 MW.

hydroelectric energy

Types of Hydroelectric Plants

There are three main types of hydropower facilities.

Impoundment Plant

An impoundment facility is the most common type of hydroelectric power plant. This system uses a dam to store the river’s water in a reservoir. The water is systematically released as the reservoir flows through the turbine, which produces electricity.

Diversion Plant

A diversion is also known as run-of-river or ROR dams. This system channels a portion of a river through a canal or penstock. As a result, a small dam may not be necessary. Additionally, this hydroelectric system does not significantly impact marine life.

A ROR plant with pondage can regulate water flow and operate as a peaking power plant, which can meet varying demands of electricity. On the other hand, a ROR dam without pondage doesn’t have storage and is reliant on seasonal river flows. As a result, it can only generate electricity when the river flow allows it.

Pumped Storage Plant

Pumped storage hydropower is similar to a battery because it stores electricity for later use. There are two dams, each with its own reservoir. The water begins at a second reservoir at a lower elevation. Electricity is stored when the water is then pumped uphill to a reservoir at a higher elevation during off-peak electrical demand times.

Fortunately, during periods of significant electrical needs, the water is released back to the lower reservoir, turning a turbine, and ultimately generating electricity. This feature of stored energy is a useful and effective tool for grid operators to help meet the demand for electricity.

Famous Hydroelectric Plants

Aside from the Three Gorges Dam that is currently the largest hydroelectric power plant in the world, there are a few other well-known hydroelectric plants.

Hoover Dam, United States

The Hoover Dam is formerly called the Boulder Dam. It was built between 1930 and 1936 and impounds or holds back Lake Mead, one of the largest artificial lakes in the world.

Hoover Dam sits in Black Canyon on the Colorado River, which borders Arizona and Nevada. Its total power capacity is 2,080 MW.

Sayano-Shushenskaya HPP, Russia

The construction of the Sayano-Shushenskaya HPP (hydropower plant) began in 1963. In 2009, it was the largest hydroelectric power plant in Russia and ranked the 9th largest hydroelectric power plant in the world, by average energy generation. It produces 6,400 MW in southern Siberia.

Aswan High Dam, Egypt

The Aswan High Dam was completed in 1970 after 11 years of construction. It sits across the Nile River, addresses the cycle of flood and drought in the region, and taps into an enormous source of renewable energy.

This hydroelectric power plant has a design capacity of 2,100 MW by impounding Lake Masser.

How Does Hydroelectric Energy Work?

Hydroelectric power requires moving water. It exploits the kinetic energy in water that flows or falls at a sufficient speed and volume to spin a turbine. As a result, the turbine rotates a generator to produce electricity.

In general, one gallon of water falling one hundred feet in one second can produce one kilowatt of electricity. Ultimately, the amount of electricity a hydroelectric power plant can produce depends on how far the water falls as well as the amount of water that falls. The farther the water falls, the more speed and power it has. Additionally, the more water the falls through the turbine will naturally produce more energy. As a result, larger rivers have more flowing water, which can then create more electricity.

Parts of a Hydroelectric Plant

Most traditional hydroelectric plants utilize four primary parts.

hydropower generation plant parts


A dam holds back water to create a large reservoir. It serves to raise the water level of a body of water and controls the flow of water, which can then generate electricity.


The turbine is a larger and more efficient version of the historic water wheel. The most common design is the Francis Turbine, which looks like a big disc with curved blades.

The force of falling water spins the turbine’s blades and converts the kinetic energy of the water into mechanical energy.


Shafts connect the turbine to a generator. When the turbine spins, a series of magnets inside the generator also spins. The magnets spin past copper coils. At this point, the mechanical energy from the turbine is converted into electric energy.

Transmission Lines

While in some plants, the electric energy may pass through a transformer first, the energy ultimately must pass through transmission lines. These wires conduct electricity and carry the energy to homes and businesses.

Pros and Cons of Hydropower Generation

While hydroelectric power may be a form of clean and renewable energy, there are disadvantages of hydropower.


  • Hydroelectric energy is clean because it does not emit greenhouse gasses or other air pollutants since it relies on water.
  • Hydroelectric power is also renewable because of snow and rainfall, as part of the natural water cycle.
  • Hydropower generation is flexible. Hydroelectric power plants can control the flow of water and the amount of energy produced. They can meet varying demands for electricity.
  • HPPs are relatively inexpensive to operate because the main raw material input is free, which makes it an attractive and competitive source of renewable energy, although there are key differences between hydroelectric energy vs. solar In general, an HPP can cost between three and five cents per kilowatt hour but have huge generation capacities.
  • Dams create reservoirs that also double as a safe recreational space for the community to enjoy nature.


  • When a body of water is restricted by a dam, fish, such as salmon, face obstacles when swimming upstream to spawn. Some dams, such as the Bonneville Dam, use fish ladders to help fish migrate, but may not always be effective. Ultimately, dams may change migration patterns and hurt fish populations. For example, dams have eliminated 40 percent of salmon and steelhead habitats in the Columbia River Basin.
  • Dams flood riverbanks, which destroy wetland habitats and impact animals, such as aquatic birds. Additionally, dams may flood communities, displacing residents. If a dam floods an area with live vegetation, the organic matter rots and eventually decomposes. Decomposition lowers the oxygen levels of the water and releases large quantities of methane, a powerful global warming gas.
  • Hydroelectric power plants may raise the temperature of the water in the reservoir. This raises environmental concerns as it disrupts the natural habitats of plants and animals.
  • Silt builds upon the ’reservoir’s bed because the natural flow of the river can no longer carry it to a delta or river mouth. As silt builds up, the amount of water in the reservoir is proportionally reduced. Less water results in lower energy output. As a result, some power plants may only be able to provide electricity for 20 to 30 years, depending on the amount of silt buildup.
  • HPPs can cause low dissolved oxygen levels in the water, disrupting ecosystems, and hurting wildlife. Some HPPs use aerating turbines to increase dissolved oxygen and implement multi-level water intakes to ensure that water is released from all levels of the reservoir. Without varying intakes, the water released may originate from the reservoir bottom, which has the lowest dissolved oxygen.
  • A reservoir has more stagnant water than a normal river. Therefore, reservoir water also has excessive amounts of sediments and nutrients, which result in a proliferation of algae and aquatic weeds. These weeds often dominate and crowd out other river animal and plant life.
  • If sufficient water is not released downstream, the river may dry out. Overall, lower water levels negatively impact animal and plant life.

What is the Future of Hydroelectric Power?

In 2016, hydropower supported more than 143,000 jobs in various industries, from engineering to utility operations and maintenance. It improves the environment, strengthens the economy, and represents 97 percent of all energy storage in the United States.

The United States Department of Energy collaborated with more than 300 experts to produce the Hydropower Vision report that defines the societal, environmental, and economic benefits of hydroelectric power from 2030 to 2050.

A few key findings include reduction of cumulative greenhouse gas emissions by an estimated 5.6 gigatonnes and an approximate savings of $58 billion in healthcare costs and economic damages from air pollution.


While investing in oil wells is still investors’ top choice, hydroelectric power has a positive future. With the Energy Department’s Hydropower Vision, the United States may see more clean renewable energy from hydropower generation by 2030.

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