What Is Hydropower And How Does It Work?

What is Hydropower?

Hydropower is electricity generated using the energy of moving water. It is one of the oldest and largest sources of renewable energy in the world. Hydropower has been used for centuries to mill grain, drive machinery, and create electricity (1).

The most common type of hydropower facility uses a dam on a river to store water in a reservoir. When the water is released from the reservoir, it flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The height of the dam creates hydraulic head (pressure), allowing the water to build up enough force to drive the turbine (2).

Other types of hydropower facilities include:

  • Run-of-river, which channels a portion of a river through a canal to spin a turbine
  • Pumped storage, which pumps water uphill into a reservoir and then releases it downhill through a turbine when electricity demand is high
  • Tidal power, which uses the flow of ocean tides to spin turbines

Hydropower provides around 16% of the world’s electricity and over 90% of U.S. renewable energy (3). It’s a flexible, reliable source of energy that avoids carbon emissions from fossil fuels.


(1) https://www.energy.gov/eere/water/articles/hydropower-key-clean-energy-future-heres-why

(2) https://www.energy.gov/eere/water/benefits-hydropower

(3) https://waterkeeper.org/news/hydropower-is-not-clean-energy/

How Hydropower Works

Hydropower plants generate electricity by using the power of moving water. There are several types of hydropower systems that harness the flow of water in different ways to produce electricity.

Dam Systems

Most hydropower plants rely on dams. Dams help create reservoirs to control water flow and provide water pressure for electricity generation. The water in the reservoir flows through an intake screen, then through tubes in the dam called penstocks. The moving water spins turbines connected to generators to produce electricity. The electricity is then transmitted through power lines to homes, businesses, and industries.

Run-of-River Systems

Some hydropower plants utilize run-of-river systems, which do not require large reservoirs or dams. Instead, they divert a portion of a river’s water through a canal or channel. The moving water rotates turbines and generates electricity without significantly altering the natural flow of the river.

Pumped Storage

Pumped storage plants store energy by pumping water uphill to a reservoir at higher elevation during times of low electricity demand. Then during periods of high demand, the water is released back downhill through turbines to generate extra power. Pumped storage provides a way to store energy and adapt hydropower generation to match electricity needs.

Hydropower Generation Process

The hydropower generation process converts the kinetic energy from falling water into electrical energy. Here are the main steps:

Water from a high-elevation reservoir flows through an intake and down a penstock pipe. As the water flows downhill, it builds up speed and pressure, gaining kinetic energy. The pressurized water reaches the hydro turbine at the bottom end of the penstock. The force of the moving water spins the turbine blades. This turbine rotation drives the shaft of an electrical generator and the kinetic energy is converted into electrical energy.

The key components are the hydro turbine and generator. The turbine blades capture the kinetic energy of the falling water. This rotary motion spins the electromagnet rotor within the generator. Surrounding wire coils cut through the magnetic field to produce an electric current, via electromagnetic induction. The electricity is then transmitted through transformers and power lines to homes, businesses, and the grid.

There are several types of hydro turbines used, such as Pelton, Turgo, Kaplan, Francis and propeller turbines. The specific turbine selected depends on the height and flow of the water source. The turbine turns the generator, which converts the mechanical rotation into electrical power (source).

Benefits of Hydropower

Hydropower offers several key benefits that make it an advantageous source of renewable energy. First, it is renewable – hydropower relies on the water cycle, which is continuously renewed through precipitation and evaporation. Unlike fossil fuels, hydropower will not be depleted over time. According to the U.S. Department of Energy, hydropower is the largest source of renewable electricity generation in the United States, producing over 6% of total U.S. electricity generation in 2019 1

Second, hydropower has relatively low operating costs compared to other energy sources. The fuel itself – flowing water – is free, so operating costs are primarily maintenance and equipment costs. This makes the cost per kilowatt-hour of hydroelectricity very competitive 2.

Third, hydropower facilities tend to have long lifespans. With regular maintenance and upkeep, hydroelectric plants can operate for many decades. Some facilities built over a century ago are still producing electricity today.

Finally, hydropower offers unique energy storage capabilities. By damming water, hydropower systems can effectively act as large batteries, storing energy in the form of potential energy. Water can be held back or released from the reservoir as needed to meet electricity demands.

Limitations of Hydropower

While hydropower provides clean renewable energy, it also comes with some limitations and disadvantages that should be considered. Some key limitations of hydropower include:

  • High upfront costs – Constructing hydropower plants and dams requires very large upfront capital investment. The costs include expenses for site preparation, dam construction, turbines and other equipment. According to the Quora, the average hydropower project takes 5-10 years to complete and can cost billions of dollars.

  • Drought risk – Hydropower is dependent on water flow, so droughts can severely impact electricity generation capabilities. During periods of low rainfall, reservoirs and dams can run low, reducing the power output.

  • Wildlife habitat disruption – Dams and reservoirs create barriers that can obstruct fish migration and damage surrounding ecosystems and vegetation. This can negatively impact local wildlife habitats.

  • Geological effects – Hydropower projects can increase erosion, induce seismic activity, and lower downstream water quality in some cases. The reservoirs formed by dams drastically alter local geography, sedimentation and rock formations.

Overall, while hydropower is a major source of renewable energy, the high costs, environmental impacts, and reliance on precipitation can serve as limitations.

Major Hydropower Projects

Some of the largest and most famous hydropower dams in the world include:

The Hoover Dam on the Colorado River is one of the best-known hydropower projects in the United States. With a capacity of 2,080 megawatts, the Hoover Dam provides electricity to Nevada, Arizona, and California. The dam was completed in 1936 and was an engineering marvel of its time, standing at 726 feet tall. The Hoover Dam created Lake Mead, one of the largest manmade reservoirs in the country (Source).

The Three Gorges Dam in China is the world’s largest hydropower project. Completed in 2012, it spans the Yangtze River and has a massive capacity of 22,500 megawatts. The dam is 7,660 feet long and 600 feet high. While providing immense hydroelectric power, the Three Gorges Dam project was also controversial for its environmental and social impacts, including relocating over 1 million people (Source).

The Itaipu Dam on the Paraná River bordering Brazil and Paraguay is one of the largest hydroelectric dams in the world. With an installed capacity of 14,000 megawatts, Itaipu can meet about 75% of the electricity needs of Paraguay and 17% of Brazil’s needs. At 7,919 feet long and 720 feet high, the Itaipu Dam is a major provider of renewable energy in South America.

Hydropower Capacity

Global hydropower capacity reached approximately 1,308 gigawatts (GW) in 2020, led by China, Brazil, Canada, the United States, and Russia as the countries with the highest installed capacity according to Global Energy Monitor’s Global Hydropower Tracker (https://globalenergymonitor.org/projects/global-hydropower-tracker/). China has the most hydropower capacity at over 352 GW, accounting for around 27% of total global capacity.

Other major countries for hydropower capacity include Brazil at 109 GW, Canada at 81 GW, the United States at 80 GW, and Russia at 48 GW as of 2020. In Europe, Norway leads with over 33 GW of installed hydropower capacity according to Statista (https://www.statista.com/statistics/690006/hydropower-capacity-ranking-europe/). Significant growth in global hydropower capacity is expected in the coming years, especially in developing countries.

Future of Hydropower

Hydropower is projected to continue growing in the coming decades. According to the Hydropower Vision report, U.S. hydropower capacity could grow from 101 GW in 2015 to nearly 150 GW by 2050. This growth will come from upgrading existing hydropower infrastructure, powering existing dams that do not currently produce electricity, and limited development of new stream-reaches.

Advances in hydropower technology will also enable growth and improved performance. Areas of innovation include enhancements to turbines, generators, drivetrains, and civil structures. For example, modular and standardized turbine designs allow for rapid deployment and tailoring to specific sites. Variable speed turbines can improve grid reliability and integrate renewable energy. Technologies like advanced sensors, controls, and materials help maximize performance and reduce operation and maintenance costs.

Source: https://www.energy.gov/articles/hydropower-vision-new-report-highlights-future-pathways-us-hydropower

Hydropower Sustainability

Hydropower projects must be developed and operated sustainably to mitigate environmental impacts and maintain reservoirs and dams. According to the Hydropower Sustainability Council, sustainability involves assessing and managing environmental and social issues at all stages of a project. Some key aspects of sustainability include:

Mitigating environmental impacts:

  • Minimizing disruption to water flows and aquatic ecosystems through environmental flow assessments.
  • Implementing fish passages and protection measures.
  • Reforesting watersheds and restoring habitats.
  • Offsetting carbon emissions.

Maintaining reservoirs and dams:

  • Monitoring dam safety and stability.
  • Managing sedimentation and erosion.
  • Developing emergency preparedness plans.
  • Monitoring water quality and controlling algal blooms.

Many organizations like the International Hydropower Association provide training and guidance on implementing sustainable practices. Adopting standards like the Hydropower Sustainability Assessment Protocol can help projects improve their sustainability performance.


In conclusion, hydropower is a significant renewable energy source that offers a number of benefits. Hydropower harnesses the energy of flowing or falling water to generate electricity through hydropower turbines and generators. Some key advantages of hydropower include its renewable, reliable nature, low operating costs, ability to quickly adjust to changes in demand, and lack of greenhouse gas emissions.

While hydropower facilities can have high upfront costs and some environmental impacts, technological advances are helping address these challenges. With the growing demand for clean electricity around the world, hydropower is poised to continue supplying an important share of renewable power generation for decades to come. When properly managed, hydropower can provide substantial amounts of sustainable and reliable electricity to support economies and communities.

Overall, hydropower offers a major renewable energy source that does not burn fossil fuels, produce air pollution or carbon emissions. With a long and established track record around the world, hydropower has proven its ability to make substantial contributions to clean energy portfolios and reduce reliance on nonrenewable sources of electricity generation.

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