Discover fascinating hydro energy facts. Learn how hydropower works around the world, from the oldest plants to the largest dams, with numbers and stories.
Hydropower has been generating electricity for over 140 years. It is the largest source of renewable electricity in the world. The numbers are impressive. Hydro powers entire countries, uses remarkably efficient turbines, and can store energy like a giant battery.
Hydropower provides about 16% of the world’s electricity. That makes it the third-largest source of electricity overall, after coal and natural gas. It is the largest source of renewable electricity by a wide margin.
Total installed hydro capacity worldwide is over 1,300 gigawatts. China leads with about 370 gigawatts. Brazil is second with 110 gigawatts. The United States is third with 102 gigawatts.
Some countries depend almost entirely on hydro. Norway gets 99% of its electricity from hydropower. Iceland gets about 70%. Brazil gets about 65%. Canada gets about 60%. These countries were lucky to have many steep rivers perfect for dams.
The Three Gorges Dam in China is the largest. It has a capacity of 22,500 megawatts. That is more than double the next largest. It produces about 100 billion kilowatt-hours per year. That is enough to power 80 million homes. Construction took 17 years and cost 37 billion dollars.
The Itaipu Dam on the Brazil-Paraguay border is second. It generates about 90 billion kilowatt-hours per year. Paraguay uses only a fraction of its share. It sells the rest to Brazil.
The Xiluodu Dam in China is third with 13,860 megawatts. Other giants include Guri in Venezuela (10,235 MW), Tucurui in Brazil (8,370 MW), and Grand Coulee in the United States (6,809 MW).
Hydro turbines are the most efficient power generation machines ever built. Modern Francis turbines convert 90-95% of water energy into mechanical energy. The generator then converts mechanical to electrical energy at 98-99% efficiency. Overall plant efficiency is typically 85-90%.
Compare that to other technologies. Coal plants are 33-40% efficient. Natural gas plants are 40-60%. Solar panels are 15-22%. Wind turbines are 35-45%. Hydro is the clear winner.
Hydro plants also have an excellent energy payback ratio. A hydro plant produces about 200 times more energy over its lifetime than was used to build it. For solar, the payback ratio is about 10-20. For wind, it is about 20-30.
Pumped storage hydropower is the most common form of grid energy storage. It accounts for about 95% of all energy storage capacity worldwide. That is over 160 gigawatts of installed capacity.
The largest pumped storage plant is Bath County in Virginia. It can generate 3,003 megawatts. It has two reservoirs 380 meters apart. It can power 750,000 homes for 8 hours.
Pumped storage plants can switch from pumping to generating in about 15 seconds. This makes them extremely valuable for balancing the grid as solar and wind power grow.
The first hydroelectric plant opened on September 30, 1882, in Appleton, Wisconsin. It powered two paper mills and one house. It used the Fox River’s water flow and a dynamo built by Thomas Edison’s company.
The oldest still-operating hydro plant is Cragside in Northumberland, England. It started in 1896 and still generates electricity today. It was the first house in the world to be lit by hydroelectricity.
The Hoover Dam was built during the Great Depression between 1931 and 1936. It employed 21,000 workers. It was completed two years ahead of schedule. It created Lake Mead, the largest man-made reservoir in the United States at the time.
The United States has over 2,000 hydroelectric plants. Total capacity is about 102 gigawatts. That is about 6% of US electricity generation.
The largest US hydro plant is the Grand Coulee Dam in Washington. It has 33 generators and a capacity of 6,809 megawatts. It also irrigates over 600,000 acres of farmland.
Washington state produces more hydro electricity than any other state. It is followed by Oregon and California. About 60% of Washington’s electricity comes from hydro.
Here are some cool numbers. A big dam can make enough electricity for 500,000 homes. That is more homes than in many cities.
The Three Gorges Dam is so long that if you walked across it, you would walk 2.3 kilometers. That is like walking across 23 football fields.
The Hoover Dam has enough concrete to build a road from New York to San Francisco.
Hydro facts reveal some interesting trends. Most good dam sites in developed countries are already used. The era of big dam building in North America and Europe is over. Future growth will come from smaller projects, upgrading existing dams, and building in developing countries.
Adding generators to non-powered dams could add 12 gigawatts of capacity in the US alone. There are over 80,000 dams in the US, but only about 2,000 generate electricity. The rest were built for flood control or irrigation.
Climate change is a growing threat to hydropower. Droughts reduce reservoir levels and cut power output. In 2022, drought in China caused the lowest water levels at Three Gorges Dam in over a century. As the climate changes, hydro-dependent regions may become less reliable.
Discussion questions:
Activity: Research the closest dam to your school. What is its capacity? What year was it built? Does it generate electricity or just control floods?
Last updated: June 15, 2026
What percentage of the world's electricity comes from hydro?
Hydro provides about 16% of the world's electricity. That is more than all other renewable sources combined.
Which country gets the most electricity from hydro?
Norway gets 99% of its electricity from hydropower. Iceland gets about 70%. China produces the most hydro electricity in absolute terms.
How old is the oldest hydroelectric plant?
The oldest still-operating hydro plant is Cragside in England, which started in 1896. The first ever was built in Appleton, Wisconsin in 1882.
How efficient are hydro turbines?
Modern hydro turbines are 85% to 95% efficient. That is higher than any other power generation technology.
How long do hydro dams last?
Dams can last 50 to 100 years with proper maintenance. Some have been operating for over a century.
