Hydroelectric energy is the electricity produced using the kinetic power of the falling or fast-flowing water that is turned into mechanical energy and then into clean electricity using generators.
Hydroelectric energy or simply hydropower is produced today in almost all the countries on the planet, and represents the most developed source of renewable energy available today for mankind.
What is Hydroelectric Energy?
Hydroelectric energy represents the electricity produced by the kinetic energy of the moving or falling water that spins underwater turbines creating mechanical energy, which is then turned into electricity by large generators.
To generate electricity, the water needs to move with a certain speed and volume, which are required by the hydroelectric power plant.
Types of Hydroelectric Power Plants
There are several types of hydroelectric power plants in the world today.
1. Hydroelectric power plant that uses a dam
The underwater turbines are pretty robust and this is the reason why dams are created where water is collected and released when necessary.
Gravity is the force that makes the water from the dam to move down through a large pipe with high speed, which is required to spin the turbine and make the large magnets inside a generator to spin and create electricity.
Hoover Dam is the most popular dam in the U.S. and consists of an arch-gravity dam that is built in the Black Canyon of the Colorado River, at the border between Nevada and Arizona.
2. Run-of-the-river hydroelectric power plant
Hydroelectric energy can also be produced without using a dam, but using the fast moving water of a stream or river, which is also turned into electricity using the spinning turbines and the generators.
Run-of-the-river projects do not store any water, so they have no ability to control the amount of electricity produced and also the timing when electricity can be generated.
Chief Joseph Dam built near Bridgeport, Washington, is a major run-of-the-river power station in the U.S. that is not relying on an external reservoir.
3. Pumped storage plant
This type of hydroelectric power plants, pumps water from a lower reservoir to a reservoir located at a higher altitude during off-peak times when the electricity demand is low and the price cheap.
To pump the water to the reservoir located above, the power plant will use electricity produced from other sources of energy.
The water moved to the reservoir located higher, will be used to generate electricity when needed.
Stored water will be released to flow back to the lower reservoir and spin the turbines to generate electricity.
Bath County Pumped Storage Station is the largest pumped-storage power station in the world, and is located in the U.S. in Bath County, Virginia.
The output of this hydroelectric power plant is 3,003 MW (3 GW).
How is Moving or Falling Water Converted into Electricity?
I already mentioned that the moving or the falling water needs to have a certain speed and volume to be able to generate electricity.
This is the reason why gravity is used to move the stored water from a reservoir located above to the turbines located downhill.
If there is no reservoir involved in the process, the power plant will be able to generate electricity only if the speed and the volume of the stream or fast-moving river is high enough.
Relying only on the speed and the water volume of the stream, the power plant will halt the energy production if the volume of water in the stream or river decreases (during drought periods).
However, in both cases (with or without using a dam), the hydroelectric power plant will turn the kinetic power of the moving or falling water into mechanical energy (the spinning turbines), which will be then turned into electricity by the spinning magnets of a generator.
The price of the clean electricity produced today by hydroelectric power plants on the planet makes hydropower a competitive source of renewable electricity on the global energy market.
At the end of 2017, hydropower accounted for 7.5% share in the U.S. energy mix (generation capacity by source), which represents the highest share of a renewable energy source in the country’s energy mix.
A hydroelectric power station with an output that exceeds 10 MW, has an average cost of the electricity produced of only 3 to 5 U.S. cents (between $0.03 and $0.05).
Top 10 Largest Operational Hydroelectric Power Stations in the World
In the list we are presenting hydroelectric power stations with an output that is equal or exceeds 6,000 MW (6 GW).
1. Three Gorges Dam China – installed capacity 22,500 MW (22.5 GW)
The hydroelectric gravity dam called “Three Gorges Dam” is the largest hydroelectric power plant in the world and is built on the Yangtze River in the Hubei province of China.
The dam already flooded an area of 1,084 km2 that included archaeological and cultural sites and displaced about 1.3 million people.
In 2014, Three Gorges Dam established a world record by generating 98.8 terawatt-hours (TWh) of clean electricity, but was surpassed in 2016 by the Itaipú Dam that generated 103.1 TWh.
2. Itaipu Dam Brazil and Paraguay – installed capacity 14,000 MW (14 GW)
Itaipu Dam is a large hydroelectric dam built on the Paraná River and located between the borders of Brazil and Paraguay in South America.
The dam holds today the world record in terms of electricity generation (103.1 Twh in 2016).
The construction of the dam displaced about 10,000 families living on the Paraná River and the area flooded by the reservoir represents 1,350 square kilometres.
3. Xiluodu China – installed capacity 13,860 MW (13.86 GW)
Xiluodu Dam is an arch shaped dam built on the Jinsha River (upper course of the Yangtze river), and located between the Yunnan and the Sichuan Provinces in China.
The annual production of electricity reached the level of 55.2 Twh.
The dam reaches a height of 285.5 m (937 ft) and a length of 700 m (2,300 ft), and is today the fourth-tallest dam on the planet.
4. Guri Dam Venezuela – installed capacity 10,235 MW (10.23 GW)
Guri Dam also known as the Simón Bolívar Hydroelectric Plant is a concrete gravity and embankment dam built on the Caroni River in the Bolívar State, Venezuela.
Guri Dam has a height of 162 meters and a length of 7.4 kilometers.
The reservoir used by the Guri Dam flooded an area of 4,250 square kilometers (Guri reservoir is the largest in the world).
The power station produces every year 53.41 Twh of clean electricity.
5. Tucurui Dam Brazil – installed capacity 8,370 MW (8.3 GW)
Tucurui Dam is a concrete gravity dam built on the Tocantins River and located in Pará, Brazil.
Tucurui Dam reaches a height of 78 meters and a length of 12.5 kilometers.
The power station produces 41.43 Twh per year.
The reservoir flooded an area of 3,014 square kilometers and its construction displaced between 25,000 and 35,000 people.
6. Xiangjiaba Dam China – installed capacity 7,750 MW (7.75 GW)
Xiangjiaba Dam is a large gravity dam built on the Jinsha River and located between the Yunnan and the Sichuan Provinces in southwest China.
The dam has a height of 161 meters (528 ft) and a length of 909 meters (2,982 ft).
The annual output of the power station is 30.7 Twh.
The reservoir flooded an area of 95.6 square kilometers, and produces electricity for Shanghai.
7. Grand Coulee Dam in the U.S. – installed capacity 6,809 MW (6.80 GW)
Grand Coulee Dam is a concrete gravity dam built on the Columbia River in the state of Washington.
The dam reaches a height of 168 m (550 ft), and a length of 1,592 m (5,223 feet).
The annual output of the power plant is 20 Twh.
The reservoir flooded an area of 324 km2, and about 3,000 residents were relocated.
8. Longtan Dam China – installed capacity 6,426 MW (6.42 GW)
Longtan Dam is a very tall roller-compacted concrete gravity dam (RCC), that was built on the Hongshui River in the Guangxi Zhuang Autonomous Region of China.
The dam reaches a height of 216.2 meters (709.3 ft), which makes it the tallest of its type in the world, and has a length of 849 m (2,785 ft).
The power station generates 18.7 Twh per year.
9. Sayano–Shushenskaya Dam in Russia – installed capacity 6,400 MW (6.4 GW)
Sayano–Shushenskaya Dam was built on the Yenisei River, and is located close to the Sayanogorsk town in Khakassia, Russia.
This is an arch-gravity dam with the height of 242 meters (794 ft), and the length of 1,066 meters (3,497 ft).
The power station produces annually 26.8 Twh.
The reservoir flooded an area of 621 square kilometers.
10. Krasnoyarsk Dam Russia – installed capacity 6,000 MW (6 GW)
Krasnoyarsk Dam is a concrete gravity dam built on the Yenisey River about 19 miles upstream of Krasnoyarsk, Russia.
The dam reaches a height of 124 m (407 ft), and a length of 1,065 m (3,494 ft).
The power plant generates 15 Twh per year.
The Krasnoyarsk Reservoir flooded an area of 2,000 square kilometers.
Hydroelectric Energy Environmental and Social Impact
Hydroelectric power plants are producing electricity without consuming water (power plants burning fossil fuels are large consumers of water) and without releasing harmful emissions into the atmosphere.
However, the construction of the dams and the large reservoirs required to feed the dams, have flooded large areas of land on the planet and displaced and relocated millions of people.
Avoiding to remove all the trees from the area intended for the construction of the reservoir will lead to the release of large quantities of methane (a greenhouse gas) in the area (produced by the decomposing process of the organic materials such as trees, plants and animals that are sunk).
The construction of the reservoirs lead to the destruction of several wildlife habitats, and the relocation of many human settlements and even graveyards.
Final conclusion
Hydroelectric energy is the renewable energy source with the highest share in the global energy mix among all the other renewables.
The evolution of the technology will only create new opportunities for the development of more powerful hydroelectric power stations that are required to reduce the use of fossil fuels.
