Learn the definition of hydroelectric power and see examples. Understand how hydroelectric energy works and its disadvantages and advantages.
Updated: 08/27/2021
What is Hydroelectric Energy?
Hydroelectric Power Definition
The United States Office of Energy Efficiency and Renewable Energy defines hydroelectric energy, also referred to as hydroelectric power, as "a renewable source of energy that generates power by using a dam or diversion structure to alter the natural flow of a river or other body of water." The definition can even be glimpsed within the term itself, which combines the Greek word hydro, which means "water," and the Phoenician word elekron, which means "shining light."
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The history of hydropower goes back thousands of years to the Ancient Greeks, who used water wheels to grind flour, and the Ancient Egyptians, who used water screws for irrigation. But in the modern world, hydroelectric power has been in use since the late 19th century, in facilities like the one pictured above, where it uses the power of moving water to generate electricity.
What Does Hydroelectric Mean to the World?
Hydroelectric power is considered one of the most important energy sources in the world. It is the most common form of renewable energy, producing about 16% of the world's electricity, which is three times as much as wind power and six times as much as solar power. All told, approximately 71% of all of the renewable electricity generated on Earth is from hydropower. In the United States, hydropower is the leading renewable energy source by far, accounting for about 96% of all renewable energy production.
Hydroelectricity has a few major advantages. The first is the high energy density contained by flowing water. The second is that the power source is dispatchable, meaning that power plant operators can regulate the flow of water thereby generating more or less electricity, as needed. This helps hydroelectric power plants to meet the ever-changing demands of electricity customers worldwide. Hydroelectric power plants are particularly common in developed nations such as the United States, China, Brazil, Canada, India, and Russia.
Hydroelectric Energy Examples
Hydroelectric plants come in three main types: impoundment dams, run-of-river facilities, and pump storage. Impoundment dams may be the most iconic. They are massive dams created on major rivers with the goal of collecting a large, deep reservoir of water behind them. These reservoirs serve to store energy, in high volumes and at high pressure, that can then be sent through the dam and used to generate electricity as needed. One famous example is the Hoover Dam, built in the 1930s on the border between Nevada and Arizona.
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A second common type of hydroelectric plant is called a "run of river" facility. Rather than damming an entire river, these facilities channel a portion of a river into a smaller power plant, leaving the majority of the river's natural flow intact. One example is Chief Joseph Dam in Bridgeport, Washington. Of course, it is important to note that, although these run-of-river facilities are more ecologically friendly, they do not generate nearly as much energy as the impoundment dams discussed above.
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The third and final type of hydroelectric energy is pump storage. These facilities store energy by pumping water from lower-elevation reservoirs to higher-elevation reservoirs. Then, the water can be released downhill and used to generate electricity as needed. They can be combined with sources like solar power to store excess energy during the daytime and then make that energy available when demand peaks in the early evening.
What is the Largest Hydroelectric Energy Plant in the World?
China is now the largest producer of hydroelectric power in the world. It is also home to the world's biggest hydroelectric dam: The Three Gorges Dam Project located in the Xilingxia Gorge, in Hubei province, China.
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Construction began on the Three Gorges Dam in 1994 and it wasn't finished until 2003. The dam is a missive impoundment dam that is almost a mile and a half long. The dam holds back a giant wall of water almost 600 feet high. Beneath the dam, water flows at a rate of 20,000-30,000 cubic feet per second through thirty-two large turbines capable of generating up to 22,500 megawatts, which is something like thirty times the capacity of a typical power plant.
What Is Hydroelectric Energy?
Water is pretty powerful stuff! You know this if you have stood in a flowing stream and felt the water rushing past you. Or, if you've gone whitewater rafting down a raging river. Even mere images of a place like Niagara Falls help you appreciate just how strong moving water is. This is not a new observation, and water has been used to produce different forms of energy for a very long time. When electricity is generated from flowing water, this is called hydroelectric energy, and the prefix 'hydro' refers to water.
Hydroelectric energy is considered a renewable energy resource because it's an energy resource that regenerates in a short time period. You can think of this like the hair on your head. If you get a bad haircut that you don't like, you don't have to worry about it too much because it will grow back in a reasonable amount of time. However, if you lose an arm, you certainly can't regenerate that! Your hair is a renewable resource, whereas your arm is a non-renewable resource.
Sunlight, wind and heat generated from the earth are similar types of renewable energy resources. Just like you can't stop water from flowing, you can't stop the sun from shining or the wind from blowing. The resource 'renews' itself as it is used, and unlike things such as minerals and metals, does not occur on Earth in a limited supply.
Hydroelectric energy is a very important energy source, both nationally and worldwide. About 19% of the world's total electricity production comes from hydroelectric energy and about 7% of the power in the U.S. When we look at hydroelectric energy for the U.S. in terms of renewable energy sources (so comparing this to things like solar power, wind power, geothermal energy and biofuels), it makes up 96% of renewable energy electricity production. That means that almost all of our energy production that comes from renewable energy sources comes from water!
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How Does Hydroelectric Energy Work?
All modern hydroelectric plants operate using the same basic principles. They use channel flowing water through a large turbine, which turns the turbine and thus generates electricity.
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The dam pictured above is an impoundment dam with a large reservoir behind it. The dam funnels the high-pressure reservoir water through a long penstock, which brings it to a turbine. The turbine is like a giant fan blade - or imagine the propeller on a massive boat - that turns as the water flows past it. The turbine is attached to a generator that uses the spinning motion to pull electrons through a wire. This electricity is then processed and sent to consumers. Meanwhile, the water exits the dam and returns to the river, albeit at a lower elevation.
Advantages of Hydroelectric Energy
There are several advantages of hydroelectric energy, as compared to other forms of renewable energy and to fossil fuels.
- No Fuel Required - Unlike coal or other fossil fuels, hydroelectric power requires only a suitable river and buildable site.
- Renewable and Clean - Hydroelectric power does not generate air pollution like fossil fuels.
- Dispatchable - Unlike other forms of renewable energy, hydroelectric power is "dispatchable," meaning the plant operators can adjust the flowing water to meet the demand for electricity.
- Reliable - Hydroelectric power is available twenty-four hours a day, seven days a week, unlike solar and wind power whose supply is more intermittent.
- Inexpensive to Maintain - Although hydroelectric dams are expensive to build, they typically have low maintenance costs when compared to other energy sources.
Disadvantages of Hydroelectric Energy
As with any energy source, hydroelectric power has several disadvantages as well.
- Limited Availability - Hydroelectric power requires a suitable river, which is not available everywhere.
- Running Out of Sites - Many of the best rivers are already full, meaning there is little space for additional hydroelectric dams.
- High Cost - Hydroelectric dams require large construction costs. The Three Gorges Dam, for example, cost more than $30 billion.
- Ecological Costs - Impoundment dams block fragile river ecosystems, disrupting fish migration among other problems.
Lesson Summary
Hydroelectric energy is the most popular renewable energy source in the world. It provides clean, dispatchable power to millions of people worldwide. The country of Norway, for example, generates roughly 99% of its electricity using hydropower. It is a proven, reliable technology that does not produce air pollution or contribute to climate change.
However, it has many disadvantages as well. Chief among them is the lack of suitable river sites. As such, the future of hydropower remains uncertain. Will there be new investments in hydroelectric dams? Will rainfall patterns shift as a result of climate change? Will pump storage become more common? In an energy-hungry world, only time will tell.
Water Generates Electricity
So, how exactly is electricity generated from water? This usually occurs through a hydroelectric dam that is built along a flowing waterway. Think of the water at Niagara. The water flowing over the falls is travelling faster than the water approaching the falls. As water travels downhill, it picks up speed and power.
To take advantage of this, dams are constructed along the waterway where there is a large elevation drop. This is exactly why you wouldn't expect to find dams in flat places like Florida, but would expect to find them in the hilly, mountainous regions of the Southwest U.S.
Like going down a slide at the playground, water is pulled downhill by gravity and picks up speed as it goes (you're moving faster at the bottom of the slide than at the top, right?). Inside the dam are turbines that get spun by the moving water - similar to how a pinwheel gets spun by the wind blowing by.
The spinning turbine shafts are connected to a generator, and the spinning of the turbines themselves creates electricity inside the generator. The generator is connected to power lines, which transmit the electricity to homes and buildings just like they do with coal-fired and natural gas power plants.
Just like wind blowing past the pinwheel is not affected by the pinwheel itself, water flowing by the turbines is not affected as it passes through the dam. It flows on downstream as if nothing has happened. You can see why this is such a valuable and widely used energy resource all around the world! However, with every source of energy, there are pros and cons. Let's look at the benefits and drawbacks that come with harnessing the amazing power of moving water.
Pros and Cons of Hydroelectric Energy
As you already know, hydroelectric energy is beneficial because it's a renewable resource. The water is not affected as it flows through the dam and spins the turbines - water will flow whether there's a dam there or not! This also means that there is minimal pollution, unlike the air and water pollution generated from coal and nuclear power plants.
Because water flows along naturally, we also do not have to create any water to run through the dam. Water is provided by nature, and we simply have to sit back and let it do all the work! This also means that maintenance and operational costs are relatively low for the dam itself.
One reason that hydroelectric energy is so popular is its reliability. Wind power is great, but if the wind isn't blowing, you don't generate any electricity. Solar power has a similar issue. If the sun isn't shining, you're not generating any electricity from the sunlight. Dams, however, are specifically designed to hold water behind them. This provides a steady, constant flow of energy from the water that runs through it. So instead of depending on rainfall to deliver water, we know that the water will be there waiting to spin those turbines inside the dam.
While hydroelectric energy can be a very beneficial renewable resource, there are also drawbacks to using water to generate electricity. While the maintenance costs are low after the dam is built, they're very expensive to construct and require large up-front investments.
And you know those reservoirs behind the dam? For the most part, these are a steady, reliable source of water. But they are dependent on water coming from their own sources, such as rain. If it doesn't rain, the reservoir may dry up. It's like having a slow leak in your bathtub. If you sit in there long enough and you don't turn the water back on to refill the tub, eventually you'll be sitting in a dry tub, which doesn't work very well!
Dams can have serious impacts on the surrounding environment as well. Think of it this way: There is a busy street that runs through the center of town that seems to move along pretty well. All of a sudden, a large wall gets constructed across the road that reduces it from four lanes to one. Traffic will likely get backed up, and some people will simply not be able to make it to work any longer. And, any homes, plants and animals will be forced to move where the wall was constructed.
A dam has the same effect on a river environment. The water is not allowed to flow downstream as it would without the dam, so it backs up, creating the reservoir behind it. The reservoir can only be made by flooding the land behind the dam, so people, plants and animals are displaced. Since the flow is altered at the dam, the downstream areas get less water than they would normally.
This is like our traffic issue where only so many people can get through the wall to work. If the water can't get to the ecosystems that depend on it, those plants, animals and people are greatly affected.
Fish populations also suffer at dams because many fish migrate through rivers and streams. You might be able to climb over the wall on the road, but fish don't have arms. They get stuck on one side of the dam or the other, or get killed passing through those spinning turbine blades inside.
Lesson Summary
When you think about how amazing and powerful water is, it's not too surprising to think of how useful it can be to us. Humans have long used water as a source of power and energy, and when we use passing water to generate electrical energy, we call this hydroelectric energy. This makes sense because 'hydro' means water, like with hydration and hydrology.
A renewable resource, hydroelectric energy is generated when flowing water passes through a dam. The dam has turbines inside, and just like the wind blows the blades of a pinwheel without a passing thought, water spins the turbines without blinking an eye. The turbine shafts spin inside a generator, which produces electricity. This electricity is then carried to homes, businesses and other locations by power lines coming from the dam.
Hydroelectric energy is the most popular type of renewable energy for many reasons. Dams have relatively low maintenance costs, and there is little to no pollution of either the air or water. Since nature is kind enough to provide the water, you don't have to go out and get it! Simply sit back and let the water do all the hard work as it flows through the dam. Hydroelectric energy is also fairly reliable and predictable because as the water builds up behind the dam, it provides a steady, constant supply.
Hydroelectric energy is great, but it's certainly not perfect. Those reservoirs that build up can only do so if they flood the land behind the dam. This means that any people, plants and animals living there no longer have a place to call 'home.' And while the reservoir provides a steady supply to the dam, the reservoirs have to get filled from somewhere too. If their supplies run low, their reservoir may dry up, which means no electricity gets generated.
Dams also impact the surrounding environment because like putting up a wall across a busy road into town, they drastically alter the natural flow of water heading downstream. Those people, plants and animals living below the dam all depend on that water flow, and problems arise if it no longer reaches them. Fish are especially affected because they migrate through streams and rivers. They certainly can't get around the dam by climbing it, and if they do pass through it, they risk injury or death from the spinning turbine blades.
Learning Outcomes
After this lesson is finished, you should be able to:
- Describe the reliability of hydroelectric energy
- Determine the advantages and disadvantages of hydroelectric power
To unlock this lesson you must be a Study.com Member.
Create your account
Video Transcript
What Is Hydroelectric Energy?
Water is pretty powerful stuff! You know this if you have stood in a flowing stream and felt the water rushing past you. Or, if you've gone whitewater rafting down a raging river. Even mere images of a place like Niagara Falls help you appreciate just how strong moving water is. This is not a new observation, and water has been used to produce different forms of energy for a very long time. When electricity is generated from flowing water, this is called hydroelectric energy, and the prefix 'hydro' refers to water.
Hydroelectric energy is considered a renewable energy resource because it's an energy resource that regenerates in a short time period. You can think of this like the hair on your head. If you get a bad haircut that you don't like, you don't have to worry about it too much because it will grow back in a reasonable amount of time. However, if you lose an arm, you certainly can't regenerate that! Your hair is a renewable resource, whereas your arm is a non-renewable resource.
Sunlight, wind and heat generated from the earth are similar types of renewable energy resources. Just like you can't stop water from flowing, you can't stop the sun from shining or the wind from blowing. The resource 'renews' itself as it is used, and unlike things such as minerals and metals, does not occur on Earth in a limited supply.
Hydroelectric energy is a very important energy source, both nationally and worldwide. About 19% of the world's total electricity production comes from hydroelectric energy and about 7% of the power in the U.S. When we look at hydroelectric energy for the U.S. in terms of renewable energy sources (so comparing this to things like solar power, wind power, geothermal energy and biofuels), it makes up 96% of renewable energy electricity production. That means that almost all of our energy production that comes from renewable energy sources comes from water!
Water Generates Electricity
So, how exactly is electricity generated from water? This usually occurs through a hydroelectric dam that is built along a flowing waterway. Think of the water at Niagara. The water flowing over the falls is travelling faster than the water approaching the falls. As water travels downhill, it picks up speed and power.
To take advantage of this, dams are constructed along the waterway where there is a large elevation drop. This is exactly why you wouldn't expect to find dams in flat places like Florida, but would expect to find them in the hilly, mountainous regions of the Southwest U.S.
Like going down a slide at the playground, water is pulled downhill by gravity and picks up speed as it goes (you're moving faster at the bottom of the slide than at the top, right?). Inside the dam are turbines that get spun by the moving water - similar to how a pinwheel gets spun by the wind blowing by.
The spinning turbine shafts are connected to a generator, and the spinning of the turbines themselves creates electricity inside the generator. The generator is connected to power lines, which transmit the electricity to homes and buildings just like they do with coal-fired and natural gas power plants.
Just like wind blowing past the pinwheel is not affected by the pinwheel itself, water flowing by the turbines is not affected as it passes through the dam. It flows on downstream as if nothing has happened. You can see why this is such a valuable and widely used energy resource all around the world! However, with every source of energy, there are pros and cons. Let's look at the benefits and drawbacks that come with harnessing the amazing power of moving water.
Pros and Cons of Hydroelectric Energy
As you already know, hydroelectric energy is beneficial because it's a renewable resource. The water is not affected as it flows through the dam and spins the turbines - water will flow whether there's a dam there or not! This also means that there is minimal pollution, unlike the air and water pollution generated from coal and nuclear power plants.
Because water flows along naturally, we also do not have to create any water to run through the dam. Water is provided by nature, and we simply have to sit back and let it do all the work! This also means that maintenance and operational costs are relatively low for the dam itself.
One reason that hydroelectric energy is so popular is its reliability. Wind power is great, but if the wind isn't blowing, you don't generate any electricity. Solar power has a similar issue. If the sun isn't shining, you're not generating any electricity from the sunlight. Dams, however, are specifically designed to hold water behind them. This provides a steady, constant flow of energy from the water that runs through it. So instead of depending on rainfall to deliver water, we know that the water will be there waiting to spin those turbines inside the dam.
While hydroelectric energy can be a very beneficial renewable resource, there are also drawbacks to using water to generate electricity. While the maintenance costs are low after the dam is built, they're very expensive to construct and require large up-front investments.
And you know those reservoirs behind the dam? For the most part, these are a steady, reliable source of water. But they are dependent on water coming from their own sources, such as rain. If it doesn't rain, the reservoir may dry up. It's like having a slow leak in your bathtub. If you sit in there long enough and you don't turn the water back on to refill the tub, eventually you'll be sitting in a dry tub, which doesn't work very well!
Dams can have serious impacts on the surrounding environment as well. Think of it this way: There is a busy street that runs through the center of town that seems to move along pretty well. All of a sudden, a large wall gets constructed across the road that reduces it from four lanes to one. Traffic will likely get backed up, and some people will simply not be able to make it to work any longer. And, any homes, plants and animals will be forced to move where the wall was constructed.
A dam has the same effect on a river environment. The water is not allowed to flow downstream as it would without the dam, so it backs up, creating the reservoir behind it. The reservoir can only be made by flooding the land behind the dam, so people, plants and animals are displaced. Since the flow is altered at the dam, the downstream areas get less water than they would normally.
This is like our traffic issue where only so many people can get through the wall to work. If the water can't get to the ecosystems that depend on it, those plants, animals and people are greatly affected.
Fish populations also suffer at dams because many fish migrate through rivers and streams. You might be able to climb over the wall on the road, but fish don't have arms. They get stuck on one side of the dam or the other, or get killed passing through those spinning turbine blades inside.
Lesson Summary
When you think about how amazing and powerful water is, it's not too surprising to think of how useful it can be to us. Humans have long used water as a source of power and energy, and when we use passing water to generate electrical energy, we call this hydroelectric energy. This makes sense because 'hydro' means water, like with hydration and hydrology.
A renewable resource, hydroelectric energy is generated when flowing water passes through a dam. The dam has turbines inside, and just like the wind blows the blades of a pinwheel without a passing thought, water spins the turbines without blinking an eye. The turbine shafts spin inside a generator, which produces electricity. This electricity is then carried to homes, businesses and other locations by power lines coming from the dam.
Hydroelectric energy is the most popular type of renewable energy for many reasons. Dams have relatively low maintenance costs, and there is little to no pollution of either the air or water. Since nature is kind enough to provide the water, you don't have to go out and get it! Simply sit back and let the water do all the hard work as it flows through the dam. Hydroelectric energy is also fairly reliable and predictable because as the water builds up behind the dam, it provides a steady, constant supply.
Hydroelectric energy is great, but it's certainly not perfect. Those reservoirs that build up can only do so if they flood the land behind the dam. This means that any people, plants and animals living there no longer have a place to call 'home.' And while the reservoir provides a steady supply to the dam, the reservoirs have to get filled from somewhere too. If their supplies run low, their reservoir may dry up, which means no electricity gets generated.
Dams also impact the surrounding environment because like putting up a wall across a busy road into town, they drastically alter the natural flow of water heading downstream. Those people, plants and animals living below the dam all depend on that water flow, and problems arise if it no longer reaches them. Fish are especially affected because they migrate through streams and rivers. They certainly can't get around the dam by climbing it, and if they do pass through it, they risk injury or death from the spinning turbine blades.
Learning Outcomes
After this lesson is finished, you should be able to:
- Describe the reliability of hydroelectric energy
- Determine the advantages and disadvantages of hydroelectric power
To unlock this lesson you must be a Study.com Member.
Create your account
Frequently Asked Questions
What is hydroelectric power and how does it work?
Hydroelectric power is electricity generated via flowing water. Most hydroelectric plants work by channeling flowing water through a large turbine. The spinning turbine is attached to a generator which generates electricity.
What are advantages and disadvantages of hydropower?
The advantages of hydropower include that there is no fuel required, it is renewable and clean, it is dispatchable, and it is reliable. The disadvantages include limited availability, that the world is running out of sites, its high cost, and its ecological costs.
What is an example of hydroelectric power?
Two famous examples of hydroelectric power are the Hoover Dam in the United States and the massive Three Gorges Dam in China.
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Advantages of Hydropower | What is Hydroelectric Energy?
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