Hydropower
- Hydropower (or waterpower) harnesses the energy of moving or falling water. This is usually in the form of hydroelectricity from a dam, but it can be used directly as a mechanical force.
- Hydroelectricity is electricity obtained from hydropower. Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. Less common variations make use of water's kinetic energy or undammed sources such as tidal power. Hydroelectricity is a renewable energy source.
- Also see: Ocean energy
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[edit] Hydropower
Hydropower is electricity generated using the energy of moving water. Rain or melted snow, usually originating in hills and mountains, create streams and rivers that eventually run to the ocean. The energy of that moving water can be substantial, as anyone who has been whitewater rafting knows.
This energy has been exploited for centuries. Farmers since the ancient Greeks have used water wheels to grind wheat into flour. Placed in a river, a water wheel picks up flowing water in buckets located around the wheel. The kinetic energy of the flowing river turns the wheel and is converted into mechanical energy that runs the mill.
In the late 19th century, hydropower became a source for generating electricity. The first hydroelectric power plant was built at Niagara Falls in 1879. In 1881, street lamps in the city of Niagara Falls were powered by hydropower. In 1882 the world’s first hydroelectric power plant began operating in the United States in Appleton, Wisconsin.
A typical hydro plant is a system with three parts: an electric plant where the electricity is produced; a dam that can be opened or closed to control water flow; and a reservoir where water can be stored. The water behind the dam flows through an intake and pushes against blades in a turbine, causing them to turn. The turbine spins a generator to produce electricity. The amount of electricity that can be generated depends on how far the water drops and how much water moves through the system. The electricity can be transported over long-distance electric lines to homes, factories, and businesses.
Hydroelectric power provides almost one-fifth of the world's electricity. China, Canada, Brazil, the United States, and Russia were the five largest producers of hydropower in 2004. One of the world's largest hydro plants is at Three Gorges on China's Yangtze River. The reservoir for this facility started filling in 2003, but the plant is not expected to be fully operational until 2009. The dam is 1.4 miles (2.3 kilometers) wide and 607 feet (185 meters) high.
The biggest hydro plant in the United States is located at the Grand Coulee Dam on the Columbia River in northern Washington. More than 70 percent of the electricity made in Washington State is produced by hydroelectric facilities.
Hydropower is the cheapest way to generate electricity today. That's because once a dam has been built and the equipment installed, the energy source—flowing water—is free. It's a clean fuel source that is renewable yearly by snow and rainfall.
Hydropower is also readily available; engineers can control the flow of water through the turbines to produce electricity on demand. In addition, reservoirs may offer recreational opportunities, such as swimming and boating.
But damming rivers may destroy or disrupt wildlife and other natural resources. Some fish, like salmon, may be prevented from swimming upstream to spawn. Technologies like fish ladders help salmon go up over dams and enter upstream spawning areas, but the presence of hydroelectric dams changes their migration patterns and hurts fish populations. Hydropower plants can also cause low dissolved oxygen levels in the water, which is harmful to river habitats.
[edit] Advantages of hydropower
1. Once a dam is constructed, electricity can be produced at a constant rate.
2. If electricity is not needed, the sluice gates can be shut, stopping electricity generation. The water can be saved for use another time when electricity demand is high.
3. Dams are designed to last many decades and so can contribute to the generation of electricity for many years / decades.
4. The lake that forms behind the dam can be used for water sports and leisure / pleasure activities. Often large dams become tourist attractions in their own right.
5. The lake's water can be used for irrigation purposes.
6. The build up of water in the lake means that energy can be stored until needed, when the water is released to produce electricity.
7. When in use, electricity produced by dam systems do not produce green house gases. They do not pollute the atmosphere.
[edit] Disadvantages of hydropower
- There are disadvantages with hydropower, particularly with large scale dams. See:
- www.hydroreform.org and
- The World Commission On Dams.
- There is also a great deal of concern over the carbon dioxide and methane emissions produced by the large amount of organic matter trapped when land is flooded to create the dam www.newscientist.com, Hydroelectric power's dirty secret revealed.
1. Dams are extremely expensive to build and must be built to a very high standard.
2. The high cost of dam construction means that they must operate for many decades to become profitable.
3. The flooding of large areas of land means that the natural environment is destroyed.
4. People living in villages and towns that are in the valley to be flooded, must move out. This means that they lose their farms and businesses. In some countries, people are forcibly removed so that hydro-power schemes can go ahead.
5. The building of large dams can cause serious geological damage. For example, the building of the Hoover Dam in the USA triggered a number of earth quakes and has depressed the earth’s surface at its location.
6. Although modern planning and design of dams is good, in the past old dams have been known to be breached (the dam gives under the weight of water in the lake). This has led to deaths and flooding.
7. Dams built blocking the progress of a river in one country usually means that the water supply from the same river in the following country is out of their control. This can lead to serious problems between neighbouring countries.
8. Building a large dam alters the natural water table level. For example, the building of the Aswan Dam in Egypt has altered the level of the water table. This is slowly leading to damage of many of its ancient monuments as salts and destructive minerals are deposited in the stone work from ‘rising damp’ caused by the changing water table level.
[edit] Hydropower tips
- Help set up a micro-hydro power generator: Practilce Action, Micro-Hydro Power
- What is hydropower and how does it work?
Modern hydro facilities incorporate turbines that spin when in contact with moving water, as well as generators that transform this rotational energy into electricity. These components are installed in or adjacent to dams and diversion structures that take advantage of gravity as water flows or cascades downward.
In Massachusetts, waterwheels have supplied mechanical power for centuries, and conventional turbine-based systems have generated electric power since late in the 19 th century. Today, numerous hydro facilities supply electricity to the New England grid or meet on-site power needs within the state. These installations range from large-scale plants producing hundreds of megawatts down to small-scale facilities creating anywhere from tens to hundreds of kilowatts.
Visit the Hydropower Technology section to learn more.
- Why is hydropower considered clean, or renewable, energy?
Hydropower is a renewable resource because it uses the continuous flow of rivers and streams to produce electricity without using up the water resource. It is also a clean technology because it does not rely on the burning of fuels like oil, coal, or natural gas to produce power.
- Where is hydropower used?
Hydropower is most often used as a commercial electric technology and occassionally can be used to power existing mill sites that are being renovated for commercial, industrial, or even residential use. Because most hydropower facilities are large in scale, it would be difficult to find and rehabilitate a site for a single residence.
- Why should people use it?
Hydro plants generate cost-competitive electricity on a continuous, largely predictable basis, and the output of many facilities can be controlled to match changes in electricity demand and to provide energy storage capabilities. These are important advantages over intermittent renewables such as the wind and sun. Like all green sources, hydropower also diversifies the state’s electricity supply portfolio, increases energy security, reduces dependence on finite resources, and decreases emissions of harmful pollutants and greenhouses gases.
Despite these advantages, significant increases in the Commonwealth’s hydro generating capacity are very unlikely because dams and diversion structures alter natural watercourses and habitats. The adverse impacts of existing facilities can be reduced with state-of-the-art operational practices and fish protection measures, and many facilities that are underperforming or dormant can be upgraded or restored with efficient, modern, low-impact technology. Emerging “free flow” energy conversion systems represent a promising option for tapping hydroelectricity without disrupting aquatic environments.
To maintain the important role of hydropower in the state’s electricity supply portfolio, upgrading and restoration projects are under way at several sites in Massachusetts, and demonstrations of emerging technologies are planned.
Visit the Benefits and Barriers section to learn more.
- How can I get involved?
The majority of hydropower capacity in the state has existed for at least several decades, and it is now very difficult to develop new hydropower resources. The most practical way to develop a hydropower project in Massachusetts is to rehabilitate an existing hydro site, though this also requires a significant approval process.
However, most electricity customers can support hydropower through the purchase of green electricity. Most green electricity suppliers rely in part on hydropower because it is the most prevalent clean energy technology today.
[edit] 1. How Hydropower works?
Hydropower captures the energy produced by moving water. The methods for harnessing this power are remarkably simple; in fact, our use of water power goes back hundreds of years. Today’s modern hydroelectricity plants may be many times more sophisticated, but they rely on the same principles used to power mankind’s earliest machines.
The most important thing to remember is that water must be moving to generate power. A quiet lake may have the potential to generate power, but nothing happens until the water moves. Fortunately, Mother Nature does a terrific job of moving water.
Remember learning about the Water Cycle when you were a kid? It’s the natural process we rely on for hydropower. Water evaporates from the ocean into the atmosphere and forms clouds as it cools. Then, while we duck under cover, the water returns to the earth as rain and snow, eventually forming streams and rivers as it heads back to the ocean to start the process all over again. Thanks to gravity, the water moving down those streams and rivers can pick up tremendous force – energy we can put to work as hydropower.
Putting the Energy to Work
That’s the essence of Hydropower: extracting energy from water as it flows by. A simple example is shown with the water-powered mill wheel. Water coming down a stream is diverted to the top of the water wheel. As each bucket fills, the added weight carries it to the bottom, turning the wheel as it goes. Notice that the water wheel is connected to a shaft, which connects to machinery inside the mill. The water flows and the machines turn – all by capturing a little energy from water as it follows its natural path back to the ocean.
It’s easy to see why water power can be so compelling. As long as water is flowing down the hill (thanks to the Water Cycle), energy can be extracted from it. Nothing is consumed; the water continues on. Water is a 100% clean, renewable resource – but with some substantial advantages: streams and rivers still flow when the sun goes down and the wind stops blowing. Plus, electricity from water power is far less expensive to produce than solar or wind power.
The vintage water wheel shown in the mill picture above is rarely used today, having been replaced with more efficient water turbines that are typically used to generate electricity. As shown in the diagram, however, the fundamentals of water power are the same. Water flows across the turbine, turning a shaft connected to a generator that produces electricity.
How Much Power?
Any moving water can produce hydropower. Add more moving water, or Flow, and you can produce more power. You can tell by looking that a raging river contains more energy than a small stream.
But if you add pressure to the water, you can get a lot more energy from it. (Ever see how far a fire hose can squirt water?) As it turns out, it’s pretty easy to add pressure to water, simply by putting it in a container.
Water weighs quite a bit, and the sheer weight of a container of water puts pressure on the bottom. The water in a medium-sized aquarium puts about 1 pound per square inch (psi) of pressure on the bottom of the aquarium. Now imagine an aquarium 100 feet tall. The water pressure at the bottom of that tall aquarium will be about 43 psi – roughly the same as the average outdoor faucet.
Hydropower systems build pressure either by containing the water behind a dam, or within a pipe that runs down a hill. The weight of the water behind the dam or in the pipe creates pressure at the bottom. More height creates more pressure, and more pressure means we can get more power from the flow of water. (The technical term for this vertical distance is Head.)
[edit] 2. Types of Hydropower
In the previous section, How Hydropower Works, we learned about the natural energy available in moving water, and how we can extract some of it as hydropower. The concepts are simple and the technology is proven; clean hydropower is one of the least expensive ways to generate electricity. Not surprisingly, regions able to support hydroelectric systems tend to enjoy lower electricity rates than those that rely primarily on coal and other fossil fuels.
Now we turn to the two major methods we use today to generate electricity from this remarkable source of renewable energy.
- The Two Major Designs for Hydropower
Most hydroelectric systems can be classified into one of two groups:
- Reservoir Hydro Systems
Most people visualize a Reservoir system when they hear the term “hydroelectric project.” Reservoir systems can easily be recognized by the large dam that creates a sizeable lake behind it. Examples include Hoover Dam (and Lake Mead) in Nevada, Grand Coulee Dam (and Lake Roosevelt) in Washington, and the massive Three Gorges Dam in China.
Reservoir Systems Can Produce More Power on Demand
A Reservoir hydropower system is easily recognized by its dam, which typically holds back a large body of water. Many of the lakes behind these large dams stretch for several miles, and are often used as recreational destinations.
The height of the dam determines the pressure at the bottom, created by the weight of the water behind the dam. The hydroelectric turbine sits at the bottom of the dam (or sometimes even further downstream), allowing it to take full advantage of the pressure created by the dam. The amount of water moving through the turbine can be controlled, allowing the Reservoir hydro system to vary the amount of electricity it produces.
Power in Reserve
Reservoir Hydro systems, by virtue of the large body of water they hold in reserve, have tremendous capacity to handle peak electricity loads. During light usage periods, the amount of water flowing through the turbines is reduced, generating less electricity. This allows the natural water flow of the river to add more water to the reservoir, raising the water level. During periods of peak demand, this reserve capacity is drawn down, allowing more water to flow through the turbine that the river alone could supply.
High power output is characteristic of large Reservoir systems. These projects are typically rated in hundreds or thousands of megawatts. The Three Gorges project in China (shown at left), the world’s largest reservoir project to date, is projected to deliver a staggering 22.5 billion watts.
Dams Provide Critical Flood Control and Water Management
Like other dam projects, a major objective of Three Gorges Dam is to control flooding of the Yangtze River. In 1954, a major flood on the river killed 33,000 people and displaced another 18 million. Another flood in 1998 resulted in billions of dollars in damage, killed more than 1,500 people, and displaced more than 2 million. The new dam is expected to completely eliminate these massive floods, and reduce the frequency of major flooding to once every 100 years.
Most dams, in fact, are constructed for flood control or to supply water to communities and agriculture - not for electricity generation. Today, only about 3% of installed dams are used generate electricity. This creates a tremendous opportunity to produce clean, CO2-free electricity from these dams with virtually no incremental environmental impact.
Moving the Power to the Customer
The very large output from Reservoir systems makes them suitable for providing power to large cities, although there are usually many miles (sometimes hundreds) between the dams and the populations they serve. You’ve probably seen rows of high-tension lines that transport these millions of watts across the country. Unfortunately, an appreciable percentage of this power is simply lost along the way due to transmission losses. Streaming Hydropower projects, discussed in the next segment, can help reduce these transmission losses because their smaller size allows them to be located closer to the point of electricity usage. Obviously, there are environmental downsides to large reservoir projects. Many early installations did not make adequate provisions for fish migration upstream, requiring expensive remedial efforts to solve the problem. Another issue is the reservoir itself, which floods lands that may have been long-standing habitat for humans and other species. These issues are discussed further in Part 3: Environmental Considerations.
- Streaming (Run of River) Systems
In many respects, Streaming Hydro (also known as Run of River) systems are the opposite of Reservoir systems. There are no dams and lakes, only diversion systems that direct a portion of a stream or river through the hydroelectric turbine. Streaming systems are typically installed on smaller streams and rivers, and generate less power than large Reservoir systems. They are rapidly gaining popularity due to their ease of installation and small ecological footprint.
Streaming (Run of River) Hydroelectric Projects In contrast to Reservoir designs, Streaming Hydro projects use a completely different approach. First, there is no dam or reservoir. Instead of a dam, Streaming Hydro systems use a diversion to channel some of the water from a stream into a pipe that supplies the water turbine. The rest of the stream water continues past the diversion down its natural path.
How Streaming Hydro Works
The diverted water flows down a pipeline (known as a penstock), passing through a turbine to generate electricity, and then recombining with the original stream. As we discussed earlier, this pipeline is used to contain the water to build high pressure at the bottom where it enters the turbine.
In effect, Streaming Hydro systems “borrow” a portion of the stream’s water to produce power, returning it to the stream after the energy is extracted. Unlike the Reservoir system, Streaming Hydro does not change the natural course of the stream or store water for future use.
This creates a couple of disadvantages. First, without a reservoir there is no reserve capacity for peak load periods. Second, because not all the water from the stream is being used to generate electricity, the output of the hydroelectric system is less than it could be with a Reservoir system.
Streaming Hydro Advantages
But Streaming Hydro has many advantages. First, these systems help resolve the two major disadvantages of the Reservoir system: fish migration and flooding. The stream still flows in parallel with the hydro system, providing an unencumbered path for fish migration. And since there is no reservoir, habitat flooding is not an issue.
Another example of a Streaming Hydroelectric powerhouse. Notice the pipeline feeding into the the rear of the powerhouse.
Because most Streaming Hydro systems are smaller – typically less than 30 megawatts – they occupy very little space and tend to blend into the environment. This makes them ideal for smaller streams and rivers where a Reservoir system wouldn’t be appropriate. A side benefit is that transmission lines are much shorter; in fact, they often reduce transmission losses by providing locally generated power instead of requiring lines from large generating plants that may be hundreds of miles away. These are important considerations today, as potential sites for large reservoir systems are extremely limited. There are thousands of smaller streams that could be used for Streaming Hydro with minimal visual and environmental impact.
- Contrasting Reservoir and Streaming Hydro
Both Reservoir and Streaming Hydro systems use moving water to produce electricity. The two types of hydro systems are designed much differently, however, and each approach has its own advantages and disadvantages. In our next segment of the Hydropower Tour, we’ll examine each approach in more detail and contrast the differences.
[edit] Environmental Considerations
How Energy Impacts our Environment
Every time we use energy, we impact the environment.
It’s been said there is no such thing as clean energy, which is not far from the truth. If we burn any number of different fuels, we produce pollutants and lots of CO2. Solar PV panels – a shining (sorry) example of “green energy” – rely on a manufacturing process that consumes considerable amounts of energy and throws off toxic silicon tetrachloride waste. Wind and water, both excellent renewable energy sources, carry their own environmental footprints. We won’t even go into fossil fuels and nuclear power. Face it: every time we use solar, wind, water, nuclear, coal or any other energy resource, we alter our environment.
When you think about it, the simple act of eating an energy-packed apple interrupts the natural return of nutrients to the earth and forces us to produce, shall we say, toxic waste. So we find ourselves in a bit a quandary. We must consume energy. At the very least, we must feed our bodies, keep warm, and get from place to place. Then come the non-essentials, where even the most environmentally conscious of us consume energy for things we don’t absolutely need – such as reading this web page. Okay, but we still want to protect our environment. What do we do?
Comparing Energy Sources for Electricity
By itself, electricity is an exceptionally clean form of energy – but we have to consider how it is generated. Today, about 70% of U.S. electricity is produced from fossil fuels (about 50% from coal, and 20% from natural gas). Nuclear power accounts for another 20%, leaving about 10% coming from renewable resources like wind, water and solar. The result of this mix is that electricity generation is currently the largest source of energy-related CO2 emissions in the United States.
The top blue line shows the total amount of electricity generated in the Untied States over the course of a year. Individual lines below show the amount generated by various energy sources. Source: U.S. Energy Information Administration
Evaluating Environmental Impact
Each method of generating electricity has advantages and disadvantages, as well as significantly different effects on the environment. The chart below helps illustrate the differences between the various energy sources used to generate electricity:
[edit] Where Hydropower Fits In
Like all energy sources, hydropower projects have an impact on the environment. Comparing hydropower with the alternatives, however, helps put it in perspective.
As with wind and solar power, hydropower is fully renewable, 100% clean, green energy. It consumes no natural resources, produces no emissions, and creates no waste. It is not our objective here to talk you out of solar and wind as viable energy sources; they play important roles in our energy future. But when the wind stops blowing and the sun goes down, hydropower systems continue to generate electricity. And, unlike solar and wind systems, hydropower projects have repeatedly paid for themselves without requiring government subsidies. Hydropower is the most efficient means we know of to convert energy into electricity. Typically 85%-95% of the energy in water is converted to electricity, compared to 15%-20% for PV solar, 35%-45% for wind, and 30%-45% for coal. Combined with an ongoing fuel cost of zero, it becomes clear why hydropower is the least expensive technology for generating electricity today.
In other words, hydroelectricity is an extremely efficient, clean, inexpensive way to produce electricity.
