Trystan Casey
The United States has over 2,100 operational hydroelectric dams, with locations in nearly every state. They play an essential role in their regional power grids, but most were built in the past century under a different climate than they face today. The amount of power generated each year from the nation's hydroelectric facilities varies depending on the water available in dams and rivers. Many reservoirs must balance power output with competing water demand for irrigation, municipal, industrial, and other needs, as well as fish migration.
| Characteristics | Values |
|---|---|
| Number of operational hydroelectric dams | Over 2,100 |
| Number of non-powered dams | Over 80,000 |
| Number of states with at least one hydroelectric power station | 48 |
| Number of states with no utility-scale hydroelectricity generating facilities | 2 (Delaware and Mississippi) |
| Average number of years a hydroelectric facility has been operating | 64 |
| Percentage of total capacity added in the last decade (2007-2016) that was conventional hydro | 1.7 GW out of nearly 200 GW (0.85%) |
| Number of states where half or more of in-state utility-scale generating capacity comes from hydroelectricity | 4 (Washington, Idaho, Oregon, and Vermont) |
| Percentage of power generation in the U.S. from conventional hydroelectric generators | 6-7% |
| Percentage of hydroelectricity generation that could be added by the top 100 NPDs | 15% |
| Number of megawatts of pumped storage generating capacity in the U.S. in 2009 | 21.5 GW |
| Percentage of baseload generating capacity that was pumped storage in 2009 | 2.5% |
| Percentage of 2008 hydroelectricity generation that could be generated by harnessing the currently unpowered dams | 16% |
| Number of megawatts of potential hydroelectricity capacity in the U.S. across 80,000 unpowered dams | Over 12,000 MW |
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What You'll Learn
The US has over 2,100 hydro-electric dams
The United States has over 2,100 hydro-electric dams, with locations in nearly every state. They play an essential role in their regional power grids, and hydropower contributes about 6% to 7% of all power generation in the U.S. Hydropower is a crucial resource for managing the U.S. electric grids due to its ability to be quickly turned on and off, helping to control minute-to-minute supply and demand changes.
The first hydroelectric power station in the United States was the Hoover Dam in Arizona and Nevada, which began operating in 1936 and had a capacity of at least 1,000 MW. Since then, numerous other hydroelectric power stations have surpassed the 1,000 MW threshold, often through the expansion of existing facilities. Hydropower facilities range in size from large power plants that supply electricity to many consumers, to small or even 'micro' plants that are operated by individuals for their own energy needs or to sell power to utilities.
Although the U.S. has a large number of hydro-electric dams, it is important to note that not all dams were built for hydropower. Of the more than 90,000 dams in the United States, less than 3% produce power. The other dams are used for recreation, stock/farm ponds, flood control, water supply, and irrigation. There are also over 80,000 non-powered dams (NPDs) in the U.S. that could be converted to hydroelectric dams, adding significant power generation capacity.
The future of hydropower in the U.S. is uncertain due to changing climate conditions and increasing competition for water resources. Climate change will impact how hydropower plants are used and managed, and droughts and increased agricultural water use can lead to generation limits. However, the importance of hydropower across the U.S. power grid means that most dams are likely to remain in place, and repowering old stations has already increased the capacity of several facilities.
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Only 3% of 90,000+ US dams produce power
The United States has over 90,000 dams, but only 3% of them support hydroelectric generators. These generators have a total hydroelectric capacity of nearly 80,000 MW as of February 2019. The remaining 97% of dams are used for recreation, stock/farm ponds, flood control, water supply, and irrigation. Hydropower plants vary in size, from small systems that can power a single home, to large projects that produce electricity for utilities. The most common type of hydroelectric power plant is an impoundment facility, which uses a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it and activating a generator to produce electricity.
The Hoover Dam, the Grand Coulee Dam, and the Tennessee Valley Authority are iconic large construction projects that have contributed significantly to hydroelectric power in the United States. Despite their impact, environmental concerns have led to a shift in perception regarding large hydroelectric facilities. California, for instance, does not consider power generated from such facilities as "renewable" due to their ecological impact. This has resulted in electricity generated from these sources not counting toward California's Renewable Portfolio Standards.
The recognition of environmental issues associated with dams has led to the removal of some older and smaller structures and the installation of fish ladders in others. The enormous Rampart Dam project was cancelled in 1967 due to environmental and economic concerns. Instead of constructing new dams, efforts have been made to repower old stations, increasing their capacity. The Hoover Dam, for example, replaced its generators between 1986 and 1993. Additionally, seasonal drawdowns at some dams are implemented to address ecological needs, such as eliminating invasive species and sedimentation, which can impact water availability for power generation.
Despite the potential for increased hydroelectric capacity, the expansion of hydropower retrofits faces challenges. While companies are willing to invest in infrastructure and technology, the regulatory and relicensing processes can be cumbersome. The United States Congress passed the America's Water Infrastructure Act of 2018 to support the development of new hydroelectric resources. However, the slow progress in hydropower expansion and the concurrent momentum behind dam removal initiatives have raised questions about the perceived opposition between these two efforts.
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California doesn't consider large hydro-electric facilities as renewable
There are over 80,000 non-powered dams in the United States, with less than 3% of all dams in the country producing power. The US has a nameplate capacity of at least 100 MW, with the Hoover Dam in Arizona and Nevada being the first dam to surpass 1,000 MW upon its completion in 1936. Several other dams have since exceeded this threshold, often through the expansion of existing hydroelectric facilities.
Hydropower is critical to California's clean energy goals. The state is the fourth-largest hydro producer in the US, with 386 hydro facilities that produce 10,890,000 megawatt-hours of net electricity generation annually, representing 13% of its total renewable energy. However, California does not consider power generated from large hydroelectric facilities (those with a capacity of more than 30 megawatts) as meeting its strictest definition of "renewable". This is due to concerns over the environmental impact of large hydroelectric projects, such as their significant impact on the power sector, water use, river flow, and other ecological factors.
As a result, electricity generated from large hydroelectric facilities does not count toward California's strict Renewable Portfolio Standards, even though other states recognize water as a renewable resource in the hydrological cycle. Approximately 10 to 15% of California's energy generation comes from large hydroelectric generation that is not eligible for the state's Renewable Portfolio Standards.
California's decision to exclude large hydroelectric facilities from its definition of renewable energy highlights the complexities of transitioning to clean energy sources. While hydropower is widely considered a clean and renewable energy source, the state's approach underscores the need to balance energy production with potential environmental consequences.
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The importance of hydropower means most dams will remain
The United States has over 90,000 dams, but less than 3% of them produce power. Despite the low percentage, the importance of hydropower means most dams will likely remain. Hydropower is a renewable source of energy that offers a range of benefits to the communities they serve.
Firstly, hydropower is fuelled by water, a renewable resource, and is thus more reliable and affordable than fossil fuels. Unlike other energy sources, hydropower does not pollute the air, making it a clean fuel source. Secondly, hydropower is a domestic source of energy, allowing each state to produce its own energy without relying on international fuel sources. This reduces the need for international fuel transportation, which has a positive environmental impact.
Hydropower facilities range in size from large power plants that supply electricity to many consumers, to small and even 'micro' plants that are operated by individuals for their energy needs or to sell power to utilities. Small and micro hydropower plants can produce enough electricity for a single home, farm, ranch, or village. This flexibility in size means that hydropower plants can be constructed in rural areas, boosting local economies.
Hydropower also provides benefits beyond electricity generation. For instance, most hydropower installations are required to provide some level of public access to the reservoirs they create, which offer recreational opportunities such as fishing, swimming, and boating. Additionally, hydropower provides flood control, irrigation support, and clean drinking water.
The importance of hydropower as a renewable, domestic, flexible, and affordable energy source, as well as its benefits beyond electricity generation, means that most hydropower dams will likely remain. However, it is important to note that the construction and presence of hydropower dams can have negative environmental and ecological impacts, such as altering downstream water flow and flooding large areas of land.
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Hydropower contributes 6-7% of US power generation
Hydropower is a significant source of electricity generation in the United States, contributing approximately 6-7% of the country's power generation. This percentage translates to about 274 terawatt-hours (TWh) of electricity generated through hydropower in 2019, accounting for 38% of electricity from renewable sources. The United States has the third-largest hydropower fleet in the world, and its importance in the energy mix is notable.
The contribution of hydropower to the US energy landscape varies across different states. Washington, California, and Oregon account for about half of the total US utility-scale conventional hydroelectricity-generation capacity. Washington, home to the Grand Coulee Dam, leads the nation in hydroelectric power generation. East of the Mississippi River, New York stands out for its hydroelectric power capabilities.
Hydropower's flexibility and reliability are crucial in a changing US generation mix that increasingly incorporates variable renewable resources like wind and solar power. Hydropower plants come in various sizes, from large power plants supplying many consumers to small or even 'micro' plants meeting the energy needs of individuals or small communities. The most common type of hydroelectric power plant is an impoundment facility, which uses a dam to store river water in a reservoir.
While the number of hydropower plants has grown, the availability factors have decreased over the last decade, impacting new hydropower development and increasing maintenance costs for ageing infrastructure. Additionally, environmental concerns have led to the removal of some older and smaller dams, and policies specific to hydropower are necessary to address these issues. Despite these challenges, the US hydropower market is evolving, with a focus on optimising existing assets and constructing new projects.
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Frequently asked questions
There are over 2,100 operational hydroelectric dams in the United States, with locations in nearly every state.
Less than 3% of the 90,000 dams in the US produce power.
Some of the most well-known hydroelectric power stations in the US include the Hoover Dam, Grand Coulee Dam, and the Tennessee Valley Authority.
Hydropower contributes about 6% to 7% of all power generation in the US.
