Hydropower

Quick Facts

Hydropower is a renewable, efficient, and reliable source of energy that does not directly emit greenhouse gases or other air pollutants and that can be scheduled to produce power as needed.
There are about 78,000 megawatts of hydropower generation capacity in the United States.
Depending on water availability, hydroelectricity provides 5 to 10 percent of the electricity used in the United States and 70 percent of the electricity from all renewable sources.
More than half of the total U.S. hydroelectric capacity for electricity generation is concentrated in three western states--Washington, California and Oregon--with approximately 27 percent in Washington alone. Canada is a major electricity supplier to New York, New England, the Upper Midwest, the Pacific Northwest, and California.
Only about 3 percent of the roughly 79,000 dams in the United States have hydropower plants and can generate electricity.
Existing hydropower is very inexpensive to operate (generation costs 2 to 4 cents per kilowatt-hour) and the levelized cost of electricity from new hydropower puts it among the least expensive forms of low-carbon electricity.
The effects of climate change on water availability are expected to affect hydropower generation.

Background

Hydropower, or hydroelectricity, is electricity generated by the force of moving water in the penstock¹ of a hydropower unit. Turbines are used to capture the kinetic energy of water by converting it to electricity as the falling water spins the turbine. Hydropower plants may be located below reservoirs or built in rivers (run-of-the-river units) with no water storage capacity. Hydropower is considered a renewable source of energy, as it relies on water which is continuously renewed through the natural water cycle.

Hydroelectricity’s low cost, near-zero emissions, and ability to be dispatched quickly to meet peak electricity demand have made it one of the most valuable renewable energy sources worldwide. Hydropower accounts for about 17 percent of the world’s total electricity generation.²

Depending on water availability and annual precipitation, hydroelectricity has provided 6 to 9 percent of the electricity used in the United States in the last ten years and is the largest renewable source of electricity in the United States.^3,4 U.S. hydropower generation accounts for 10 and 1.5 percent of global hydropower and electricity generation, respectively.⁵

Description

The amount of electricity generated by a hydropower facility depends on three factors: 1) the turbine generating capacity; 2) the turbine discharge flow (the volume of water passing through the turbine in a given amount of time), and 3) the site head (the height of the water source or vertical distance between the highest point of water source and the turbine). The higher the head, the more gravitational energy the water has as it passes through the turbine. Most existing hydropower facilities in the United States can convert about 90 percent of the energy of falling water into electricity, which makes hydropower a technically efficient source of energy.

U.S. hydropower plants are very diverse. They might be located at dams with various storage capacities or be run-of-the-river facilities with no water storage capacity. Their elevation also varies. Only 3 percent of the dams in the United States have hydropower plants and can generate electricity.

Generally, based on the head and storage capacity availability, hydropower plants are categorized as follows:
- Low-Head High-Storage Hydropower Plants
  These facilities are usually located behind multi-purpose (water supply, flood control, etc.) dams which have hydropower generation as an ancillary benefit. The reservoirs associated with these units are large (high storage capacity) while the head is relatively low at these facilities.
- High-Head Low-Storage Hydropower Plants
  These facilities are often located behind reservoirs which have hydropower generation as their single objective. The reservoirs associated with these units are small (low storage capacity) while the head is relatively high. These units are usually located at higher elevations.
- Run-of-the-River Hydropower Plants
  These facilities are usually built on rivers with steady natural flows or regulated flows discharged from upstream reservoirs. These units have little or no storage capacity, and hydropower is generated using the river flow and water head. Run-of-the-river hydropower plants are less appropriate for rivers with large seasonal fluctuations.
- Pumped-Storage Hydropower Plants
  At these facilities water is stored in a lower reservoir after it is released from an upper reservoir to drive the turbine and generate power. Later, water is pumped back to the upper reservoir for reuse. Pumping water back to the upper pool requires energy (electricity). Pumped-storage systems are considered as flexible sources of electricity generation. These units generate electricity when demand and price are higher (during peak hours) and pump water back to the upper pools when electricity demand and price are lower. Pumped-storage plants are not net energy producers; rather, they provide energy storage and electricity at its peak demand times (see Energy Storage factsheet).
Hydropower plants can also be categorized based on their capacities:
- Large Conventional Hydropower plants
  These facilities have a generation capacity of more than 30 megawatts. The installed large hydropower capacity in the U.S. is approximately 66,500 megawatts.⁶
- Small Conventional Hydropower plants
  These facilities have a generation capacity of 1 to 30 megawatts. The installed small hydropower capacity in the U.S. is approximated as 8,000 megawatts.⁷
- Low Power Hydropower Plants
  These facilities have a generation capacity of 100 kilowatts to 30 megawatts. The installed low power hydropower capacity in the U.S. is approximated as 350 megawatts.⁸
- Micro Hydropower Plants
  These facilities have a generation capacity of less than 100 kilowatts.⁹

Electricity demand fluctuates during the day and between months depending on different factors, most importantly the hour of the day and temperature. One of the advantages of hydropower over other sources of electricity (e.g., variable wind and solar power or baseload coal and nuclear plants) is its generation flexibility. Such flexibility enables hydropower to meet sudden fluctuations in demand or help to compensate for the loss of power from other sources. Hydropower can be used for both baseload and peak generation.

Environmental Benefit/Emission Reduction Potential

Hydropower is a clean source of energy, as it burns no fuel and does not produce greenhouse gas (GHG) emissions, other pollutants, or wastes associated with fossil fuels or nuclear power. However, hydropower does cause indirect GHG emissions, mainly during the construction and flooding of the reservoirs. This may be due to decomposition of a fraction of the flooded biomass (forests, peatlands, and other soil types) and an increase in the aquatic wildlife and vegetation in the reservoir.¹⁰ Hydropower’s GHG emissions factor (4 to 18 grams CO₂ equivalent per kilowatt-hour^11,12,13,14) is 36 to 167 times lower than the emissions produced by electricity generation from fossil fuels.^15,16 Compared to other renewables, on a lifecycle basis hydropower releases fewer GHG emissions than electricity generation from biomass and solar and about the same as emissions from wind, nuclear, and geothermal plants.¹⁷

Hydropower is mainly criticized for its negative environmental impacts on local ecosystems and habitats. Damming a river alters its natural flow regime and temperature, which in turn changes the aquatic habitat. Such a change disturbs the river’s natural flora and fauna. Fish are very sensitive to hydropower operations, and fish species (especially migratory species) have been significantly affected by hydropower dams across the United States. Small, low and micro hydropower facilities have much smaller negative environmental impacts than large hydropower facilities, but even they can engender public concern.^18,19

Studies have estimated significant potential for increased deployment of hydropower in the United States, with estimated incremental potential generation capacities from 81,000 to 217,000 megawatts, provided through development of new small, low, and micro hydroelectric plants (accounting for 60,000 to 180,000 megawatts), development of new hydroelectric capacity at existing dams without hydropower facilities (17,000 to 30,000 megawatts), and generation efficiency improvements at existing facilities (4,000 to 7,000 megawatts).²⁰ Fully realizing the aforementioned low or high estimates of new hydropower potential might reduce or avoid CO₂ emissions from electricity generation equal to roughly 8 to 25 percent of total current U.S. CO₂ emissions from electricity generation.²¹ In its recent modeling analysis of the 2009 climate and energy bill passed by the United States House of Representatives (H.R. 2454, the American Clean Energy and Security Act, or Waxman-Markey bill, which includes a GHG cap-and-trade program), the U.S. Energy Information Administration (EIA) projected that a carbon price would lead to more rapid growth of U.S. hydropower generation than under “business-as-usual” but that hydropower would grow considerably more slowly than other renewable electricity generation technologies (notably wind and biopower), accounting for only 8 percent of the growth in renewable electricity generation from 2009 to 2030.²²

A 2008 report from the International Energy Agency (IEA) projected that global hydropower production might grow by nearly 60 percent from 2005 to 2050 under “business-as-usual” but that it could grow by roughly 80 percent over the same period in a scenario with aggressive action to reduce GHG emissions. However, even under this latter scenario, increased hydropower generation is projected to provide only about 2 percent of the total GHG emission reductions from the global electric power sector compared to “business-as-usual” by 2050 (with all renewable technologies nonetheless providing nearly 40 percent of GHG abatement from the power sector).²³ According to IEA, a realistic potential for global hydropower is 2 to 3 times higher than the current production, with most remaining development potential in Africa, Asia, and Latin America.²⁴ IEA also notes that, while small hydropower plants could provide as much as 150 to 200 GW of new generating capacity worldwide, only 5 percent of the world’s small-scale (i.e. small, low, and hydro) hydropower potential has yet been exploited.²⁵

Cost

Existing hydropower is one of the least expensive sources of power since the cost of hydropower is dominated by the initial capital cost of building the facility while the ongoing operating and maintenance (variable) costs are low. Moreover, since hydropower generation does not require burning fuels, operations costs are not vulnerable to fuel price fluctuations. Existing hydropower facilities are very cheap to operate and they can operate for 50 years or more without major replacement.²⁶ The cost of hydropower is highly site-specific and depends on different factors, including hydrologic characteristics, site accessibility, and distance from transmission. A recent study of the cost of new renewable electricity generation in the western United States (where much of the potential for new U.S. hydropower is located) estimated the levelized cost of incremental hydropower at existing dams to be $0.01 to $0.10 per kilowatt-hour (kWh) and the levelized cost of new small and micro hydropower to be between $0.06 and $0.14 per kWh, making incremental hydropower the least expensive option for new renewable generation and new hydropower roughly on par with new wind and biopower.²⁷

Current Status of Hydropower

The first U.S. hydropower facility was built in 1879 in Niagara Falls, and many more hydropower plants were installed in the following decades. By the 1940s many suitable large sites for hydroelectric generation were developed and hydropower provided 33 percent of electricity generation in the U.S.²⁸ At present, there are about 78,000 megawatts of hydropower generating capacity in the United States, enough to supply 29 million households with electricity.²⁹ Pumped-storage facilities add up to 21,000 megawatts of that amount.³⁰ More than half of the total U.S. hydroelectric capacity for electricity generation is concentrated in three western states-- Washington, California and Oregon--with approximately 27 percent in Washington alone.³¹ There are nearly 2,400 hydropower facilities in the United States, although the United States has roughly 79,000 dams.^32,33 In the past 10 years, hydropower has provided between 6 and 9 percent of total U.S. electricity, and, in 2008, hydropower accounted for nearly 70 percent of all renewable electricity generated in the United States.³⁴ The United States has constructed very few new large dams since the early 1980s owing to concerns over their negative impacts on rivers, and the construction of new large hydropower dams is not considered a practical option for increasing hydropower generation due to the environmental impacts and unavailability of proper sites to develop for large-scale hydropower generation.³⁵

The U.S. Army Corps of Engineers is the largest hydropower operator in the country, running 75 plants with a total installed capacity of 20,474 megawatts (26 percent of nationwide capacity). These federal plants produce about 100 billion kilowatt-hours a year, nearly a third of the nation’s total hydropower output, or enough to serve about ten million households.³⁶ The privately owned dams in the United States which generate hydroelectric power are under the regulatory authority of the Federal Energy Regulatory Commission (FERC). FERC issues licenses for legal operation of hydropower dams to permit the dam owner to use public waters for hydropower generation. FERC licenses are renewed every 30 to 50 years. License renewal is an opportunity to balance the hydropower benefits against the negative effects of hydropower generation on the health of aquatic and riparian ecosystems.³⁷

Currently, 808,000 megawatts of hydropower generation capacity are in operation or under construction around the world.³⁸ Globally, hydropower accounts for about 17 percent of total electricity generation and nearly 90 percent of renewable electricity generation.^39,40 As regions, Central and South America generate nearly 70 percent of their electricity from hydropower, and many countries, including several large countries such as Canada and Brazil, rely on hydropower for more than half of their electricity.⁴¹ China currently obtains about 17 percent of its electricity from hydropower; from 1990 to 2006, Chinese hydropower generation grew at a compound annual growth rate of 8 percent (compared to 1.5 percent for the rest of the world), with the increase in Chinese hydropower generation over this period accounting for 36 percent of the global increase in hydropower generation.⁴²

Obstacles to Further Development or Deployment of Hydropower

Unavailability of Proper Sites for New Large Hydro Facilities
The best sites for large hydropower generation in the United States have already been developed, and developing new sites for hydropower generation without negative ecological and recreational impacts is challenging. Storage and generation capacity expansions at existing hydropower sites or adding hydropower generation to reservoirs with existing dams that currently lack hydroelectricity generation is more likely.
Regulatory Hurdles
Hydropower is the most heavily regulated electricity generating technology after nuclear power, with regulatory requirements that may be time-consuming, expensive, and redundant as well as tailored to past experience with large hydropower projects, despite the likelihood that small-scale and incremental hydropower will be most important for future U.S. hydropower growth.⁴³
Environmental Tradeoffs
There is a tradeoff between the GHG avoidance or reduction benefits of hydropower and other environmental impacts. Increasing hydropower generation can have negative ecological and recreational impacts. For example, FERC, in an effort to protect riverine ecosystems, has often mandated reduced hydropower production levels under hydropower licenses.⁴⁴
Climate Change
Climate change and the alteration of rainfall and temperature regimes can affect hydropower generation. Hydropower systems with less storage capacities are more vulnerable to climate change, as storage capacity provides more flexibility in operations. Although hydropower systems may benefit from more storage and generation capacity, expansion of such capacities may not be economically and environmentally justified.⁴⁵

Policy Options to Help Promote Hydropower

Price on Carbon
A price on carbon, such as that which would exist under a GHG cap-and-trade program (see Climate Change 101: Cap and Trade), would raise the cost of electricity produced from fossil fuels relative to the cost of electricity from renewable sources, such as hydropower, and other low carbon technologies.
Renewable Electricity Standards
Renewable electricity standards (renewable portfolio standards) require electricity providers to gradually increase the amount of renewable energy resources—such as wind, solar, bioenergy, and geothermal—in their electricity supplies, until they reach a specified target by a specified date.⁴⁶ The hydropower production growth under these standards is mostly provided through development of small-scale hydropower and this growth is considerably slower than increase in electricity generation from other renewable sources.
Economic Incentives
Different financial incentives (e.g. tax credit bonds, production tax credit, incentive payments⁴⁷) are provided to encourage the growth of hydropower generation, improving efficiency at existing projects, and more reliance on renewable electricity sources in the United States.
R&D Efforts
R&D efforts are required to improve efficiencies, reduce costs and negative environmental impacts, and improve reliability and durability of hydropower technologies. Integration of hydropower systems with other renewable sources (developing hybrid systems) of electricity generation are recommended. There is a need for further R&D to improve equipment designs, investigate different materials, improve control systems, and optimize generation as part of integrated water-management systems.⁴⁸
Hydropower generation is an ancillary benefit of most dams that currently have it. Absence of reliable hydrological forecasts may result in needlessly foregone hydropower. For instance, a reservoir may be emptied to minimize the flood risks and ensure that flooding does not occur. In that case minimizing flood risks results in loss of hydropower benefits. R&D efforts are required for improving the meteorological and hydrological forecasting abilities for better performance of hydropower systems.
Adaptive FERC Licenses
FERC licenses are issued for periods of 30 to 50 years. Hydrological and ecological changes of hydropower systems during this period may require changes in the license requirements to increase the hydropower and environmental benefits. Adaptive FERC licenses may help to avoid the need to change license requirements and improve the performance of hydropower systems.⁴⁹

Related Business Environmental Leadership Council (BELC) Company Activities

Related Pew Center Resources

Climate Change 101: Technological Solutions, 2009.

Race to the Top: The Expanding Role of U.S. State Renewable Portfolio Standards, 2006

The U.S. Electric Power Sector and Climate Change Mitigation, 2005.

Further Reading/Additional Resources

Aspen Environmental Group and M. Cubed (2005); “Potential changes in hydropower production from global climate change in California and the western United States”. California Climate Change Center, CEC-700-2005-010, June 2005.

Casola, J. H., Kay J. E., Snover A. K., Norheim R.A., Whitely Binder L. C., the Climate Impacts Group (2005), “Climate Impacts on Washington’s Hydropower, Water Supply, Forests, Fish, and Agriculture”, Center for Science in the Earth System, Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle.

Electric Power Research Institute (EPRI) (2007), Assessment of Waterpower Potential and Development Needs.

Energy Information Administration, World Electricity Data (Official Energy Statistics from the U.S. Government).

European Commission (2000) 1999 annual energy review, Energy in Europe special issue—January 2000, Directorate-General for Energy, Brussels, ISBN 92-828-7448-6.

Hall D. G. and K. Reeves (2006) A Study of United States Hydroelectric Plant Ownership, Report prepared for the National Renewable Energy Laboratory, Idaho National Laboratory, INL/EXT-06-11519.

Idaho National Laboratory, Hydropower Program.

IEA (2008) Energy Technology Perspectives, Scenarios and Strategies to 2050, In support of the G8 Plan of Action, Chapter 12 (pp. 387-391).

International Hydropower Association

Kosnik L. (2008), “The Potential of Water Power in the Fight against Global Warming in the US”, Energy Policy (36): 3252-3265.

Low Impact Hydropower Institute

Madani K., Lund J. R. (in review) "Estimated Impacts of Climate Warming on California’s High-Elevation Hydropower", Climatic Change.

Miles, E. L., Snover, A. K., Hamlet, A. F., Callahan, B., Fluharty D. (2000), “Pacific Northwest Regional Assessment: The Impacts of Climate Variability and Climate Change on the Water resources of the Columbia River Basin”, Journal of the American Water Resources Association, 36(2): 399-420.

National Energy Education and Development Project (2008) Hydropower, Secondary Info Book, pp. 24-27.

National Hydropower Association

U.S. Army Corps of Engineers (2009) Hydropower; Value to the Nation.

U.S. Department of Energy, Wind and Hydropower Technologies Program Website, Hydropower.

Wilbanks T. J., T. Bhatt, D. E. Bilello, S. R. Bull, J. Ekmann, W. C. Horak, Y. J. Huang, M. D. Levine, M. J. Sale, D. K. Schmalzer, and M. J. Scott (2007) Effects of Climate Change on Energy Production and Use in the United States, Synthesis and Assessment Product 4.5, Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research, October 2007.

World Bank Group (2009), Directions in Hydropower

¹ A penstock is an intake structure or enclosed pipe that that delivers water to turbines.
² U.S. Energy Information Administration (EIA) (2005) World Net Electricity Generation by Type, Table 6.3.
³ National Energy Education and Development Project (2008) Hydropower, Secondary Info Book, pp. 24-27.
⁴ Wilbanks T. J., T. Bhatt, D. E. Bilello, S. R. Bull, J. Ekmann, W. C. Horak, Y. J. Huang, M. D. Levine, M. J. Sale, D. K. Schmalzer, and M. J. Scott (2007) Effects of Climate Change on Energy Production and Use in the United States, Synthesis and Assessment Product 4.5, Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research, October 2007.
⁵ EIA (2005) World Net Electricity Generation by Type, Table 6.3.
⁶ Electric Power Research Institute (EPRI) (2007), Assessment of Waterpower Potential and Development Needs.
⁷ EPRI, 2007.
⁸ EPRI, 2007.
⁹ EPRI, 2007.
¹⁰ Hydro Quebec (2009) Greenhouse Gas Emissions and Hydroelectric Reservoirs.
¹¹ Tremblay A., Varfalvy L., Roehm C. and Garneau M., The Issue of Greenhouse Gases from Hydroelectric Reservoirs: From Boreal to Tropical Regions, Table 1, p. 3.
¹² Meier P. J. (2002) Life-Cycle Assessment of Electricity Generation Systems and Applications for Climate Change Policy Analysis, Ph.D. Dissertation, University of Wisconsin, Madison.
¹³ Van de Vate, J. F. (2002) Full-energy-chain greenhouse-gas emissions: a comparison between nuclear power, hydropower, solar power and wind power, International Journal of Risk Assessment and Management, Vol. 3, No.1 pp. 59-74.
¹⁴ Gapnon L. and Van de Vate, J. F. (1997) Greenhouse gas emissions from hydropower: The state of research in 1996, Energy Policy, Vol. 25, No.1, pp. 7-18.
¹⁵ Tremblay et al. GHG emissions from reservoir flooding are higher in tropical areas, and in other regions reservoirs older than 10 years produce GHG emissions similar to natural lakes.
¹⁶ Van de Vate, 2002. Run-of-the-river systems produce less GHG emissions (5 to 10 g CO2 equivalent per kilowatt-hour) due to absence of reservoirs.
¹⁷ Meier P. J. (2002) Life-Cycle Assessment of Electricity Generation Systems and Applications for Climate Change Policy Analysis, Ph.D. Dissertation, University of Wisconsin, Madison.
¹⁸ Kosnik, L-R (2008a), “The Potential of Water Power in the Fight against Global Warming in the U.S.,” Energy Policy (36): 3252-3265.
¹⁹ Carlton, Jim, “Deep in the Wilderness, Power Companies Wade In,” Wall Street Journal, 21 August 2009.
²⁰ Meier P. J. (2002) Life-Cycle Assessment of Electricity Generation Systems and Applications for Climate Change Policy Analysis, Ph.D. Dissertation, University of Wisconsin, Madison.
²¹ Kosnik L-R (2008a).
²² EIA, Energy Market and Economic Impacts of H.R. 2454, the American Clean Energy and Security Act of 2009, August 2009.
²³ IEA (2008) Energy Technology Perspectives, Scenarios and Strategies to 2050, In support of the G8 Plan of Action.
²⁴ IEA, 2008.
²⁵ IEA, 2008.
²⁶ IEA, 2008.
²⁷ Black & Veatch, Renewable Energy Transmission Initiative Phase 1a Final Report, April 2008.
²⁸ National Energy Education and Development Project (2008) Hydropower, Secondary Info Book, pp. 24-27.
²⁹ EIA (2005) World Hydroelectricity Installed Capacity, Table 6.4h.
³⁰ EPRI, 2007.
³¹EIA (2005) Renewable Energy Trends 2004, Table 18, Renewable Electric Power Sector Net Generation by Energy Source and State, 2003, Energy Information Administration, Washington, DC.
³² Hall D. G. and K. Reeves (2006) A Study of United States Hydroelectric Plant Ownership, Report prepared for the National Renewable Energy Laboratory, Idaho National Laboratory, INL/EXT-06-11519.
³³ U.S. Army Corps of Engineers, National Inventory of Dams.
³⁴ EIA, Annual Energy Review 2008, Table 8.2a.
³⁵ Kosnik L-R (2008a).
³⁶ U.S. Army Corps of Engineers (2009) Hydropower; Value to the Nation.
³⁷ Madani K (2009) Climate Change Effects on High-Elevation Hydropower System in California, Ph.D. Dissertation, University of California - Davis.
³⁸ IEA, 2008.
³⁹ EIA, International Energy Annual 2006, Table 6.3.
⁴⁰ IEA (2008) Energy Technology Perspectives, Scenarios and Strategies to 2050, In support of the G8 Plan of Action.
⁴¹ EIA, International Energy Annual 2006, Table 6.3.
⁴² EIA, International Energy Annual 2006, Table 2.6.
⁴³ Kosnik L-R (2008b), “Consolidation & ownership trends of nonfederal hydropower generating assets”, 1980–2003. Energy Economics 30 (3), 715–731.
⁴⁴ Kosnik L-R (2008b).
⁴⁵ Madani K., Lund J. R. (in review) "Estimated Impacts of Climate Warming on California’s High-Elevation Hydropower", Climatic Change.
⁴⁶ Union of Concerned Scientists.
⁴⁷ For details on financial incentives see http://www.hydro.org/hydrofacts/backgrounders.php.
⁴⁸ IEA, 2008.
⁴⁹ Madani K (2009) “Climate Change Effects on High-Elevation Hydropower System in California”, Ph.D. Dissertation, University of California - Davis.

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