26 August 2011

Hydroelectric power

Hydroelectric power plants use the planet's hydrologic (water) cycle to create electricity.



General: Hydroelectric power plants use the planet's hydrologic (water) cycle to create electricity.

Hydrologic cycle: The sun evaporates water from lakes and oceans. This water vapor combines to form clouds, which create precipitation that falls as rain or snow. Rain and water from melting snow flows back to the ocean through various streams and river systems. Hydropower facilities that are strategically placed next to rivers or other water sources are able to use this continually-renewable water source to generate electricity.

Hydroelectric power generation: Water at the hydropower facility is released or diverted from its source and falls naturally through the force of gravity. As the water falls, it strikes the blades of one or more turbines. A turbine is a piece of machinery that changes the energy of the falling water (kinetic energy) into mechanical power. As the turbines' blades move, they turn a shaft that causes electromagnets to move past coils of copper in a generator. This movement creates an alternating current (AC), which is converted to higher-voltage current by a transformer. When this high-voltage current passes through the transformer, it is carried by transmission lines to households and businesses.

Hydroelectric power plant sizes: According to the U.S. Department of Energy (DOE), large hydroelectric plants have a generating capacity of more than 30 megawatts (MW). An example of a large facility is the Hoover Dam on the Arizona/Nevada border in the United States; it generates four billion kilowatts (kW) per year, enough electricity for 1.3 million people.

Small plants have a generating capacity that ranges from 100kW to 30MW. The Kensico Reservoir Project in Westchester County, NY, produces 3,000kW per year. It has only three turbines to generate power, compared to the 17 turbines located at the Hoover Dam.

Mini plants generate less than 2MW of electricity. A new mini-hydro plant at the Grasse River in Massena, New York, will create enough power for 2,500 homes in Massena.

Micro plants generate 100kW or less. These smallest hydroelectric plants produce enough electricity to power an individual home, ranch, or small village.

Types of hydroelectric facilities: An impoundment facility stores water in a dam and releases that water when needed, either to keep the water reservoir at a consistent height or to generate electricity to handle fluctuating energy needs. Impoundment plants are the most commonly-constructed type of hydropower facilities because they are able to produce electricity only when needed during times of peak demand.

A pumped-storage facility uses two reservoirs of water. During periods of low electricity demand, water is pumped from a lower reservoir to an upper water storage area. When there is a high demand for electricity, water is sent back to the lower reservoir, generating electric power during its travel.

A diversion facility channels a section of a river through a canal or penstock (a pipe that carries water directly to power-generating turbines). When water passes through the turbines, it is returned to the river. A diversion facility is also referred to as a run-of-river project. A dam is usually not required.

Scope of hydroelectric power worldwide: More than 60 countries around the world use hydropower to meet 50% or more of their needs for electricity.

The top-10 hydroelectric-generating countries are Canada, the United States, Brazil, China, Russia, Norway, Japan, India, Sweden, and France.

Future hydropower planning is expected to focus on undeveloped areas of Africa, South/Central America, and Asia.

Hydropower generates 19% of the world's electricity. The top electricity sources include coal (36%); nuclear power (18%), gas (13%), and oil (10%).

In 1995, hydroelectric power generated 22 times more electricity worldwide than the combined generating capacities of geothermal, solar, and wind powers.

There are twice as many pumped-storage facilities worldwide that are under construction or in the planning stages than there are in operation; 551 plants are being planned, 42 plants are under construction, and 290 plants around the world are currently in operation. In Japan alone, there are 440 possible sites for new pumped-storage facilities; eight sites are presently under construction and 38 plants are in use.

Micro-hydroelectric power plants are able to help developing nations improve their standards of living with minimal disruption to the environment. Vietnam, for example, has about 2,500 micro-hydroelectric facilities that generate power for 200,000 households. In Nepal, a million rural people who are unable to receive power from their national power grid are still able to access electricity due to mini/micro-sized hydropower facilities in their areas.

Organizations that support responsible hydropower development include: the International Hydropower Association (IHA); the Implementing Agreement on Hydropower Technologies and Programmes of the International Energy Agency (IEA/Hydro); the Canadian Hydropower Association (CHA); the International Commission on Large Dams (ICOLD); the Hangzhou [China] International Center on Small Hydro Power; the Norwegian Water Resource and Energy Administration's Water Resources Department (NVE); Hydro-Quebec; the U.S. Department of Energy's Energy Information Agency; the Idaho National Laboratory Hydropower Program; the World Energy Council; and the U.S. Department of the Interior Bureau of Reclamation.


Rudimentary hydropower was first used by the Greeks about 2,000 years ago to turn wheels that ground wheat into flour.

According to the Energy Information Agency at the U.S. Department of Energy, total worldwide energy use is expected to increase by 60% between 1997 and 2020, from 111,000 terawatt-hours (TWh) per year to 178,000TWh/year; a terawatt-hour is one trillion watt hours. Of this amount, electricity consumption is expected to grow the most from 12,000TWh in 1997, to a possible 22,000TWh in 2020; this is a 76% increase.

According to a study by the Utility Data Institute, in the next 10 years there may be a worldwide total increase of 695 gigawatts (GW, a billion watts) of newly-generated electricity. Hydropower is expected to create 22% of that capacity; 26% will likely come from gas, 27% will likely come from coal, and the remaining 25% will likely be generated by other sources. As of 2000, 700GW is already being generated worldwide.

The International Energy Agency states that Europe and North America lead the world in the development of hydropower: more than 60% of their possible hydroelectric facility locations have been developed. Emerging nations in Asia, South America, and Africa, however, still have unrealized hydropower potential. In Africa, for example, only seven percent of its possible hydroelectric resources have been developed.


General: Because hydroelectric power relies on water, it is a continuously renewable and sustainable resource; its supplies are replenished at the same speed at which they are used. Unlike power plants that burn fossils fuels for energy, hydropower does not pollute the air and is therefore considered a clean source of energy.

The environmental impact of impoundment hydropower plants may be significant. It is possible for large reservoirs of water created in these facilities to displace human populations, disrupt the migration and reproduction of fish, or flood surrounding areas.

There is also concern about the environmental impact of hydropower facilities overall, even though these plants produce few emissions. For example, the quality of water that flows downstream from a water plant may be reduced by the addition of sediment and turbidity, and by the amounts of methane included in the water from decomposing plants in flooded areas. If water is diverted from a river for use in the plant, it may also disrupt the downstream ecosystem by reducing the natural flow of the river.

Resettlement issues: The resettlement of people located near hydropower dam projects has been found to have devastating social and psychological impacts. In China, 86,000 dams have been built since 1949, with 12.5 million people forced to relocate. At least 1.4 million people have been moved due to the Three Gorges Dam Project alone. An unknown number of additional citizens have waited for years for resettlement orders to be issued, as their local dams progress through governmental planning stages. According to a 2007 study on the psychological stress of relocation due to the Three Gorges Project, the worry associated with future relocation may be a "robust" predictor of high stress levels. The study also showed that governmental compensation for people forced to relocate did not increase the citizens' feelings of well-being.

The 2008 resettlement of Vietnamese people due to the construction of the Dak Mi 4 Hydropower Project in Quang Nam Province has also led to considerable unrest. According to news reports from Saigon, relocated citizens were offered inadequate substitute housing with insufficient land for their farming needs.

According to a 1991 report on environmental projects in India, 1,589 large dams have been built since 1947, displacing 11 million people. Of those citizens, only 2.75 million have been rehabilitated (i.e., provided new homes and land), while more than eight million have not received assistance. Without access to traditional farm land, many have turned to alternate occupations in construction and migrant farm labor.

Hydropower projects and human disease: Hydropower and water management projects have been linked to the spread of disease. Schistosomiasis (also known as snail fever) is an illness caused by parasitic worms that are released by some species of freshwater snails. Schistosomiasis affects more than 200 million people worldwide, primarily in Africa, South America, Southeast Asia, the Middle East, and China. It is expected that the Three Gorges Dam Project will extend the range of snails carrying the parasite within the dam's reservoir area of Dongting Lake. The range extension is due to the dam-related increase in the lake's surface area, from 2,681 to 4,350 square kilometers.

According to a systematic literature review in 2005, there is concern about a possible increase in the transmission of malaria in endemic areas where hydropower impoundment reservoirs are located. The report concluded that malaria control measures should be mandatory in these endemic areas. In addition, it was suggested that future water projects include in-depth reviews of the possible human health effects of any upcoming construction.

Greenhouse gas emissions: There is some concern that greenhouse gas emissions from the reservoirs of hydropower facilities in tropical areas may negate the "green" image of this renewable power source. Studies by Fearnside at the National Institute for Research in the Amazon suggest that a hydropower plant in a tropical location may emit four times more carbon dioxide during its first 10 years of operation than an energy plant that is run on fossil fuels. This effect, according to Fearnside, occurs because of organic matter that is trapped at the bottom of the reservoir when the water storage facility is first created; as the organic matter decays over time, it creates and releases methane gas and carbon dioxide. Both of these byproducts of decay are greenhouse gases that contribute to global warming. Over a 100-year time frame, the warming impact of methane gas is 20 times greater than that of carbon dioxide.

There is also concern that methane gas may arise from reservoir water after it is released from a hydropower facility as the water travels downstream. Because tropical areas are still ripe for the future development of hydropower facilities (only 19% of South America's available hydroelectric generating potential has been tapped as of 2000, for example), the greenhouse gas vs. hydropower controversy is expected to continue.

Researchers from Stanford University estimate that between 95 million and 122 million tons of methane are released worldwide by dams each year. Because methane emissions from dams are not typically included in global emissions calculations, their figures would increase yearly worldwide methane emission estimates by 20 percent.

Hydropower facilities and fish populations: A recent study shows that impoundment facilities on the Columbia River in the U.S. Pacific Northwest have a harmful effect on the health of white sturgeon populations. Sturgeon fish living in reservoirs behind three impoundment dams had less reproductive success than sturgeon living in free-flowing rivers nearby. Eighteen pesticides and up to 28 types of polychlorinated biphenyls (PCBs, organic chemicals widely used as coolants and lubricants for electrical equipment up until 1977) were found in the tissues of the fish living in these reservoirs, as well as in a sample of sturgeon who were in the free-flowing section of the river. Fish in the oldest reservoir, however, had the most reproductive abnormalities, as well as the highest amount of contaminants in their tissues. These contaminants may disrupt hormones necessary for proper reproduction. This study suggests that harmful chemicals may accumulate over time in the reservoirs of hydropower facilities.

Hydropower impoundment dams may affect the migration of local fish populations. Environmental groups have argued that dams disrupt the migration of fish in the Pacific Northwest; these fish include salmon, coho, chinook, and steelhead trout. Since the construction of four dams on the Snake River (a major tributary of the Columbia River in Wyoming, Idaho, Oregon, and Washington), the migrating salmon population has declined 90 percent. A recent study, however, showed that migration of some endangered steelhead and Chinook salmon through dammed waters was as high as that of fish migrating in rivers without dams. The study's authors suggest further research to determine the effect of hydropower facilities on fish migration and survival.


Although hydroelectric power facilities are sustainable and renewable sources of energy, there is still room for improvement through future research. For example, migrating fish face injury and death as they pass through the turbines of hydropower systems in order to spawn upstream; these fish face the same fate when they reverse direction toward the ocean. As a result, the U.S. Department of Energy (DOE) has begun the Advanced Hydropower Turbine System Program in an attempt to design more "fish-friendly" turbines. It is hoped that fish mortality rates will drop to less than two percent, from the current 30% or higher loss due to some of the existing equipment.

The DOE Hydropower Program is conducting its turbine research by using recently-developed sensor fish in place of live fish. Sensor fish are fish-sized tubes containing instrumentation designed to detect the forces that fish undergo as they pass through turbines. The DOE is also using virtual fish in computer programs for the same purpose.

Additional goals of the DOE Hydropower Program include: cutting down on regulatory steps that cause hydropower licensing delays, encouraging cooperation between governmental agencies and industry, and increasing the efficiency of hydropower plants to reduce consumers' electricity costs. At the current time, hydroelectric power is the most cost-effective method of generating electricity. Fossil-fuel plants are, at most, 50% efficient in converting available energy (coal, for example) into electricity; in contrast, hydropower facilities are able to use as much as 90% of the water energy that is available. In the United States, hydropower costs an average of 0.7 cents per kilowatt-hour (kWh), while fossil fuels and nuclear power create electricity for about 2.1 cents per kWh.

Tidal power may offer future hydropower options. Tidal power, also called tidal energy, taps the force of the ocean in three different ways: 1) through the kinetic energy of the ocean's waves; 2) by making use of power that is generated as tidal forces send the sea through a barrage, which is a dam stretched across a river estuary; and 3) by generating power based on thermal energy (temperature differences in the ocean). The largest and oldest tidal power station in the world (La Rance in France, which was built in 1966) generates 240MW of electricity. Smaller prototype tidal power systems have been created in several locations, such as the East River in New York City in 2007; in Northern Ireland in 2008; and in Scotland. Due to environmental issues associated with the development of tidal power, this hydropower option is still in its infancy. Some environmental drawbacks to tidal power include the buildup of sediment within the tidal basin, the changes in salinity levels within estuaries that may harm marine mammals, an increase in the growth of phytoplankton within the basin that changes the food chain dynamics of the region, and the destruction of tidal flats. As of 2008, at least 26 tidal power facilities are in the planning stages in 11 countries around the world.

In 2007, a British corporation announced the planning of the first deep-sea tidal-energy farm in the world, to be located off the coast of Wales. The most accurate description of this offshore, underwater deployment of turbines is "a wind farm under the sea."

A Canadian inventor has reduced hydropower to a diminutive size, by developing hydroelectric footwear with fluid in the sole; this fluid passes through a micro-turbine from toe to heel (and back). According to the 2001 patent, the device should generate enough power to run small personal items such as cell phones, iPods, and portable computers.

Future hydropower planning is expected to focus on undeveloped areas of Africa, South/Central America, and Asia. In Africa, for example, only seven percent of its possible hydroelectric resources have been developed.


This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (

  • Canadian Hydropower Association (CHA). Accessed March 16, 2009.
  • Feist GW, Webb MA, Gunderson DT, et al. Evidence of detrimental effects of environmental contaminants on growth and reproductive physiology of white sturgeon in impounded areas of the Columbia River. Environ Health Perspect. 2005 December;113(12):1675-1682. View abstract
  • Hwang SS, Xi J, Cao Y, et al. Anticipation of migration and psychological stress and the Three Gorges Dam project, China. Soc Sci Med. 2007 Sep;65(5):1012-24. Epub 2007 Jun 4. View abstract
  • International Energy Agency Hydropower (IEA/Hydro). Accessed March 16, 2009.
  • International Hydropower Association (IHA). Accessed March 16, 2009.
  • Keiser J, De Castro MC, Maltese MF, et al. Effect of irrigation and large dams on the burden of malaria on a global and regional scale. Am J Trop Med Hyg. 2005 Apr;72(4):392-406. View abstract
  • Li YS, Raso G, Zhao ZY, et al. Large water management projects and schistosomiasis control, Dongting Lake region, China. Emerg Infect Dis. 2007 Jul;13(7):973-9. View abstract
  • Maloney C. Environmental and project displacement of population in India. Part I: Development and deracination. Field Staff Rep. 1991;(14):1-16. View abstract
  • Natural Standard: The Authority on Integrative Medicine. Copyright © 2009. Accessed March 16, 2009.
  • Northwest Power and Conservation Council. Accessed March 16, 2009.
  • Oak Ridge National Laboratory. Accessed March 16, 2009.
  • U.S. Department of Energy (DOE). Accessed March 16, 2009.
  • U.S. Department of the Interior Bureau of Reclamation. Accessed March 16, 2009.
  • Welch DW, Rechisky EL, Melnychuk MC, et al. Survival of migrating salmon smolts in large rivers with and without dams. PLoS Biol. 2008 October;6(10):e265. View abstract

Copyright © 2011 Natural Standard (


Read Health24’s Comments Policy

Comment on this story
Comments have been closed for this article.

Live healthier

Exercise benefits for seniors »

Working out in the concrete jungle Even a little exercise may help prevent dementia Here’s an unexpected way to boost your memory: running

Seniors who exercise recover more quickly from injury or illness

When sedentary older adults got into an exercise routine, it curbed their risk of suffering a disabling injury or illness and helped them recover if anything did happen to them.