HYDROPOWER
Introduction
Hydropower uses the energy of the hydrologic cycle, which is ultimately driven by the sun, making it an indirect form of solar energy. Energy contained in sunlight evaporates water from the ocean and deposits it on land in the form of rain and other forms of precipitation. Precipitation that is not absorbed by the ground runs off the land into the ocean via the world's vast network of rivers to repeat the process. Hydroelectric plants built along these rivers, generate power by releasing water stored behind concrete dams built across the river to turn water turbines. The power plants capture the energy released by water falling through a turbine which converts the water's energy into mechanical power. The mechanical energy of the rotating turbines drives generators to produce electricity.
Dam Hydropower
Hydro dams are present in almost all regions of the globe and have played a key role in development for thousands of years. Many modern dams are multi-purpose - built primarily for irrigation, water supply, flood control, electric power and improvement of navigation. They also provide recreation, such as fishing and swimming and become refuges for fish and birds. In the last two centuries they have also played a key role in producing large-scale power and electricity. Dams also slow down streams and rivers so that the water does not carry away soil, thereby preventing erosion.
Hydropower is the only renewable resource currently used on a large scale to generate electricity. In 1998 hydropower contributed 2.7% of global primary energy and between 15-20% of the world's electricity supply. Huge estimates of the theoretical annual potential of world hydroelectricity have been made. However, this potential is much greater than what is actually technically, economically, or environmentally feasible.
Hydroelectric plants can range in size from less than 100 kilowatts to several thousand megawattsp. If completed, the Three Gorges Dam on the Yangtze will be the largest hydroelectric dam in the world. Its installed capacity will be about 17,680 MW expandable with additional turbines to 22,800 MW, which is nearly twice the power of the next largest hydropower plant, the Brazil-Paraguay Itaipu dam.
At least 35,000 large dams already exist. The number and size of large dams, built to boost economic development have increased in recent decades with most of them in developing countries. Most industrialized countries have either developed larger prospective sites or have excluded them from development due to environmental concerns. Hydropower development in these countries is now focused more on smaller sites, on the refurbishing and upgrading of existing hydroelectric plants, and on retrofitting dams constructed for other purposes. The feasibility of small hydropower facilities in particular may depend on the availability of a back-up source of electricity since smaller plants often do not have a reservoir for storage. Large-and intermediate-scale dams, however, will continue to be very important in developing countries, in the former Soviet Union and in some industrialized nations, such as Canada.
Run of the River
Run of the river hydropower schemes also seek to generate electricity, though it is typically on a smaller scale. One way to generate electricity is to divert a certain amount of water through a pipe and drive a turbine at the outlet, such as at Niagara Falls. This can be preferred to damming the river because it is significantly less costly. Electricity can also be generated from turbines in the river. While it has not yet been commercially integrated, tests are planned for the East River in New York City. Planners propose installing six small units that would produce a total of 36 kW. Although the average velocity of the water is only 4.5 mph, the density of water (and thus its total mass) allows a significant amount of energy to be produced. This slow speed reduces the amount of electricity that could be generated, but it also reduces the risk to fish. Still, more research on this technique is needed before its cost-effectiveness can be assessed and possible problems identified.
Benefits and Implications
Hydropower has the obvious benefit of displacing greenhouse gas emissions from conventional fuels. However, the process of damming a river and creating a reservoir can pose its own environmental, economic, health and social problems. Before selecting an appropriate site, several geologic, social, and environmental factors should be evaluated. This kind of analysis is not always conducted, which has resulted in occasional problems in hydropower development. Two most important issues, the displacement of floodplain residents and the loss of the most fertile and useful land in a given area, are very important issues to consider. The potentially serious social consequences of displacing the population living on the floodplain must be weighed - along with the environmental and economic costs of losing this land to a reservoir for a hydropower plant.
These two issues are some of the concerns raised by critics of megadams. The Sardar Sarova dam on the Narmada River in India gained notoriety from vigorous local opposition due to its costly social impacts and the World Bank withdrew its loan in 1993. Activists and environmentalists are opposing many other dams, such as the Three Gorges in China, Arun in Nepal, Kaeng Sua Ten in Thailand, and Bakun in Malaysia.
The social consequences of a large migration of workers and their families to hydro dam sites cause an instant population boom that can place a strain on resources. Conversely, this could ultimately lead to local economic development. Future megadams must compensate affected populations fairly. In the past not all displaced people got land for land; public health, always overlooked and underfunded, should be a major focus of the reform of dam policy.
Filling a reservoir can also change the local topography, presenting possible environmental problems. The process creates a large body of water where there was not one before which, depending on the reservoir's size, can actually influence the local climate or even cause earthquakes in geologically unstable areas.
Run of the river hydroelectric production, conversely, avoids these problems. Whether by diverting a particular amount of the water flow or integrating turbines into the existing river, large dams do not have to be built to alter ecosystems and displace communities. Siting is still an issue, however. Certain underwater turbines, if in an area with fast-flowing streams, may kill fish caught in the turbines. Yet a slower river results in less electricity generation. It is unlikely that 'run-in-the-river' schemes will produce a substantial amount of electricity.
Still, these problems can be overcome. Coupling hydropower and solar power has particular advantages since insolation may often be greater in seasons when river flow is lower and hydropower can complement variations in solar radiation.
Additional Resources
US Department of Energy: Hydropower Topics
List of websites and reports dealing with hydropower.
World Commission on Dams
This site has been redeveloped as an archive of the World Commission on Dams (WCD). The Commission was an independent, international, multi-stakeholder process which addressed the controversial issues associated with large dams. The Commission completed its work with the launch of its final report and disbanded.
The Dams and Development Project
The two-year follow-on to the process initiated by WCD is a project of the United Nations Environment Programme (UNEP). This project promotes dialogue on improving decision-making, planning and management of dams and their alternatives based on the WCD core values and strategic priorities. Also includes information about reactions to the WCD Report and submissions on good practice.
The Alternative Energy Institute
A good overview of hydropower's extent and the current debate surrounding dams for power vs. river integrity.
National Hydroelectric Power Corporation
The website of India's hydroelectric utility containing specifics on the Indian subcontinent's hydro potential and current projects.
Sustainable Minnesota
The hydro section of Sustainable Minnesota focuses on raising local public awareness of the social and environmental consequences of hydroelectric power, specifically the hydroelectric dams of Manitoba Hydro and its devastating impacts on people and the environment. It also has an extensive list of links to Canadian, US, and Minnesotan groups.
Hydroelectric Power
This site tracks the hydroelectric industry in the news.