Green Energy

Renewable Energy: Hydropower

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.

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. 

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.

Hydroelectric plants can range in size from less than 100 kilowatts to several thousand megawattsp>. p>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. 

Before selecting an appropriate site, several geologic, social, and environmental factors are evaluated - however, this kind of analysis is not always conducted which has resulted in occasional problems in hydropower development.

The process of damming a river and creating a reservoir can actually pose its own environmental, economic, health and social problems. 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 causes an instant population boom that can place a strain on resources.  Conversely, this could ultimately lead to local economic development.

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.

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.

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.