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Introduction

Hydropower is energy extracted from moving water. However it is essentially another way of trapping the sun;s energy since it is the sun which drives the flow of water on the planet – the so called hydrologic cycle.

The main water reservoirs are of course the oceans and the sun’s energy warms the ocean water and the degree of warming depends on location. The warmer the water, the greater the degree of evaporation and the higher the concentration of water vapor in the atmosphere. This process has an enormous effect on the earth’s climate and for example is the main driving force behind hurricanes. As the water vapor laden air rises, it cools, the water condenses and clouds form. The clouds are blown onshore and over land. If conditions are right, perhaps as the air mass rises over a mountain range, the clouds cool sufficiently for the condensed water to reach the point where rain, or even snow is formed. This precipitation eventually makes its way back downhill to the ocean. On its way, some of it replenishes natural underground reservoirs, irrigates agricultural lands, and some of it is used to produce power.

More than 200 years ago, the Greeks used falling water to power grinding wheels and in the 1700’s it was used extensively in the industrial revolution to power mills and pumps. Nowadays, power is normally produced by using falling water to power electrical turbines. Since the availability of water is ultimately dependent on precipitation, water is normally stored behind dams to better control the availability of electricity.

Among the renewables, water is the second greatest source of electricity production and hydroelectric plants operate where suitable waterways are available. In the developed world at least, many of the best of these sites have already been developed.

Generating electricity using water has several advantages. The major advantage is that water is a source of cheap power and requires no imported fuel. In addition, because there is no fuel combustion, there is little air pollution in comparison with fossil fuel plants and limited thermal pollution compared with nuclear plants. However the building of dams, floods land, reduces the river’s flow downstream, which affects the habitats of the local plant, fish, and animal life, and is one reason this form of renewable power has so many opponents. Thus, like other energy sources, the use of water for generation has limitations, including environmental impacts.

The generation of hydroelectric power increased by 366 billion kilowatthours between 1992 and 2001, or at an average annual rate of 1.7 percent.

Canada, Brazil, China, the United States, and Russia, were the five largest producers of hydroelectric power in 2001. Their combined hydroelectric power generation accounted for 48 percent of the world total. Canada led the world with 328 billion kilowatthours or 3.4 quadrillion Btu, Brazil ranked second with 266 billion kilowatthours or 2.8 quadrillion Btu and China was third with 263 billion kilowatthours or 2.7 quadrillion Btu. The United States was fourth with 209 billion kilowatthours or 2.1 quadrillion Btu, followed by Russia with 174 billion kilowatthours or 1.8 quadrillion Btu. This is mirrired by the installed generating capacity figures shown below

The general consensus appears to be that hydropower will not grow as rapidly as other renewable energy sources because of the concerns over its environmental impacts.

The US DOE (AEA 2004) projects no growth in hydroelectric power generation within the USA, but rather a steady state at 309,000 GWh compared to its peak of 354 GWh in 1997 and 308 GWh in 2003.

However more than 60 %of the increase in world primary energy demand, between 2000 and 2030, will come from developing countries especially in Asia. More than a quarter of the world ’s population has no access to electricity and, although the number of people without power supplies will fall in the coming decades, a projected 1.4 billion people will still be without electricity in 2030. (IEA 2002). To extend electricity supplies to the energy poor and give them better access to other forms of modern energy, stronger government policies and coordinated international action will be essential. Renewable energy will play a growing role in the world’s primary energy mix. Hydropower has long been a major source of electricity production. Its share in global primary energy will hold steady, but its share of electricity generation will fall.

This has to be set in the context however of a rapidly growing energy demand, so losing ground does not necessarily mean standing still. A study by the Utility Data Institute, USA, predicts that a world total of 695 GW of new electricity capacity will come on line in the next ten years from all sources, 22 per cent of which will be hydropower. The world’s total technical feasible hydro potential is estimated at 14,000 TWh/year, of which about 8000 TWh/year is currently considered economically feasible for development. About 700 GW (or about 2600 TWh/year) is already in operation, with a further 108 GW under construction. Most of the remaining potential is in Africa, Asia and Latin America. A number of countries, such as China India, Iran and Turkey, are undertaking large-scale hydro development programmes, and there are projects under con-struction in about 80 countries. According to the recent world surveys, conducted for the Hydropower & Dams World Atlas & Industry Guide, a number of countries see hydropower as the key to their future economic development: Examples are Sudan, Rwanda, Mali, Benin, Ghana, Liberia, Guinea, Myanmar, Bhutan, Cambodia, Armenia, Kyrgyzstan, Cuba, Costa Rica, and Guyana.