Hydro Electricity

HYDRO ELECTRICITY

Most machines that make electricity need some form of mechanical energy to get things started. Mechanical energy spins the generator to make the electricity. In the case of hydroelectricity, the mechanical energy comes from large volumes of falling water. For more than 100 years, the simplest way to produce the volumes of

falling water needed to make electricity has been to build a dam. A dam stops the natural fl ow of a river, building up a deep reservoir behind it. However, large dams and reservoirs are not always appropriate, especially in the more ecologically sensitive areas of the planet. For making small amounts of electricity without building a dam, the small-scale hydroelectric generator is often the best solution,

especially where fast-fl owing streams on steep slopes are close by. A small-scale

hydro system usually consists of an enclosed water wheel or turbine, which is made to spin by jets of high velocity water. The water is taken from the stream

and moved down slope to the turbine through a long pipe called a penstock. Water fl owing through the penstock picks up speed, and is directed at the blades of the turbine by nozzles. The turbine spins continuously, as long as there is water to drive it. The turbine is connected to an electrical generator, and the electricity is then available for running appliances or charging batteries. The spent water is

returned to the stream. This kind of system is called a “micro-hydro” system, “run-of-stream hydro” or “low-impact hydro.” Canada and many other countries

depend on large-scale hydro developments for electricity. Micro-hydro systems can provide clean, environmentally friendly electricity in rural communities.

Hydropower is one of the three principal sources of energy used to generate electricity, the other two being fossil fuels and nuclear fuels. Hydroelectricity has certain advantages over these other sources: it is continually renewable thanks to the recurring nature of the water cycle, and causes no pollution. Also, it is one of the cheapest sources of electrical energy.

The Itaipu Dam between Brazil and Paraguay, which is 190 meters high and generates more than 12,600 MW, is the largest hydro power dam in the world. (The 185-metre Three Gorges Dam, now being constructed in China on the upper Yangtze River, would take its place by 2009, producing 18,200 MW of power). The Grand Coulee Dam, located near Spokane, Washington, is the largest hydropower dam in the United States, producing 6,480 MW. The Rogun Dam, in Russia, the tallest in the world, is 335 meters high. The Oroville dam, located in California, the tallest in the United States, is 235 meters high. Idukki dam in India is Asia's first and largest arch dam.

Advantages

More Economic than other fuels

The major advantage of hydroelectricity is elimination of the cost of fuel. The cost of operating a hydroelectric plant is nearly immune to increases in the cost of fossil fuels such as oil , natural gas or coal, and no imports are needed. Hydroelectric plants also tend to have longer economic lives than fuel-fired generation, with some plants now in service which were built 50 to 100 years ago. Operating labor cost is also usually low, as plants are automated and have few personnel on site during normal operation.

No Greenhouse gas emissions

Since hydroelectric dams do not burn fossil fuels, they do not directly produce Carbondioxide(a greenhouse gas). While some carbon dioxide is produced during manufacture and construction of the project, this is a tiny fraction of the operating emissions of equivalent fossil-fuel electricity generation.

Disadvantages

Environmental damage

Hydroelectric projects can be disruptive to surrounding aquatic ecosystems both upstream and downstream of the plant site. Generation of hydroelectric power changes the downstream river environment. Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks. Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed. Dissolved oxygen content of the water may change from pre-construction conditions. Depending on the location, water exiting from turbines is typically much warmer than the pre-dam water, which can change aquatic faunal populations, including endangered species and prevent natural freezing processes from occurring. Some hydroelectric projects also use canals to divert a river at a shallower gradient to increase the head of the scheme. In some cases, the entire river may be diverted leaving a dry riverbed..

A further concern is the impact of major schemes on birds. Since damming and redirecting the waters of the for agricultural and energy use, many native and migratory birds have become increasingly endangered