Worldwide, hydropower plants produce about 24 percent of the world’s electricity and supply more than 1 billion people with power. The world’s hydropower plants output a combined total of675,000 megawatts, the energy equivalent of 3.6 billion barrels of oil, according to the National Renewable Energy Laboratory. There are more than 2,000 hydropower plants operating in the United States, making hydropower the country’s largest renewable energy source. In this article, we’ll take a look at how falling water creates energy and learn about the hydrologic cycle that creates the water flow essential for hydropower. You will also get a glimpse at one unique application of hydropower that may affect your daily life.
The basic principle of hydropower is that if water can be piped from a certain level to a lower level, then the resulting water pressure can be used to do work. If the water pressure is allowed to move a mechanical component then that movement involves the conversion of the potential energy of the water into mechanical energy. Hydro turbines convert water pressure into mechanical shaft power, which can be used to drive an electricity generator, a grinding mill or some other useful device.
2.HistoryThe use of falling water as a source of energy is known for a long time. In the ancient times waterwheels were used already, but only at the beginning of the nineteenth century with the invention of the hydro turbine the use of hydropower got a new impulse.Small-scale hydropower was the most common way of electricity generating in the early 20th century. In 1924 for example in Switzerland nearly 7000 small scale hydropower stations were in use. The improvement of distribution possibilities of electricity by means of high voltage transmission lines caused fainted interest in small scale hydropower.Renewed interest in the technology of small scale hydropower started in China. Estimates say that between 1970 and 1985 nearly 76,000 small scale hydro stations have been built there!
3.Advantages and disadvantagesHydropower is a very clean source of energy. It does not consume but only uses the water, after use it is available for other purposes (although on a lower horizontal level). The conversion of the potential energy of water into mechanical energy is a technology with a high efficiency (in most cases double that of conventional thermal power stations).The use of hydropower can make a contribution to savings on exhaustible energy sources. Each 600 kWh of electricity generated with a hydro plant is equivalent to 1 barrel of oil (assuming an efficiency of 38 % for the conversion of oil into electricity).
The main advantages of hydropower are: * power is usually continuously available on demand, * given a reasonable head, it is a concentrated energy source, * the energy available is predictable, * no fuel and limited maintenance are required, so running costs are low (compared with diesel power) and in many cases imports are displaced to the benefit of the local economy, * it is a long-lasting and robust technology; systems can last for 50 years or more without major new investments.Against these, the main shortcomings are: * it is a site specific technology and sites that are well suited to the harnessing of water power and are also close to a location where the power can be economically exploited are not very common, * there is always a maximum useful power output available from a given hydropower site, which limits the level of expansion of activities which make use of the power, * river flows often vary considerably with the seasons, especially where there are monsoon-type climates and this can limit the firm power output to quite a small fraction of the possible peak output, * lack of familiarity with the technology and how to apply it inhibits the exploitation of hydro resources in some areas.
4.From water to WattsTo know the power potential of water in a river it is necessary to know the flow in the river and the available head.The flow of the river is the amount of water (in m3 or litres) which passes in a certain amount of time a cross section of the river. Flows are normally given in cubic meters per second (m3/s) or in litres per second (l/s).Head is the vertical difference in level (in meters) the water falls down.The theoretical power (P) available from a given head of water is in exact proportion to the head H and the flow Q.P=Q × H × c c = constantThe constant c is the product of the density of water and the acceleration due to gravity (g).If P is measured in Watts, Q in m3/s and H in meters, the gross power of the flow of water is:P=1000 × 9.8 × Q × HThis available power will be converted by the hydro turbine in mechanical power. As a turbine has an efficiency lower than 1, the generated power will be a fraction of the available gross power.
Hydro power is also utilised by large scale companies as a private use. Many large mining companies or aluminium manufacturers use vast amounts of electrical so rather than buying from the state they can generate their own power by using hydro power generation.
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