29-08-2011, 10:42 AM
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NON CONVENTIONAL ENERGY SOURCES
Abstract
The ever increasing rapid use of the fossile fuels day by day has threatened exhausting of conventional energy sources very soon. Also the use of conventional energy sources has increased the global pollution level which is resulting in climate change. Therefore time has come for searching altogether other sources of energy which are inexhaustible and gradually replace the conventional sources. The non conventional energy sources such as solar, wind, tidal, ocean etc are basically renewable energy resources. The energy available from each of theses sources can be used to produce mechanical and electrical power. These are produced continuously in nature and are essentially inexhaustible atleast in the frame work of human societies.Wind energy is one of non conventional energy source. Wind power is one of the most ecofriendly means to generate electricity . The time taken to set up wind power project is very short compare to set up a conventional thermal power plant using coal or nuclear energy.
Introduction
“Energy“ , a word derived from Greek word “Energia”, meaning capacity for doing work. All forms of energy are interconvertable by appropriate processes. Energy can also be classified as conventional and non conventional eneegy sources. Presently most of our energy sources comes mainly from fossile fuels such as coal, petrolium, and natural gas.The ever increasing rapid use of fossile fuels day by day has threatened exhausting of these sources very soon. . Without energy, the world's entire industrialized infrastructure would collapse; agriculture, transportation, waste collection, information technology, communications and much of the prerequisites that a developed nation takes for granted.Therefore time has come for searching altogether other sourceses of energy which are inexhaustible called non conventional energy sources such as wind energy, tidal energy, solar energy, bio energy and so on. These energy resources replenish themselves naturally in a relatively short time and therefore will always be available.Except the biomass energy sources all other renewable energy sources offer pollution free environment and also help in maintaining the ecological balance.
Introduction to Wind Energy
Wind energy is the energy contained in the force of the winds blowing across the earths surface.When harnessed, wind energy can be converted into mechanical energy for performing work such as pumping water, grinding grain by wind mills and producing electrical energy, by wind turbines.The circulation of air in the atmosphere is caused by the non uniform heating of the earth’s surface by the sun. The air immediately above a warm area expands and becomes less dense. It is then forced upwards by a cool denser air which flows in the surrounding areas causing a wind.
Wind machines were used for grinding grain in Persia as early as 200 B.C. This type of machine was introduced into the Roman Empire by 250 A.D. By the 14th century Dutch windmills were in use to drain areas of the Rhine River delta. In Denmark by 1900 there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The first windmill for electricity production was built in Cleveland, Ohio by Charles F. Brush in 1888[1], and in 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW fig(1). The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors. In Denmark wind power was an important part of a decentralized electrification in the first quarter of the 20th century, partly because of the Danish wind power scientist Poul la Cour.
Fig (1) A Two Bladed Wind Turbine
By the 1930s windmills were mainly used to generate electricity on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers. A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual load factor of 32 per cent, not much different from current wind machines. Construction Materials
Wood and canvas sails were originally used on early windmills due to being cheap and easily manufactured. Unfortunately they require much maintenance over their service life. Also, they have a relatively high drag (low aerodynamic efficiency) for the force they capture. For these reasons they were superseded with solid airfoils.
One of the strongest and stiffest construction materials available for wind turbine blades is carbon-fibre in an epoxy resin matrix, however is very expensive and only used by some blade manufactures for highly loaded parts of the rotor blades and when stiffness is critical. Modern rotor blades (up to 126 m (413 ft) diameter) are made of lightweight glass-reinforced plastic (GRP) with an epoxy or polyester resin matrix. Smaller blades can sometimes be made from aluminium, however GRP is the most common material for modern wind turbine blades. Fig(2)Wind turbine blades can however be made from a wide variety of materials
