Changes
==Brief History of Wind Energy==
Although the use of wind power started around 5000 BC, but electric power generation through wind energy started in 18th century and increasing drastically in 19th and 20th centuries. A brief view on developments on wind power sector are listed below.
[[Image:totalcapacityworld2009.JPEG|thumb|right|400px|Fig 1 '''[http://www.wwindea.org/home/index.php Development of wind power worldwide]''']]
* [http://www.brighthub.com/environment/renewable-energy/articles/71440.aspx 1887] : Prof. James Blyth of Scotland used windmills for generating electricity.
* [http://www.brighthub.com/environment/renewable-energy/articles/71440.aspx 1888] : Charles Brush developed the first wind-powered turbine that generated electricity in the United States based on emulated James Blyth work.
The total installed wind power capacity from 2001 to 2010 is shown in fig. 1. All wind turbines installed by the end of year 2009 worldwide are generating 340 TWh per annum.
The country wise share of wind energy by the end of year 2009 is shown in fig. 2.
[[Image:countryshare.JPEG|thumb|center|350px|Fig 2 '''[http://www.wwindea.org/home/index.php Country share of total capacity]''']]
==Working Principle of Wind Turbine ==
Wind is air in motion. It is a form of solar energy. Solar radiation heats every part of the Earth’s surface unevenly due to irregularities and rotation of earth. The flow of wind patterns are modified by the earth's terrain, bodies of water, and vegetative cover. When air moves, causing wind, it has kinetic energy. The kinetic energy of wind can be captured by a wind turbine and converted to other forms of energy such as electricity or mechanical power.
[[Image:windprinciple.png|center|550px|thumb|Fig 3 '''[http://www.atlantissolar.com/wind_story.html Wind turbine principle]''']]
Sources:[http://windeis.anl.gov/guide/basics/index.cfm Wind Energy Basics],[http://www1.eere.energy.gov/windandhydro/wind_how.html#inside How Wind Turbines Work]
* It can be constructed in off-shores.
* It produces large amount of electricity with high efficiency.
[[Image:Horizontal.jpg|center|thumb|Fig 4(a) '''[http://www.windturbinesnow.com/horizontalaxis-windturbines.htm Horizontal axis wind turbine]''']]
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* These are easy to build and maintain, safer, easier to transport and they can be mounted close to the ground.
* It operates with any direction of wind
* Production of electricity is less due to low wind speeds near to ground
[[Image:vertical.jpg|center|thumb|Fig 4(b)'''[http://www.solarpowerwindenergy.org/2009/12/25/types-of-wind-turbines/ Vertical axis wind turbine]''']]
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=Horizontal Axis Wind Turbines=
[[Image:HWAT1.PNG|right|131px|thumb|Fig]]
|align = "center" bgcolor = "#83caff"|'''Description'''
| A method of controlling the speed of a wind turbine by varying the orientation, or pitch, of the blades, and thereby altering its aerodynamics and efficiency.
[[Image:pitch.jpg|thumb|center|175px|Fig 16(a) '''[http://zone.ni.com/devzone/cda/tut/p/id/8189 Pitch control]''']]
Source:[http://www.moog.com/markets/energy/wind-turbines/blade-pitch-control/ Blade Pitch Control]
| The rotation of horizontal axis wind turbine around its tower to orient the turbine in upwind or down wind direction.
[[Image:Yaw.jpg|thumb|center|175px||Fig 16(b) '''[http://zone.ni.com/devzone/cda/tut/p/id/8189 Yaw control]''']]
Source:[http://zone.ni.com/devzone/cda/tut/p/id/8189 Wind Turbine Control Methods]
|Stall control works by increasing the angle at which the relative wind strikes the blades (angle of attack). As the wind speed increases drag force on the blade increase and lift force gets reduces, thus finally reduces the speed of turbine.A fully stalled turbine blade, when stopped, has the flat side of the blade facing directly into the wind. Compare with furling.
