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Wind issimple air in motion. It iscaused by the uneven heatingof the earth’s surface bythe sun. Since the earth’ssurface is made of verydifferent types of land andwater, it absorbs the sun’sheat at different rates.
During theday, the air above the landheats up more quickly thanthe air over water. The warmair over the land expandsand rises, and the heavier,cooler air rushes in to takeits place, creating winds.At night, the winds arereversed because the aircools more rapidl y over landthan over water.
In the sameway, the large atmosphericwinds that circle the earthare created because the landnear the earth's equator isheated more by the sun thanthe land near the North andSouth Poles.
Today, windenergy is mainly used togenerate electricity. Windis
called a renewable energysource because the wind willblow as long
as the sunshines.
Sinceancient times, people haveharnessed the winds energy.Over 5,000 years ago, theancient Egyptians used windto sail ships on the NileRiver. Later, people builtwindmills to grind wheat andother grains. The earliestknown windmills were inPersia (Iran). These earlywindmills looked like largepaddle wheels. Centurieslater, the people of Hollandimproved the basic design ofthe windmill. They gave itpropeller-type blades, stillmade with sails. Holland isfamous for its windmills.
Americancolonists used windmills togrind wheat and corn, topump water, and to cut woodat sawmills. As late as the1920s, Americans used smallwindmills to generateelectricity in rural areaswithout electric service.When power lines began totransport electricity torural areas in the 1930s,local windmills were usedless and less, though theycan still be seen on someWestern ranches.
The oilshortages of the 1970schanged the energy picturefor the country and theworld. It created aninterest in alternativeenergy sources, paving theway for the re-entry of thewindmill to generateelectricity. In the early1980s wind energy reallytook off in California,partly because of statepolicies that encouragedrenewable energy sources.Support for wind developmenthas since spread to otherstates, but California stillproduces more than twice asmuch wind energy as anyother state.
The firstoffshore wind park in theUnited States is planned foran
area off the coast ofCape Cod, Massachusetts(read an article about
theCape Cod Wind Project).
Like oldfashioned windmills, today’swind machines use blades tocollect the wind’s kineticenergy. Windmills workbecause they slow down thespeed of the wind. The windflows over the airfoilshaped blades causing lift,like the effect on airplanewings, causing them to turn.The blades are connected toa drive shaft that turns anelectric generator toproduce electricity.
With the newwind machines, there isstill the problem of what todo when the wind isn’tblowing. At those times,other types of power plantsmust be used to makeelectricity.
There aretwo types of wind machines(turbines) used today basedon the direction of therotating shaft (axis)horizontalaxis windmachines and vertical-axiswind machines. The size ofwind machines varies widely.Small turbines used to powera single home or businessmay have a capacity of lessthan 100 kilowatts. Somelarge commercial sizedturbines may have a capacityof 5 million watts, or 5megawatts. Larger turbinesare often grouped togetherinto wind farms that provide power to theelectrical grid.
Horizontal-axis
Most windmachines being used todayare the horizontal-axistype.
Horizontal-axis windmachines have blades likeairplane propellers.
Atypical horizontal windmachine stands as tall as a20-story
building and hasthree blades that span 200feet across. The
largestwind machines in the worldhave blades longer than afootball
field! Windmachines stand tall and wideto capture more wind.
Vertical-axis
Verticalaxis wind machineshave blades that go from topto bottom and the mostcommon type (Darrieus windturbine) looks like a gianttwo-bladed egg beaters. Thetype of vertical windmachine typically stands 100feet tall and 50 feet wide.Vertical-axis wind machinesmake up
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