For many centuries wind has been used as a reliable source of energy. It is
clean and inexhaustible. Wind is used to make the job of a human simpliar. It is
used for grinding grain, pumping water, and to enable sail boats to move. Though
often the amount of wind power varies depending on the climate of an area.
Although wind power is only used in selected areas the recent interest in fuel
conservation has sparked the development of windfarms. In the 1980’s a studied
showed that in order to produce one kilowatt- hour of energy cost 4 cents. The
best known horizontal axis machine in the United States is the American farm
windmill which is frequently used to pump water. This machine has rotor with up
to 20 blades mounted on a horizontal shaft and a tail-vane. A tail-vane is to
keep the rotor facing inot the wind by swiveling the machine. Unlike the farm
windmill, the modern windmill only use four blades to generate electricity and
are able to operate at high rotor speeds. The Jacobs three blade windmill, which
was used widely between 1930 and 1960, could deliver about I kilowatt of power
at a typical wind speed of 14 miles per hour. Lately a different type of
windmill has been used. It is a large horizontal two bladed wind turbine. These
were first installed in Ohio in 1975. Another type of windmill which has a rotor
diameter of 400 feet and a shaft height of 250 can produce 6,200 kilowatts of
power . These were first places in oahu, Hawaii. The term “wind farm” is
used for a large number of wind mills, that are clusters at a site with a
moderately constant wind, These are generally near mountain passes. With in the
united states wind farms appear in New Hampshire, California, and Hawaii. At
these sites the machine capacities range from 10 to 500 kilowatts. In 1984 the
total energy output of all the wind farms in the united states exceeded 150
million kilowatt-hours.