NON-CONVENTIONAL ENERGY RESOURCES AND UTILISATION 59
During the day, air above the land heats more quickly than air above water. The hot air over the
land expands and rises, and the heavier, cooler air over a body of water rushes in to take its place,
creating local winds. At night, the winds are reversed because air-cools more rapidly over land than
over water. Similarly, the large atmospheric winds that circle the earth are created because land near the
equator is heated more by the sun than land near the North and South Poles.
Today people can use wind energy to produce electricity. Wind is called a renewable energy
source because we will never run out of it. Winds are natural phenomena in the atmosphere and have
two different origins.
(1) Planetary winds are caused by daily rotation of earth around its polar axis and unequal
temperature between Polar Regions and equatorial regions.
(2) Local Winds are caused by unequal and heating and cooling of ground surface of ocean 1
lake surfaces during day and night.
2.15.1 Wind Machine Fundamentals
Throughout history people have harnessed the wind. Over 5,000 years ago, the ancient Egyp-
tians used wind power to sail their ships on the Nile River. Later people built windmills to grind their
grain. The earliest known windmills were in Persia (the area now occupied by Iran). The early wind-
mills looked like large paddle wheels. Centuries later, the people in Holland improved the windmill.
They gave it propeller type blades and made it so it could be turned to face the wind. They have been
used for pumping water or grinding grain. Windmills helped Holland become one of the world's most
industrialized countries by the 17th century. Today, the windmill's modern equivalent — a wind turbine —
can use the wind’s energy to generate electricity.
American colonists used windmills to grind wheat and corn, to pump water, and to cut wood at
sawmills.
In this century, people used windmills to generate electricity in rural areas that did not have
electric service. When power lines began to transport electricity to rural areas in the 1930s, the electric
windmills were used less and less.
Then in the early 1970s, oil shortages created an environment eager for alternative energy sources,
paving the way for the re-entry of the electric windmill on the American landscape.
Today’s wind machine is very different from yesterday’s windmill. Along with the change in
name have come changes in the use and technology of the windmill. While yesterday’s machines were
used primarily to convert the wind’s kinetic energy into mechanical power to grind grain or pump
water, today’s wind machines are used primarily to generate electricity. Like old-fashioned windmills,
today's wind machines still use blades to collect the wind's kinetic energy. Windmills work because
they stow down the speed of the wind. The wind flows over the airfoil shaped blades causing lift, like
the effect on airplane wings, causing them to turn. The blades are connected to a drive shaft that turns
an electric generator to produce electricity.
Modern wind machines are still wrestling with the problem of what to do when the wind isn't
blowing. Large turbines are connected to the utility power network-some other type of generator picks
up the load when there is no wind. Small turbines are often connected to diesel/electric generators or
sometimes have a battery to store the extra energy they collect when the wind is blowing hard.