Renewable Energy Resources for Irrigation - Practices of Irrigation and On-farm Water Management - page 492

built windmills to grind wheat and other grains. Wind filled the sails of explorers
and fueled trade throughout the world. The Dutch used wind to claim land from
the ocean, and early European settlers in the American West used wind to pump
water for farms. The earliest known windmills were in Persia (Iran). These early
windmills looked like large paddle wheels. Centuries later, the people of Holland
improved the basic design of the windmill. They gave it propeller-type blades, still
made with sails. Holland is famous for its windmills. During the first half of the
twentieth century, wind was used to provide electricity for many rural areas before
the expansion of the electrical grid and offered a cheaper and more reliable form of
power.
American colonists used windmills to grind wheat and corn, to pump water, and
to cut wood at sawmills. As late as the 1920s, Americans used small windmills to
generate electricity in rural areas without electric service. When power lines began
to transport electricity to rural areas in the 1930s, local windmills were used less
and less, though they can still be seen on some Western ranches.
The oil shortages of the 1970s changed the energy picture for the country and the
world. It created an interest in alternative energy sources, paving the way for the re-
entry of the windmill to generate electricity. In the early 1980s wind energy really
took off in California, partly because of state policies that encouraged renewable
energy sources. Support for wind development has since spread to other states, but
California still produces more than twice as much wind energy as any other state.
The first offshore wind park in the United States is planned for an area off the coast
of Cape Cod, Massachusetts.
13.5.3 Causes of Wind Flow
Wind is simple air in motion. It is caused by the uneven heating of the earth's surface
by the sun (Fig. 13.3 ) . Since the earth's surface is made of very different types of
Fig. 13.3 Schematic of mechanism of air-flow