Wind Energy

Worldwide, 30,000 megawatts or less than one percent of the total electricity generated is by wind turbines, but numbers are growing. In the last decade, the average annual growth of installed capacity of wind power plants has been increasing by 32%.  Many European countries, in particular, Denmark, Germany and Spain, have been heavily investing in wind energy. Germany with more than 12000 MW is the leader in wind generation capacity. Spain, the United States, Denmark and India are the second, third, fourth and fifth. Denmark currently produces 10% of its energy from wind, and is expecting to raise this figure to 40% by 2030.  

In the United States, only three states, North Dakota, Kansas, and Texas have sufficient wind that can be harnessed to satisfy national electricity needs. Theses states have the most wind, but they are sparsely populated and there are not many transmission lines. Most wind turbines are however in three areas, all of which located in California. Today, the U.S. wind industry generates about 4300 MW of electricity each year, or a little more than half a percent of its total electrical generation capacity. The U.S. Department of energy has recently announced its goal that by 2025, about 5% of its total electricity demand is going to be met using wind energy.

Wind is air in motion. It occurs at all scales from local breezes such as those occurring near oceans and in mountainous areas, to high speed gusts of air in hurricanes and tornados, and global winds such as trade winds and jet. We can’t see it, but we can see its effect all around us. Just like moving water, the wind represents a tremendous source of natural energy.

Like waterwheels, windmills were among the original prime movers that replaced human beings as a source of power. Wind power has been used as early as 5000 years ago by the Egyptians to sail ships across the Nile. The first windmills were invented by Persians around 500 AD to pump water from wells and to grind grain. They were constructed by fastening bundles of reeds onto wooden frames mounted on vertical shafts (hence called vertical windmills) housed in brick or clay walls. Wind entered through an opening at the side, and was caught between the spokes radiating from the shaft.

The technology was exported to China after Genghis Khan imprisoned Persian millers and forced them to build windmills to power irrigation systems in China.

It was not until the 12th century that windmills found their way to Europe, where their use became increasingly widespread until the early 19th century. These mills used vanes that looked like huge paddles mounted on a horizontal pole (hence called horizontal windmills). The Dutch made productive use of windmills in draining water from their low-lying land (hence Netherlands), which was quite prone to flooding.

The first use of a large windmill to generate electricity was in Cleveland, Ohio, in 1888 by Charles Brush[1]. The Brush machine had a rotor 17 meters in diameter with 144 blades. The huge slow-moving blades drove a gearbox and turned an electric dynamo that provided electricity to 350 incandescent lamps. The device worked for 20 years until the importance of windmills declined with the advent of steam engines and the popularization of low-cost and seemingly inexhaustible fossil fuels. Later works by aerodynamicists showed that the most efficient number of blades is 2-4, far smaller than those of earlier windmills.