Wind Energy Overview

From Thermal-FluidsPedia

Of all the forces of nature, I should think the wind contains the greatest amount of power. ~ Abraham Lincoln

In the last quarter of a century, wind energy technology has gone through revolutionary changes making wind the fastest growing source of electricity in the world. Worldwide, 120 gigawatts (120,000 megawatts), or about 1.5 percent of the total electricity, is generated by wind turbines, though numbers are growing rapidly. In the last decade, the average annual growth of the installed capacity of wind power plants has been increasing by 32%. (1) Many European countries, in particular Denmark, Germany, and Spain, have been heavily investing in wind energy. Germany, with more than 18,400 MW, is the leader in wind generation capacity with Spain, the United States, India, and Denmark ranking next. In terms of the percentage of total electricity production, Denmark ranks first; it currently produces 20% of its electricity from wind and is planning to raise this figure to 40% by 2030.

Figure 1: Persians invented the first practical windmills for grinding wheat and pumping water.

In the United States, only three states - North Dakota, Kansas, and Texas - have sufficient wind that, if harnessed, could satisfy national electricity needs. Though these states have the most wind, they are sparsely populated and there are not many transmission lines. Most wind turbines are located in three areas, all of them in California. Today, the US generates about 9,100 MW, or a little more than half a percent of its annual electrical generation capacity from wind, but is expected to increase its capacity to about 5% of its total electricity demand by 2025. (2)

Overview

Figure 2: Dutch horizontal wind turbine

Figure 3: Brush windmill in Cleveland

Figure 4: Two-bladed wind turbines

Wind is air in motion. 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 200 BC 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 (Figure 1). 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 twelfth 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 used windmills mainly for draining water from their low-lying land (hence Netherlands), which was quite prone to flooding (Figure 2).

Figure 5: As the electricity output from wind energy has increased, cost of electrical generation has decreased dramatically.

The first use of a large windmill to generate electricity was in 1888 by Charles Brush in Cleveland, Ohio. (3) The Brush machine shown in Figure 3 had a rotor 17 meters in diameter with 144 blades and provided enough electricity to light 350 incandescent lamps. The device worked for 20 years until the advent of steam engines and the popularization of low-cost, seemingly inexhaustible fossil fuels made windmills less and less attractive. Later works by aerodynamicists showed that the most efficient number of blades is 2-4, a far smaller number than those found in earlier windmills (Figure 4).

The world’s wind electric energy generation capacity has been climbing steadily since 1980, reaching 60,000 megawatts in 2005, and 120,000 megawatts in 2008; this is largely due to new technological innovations that have reduced production cost from $1.00 to around $0.04 for one kilowatt-hour (Figure 5). In 1980, the United States was the leading producer of electricity from wind and accounted for 80% of the world’s capacity. Its share, however, has been declining ever since and accounts for only 15% of the world’s capacity today. (4)

References

(1) Kenisarin, M. M., “Worldwide State of Wind Power Engineering,” Applied Solar Energy, Vol. 38, No. 4, 2002, Allerton Press, Inc., New York.

(2) American Wind Energy Association Website, http://www.awea.org.

(3) “Mr. Brush’s Windmill Dynamo,” Scientific American, December 20, 1890.

(4) Global Wind Energy Council, “Global Wind Power Continues Expansion,” press release, 17 February 2006.

(5) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

Gipe P., Wind Energy Basics, —A comprehensive guide to modern small wind technology. AWEA (http://www.awea.org).

Elliott, D. et al., Wind Energy Resource Atlas of the United States, by American Wind Energy Association (http://rredc.nrel.gov/wind/pubs/atlas).

Khennas, S., Small wind systems for rural energy services, London: ITDG Pub., 2003.

Solar Energy, Direct Science Elsevier Publishing Company, the official journal of the International Solar Energy Society ®, is devoted to the science and technology of solar energy applications, and includes the indirect uses such as wind energy and biomass.

Home Power Magazine—bimonthly magazine for farm and home wind turbines (http://www.homepower.com).

External Links

Energy Efficiency and Renewable Energy Clearinghouse (http://www.eren.doe.gov).

National Wind Technology Center, National Renewable Energy Laboratory (http://www.nrel.gov/wind).

Energy Efficiency and Renewable Energy: Wind Energy Technologies, US DOE (http://www.eere.energy.gov/windandhydro/wind_technologies.html).

American Wind Energy Association (http://www.awea.org).