Wind Power

Wind power harnesses the energy of the wind to produce electricity or other forms of energy using turbines. It is a clean and sustainable fuel source, which does not emit greenhouse gases, and does not run out.

Wind energy is one of the fastest growing energy sources worldwide. In 1998 the market for new wind turbines had a size of 2,187 MW, which is less than one tenth of its size in 2008, and since 2005 global wind installations have more than doubled. The turnover of the wind sector worldwide reached 40 billion in 2008. It is expected that wind energy will continue its dynamic development in the coming years.¹

Old fashioned windmill in Gouda, the Netherlands. Built in 1862, this mill used wind energy for pumping water.

Dutch windmill from 1862, used in the past for pumping water.

Source: nl.wikimidia. Author: Gouwenaar. Permission: Public Domain.

Technology basics

Wind is caused by the combination of the spinning of the planet on its axis and the uneven heating of the earth’s surface by the sun. For example, land absorbs and reflects heat at a different rate than water does.² As a result of the uneven heating, certain areas of the atmosphere become warmer than others. The warmer sections rise, and more air blows in to replace them. This is felt as wind.³

Through history, wind energy has been used for diverse purposes, including for crop irrigation, sailing, and in windmills for grinding grain and pumping water. Today, it is mainly used to generate electricity through turbines, placed either on land or at sea in a windy area.⁴ Turbines basically consist of a tower with a large propeller. The wind blows on the propeller and makes it move. The propeller powers a generator, which uses magnetic fields to convert the rotational energy into electrical energy. The power output then goes to a transformer, which converts the electricity to a right voltage for distribution or use. ⁵

Large wind turbines are used individually or in wind parks to provide electricity to national grids. Smaller turbines (below 100 kilowatts) can be used by single homes to power appliances or a water pump.⁶ There are two types of wind turbines: the horizontal-axis design (HAWT) and the vertical-axis design (VAWT).

Types of turbines

Almost all turbines currently installed to produce electricity for national or regional grids are horizontal-axis wind turbines (HAWT). HAWTs have the main rotor shaft and electrical generator at the top of a tower. The rotors spin horizontally, parallel to the wind stream and the ground. Turbines usually have three blades, made of fiberglass-reinforced polyester or wood-epoxy.⁷ Types with one or two blades exist as well.

Horizontal-Axis Wind Turbine

Source: Own Picture. Author: Flowminator. Permission: GNU Free Documentation License.

The blades, which are fixed to a rotor, are shaped in such a way that wind causes them to turn. Most HAWTs are operated upwind, with the blades facing into the wind. Downwind HAWTs also exist, but are less efficient as the tower is between the wind and the propeller. A yaw mechanism in the turbine shaft is utilized to turn the wind turbine rotor into the wind, increasing efficiency.⁸ Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most HAWTs also have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.⁹

Vertical-axis wind turbines (VAWT) use rotors that run vertically. Two well-known types of VAWTs are the Savonius rotor - a dragtype devise consisting of two or three scoops causing a turbine to spin,-, and the Darrieus rotor - a model that collects wind in cups dragging a turbine around, and that looks much like a 'giant eggbeater'.¹⁰

Most of the currently used VAWTs use Savonius rotors. VAWTs have some advantages over HAWTs. The turbines can be used at much lower windspeeds than those of HAWTs, and that they do not need to be pointed into the wind to be effective and can thus utilize winds from varying directions. In addition the generator of HAWTs can be placed close to the ground, so maintenance is relatively easy.¹¹

Vertical-Axis Wind Turbine

Source: commons.wikimedia.org. Author: Frommcc. Permission: GNU Free Documentation License.

Still, VAWTs are almost never used for commercial purposes, as they are far less efficient in terms of cost per kWh than HAWTs, require a relatively large amount of expensive materials, and can only be installed close to the ground, where the wind naturally blows less strongly than at greater heights.¹², ¹³

Wind farms

Wind farms are clusters of larger (10kW to as large as 5 MW) wind turbines , which are erected in the same location for the purpose of generating large amounts of electric power.¹⁴They are controlled and operated through SCADA (supervisory control and data acquisition) systems, which manages information including how much each turbine is producing, the temperature inside and outside of each turbine, wind direction and if any one turbine needs service or repair.¹⁵

Wind farms are economically efficient, as they space turbines together and thus minimize land use and the cost of connection to the electrical grid. The windfarms, which can consist of several hundreds of horizontal-axis wind turbines, are placed in areas where there is a nearly steady prevalent wind.¹⁶ More and more wind farms are being built offshore, various kilometers off the coast, where wind conditions are often more optimal than on land. In 2008 offshore wind farms represented 1% of all wind power. 99% of the offshore wind parks are currently located in Europe.¹⁷ Offshore wind turbines are much more expensive to build, more expensive to maintenain and require more frequent maintenance due to the corrosive effects of salt water; however, the increased windspeed often makes up for these limitations.¹⁸ To avoid the so-called 'wind park effect', where efficiency of turbines is lost as a result of turbines blocking each other's wind, specific formulas are used to define how to place the turbines . As a rule of thumb, turbines are usually spaced between 5 and 9 rotor diameters apart in the prevailing wind direction, and between 3 and 5 diameters apart in the direction perpendicular to the prevailing winds.¹⁹

Selection of sites

Anemometer

Source: commons.wikimedia.org. Author: Stefan Kuhn. Permission: GNU Free Doc License.

Wind speed is the most important factor in the selection of sites for wind turbines and farms. Power goes as the cube of windspeed; that is, twice the wind speed generates eight times the power²⁰. Wind is slowed down by the roughness of terrain. When evaluating wind conditions in an area, people usually refer to roughness classes or roughness length. A high roughness class of 3 to 4 refers to landscapes with many trees and buildings, while a smooth sea surface is roughness class 0.²¹ Many times decisions on location of turbines are based on data collected by meteorologists for weather forecasts and aviation. Although this can be helpful, the data is rarely precise enough to base a final decision on and should be combined with on site measurements. For this purpose anemometers are often used. They are placed to the top of a mast with the same height as the expected height of the wind turbine which would be used. The data on wind speeds and wind directions from the anemometer is collected on electronic chips on a small computer.²²

Other important factors in the selection of sites for wind turbines include proximity of electrical grids (mostly for large turbines), soil condition, and impacts on negative impacts on living conditions of nearby communities, and on animal lives.

Global wind resources

A 2005 study by Stanford University professor Mark Jacobson and graduate student Christina Archer of economically feasible wind resources concluded that there is as much 72 terawatts of commercially viable wind capacity available globally. Capturing less than 5 percent of this potential would meet all of the world's energy needs. ²³

Advantages

Wind energy offers numerous benefits over conventional energy sources:

In many parts of the world, wind energy is abundant and can be harnessed at low cost by modern technology.
Wind power is clean and renewable: Except for the building materials of the wind turbines, wind energy produces no byproducts that contribute to global warming, and the power from a single utility-scale wind turbine can prevent the emission of 5,000 tons of carbon dioxide (CO2) into the atmosphere each year. ²⁴In addition, it can also reduce water consumption associated with electricity generation by 4 trillion gallons by 2030.
Remote areas that are not connected to the electricity power grid can use wind turbines to produce their own supply.
Wind industry can boost local economy. Wind energy can diversify the economies of rural communities, adding to the tax base and providing new types of income. It is estimated that wind power market increase annual revenues to local communities to more than $1.5 billion by 2030; and support roughly 500,000 jobs in the U.S., with an average of more than 150,000 workers directly employed by the wind industry.²⁵

Drawbacks and limitations

Setbacks for wind power include:

The most significant barriers towards implementing wind power systems regard cost and transmission issues. The natural variation of wind power over time presents a challenge to integrate a large amount of wind power into a grid system, which requires balanced generation and consumption to main grid stability. Scarce investment in transmission during the past two decades has presented a hurdle to the development of the wind power market. Federal regulations are being developed, however, to address the transmission issues in an effort to support the development of wind power.
Some communities have expressed negativity regarding the aesthetic view of windfarms. ²⁶
Many communities have fears about the noise generated by local wind turbines²⁷
Even though wind power does not generate pollution, the manufacturing process of wind turbines does produce pollution.

Market

Wind power currently produces about 1.5% of world-wide electricity, and has become one of the leading electricity-producing power sources in various countries. In 2008 the worldwide newly installed capacity of wind power was 27,000 megawatts (MW),²⁸ an increase of 29% compared to 2007. The total generated capacity worldwide at the end of 2008 was 121,188 MW, generating 260 terawatt hours (TWh). The World Wind Energy Association (WWEA) expects the installed capacity to keep increasing at a very fast rate, and to be around 190.000 MW in 2010 and 1.500.000 MW in 2020 equaling around 12 % of global electricity consumption.²⁹ According to Clean Edge, capital costs of new installations of are projected to expand from $51.4 billion in 2008 to $139.1 billion in 2018.³⁰ This is expected to be the case even with the current finance crisis, as wind power is attractive to investors due to its relatively low-risk character, it's societal and economic benefits, and the growing need for clean and reliable energy sources. In 2008, Europe accounted for 32.8% of the world's wind market, North America for 32.6 %, and Asia for 31.5 %. Latin America's share was 0.6% and Africa's share 0.5%.³¹

In 2008 the United States installed more than 8,000 MW of wind installations, representing more than forty percent of the total new electricity generating capacity in the country in that year.³² Its total installed capacity was 25.170 MW, 1.5% of the total energy used in the country, powering the equivalent of around 5.5 million homes., making the U.S. the country with the and the largest installed capacity worldwide. Technology is being innovated constantly, and an increasing number of U.S. states are establishing favorable legal frameworks for wind energy and are attempting to attract investors in manufacturing facilities. Texas, Minnesota and Washington currently have the largest installed capacity of electricity.In Canada development of wind power has been slow.³³

World Capacity of Installed Wind Power 1980-20087

World Capacity of Installed Wind Power 1980-2007

Source: GWEC, WorldWatch. Author: GWEC, WorldWatch. Permission: Earth Policy Institute, www.earth-policy.org.

Europe has been the leader both in wind energy development and innovation, and in installed capacity for the last twenty years, but is currently being surpassed by North America and Asia. Its installed capacity was 66,160 MW in 2008. Denmark was the pioneer worldwide. Even though Denmark's installed capacity has been surpassed by various countries, wind power still provides around 20% of all energy needs in the country; the highest percentage worldwide. Germany has had the largest installed capacity for a decade until 2007. Since 2008 the country ranks number two after the U.S, but is still showing sustainable growth and is providing more than 7 % of Germany’s total electricity consumption. Spain has the third largest installed capacity worldwide. The most dynamic growth markets in Europe currently are in Poland and Ireland.³⁴

Asia had 24,439 MW of installed capacity in 2008, and its market share in wind energy is growing extremely rapidly. China and India rank number four and five respectively on the list of countries with the largest installed capacity worldwide. These two countries have also started producing their own models of wind turbines, and are likely to become big exporters of turbines in the recent future. The wind power market in South Korea is also growing at a fast rate.³⁵

The installed capacity in Australia and Oceania was 1,819 MW in 2008, a large increase compared to the installed capacity in 2007. The large majority of installed capacity was created in Australia, and this trend is likely to continue in the near future. New Zealand has made very little progress in installing wind power.³⁶

In Latin America development of wind power has been slow, with a total installed capacity of 667 MW in 2008. Only Brazil and Argentina installed large wind farms in that year. In Argentina, Brazil, Chile, Costa Rica and Mexico projects are planned and under construction. These projects are likely to significantly increase installed capacity in 2009.³⁷

Africa has very good potentials for wind energy that have not yet been developed; mostly in the southern and northern parts of the continent. Few major wind farms exist in Morocco, Egypt and Tunisia, but in sub-Saharan Africa only South Africa has a large windfarm. The total installed capacity currently is 563MW. Apart from large scale wind farms, decentralized and stand-alone wind energy systems can have an important role in Africa. Together with other renewable energy technologies, they can provide an important tool in the provision of sustainable rural electrification in so far unserved areas of Africa.³⁸ Many of such areas exist, as in some sub-Saharan countries less than 5 percent of rural households currently receive electricity service.³⁹

An estimated 72 terawatt (trillion watts, TW) of wind energy worldwide is potentially available for commercial use.⁴⁰

Footnotes

1. WWEA, World Wide Energy Report 2008, www.wwindea.org.

2. : AWEA, Wind Web Tutorial, www.awea.org.

3. : Pier55.com, How Does Wind Energy Work?, www.pier55.com.

4. : EIA, Wind Energy - Energy from Moving Air, www.eia.doe.gov.

5. : BWEA, How Does Wind Energy Work?, www.bwea.com.

6. : DOE, EERE, How Wind Turbines Work, www1.eere.energy.gov.

7. BWEA, Wind Energy Technology, www.bwea.com.

8. Carbonify.com, How Wind Turbines Work, www.greenlivingtips.com.

9. : DWIA, Wind Turbine Components, www.windpower.org.

10. : Absolute Astronomy.com, Savonius Wind Turbine, www.absoluteastronomy.com.

11. : DWIA, Wind Turbines: Horizontal or Vertical Axis Machines? , www.windpower.org.

12. : ReFocus, HAWT versus VAWT,2003, www.re-focus.net.

13. : Mother Earth News, Wind Power: Are Vertical Axis Turbines Better?, www.motherearthnews.com.

14. : AE, Wind Farms, www.alternative-energy-news.info.

15. : Horizon Wind Energy, How Is Electricity Made From Windmills?, www.horizonwind.com.

16. : Encyclopedia Bittannica, Wind Farms, www.britannica.com.

17. WWEA, World Wide Energy Report 2008, www.wwindea.org.

18. Offshore Wind Energy

19. : DWIA, Park Effect, www.windpower.org.

20. Wind Power Basics, part 1

21. : DWIA, Roughness and Wind Shear, www.windpower.org.

22. : DWIA, Wind Speed Measurement in Practice, www.windpower.org.

23. American Geophysical Union, "Global Wind Map Identifies Wind Power Potential" (May 16, 2005), from Geoffrey Holand and James Provenzano, The Hydrogen Age. 2007.

24. : Environmental Defence - Wind Power Working Group, Why Wind Power for North Carolina?, www.ncsc.ncsu.edu.

25. AWEA, U.S. Wind Energy Installations Top 20,000 MW, www.awea.org.

26. : Technologystudent.com - V.Ryan, Advantages and Disadvantages of Wind Power,www.technologystudent.com.

27. Wind Turbine Syndrome

28. Clean Edge - Makower, J., Pernick, R., Wilder, C., Clean Energy Trends 2009.

29. WWEA, World Wide Energy Report 2008, www.wwindea.org.

30. Clean Edge - Makower, J., Pernick, R., Wilder, C., Clean Energy Trends 2009, page 3.

31. WWEA, World Wide Energy Report 2008, www.wwindea.org.

32. Clean Edge - Makower, J., Pernick, R., Wilder, C., Clean Energy Trends 2009, page 3.

33. AWEA, U.S. Wind Energy Installations Top 20,000 MW, www.awea.org.

34. WWEA, World Wide Energy Report 2008, www.wwindea.org.

35. WWEA, World Wide Energy Report 2008, www.wwindea.org.

36. WWEA, World Wide Energy Report 2008, www.wwindea.org.

37. WWEA, World Wide Energy Report 2008, www.wwindea.org.

38. : WWEA, World Wide Energy Report 2008, www.wwindea.org.

39. The World Bank, Energy in Focus 2008, page 15.

40. University of Delaware - College of Marine & Earth Studies, Mapping the global wind power resource, www.ocean.udel.edu.

Resources

American Wind Energy Association : "AWEA is a national trade association representing wind power project developers, equipment suppliers, services providers, parts manufacturers, utilities, researchers, and others involved in the wind industry - one of the world's fastest growing energy industries. In addition, AWEA represents hundreds of wind energy advocates from around the world"6.
National Renewable Energy Laboratory: Introduces wind power energy and has various research projects.

Wind Power Producers