There is evidence that wind energy was used to propel boats along the Nile River as early as 5000 B.C. Simple windmills were also used in China to pump water and grind grain. In the United States, millions of windmills were erected to pump water for farms and ranches as the American West was developed during the late 19th century.

Wind is thermal power that has already been converted to mechanical power. As the wind turns the blades of the turbine, the rotating motion drives a generator, producing electricity with zero emissions. This is referred to as "wind energy" or "wind power." This power can then be used for specific tasks (such as grinding grain or pumping water) or can be converted to electricity (through a turbine).

Although wind currently produces just over 1% of world-wide electricity use, it accounts for approximately 19% of electricity production in Denmark, 9% in Spain and Portugal, and 6% in Germany and the Republic of Ireland (2007 data). Globally, wind power generation more than quadrupled between 2000 and 2006. At the end of 2006, worldwide capacity of wind-powered generators was 73.9 gigawatts. Wind power is produced in large scale wind farms connected to electrical grids, as well as in individual turbines for providing electricity to isolated locations.

Modern wind turbines fall into two basic groups; the horizontal-axis variety, like the traditional farm windmills used for pumping water; and the vertical-axis design, like the eggbeater-style Darrieus model, named after its French inventor. Wind turbines are often grouped together into a single wind power plant, also known as a wind farm, and generate bulk electrical power. Electricity from these turbines is fed into the local utility grid and distributed to customers just as it is with conventional power plants.

All electric-generating wind turbines, no matter what size, are comprised of a few basic components: the rotor (the part that actually rotates in the wind), the electrical generator, a speed control system, and a tower.

Wind turbines are available in a variety of sizes and power ratings. There are machines that have propellers that span more than the length of a football field, stand 20 building stories high, and produce enough electricity to power 1400 homes. A small home-sized wind machine has rotors between 8 and 25 feet in diameter and stands upwards of 30 feet and can supply the power needs of an all-electric home or small business.

Wind turbine power capacity can range from several kilowatts to several megawatts, depending on the turbine design and the length of the blades. Most turbines now produce about 600 kW but more powerful machines are becoming more common as the market expands and technology improves. There are currently several different types of turbines available - with 1, 2, or 3 blades, different blade designs, and varying orientations to the wind.

The feasibility of wind power for a particular location depends on the amount of wind available at the site. Wind speed is a critical feature of wind resources, because the energy in wind is proportional to the cube of the wind speed. In other words, a stronger wind means a lot more power.

Wind power is the most economically competitive of the renewables. By 2010, the World Wind Energy Association expects 160GW of capacity to be installed worldwide, up from 73.9GW at the end of 2006, implying an anticipated net growth rate of more than 21% per year.

Wind turbines in Denmark. Denmark generates over 20% of its electricity with wind turbines.

The majority of this growth has been in Europe, Germany, Spain and Denmark have made the largest investments in wind-generated electricity. Denmark is prominent in the manufacturing and use of wind turbines, with a commitment made in the 1970s to eventually produce half of the country's power by wind. Denmark generates over 20% of its electricity with wind turbines— the highest percentage of any country -- and is fifth in the world in total wind power generation.

India has also experienced tremendous growth with the private sector playing a lead role confining the government's role to that of a catalyst providing technical guidance and economic stimuli such as capital subsidies, exemption from certain duties and taxes.
Wind power is also being used extensively in the US, mostly in California. Texas has become the largest wind energy producing state, surpassing California. In 2007, the state expects to add 2 gigawatts to its existing capacity of approximately 4.5 gigawatts. Iowa and Minnesota are expected to each produce 1 gigawatt by late-2007.

In 2005, China announced it would build a 1000-megawatt wind farm in Hebei for completion in 2020. China reportedly has set a generating target of 20,000 MW by 2020 from renewable energy sources — it says indigenous wind power could generate up to 253,000 MW. Following the World Wind Energy Conference in November 2004, organized by the Chinese and the World Wind Energy Association, a Chinese renewable energy law was adopted. In late 2005, the Chinese government increased the official wind energy target for the year 2020 from 20 GW to 30 GW.

Mexico opened La Venta II wind power project as an important step in reducing Mexico's consumption of fossil fuels. The project (88MW) the first of its kind in Mexico, will provide 13 percent of the electricity needs of the state of Oaxaca and by 2012 will have a capacity of 3500 MW.

Another growing market is Brazil, with a wind potential of 143 GW. The federal government has created an incentive program, called Proinfa, to build production capacity of 3300 MW of renewable energy for 2008, of which 1422 MW through wind energy. The program seeks to produce 10% of Brazilian electricity through renewable sources.

One advantage to wind power technology is that turbines can be used singly or in small groups to provide power locally or can be part of an energy system, either with other renewable energy sources or connected to the grid.

Several factors affect the cost of wind power - for example, the wind speed at a particular site, the reliability and efficiency of the turbines, and the estimated rates of return on investment - but overall, costs are declining. With improved technology and manufacturing procedures, the cost of generating electricity from wind power has dropped to less than 7 cents per kilowatt-hour, compared to 4-6 cents per kilowatt-hour to operate a new coal or natural gas power plant-and prices are expected to drop even further over the next 10 years.

New, utility-scale wind projects are being built all around the United States today with energy costs ranging from 3.9 cents per kilowatt-hour (at very windy sites in Texas) to 5 cents or more (in the Pacific Northwest). In the US, wind energy provides more jobs per dollar invested than any other energy technology - more than five times that from coal or nuclear power. Modern wind technology takes advantage of advances in materials, engineering, electronics, and aerodynamics.

Many states in the USA now permit "net metering," in which the utility must buy wind power generated by homeowners at the same retail rate the utility charges. This essentially allows the customer's meter to turn backward while wind energy is supplied to the grid by the customer's turbine.

The amount of emissions avoided from California's wind power plants in 1990 alone was more than 2.5 billion pounds of carbon dioxide, and 15 million pounds of other pollutants. It would take a forest of 90 million to 175 million trees to provide the same air quality.

In spite of the dramatic decrease in costs over the past 10 years, the technology requires a higher initial investment than fossil-fueled generators. Roughly 80% of the cost is the machinery, with the balance being the site preparation and installation. These high initial costs are offset by the minimal operating expenses and zero fuel bill. Although wind power plants have relatively little impact on the environment compared to other conventional power plants, there is some concern over the noise produced by the rotor blades, aesthetic (visual) impacts, and occasional avian (pertaining to birds) mortality. Most of these problems have been greatly reduced through technological development or by properly sitting wind plants, although avian mortality remains an issue to be better understood and resolved.

The major challenge to using wind as a source of power is that it is intermittent and does not always blow when electricity is needed. This challenge is overcome by using batteries. In addition, good wind sites are often located in remote locations far from areas of electric power demand (such as cities). In certain regions, wind resource development may compete with other uses for the land and those alternative uses may be more highly valued than electricity generation. However, wind turbines can be located on land that is also used for grazing or even farming.

Additional Resources:

US Department of Energy: Wind Energy Topics
List of websites and reports dealing with wind power.

Windpower
This site, run by the Danish Wind Energy Association, contains information ranging from the history of wind power to publications and frequently asked questions.

Middelgrunden
The largest off-shore wind farm in the world.  In Danish and English.

Wind Power Magazine
A periodical devoted to disseminating information on wind electricity generation.