Wind resources

Summary: The clean, renewable resource of wind is rapidly becoming used throughout the world. It is actually a form of solar energy, produced by atmospheric heat, the rotation of the Earth, and irregularities in Earth’s surface topography.

Wind is considered a renewable energy resource, costing only $0.04 to $0.06 per kilowatt-hour. Because it requires a higher initial investment to develop than well-developed fossil-fueled generators, its popularity as a resource has depended on the price and availability of fossil fuels. However, after the infrastructure to harness wind power is installed, it is a low-cost resource, and most of the world, except heavily forested regions, is suitable for the erection of windmills, wind pumps, and turbines.

Although extremely variable and unpredictable, average wind speeds in any locale vary little on an annual basis. The windiest areas are often over oceans and coasts, such as those of southern Oregon and Northern California in the United States, the coast of Thailand, and smaller, isolated landmasses such as the Cape Verde Islands, Cyprus, Madagascar, Malta, and Mauritius. Even deserts in countries like Morocco and grasslands such as those of Argentina provide winds to be harnessed as an energy resource.

The facilities to capture wind power can be built on islands, coastal highlands, and windy interior rural areas as wind farms or ranches, thus benefiting rural economies. Moreover, landowners are able to place wind turbines, harvest crops, and raise livestock in the same space. Wind pumps are used in China, Kenya, Namibia, Peru, Tunisia, and Zimbabwe. The US Department of Energy (DOE) has a wind program that is researching wind resources and applications to produce hydrogen, to clean and move water, and to work in synergy with hydropower stations to provide a stable supply of electricity.

Wind Energy Applications

Wind energy has been used for transportation, ventilation, and agricultural production since prehistoric times. Its applications are useful to individuals, businesses, corporate entities, and nations. Water-pumping American windmill systems were extensively used during the nineteenth century; the United States had at least 6 million wind-operated water pumps for more than a century, from 1850 to 1970. These systems were small yet efficient, generating about 1 horsepower or less and with 4- to 8-foot rotor diameters; the water pumps were largely used to water stock. Larger windmills, with rotors up to 59 feet (18 meters) in diameter, were used to pump water for steam-driven trains.

The earliest windmills in America began with Daniel Halladay of Ellington, Connecticut, whose self-furling sail windmill appeared in 1854. Four wood blades or lightweight slats on wood rims were used. Tails oriented them into the wind, but weather-vane mills could operate downwind of the tower. Speed was controlled by hinged blade sections that folded in high winds. This reduced the rotor capture area to reduce thrust. American windmills of this type were made with steel blades from around 1870. These were light, easily shaped steel that necessitated reduction gears to turn more slowly and regularly in high winds. In 1878, C. B. Dempster’s model was developed in Carpentersville, Illinois. A decade after its use, Aermotor of San Angelo, Texas, designed a mill that is still in use today.

In 1888, Charles F. Brush of Cleveland, Ohio, and in 1891 Poul La Cour of Denmark developed automatic wind turbines for the generation of electricity. They pioneered wind energy use for electric power by building on Greek, Dutch, and Portuguese windmill designs. Capturing wind energy requires several blades driven around an opaque center by the natural force of the wind. Sails placed at regular distances from a transparent center of rotation also capture wind and use its torque for turning a circular structure. The US multiblade design empowered the first large windmill to generate electricity. Its rotor was 55 feet (17 meters) in diameter and maneuvered itself with a hinged tail. The 50:1 gearbox turned the direct current (DC) generator 500 rotations per minute (rpm).

La Cour’s aerodynamic design of low-solidity, four-bladed rotors was used in European tower mills. La Cour rotors turned at higher speeds to generate electricity, but by 1920 huge, inexpensive fossil fuel steam plants overtook the market. The fan and sail rotors were inadequate for generating electricity on a large scale. Development of wind-generator electrical systems in the United States then incorporated airplane propeller and monoplane wing designs to produce massive amounts of low-cost wind energy. Linking wind farms with high-voltage DC grids was the next step. Long-distance transmission and lower energy costs can now be realized more than 1,000 miles from the source of the wind and electricity generation. Wind production is rapidly growing to supply worldwide electricity use, with high levels of penetration in Denmark, Spain, Portugal, Germany, the United States, China, and the Republic of Ireland.

Wind Cause, Behavior, and Measurement

Wind is caused by air flowing from areas of high to low pressure. Because of the rotation of the Earth, the air does not flow directly from high to low pressure but is deflected to the east in the Northern Hemisphere and to the west in the Southern Hemisphere. Wind often flows in a circular motion around high- and low-pressure areas. When these areas are in close proximity, the pressure gradient increases to increase wind strength. Isobars on a map show increasing value in millibars by their closeness. The curvature of the isobars also indicates strong wind speed anticyclonically around the high-pressure areas. If mapped isobars are curved cyclonically around the low pressure, the wind will be weaker. This happens when wind is close to ground friction. The warmth of the sun causes convective mixing to take place, slowing or halting wind velocity. Wind transports excess heat away from the surface of the Earth, where sunlight causes an excess of residual energy. In warmer regions such as the tropics, wind moves to cooler, higher-latitude regions.

Power in wind declines with altitude, but the effect is much less than with velocity. Wind speed constantly changes, and it is impossible to stop wind completely by human or mechanical means.

Wind power density (WPD) can be effectively measured. WPD is a calculation of the effective force of the wind at a particular location by velocity and mass and by elevation above ground level over a period of time. Wind behavior maps describe mean annual power density at certain meters of elevation. The National Renewable Energy Laboratory (NREL) index identifies classes for these carefully documented locations. Higher WPD calculations produce higher class ratings.

Wind resources in the United States undergo an assessment based on daily measurements over at least a year to estimate potential energy generation. Economic feasibility is then determined for particular areas best suited for development. The US Wind Program, the NREL, and other organizations measure, characterize, and map wind resources 164–328 feet (50–100 meters) aboveground. Land use or environmental issues may deter the use of wind resources. The NREL rates wind resource potential at 1, marginal; 2, unsuitable; 3, fair; 4, good; 5, excellent; 6, outstanding; and 7, superb. The Alaskan peninsula, from Attu to Egegik, would be classified at 7.

History

Wind was used for propelling boats by Asian Pacific Rim cultures before the Neolithic period, about 9500 BCE. Early boat designs have been found in Nanshui, Zhuhai, on Gaolan Island. Baojing Bay rock carvings depict a three-story cabin with sails in the middle and at the stern.

References to wind and its importance can be found throughout antiquity. A didactic poem written in the 4th century BCE, from what became part of the Book of Job in the Bible, asks, “By what way is the light parted which scatters the east wind upon the earth?” The Dead Sea Scrolls and at least 10 authors of scripture refer to wind power. Wind is mentioned as being of heaven and earth, from four corners or quarters, and capable of striving over oceans and carrying breath or the power of life. A 3200 BCE Egyptian pottery vessel clearly shows a wooden sailboat made of conifers from Lebanon. Ruins of the Temple Khentyamentiu have produced 14 75-foot ships dating to 2950 BCE. These Abydos ships were used to represent funerary transport, but the Egyptians employed sailing ships for Nile and canal traffic carrying stone before the invention of the wheel. Tomb reliefs and red pottery motifs display sailboats in Egypt dating from the predynastic culture of Nagada II, around 4000 BCE.

Persian mechanical systems from 200 BCE used a vertical axis to capture wind energy for grinding and pumping. Grain was fed between large, heavy grindstones moved by a vertical shaft during windy episodes. Such mills had to be enclosed in a building or sheltered by a wall blocking incoming winds to the side. They slowed a drag rotor that captured the headwind. European mills of the 13th century used sails for aerodynamic lift and represented improvements in terms of rotor efficiency compared with the Persian mills. As improvements continued, rotor speed increased, and grinding and pumping action became more controlled.

The first windmills in the Netherlands had a horizontal axis, making them more efficient in rotor collection. They had four blades turning the shaft and meshed with vertical wood cog gears to rotate a grindstone. The Dutch also refined the tower mill design used along the Mediterranean seacoast. They built towers of several floors for grinding, removing chaff, and storing processed grain, along with balconies and living areas. Earlier post mills and the tower mill complex had blades that necessitated hand levers to move them into the wind. Dutch windmills were improved by craftsmen to cut and plane raw timber and grind dry imported spices, cocoa, paint pigments, dyes, and tobacco.

The specialized mills used aerodynamic brakes, spoilers to hinder unfavorable wind movement, blades with a camber bend (arch) or curve affixed at the ends of braces, and retractable flaps. The development of steam engines signaled their partial demise, but industrial, utility-scale wind energy conversion systems were to be developed in Europe, Asia, and the United States. Rockport, Missouri, was the first city in the United States to utilize wind as a resource for 100 percent of its energy generation.

Bulk wind energy conversion systems were pioneered in Russia in 1931 with the 100-kilowatt Balaclava wind generator, which had the capability of producing 200 megawatt-hours of electricity annually. Wind plants in the United States (exemplified by Smith-Putnam of Vermont), in Denmark’s Gedser Mill wind turbine, in France with G. J. M. Darrieus rotors, in Germany with Ulrich Hütter’s designs, and in Great Britain produced large-scale, working wind turbines from 1935 to 1970. All inventors sought interconnections with the electric power grid for practical, economically feasible wind energy consumption. The US federal wind energy program began with the Darrieus model at Sandia National Laboratories, Taiban Mesa, New Mexico, in response to the 1973 oil embargo. Here, the Energy Research and Development Administration (ERDA) and then the DOE used a bidding system in order to subcontract the construction and test wind mechanisms for public commercial use.

Between 1974 and 1981, the US federal wind energy program developed 13 small systems, several vertical axis and innovative systems, and four large wind turbine designs, but none of these systems benefited the American private or business user of electricity. By 1995, most of the experimental multimegawatt machines developed in Germany, Sweden, and other countries were deemed infeasible. It has been suggested that government involvement in research brought a halt to the production of bulk wind energy conversion systems. Research and development programs were discarded in the early 1980s in favor of US government funding for energy tax credits. These also failed to result in broad-based private wind turbine technology development in the United States. From 1990 to 2000, the United States funded research and development under the National Wind Technology Center and the NREL at Boulder, Colorado.

Most turbines used in the United States at this time were in Altamont, Tehachapi, and San Gorgonio, California, and were Danish in design. They ranged in output from 20 to 350 kilowatts and collectively, at top performance, could have empowered a midsized American city. Europe increased private wind turbine development. Until the twenty-first century, the progress made in Europe outpaced US development. Low utility rates, natural gas imported from Canada, and threatened deregulation of the utility industry slowed US wind energy development.

Manufacturers of large, utility-scale wind systems produce 200-kilowatt to 3-megawatt systems. Some promote three-bladed machines with full-span pitch control and two-bladed, stall-control machines with teetering hubs. New developments are showcased in the industry online newsletter Windpower Monthly.

Two General Electric (GE) Innovation Awards for the “GE Ecomagination Challenge: Powering the Grid” have had an impact on the wind energy industry. WinFlex Inflatable Wind Turbines in Kiryat Yam, Israel, submitted a rotor design for wind turbines, using lightweight, low-cost, composite sheets and a rotor that can reduce installation costs by 50 percent or more. The technology was developed by Vladimir Kliatzkin, a researcher in energy production and accumulation systems for aviation, internal combustion engines, and hybrid systems.

The second winner, IceCode: Wind Turbine Blade Anti-icing and Deicing of West Lebanon, New Hampshire, submitted an ice removal technology using high-power pulses to apply internal heat. Wind turbines using the heat pulses can reduce deicing energy and downtime for ice removal and physical inspection. Collaboration with Dartmouth College in Hanover, New Hampshire, produced pulse electrothermal deicing (PETD), a simple process that saves energy, improves safety and convenience, and reduces maintenance. Deicing of turbine blades is instant and allows constant monitoring of ice buildup with electrical components. Conductive material is laminated on blade surfaces or embedded, helping wind energy farms to reduce downtime, maintenance, and damage to blades and other operating parts.

Manufacturers worldwide are experimenting with simplified drive trains that eliminate costly repairs and longer blades to harness wind gusts. Ocean winds can be better harnessed with a gearless turbine and lightweight, 176-foot blades. Such devices have no gearbox, electromagnets, starter brushes, oil changes, or coils. General Electric has designed a direct-drive mechanism that uses an approximately 20-foot ring of permanent magnets. It propels a blade that twists as it bends in a backward curve of approximately 8 feet. The innovative extension instantly angles the longer blade to bear less wind force yet capture optimal energy. The flat-edged blades are made of stiff carbon fiber instead of fiberglass. Testing of the 8- to 20-rpm blades in the Netherlands and the drive train in Norway may result in a perpetual-motion turbine that captures 25 percent more wind power than conventional models at 4 megawatts.

In 2024, the US Department of Energy was seeking to add offshore wind projects by soliciting proposals for funding. The previous year, wind accounted for 7.8 percent of power produced globally.

ContinentCity, State/Region, CountryInventor/CEOManufacturerNorth AmericaRolling Meadows, ILTal OrenMicon Components Ltd.Fairfield, CTJames G. P. DehlsenGeneral Electric EnergyPlano, TXAllen WangWindMax Green Energy Corp.Fort Wayne, INBrian RobertsonHummer Wind Power, LLCEuropeAurich, Emden, and Aloys WobbenEnerconRheine, GermanyMarkus TackeFranz TackeGermania Windpark GmbH & Co. KG,WinvestHamburg, GermanyAndreas NauenREpower (parent Suzlon)Hamburg, GermanyThomas RichterichNordex-ForumBerlin, Munich, and Peter LöscherJoe KaeseZamudio, Biscay, SpainJorge Calvet SpinatschGamesa Corporación TecnológicaAsiaBeijing, ChinaJiangsu, Mongolia Han JunliangLecheng LiSinovel Wind (Group) Co., Ltd.Urumqi, Xinjiang, ChinaWu GangXinjiang Goldwind Science & Technology Co.Chengdu, Sichuan, ChinaSi Zefu, Wen ShugangDongfang Electric Co.Shenyang, Liaoning, ChinaJinxiang LuA-Power Energy Generation SystemsGujarat, India Tulsi R.TantiSuzlon Energy Ltd.

Bibliography

Gipe, Paul. Wind Energy Comes of Age. New York: Wiley, 1995.

Lempriere, Molly. "Wind and Solar Are 'Fastest-Growing Electricity Sources in History.'" Carbon Brief, 5 Aug. 2024, www.carbonbrief.org/wind-and-solar-are-fastest-growing-electricity-sources-in-history/. Accessed 7 Aug. 2024.

Summerfield-Ryan, Oliver, and Susan Park. "The Power of Wind: The Global Wind Energy Industry's Successes and Failures." Ecological Economics, vol. 210, 2023, doi.org/10.1016/j.ecolecon.2023.107841. Accessed 7 Aug. 2024.

US Department of Energy. “Wind Program.” www1.eere.energy.gov/wind/.