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Large Wind Turbines

January 1, 2001
Paul Gipe

European Wind Experience to 2001


 


Portions of the following have been adapted from Wind Energy Comes of Age by Paul Gipe (1995) and updated to 2001. For more on this topic and for the citations, see the book.


IV. European Experience

While Putnam was managing the development of his massive turbine in Vermont, Ulrich Hütter was designing and building wind turbines for the Nazi-owned Ventimotor company outside Weimar, Germany. Wind turbines were seen by the Nazis as a means toward autarchy or the ability to supply electricity without the need for foreign supplies of energy. Hütter's team experimented with several designs, including one of the first uses of a wind turbine to drive an asynchronous or induction generator directly coupled to the electric utility network. Wartime experimentation with wind energy was not limited to Hütter in Germany. At the same time Hütter was building turbines for Ventimotor, F.L. Smidth was erecting wind turbines in occupied Denmark.

After the war, Hütter went on to become a prominent aeronautical designer who continued his experimention with wind energy. In the late 1950s Hütter installed a then novel turbine based on his PhD dissertation which concluded that the ideal wind turbine would use a rotor operating at high speeds with only two slender blades. At the opposite technical pole from Hütter was Johannes Juul in Denmark. Juul was a traditionally trained engineer, that is, outside academia. Juul's design approach grew out of the Danish craft school tradition and he built upon the experience gained by F.L. Smidth during the war. Juul built a turbine for Danish utility SEAS at Gedser incorporating the lessons learned. Meanwhile Both the British (John Brown) and the French (Best-Romani and others) installed prototype wind turbines during the 1950s and 1960s.

The abundance of cheap oil from the Middle East doomed these programs, but Juul's turbine at Gedser and Hütter's turbine in the Schwabian Alps continued in operation for the next decade. Hütter's design, and his argument for it, would captivate German and American engineers for years to come. However, it was Juul's design, and its adherents in Denmark that would come to dominate the field of wind energy many decades later.

All commercial wind turbines trace their roots to the design philosophy arising from Juul's pioneering work in Denmark in the 1950s. Juul's simple, robust design was adopted by the Danish wind revival of the late 1970s following the oil crises of the period. When the California "wind rush" began in the early 1980s, budding Danish wind turbine manufacturers were poised to seize the opportunity. Europeans of several nationalities flocked to California to seek their fortunes in wind energy, but none more so than the Danes. The trickle of Danish machines entering California in 1981 soon became turned into a flood. At the peak of the rush in 1985, Europeans shipped more than 2,000 wind turbines, most Danish, to the United States.

Following the collapse of the California market in 1985, Danish manufacturers redirected their attention to their domestic market where they sustained steady growth in sales and technology for the next decade. By then a new market, Germany, was growing rapidly. Germany would dominate world markets for wind energy in the 1990s and well into the new millenium. Soon, Germany outdistanced all other countries, accounting for 40% percent of the total world market. In 2001 Germans installed a record 2,600 MW and all were technologically derived from Juul's work at Gedser.

Europe accounted for two-thirds of total worldwide wind development in 2001 (Fig, x. World Wind Generating Capacity). Germany outdistanced all others, accounting for 40% percent of the total world market. In 2001 Germans installed 2,600 MW--a record.

IV.A. Denmark and the Danes

The development of wind energy in Denmark followed a far different path than that in North America. Unlike American wind turbine design, which was concentrated in the hands of the aerospace industry, Danish wind technology grew out of the agricultural sector as a natural byproduct of the Danish economy, where farming and metal working play a major role.

Denmark's landscape is characterized primarily by small landholders. With three-fourths of its total land area devoted to farming. Though only 10 percent one-tenth of Denmark's five million inhabitants work the land, agriculture accounts for about 40% of its exports. The country not only feeds itself but exports cheese, butter, bacon, ham, and cookies to the world.

Danes are culturally predisposed toward the wind. It powered the ships of their ir early conquests and carried Norsemen as far as the New World. European or "Dutch" windmills are still a common sight on the landscape. Danes are no newcomers to wind energy, nor are wind turbines new to Denmark. Poul la Cour, the "Danish Edison," began experimenting with wind-generated electricity in 1891. At the time, the 3,000 "Dutch" windmills then in use were providing the equivalent of half again as much as all the animal power then supporting Danish agriculture. As early as 1903, La Cour's Danish Wind Power Society was fostering wind-generated electricity.

Danes commercialized La Cour's design during World War I. By the end of the war more than one-fourth of all rural power stations in Denmark were using wind turbines. During the long wartime blockade, the 3 MW provided by these crude wind machines and the widespread use of small farm windmills for grinding grain were a valuable source of power to an impoverished rural population. Though most windmills were used for mechanical power, the Danish Energy Agency estimates that wind turbines were providing the equivalent of 120-150 MW in Denmark by 1920.

Denmark again turned to the wind during World War II, when nearly 90 turbines were installed, including the 30 kW Lykkegaard wind turbine patterned after La Cour's klapsejlsmølle, and F.L. Smidth's more modern "Aeromotors." The Lykkegaard klapsejlsmølle, like those of La Cour, used four to five wide blades resembling those of traditional windmills, except that instead of cloth sails, the blades are covered with metal shutters. Control of these wind turbines was effected by opening and closing the shutters. In contrast, The F. L. Smidth company became one of the world's first firms to marry the rapidly advancing field of aerodynamics to wind turbine design. This The diversified company produced concrete as well as small airplanes. Smidth's wind turbines incorporate both technologies and used modern airfoils upwind of a concrete tower.

After the war, interest in wind energy again waned. Juul's interest, however, did not. In 1950 he Juul began testing a prototype wind turbine for Danish utility SEAS. He subsequently modified a Smidth turbine used on the island of Bogø. With the experience gained from these two machines, Juul began work on his crowning achievement, the mill at Gedser, the forerunner of today's commercial wind turbines.

The three-bladed, stall-regulated, upwind rotor at Gedser spanned 24 meters (79 feet) in diameter. For overspeed protection, Juul devised a simple system for pitching the tips of each blade. Installed in 1956, the Gedser mill operated in regular service from 1959 through 1967. When Denmark again looked to wind energy in the late 1970s for help in meeting yet another one more energy crisis, the country had a working model still standing at Gedser 150 kilometers (90 miles) south of Copenhagen.

Engineers at Risø National Laboratory scaled up Juul's Gedser design nearly three-fold in 1980, even replicating the Juul's ungainly struts and stays for one of what were to become the twin turbines at Nibe. Like Gedser, Nibe A used a stall-regulated fixed-pitch rotor upwind of a concrete tower. They built a second turbine, Nibe B, to test their ability to vary blade pitch on a rotor 40 meters (130 feet) in diameter. Juul's design was difficult to adapt to a turbine of this size, and the rotor on Nibe A was eventually replaced. Nibe B operated in regular service for more than a decade. Yet wind energy came of age in Denmark not at Nibe but at farms and at homes throughout the countryside.

Modern wind turbine manufacturers and experimenters erected their first prototypes in the late 1970s. By 1980, when the European wind energy conference was held north of Copenhagen, there were several designs in operation. Some of these early products were still in operation more than two decades later.

In 1981 Denmark set a national goal of installing 1,000 MW of wind power by the year 2000. Denmark had become self-sufficient in oil a decade later, following its discoveries in the North Sea, but the country continued its wind development program as a means of reducing its greenhouse gas emissions. In subsequent energy plans, Denmark increased wind's expected contribution to 10% of the nation's electricity supply by the year 2000, a target they exceeded. In 2001, Denmark generated 16 percent of its electricity with wind energy.

IV.A.1. Right Product at the Right Place

During the late 1970s the European market for Danish farm equipment slackened substantially, dangerously, forcing manufacturers to seek new products for their rural customers. With generous incentives from the government Danish stimulating demand, Danish manufacturers quickly adapted their surplus capacity to the new wind turbine market. The broad distribution of the population across the Danish landscape demanding modern wind turbines, a good wind resource off the North Sea, and a manufacturing sector accustomed to building heavy machinery for a discerning rural market were the ingredients that launched the world's most successful domestic wind industry.

Danish success was also due in part to "geographical proximity." The small size of the country allowed Because the country is so small, manufacturers to could service their own turbines, often directly from the factory. This enabled companies to learn quickly from their mistakes and to keep their turbines in operation as physical proof for potential buyers that the company's machines were a good investment. (The German Wind Energy Institute, DEWI, found a similar effect in Germany during the early 1990s.)

This contrasted markedly with the situation in the United States. U.S. programs directed research toward the aerospace industry, under the assumption (an incorrect one, as it turns out) that aerospace was the industrial sector most capable of building wind turbines. Denmark has no aerospace industry. Moreover, the U.S. is a much larger country and many U.S. manufacturers found it difficult to learn from and service wind turbines scattered across a continent. Only in superficial ways do wind turbines resemble aircraft. Wind turbines produce electricity in competition with that from conventional power plants. To do so they must perform like other power plant machinery; that is, they must work reliably over long periods with little maintenance. Whereas a wind turbine must operate many hours on only a few hours of service, an aircraft flies only a few hours relative to many hours of skilled maintenance. Early U.S. designs, influenced to no small degree by Hütter's precepts, were marvels of the aerospace arts: highly efficient wind turbines operating at high speeds. Unfortunately these designs proved noisy and unreliable. By the mid 1990s no aerospace company was building wind turbines in the United States and no manufacturer of designs from that period remains.

IV.A.2.Dependable Home Market

Key to Danish success was a consistent national policy supporting a strong domestic market for Danish wind turbines. (A new government in 2001 declared the country's wind energy target achieved and reversed two decades of prior policy.) This assured manufacturers a market sufficient to finance continued development of new, more cost-effective, and more reliable wind turbines. Reflecting Danish cultural traditions, government incentives were most beneficial to farmers and cooperatives.

Danes pride themselves on their unusual ability to act individually while also working together cooperatively. Nearly all farms are owner-operated owned by their operators, yet nearly all Danish farmers are members of farm cooperatives. It is these cooperatives that process the Danish foods found on the shelves of stores worldwide. Danish wind turbine cooperatives and an association of wind turbine owners have had a profound effect on the development of wind energy in the country. Prior to the entry of the utilities into the market during the late 1980s, nearly all wind turbines in Denmark were installed individually or by cooperatives. Nearly all early wind power plants are owned cooperatively, and most of the remainder are municipally owned. Some 100,000 Danish households (about 5% of the population) own shares in a wind cooperative.

Another contributor to Danish success was the role played by the Danish Windmill Owners Association, Danske Vindkraftværker. Formed in 1978, the group grew from a series of informal quarterly meetings of backyard experimenters, hobbyists, and environmentalists. Because many early wind turbines were unreliable, the group demanded minimum design standards. The most important for the future of wind energy was the requirement for a fail-safe, redundant braking system, such as the tip brakes invented by Juul in the 1950s for use on his Gedser turbine. This single provision did more than any other to further Danish wind technology, because it attempted to ensure the survival of the wind turbine when something went wrong. The owner's association also compiled statistics on the reliability of Danish turbines and compelled Danish manufacturers to fulfill their product guarantees when the turbines underperformed. Collective action by Danish wind turbine owners was so successful that German wind turbine owners replicated the format south of the Danish-German border.

Wind energy grew rapidly in Denmark not only because of the early government incentives, but also because Danish utilities were required to pay a premium price for wind-generated electricity. By agreement with the government, utilities paid 85% of the retail rate for electricity from privately-owned wind turbines. Coupled with credits against energy taxes, Danish utilities were paying the equivalent of US$0.10 per kilowatt-hour for wind-generated electricity in the mid 1990s, in comparison to retail rates (including taxes) of nearly US$0.17 per kilowatt-hour.

One oft-overlooked aspect of Danish success with wind cooperatives and installations of single wind turbines was the backing of Danish financial. Danish banks and finance societies in the 1990s provided 10-12 year loans for 60-80% of the installed cost. Banks competed for wind projects by advertising themselves as "the wind bank" in local newpapers.

IV.A.3. Nationwide Land Use Planning

Though thousands of wind turbines had been were installed in Denmark over the years by individuals without much notoriety, difficulty, Danish utilities encountered public opposition when they proposed wind to their projects of their own. The utilities were viewed as outsiders, and the new future neighbors of their proposed wind turbines treated them no differently than they would have treated any other kind of power plant.

At the utilities' request, the government appointed a special wind turbine siting committee in 1991 to find publically (?) acceptable locations for wind turbines. Land use pPlanning became necessary as because wind turbines have dramatically increased in size since the early 1980s, and their numbers continued to increase. The government committee estimated that the Danish landscape could absorb 1000-2,800 MW of wind capacity, taking into account local objections and the preservation of scenic areas.

Danish jurisdictions now include wind energy in their regional plans. These plans designate zones where wind turbines are prohibited, where single turbines may be installed, where wind farms or wind power plants are permitted, and where clusters or single turbines may be erected with special approval. Many municipalities, including the capital, also include wind turbines in local land use plans. There are wind turbines in urban areas throughout Denmark, three within the environs of Copenhagen. One project, Lynetten, is visible from the Christianborg Palace, the seat of Denmark's parliament, the Folketing. The turbines are also visible from the most visited tourist attraction in the city: the Little Mermaid.

As a result of Danish history, culture, and energy policy most wind turbines in Denmark are dispersed across the landscape unlike the giant wind farms that typify wind development in North America, India, and Spain. Many installations comprise only one turbine. There are few wind plants in Denmark, and these are small by world standards.

After 16 years of development, Denmark reached 2,000 MW of installed wind capacity. Germany reached the same level in just only 7 years, Spain only 5 years, Texas, even less. Each successive market benefits from those that went before. It takes less and less time for new markets to reach a similar threshold. Denmark's BTM Consult explains this phenomenom by noting that newer markets begin with better technology and much larger turbines and, consequently, can more quickly achieve the 2,000 MW threshold.

IV.B. Germany Rises to Prominence

Wind development in Germany differs somewhat from that in Denmark. The German market clearly demonstrates the power of Electricity Feed Laws in stimulating the growth of wind energy. In 1991, Germany's conservative government introduced the Stromeinspeisungsgesetz (electricity in-ingfeed law), requiring utilities to pay 90 percent of their average retail rate for purchases from renewable energy sources such as wind turbines. The law, encompassing only a few paragraphs, resulted in extensive wind development. By the early part of the 21st century, wind turbines could be seen in every part of Germany, from the dikes at Kaiser-Wilhelm-Kkoog on the North Sea to the hilltops of the Eifel mountains in Germany's central highlands.

Parliament, the Bundestag, modified the feed law in 1999. The revisions fixed both the price and the period during which the price would be paid, ensuring a stable domestic market. In 2001, wind turbines were producing 3.5 percent of Germany's electricity, a nation with a population of 80 million and the world's third largest economy. As a result of its precedent-setting feed law, Germany had the most dynamic and transparent market for wind turbines in the world during the first decade of the new millenium. As with the once strong market in Denmark, Germany's large domestic market spawned the growth of some of the world's largest wind turbine manufacturers.

Like Denmark, many of the wind turbines in Germany were installed as single turbines or small clusters. While there are more wind farms in Germany than Denmark, these are much smaller than those in North America, India, or Spain.

IV.C. Spain

Spanish wind development begain in earnest during the mid 1990s when the country introduced an electricity feed law. Spain's electricity feed law is a hybrid. Wind projects can choose a fixed-price per kilowatt-hour of wind-generated electricity or the wholesale rate. Nearly all project developers have chosen the fixed-price tariff. Wind projects in Spain are massive, more like those in North America than those of Denmark and Germany. However, to qualify for the program, wind projects must use domestically-produced wind turbines, not imported products. Consequently, Danish and German manufacturer's entered joint ventures with Spanish counterparts. These firms now compete with indigenous companes that developed wind technology independently. As a result of the country's electricity feed law, good wind resources, and supportive regional governments who see wind energy as a means of economic development, Spain has a bustling wind industry that rivals that of Germany. In 2001, the world's second largest manufacturer of wind turbines was Spanish.

IV.D. Other Markets

Though Great Britian and the Netherlands launched wind development programs in the early 1980s, both countries have lagged behind their European neighbors. Both countries misdirected research and development funds toward electric utilities and large industrial concerns in "top-down" or centrally directed programs that were incapable of supplying competive products for a limited domestic market. Further, programs designed to stimulate a market instead often antagonized prospective neighbors by forcing wind development onto the most sensitive sites. While Great Britain has the best wind resource in Europe, organized opposition nearly brought the industry to collapse in the late 1990s. Despite beginning sooner and having better wind resources, total installed wind capacity in Great Britain and the Netherlands each represented only 5 percent of the total installed in Germany in 2002.

In contrast, France, with its long emphasis on nuclear power, was one of the last European countries to embrace wind energy. After watching how wind development was stymied across the Channel in Great Britain and familiar with the opposition to new nuclear construction, France sought to adapt the German feed law to French conditions. The French electricity feed law differs from that in Germany in that it offers two fixed tariffs: one price for windy sites, a second for less wind areas. The French feed law also limits the size of the wind farms that can be built under the program. The intent of these changes is to encourage a greater number of smaller projects than that found in North America for example, and to spread wind development beyond just a few windy provinces, such as Brittany in the west, and Languedoc in the south.

Outside Europe and North America, wind development is prominent in India, particularly in the states of Gujarat and Tamil Nadu. Several large projects were also built in North Africa and China during the late 1990s. Wind turbines in commercial projects were operating on every continent by the turn of the new century.

IV.E. Large Turbines

In the mid 1970s governments in both North America and Europe launched ambitious programs to build a series of multi-megawatt turbines. These machines began appearing on the landscape in the late 1970s and early 1980s. By the late 1980s most had already been abandoned, become history, and their program directors artfully designated them "technical successes;" that is, the turbines seldom operated long enough to destroy themselves. Yet in terms that a wind plant operator or banker understands, they all failed. They failed in the three areas: hours of operation, energy generated, and a contribution towards making wind technology more competitive with conventional fuels.

Another round of development began in the early 1980s with the turbines appearing in the late 1980s and early 1990s. These machines performed somewhat better than their forebears, renewing hope among government-sponsored laboratories that large wind turbines did have a future after all. In 1990, the European Commission intended to chart the way for a third round of funding for large wind turbine development. In contrast to the past, funds would be directed toward wind turbine manufacturers, not the aerospace industry or other large industries. European governments, like their North American counterparts, had promoted megawatt-sized wind turbines for more than a decade with little success. The EC worried that the steady progression of ever larger wind turbines produced by Danish and German manufacturers would take too long to arrive at what program managers in Brussels believed were the optimum size wind turbines for Europe. The new program's critics, howver, charged that it would indeed take several years for the commercial turbines of the period to grow to the megawatt size, but it may not take any longer than the six-year program of leap-frogging growth then envisioned.

Manufacturers participating in the program erected their prototype megawatt-class turbines in the mid 1990s. Commercial production began in the late 1990s and by early 2000 increasing numbers of the turbines were being installed in Germany, where increasing restrictions on siting favored large wind turbines. Where installation of only one wind turbine is permitted, the landowner prefers the largest turbine possible, thus, single-turbine installations in Germany drove the market for ever larger turbines. In 2000 the average wind turbine installed in Germany exceeded one megawatt for the first time.

In the United States during the 1970s, wind turbine development rested with NASA. The space agency consulted with famed German wind turbine deisgner Ulrich Hütter and Smith-Putnam's designer Palmer Putnam. NASA even studied the operation of Juul's machine at Gedser. In the end NASA started down a path blazed years before by Putnam. The result resembled neither Hütter's lightweight, flexible, downwind design nor Juul's rigid three-bladed upwind turbine, the model for all future Danish turbines. NASA's design incorporated none of the lessons from Europe, going so far as abandoning Putnam's most significant design element, his use of flapping blades.

Instead of the hoped-for economies, researchers instead found diseconomies-of-scale due to the costly specialized components required for NASA-s machines. Altogether, the NASA's large turbine program consumed US$350 million, or nearly three-fourths of the U.S.'s wind energy research funds from 1974 to 1992.

In North America, Germany, Great Britian, and Sweden, none of the contractors in the large wind turbine development programs were building wind turbines by the late 1980s. The one exception, General Electric, returned to wind energy with the purchase of Enron Wind's manufacturing business.

Nevertheless, by 2002 megawatt-scale wind turbines were becoming common in Europe and on large wind farms in North America, some with more than 100 turbines of 1.5 MW each.

IV.F. Offshore

Energy planners have long looked offshore as a means of reducing siting conflicts in densely populated Europe. While the offshore market has been slow to develop, small near-shore projects were completed in waters off Denmark and Sweden in the late 1990s. Because turbines offshore require more expensive infrastructure, such as wave-proof towes and foundations, projects have longer lead times and must be larger than those on land. One large project of twenty 2-MW turbines, Middlegrunden, was installed outside Copenagen's harbor in 2000. In 2002, Denmark begain installing 300 MW offshore under a government-sponsored program: the 160 MW Horns Rev project in the North Sea west of Esbjerg, and the 158 MW Rødsand project in the Baltic Sea.


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