Wind technology

Summary: Technological progress has paved the way for wind energy to become an integral part of electricity generation. The high-tech electricity generation industry is a fast-growing renewable energy source.

Wind energy belongs to the renewable energies. Its inexhaustible and clean resource is wind. For many, wind can be disruptive, but for the purpose of energy generation, it is a free resource with widespread geographic availability. Wind energy has been used from ancient times and for many purposes, from sailing to pumping water. The use of winds to cool houses was incorporated into ancient Persian architecture. Among the many uses of wind, its modern application to generate electricity is decisive for its consideration here.

Wind technology refers to the instruments and devices for capturing the wind’s force and transforming it into electricity. Such devices include wind turbines and wind energy converters (WECs). WECs are usually white, with three blades, and rotate clockwise on a horizontal axis. A wind farm is a site where a number of WECs have been installed and, combined, are operated as a power plant. The product of such facilities is electricity, measured in kilowatt-hours, which is fed into the electric transmission grid.

The development of modern wind energy has seen strong expansion since its inception. On a worldwide scale, approximately 4 percent of electricity production was generated by wind in 2014. However, this small player in power generation is growing rapidly. According to the Global Wind Energy Council Secretary General Steve Sawyer, “Wind power led all technologies in new power generation in 2015.” China was the largest wind energy market between 2009 and 2015, with a total installed wind power capacity of more than 145 gigawatts at the end of 2015. The United States, Germany, India, and Brazil were the other top markets in 2015. On a nationwide scale, energy generation from wind is well advanced in Denmark, where it contributed 18.3 percent in 2008, 33 percent in 2013, and 39.1 percent in 2014. In Spain, wind accounted for 14.4 percent of energy generation in 2009, 16 percent in 2011, and 22.5 percent in March 2015; in Germany, 8 percent in 2011, 8.9 percent in 2014, and 12.9 percent between January and July 2015; and in the United States, 1.6 percent in 2013 and 4.7 percent in 2015. On a smaller, regional scale, several regions became exporters of wind energy and temporarily reached a complete power supply from wind.

The global annual newly installed wind capacity was about 63.5 gigawatts in 2015, and the global cumulative installed wind capacity reached nearly 433 gigawatts in 2015, representing significant growth since 1999, when global capacity stood at just 13.6 gigawatts. In 2015, roughly 33 percent of the installed wind capacity was located in China, 17 percent in the United States, and 10 percent in Germany. The sector continued to experience significant growth over the following years, and by 2021 global wind power capacity had reached a total of 830 gigawatts.

Origin of Modern Wind Energy Technology

The development of modern wind energy can be traced back to the 1970s. A number of early wind energy pioneers—such as Charles Brush, Poul la Cour, Ulrich Hütter, and Johannes Juul—had laid the groundwork for modern wind technology. Several of their WEC models proved the feasibility of practical operations, but the industrial breakthrough came around 1975, and the two oil crises in 1973 and 1979 provided impetus: These crises revealed many nations’ dependency on oil imports and prompted investigations into alternative energy sources. Additional triggers for the development of renewable energies were nuclear incidents, particularly the 1979 Three Mile Island accident at Harrisburg, Pennsylvania, and the 1986 meltdown of the nuclear reactor at Chernobyl in Ukraine.

As a result, the US government and governments in Europe began to support programs focusing on technological enhancement of renewable energies. In addition to these government programs, private companies and individual citizens engaged in designing WEC models, striving to find sources of energy to make their nations energy-independent. The work of earlier WEC designers was resumed and advanced for wider application to the power system.

Whether the program was funded by the United States, German, Dutch, or Danish government, most research and development focused on multimegawatt turbines. All programs aimed to advance wind technology quickly with the goal of replacing large shares of traditional power supply by demonstrating the capabilities of wind technology. However, wind technology was not the issue as much as economic viability: Especially in the United States, the challenge was not the technological development of wind energy; instead, its economic competitiveness had to be achieved. Most of the multimegawatt turbines failed to achieve reliable and cost-competitive operations. An exemplar of the failure of big wind technology became the German program. In 1987, the 3-megawatt turbine GROWIAN (an acronym for the German for “great wind energy machine”) was disassembled after only 430 hours of operation since its installation in 1983 and preparations since 1976.

By contrast with the multimegawatt WECs, wind turbines with only a few kilowatt-hours of capacity were designed by start-up entrepreneurs and small businesses. Partially supported by public research and development grants, these efforts resulted in turbine models that made their appearance as single units not always connected to the transmission grid. Two out of many small-scale WEC designs dominated during the 1980s. A robust and heavy version adapted for coastal sites with strong wind originated in Denmark, and a lightweight design focused on maximizing efficiency dominated in the United States. Both designs came into direct competition.

Federal and state legislatures created an attractive investment environment for wind energy in California. Investors were given incentives that included tax credits of up to 55 percent plus accelerated depreciation. In 1981, these mechanisms spurred a market for WECs in California, with 15,000 units installed by 1987. During the so-called California wind rush, places like Tehachapi Pass, San Gorgonio Pass, and Altamont Pass became the sites of major wind farms. In this period, the market share for turbines of Danish companies grew from 2.6 percent in 1982 to 71 percent in 1986. At the end of the wind boom, about half the turbines installed in California were Danish imports, illustrating the success of the robust Danish WEC design. High failure rates and unreliable operation for many lightweight models, on one hand, and dependable technology with several years of advanced experience, on the other, characterize the predominance of the Danish manufacturers. Combined with the burst of the California market’s bubble—the result of the discontinuation of incentivizing support mechanisms in the mid-1980s—many US manufacturers left the wind sector, having not yet been able to reach a point where they could surmount the technological problems cost-effectively without government support.

Upscaling of Turbines and Capacity

Beginning in the early 1980s and accelerating during the 1990s, the demand for WEC technology changed. In Denmark and Germany, reduced land availability in coastal zones led to higher consumer demand for energy on a per-turbine basis. The effort per turbine with regard to installation and maintenance increased on average, in comparison with the higher cost of the capacity. This led to a trend of upscaling WEC models while reducing costs. As a consequence, the old, robust WEC model was quickly left behind. While the common WEC capacity during the 1980s was generally less than 100 kilowatts, it increased to 930 kilowatts by the end of the 1990s and to 1,600 kilowatts (1.6 megawatts) by 2009, with the most advanced WECs having a capacity 8,000 kilowatts (8 megawatts).

Upscaling was accomplished by expanding rotor diameters and raising tower heights. Both enhancements aimed to absorb more wind force, either by expanding the area swept by the rotor or by reaching areas of stronger and constant wind regimes with higher towers. Access to more wind is essential to increasing energy yields and turbine efficiency. As a rule of thumb, each additional meter in altitude for a modern WEC is equal to one additional percentage point of energy yield. A difference of wind speed from 14 to 16 miles per hour results in an additional energy output of about 50 percent. Modern rotor blades reach lengths of up to 150 feet for a common 2-megawatt turbine. The longest blades for bigger WECs can exceed 200 feet.

These ongoing trends in upscaling WECs have been accompanied by continuous optimizations in grid products, sound reduction, and product diversification (such as hot- and cold-climate versions). Technological progress has been responsible for a continual decline in production costs for wind energy. Since the early 2000s, the price per kilowatt-hour for a newly installed WEC has dropped significantly. The specific production costs per kilowatt-hour for a WEC vary by site. The size of a wind farm, the individual cost of installation, and especially the local wind speeds influence the specific generation price. In a huge wind farm with strong wind conditions and low installation efforts, the cost per kilowatt-hour may be as low as 2.5 cents.

Drive-Train and Direct-Drive Construction Concepts

Alongside the upscaling process, two general construction concepts for the power transmission within the nacelle (machine house) were established. Many of all turbines worldwide are based on a drive-train concept, comprising a rotor shaft, gearbox, and generator. The mechanical power of the wind is captured by the slow-turning rotor. The slow rotation is transformed successively through a gearbox into a high-speed rotation, which is finally converted into electrical power by the generator. Direct-drive turbines relinquish the use of a gearbox. Here, a capacious ring generator directly converts the mechanical force of the rotor into electrical power, followed by a converter that changes the frequency in correspondence to the transmission grid.

Although the drive-train technology is dominant, both technologies have advantages. In the past, gearboxes were, in many cases, responsible for major defects in WECs. Previously, some observers claimed that an average gearbox would not last more than seven years and therefore needed to be changed frequently over the lifetime of the turbine. WEC manufacturers simultaneously reported WEC failure rates below 3 percent caused by gearbox problems, emphasizing the importance of high-quality standards for components. A lack of available components for the specialized direct-drive construction averted a wider distribution for many years. Only the German company Enercon moved to the gearless concept in 1991, building up an integrated production structure for all essential parts. With maturation of the industry, several new manufacturers began designing direct-drive turbines.

Challenges to Wind Energy

A continuous upscaling of turbines, further reductions of generation costs, and offshore applications are technological challenges for wind technology. However, wind energy faces additional challenges to its expansion in the lack of transmission grid capacities or simple grid connections. Normally, wind farms are located in rural and remote areas and are therefore usually far from centers of power consumption. This creates the challenge to adapt the grid infrastructure to enable the electricity generated on wind farms to be transported from rural to urban and industrial areas. Commonly, however, rural grid infrastructures have not been designed to absorb great amounts of energy, creating a demand for strengthening the existing structures. Additionally, new power lines will be needed to connect windy areas.

Another challenge to integrating wind power into the energy mix of fossil, nuclear, and nonwind renewable energies is to accommodate its characteristic unstable power production. The power generation can fluctuate, depending on wind conditions. At the moment, this requires other power plants as backup systems to balance the gaps. Precise meteorological wind forecasting already facilitates the matching of wind generation with other capacities. If wind energy is to contribute a greater share of the power mix, additional strategies for energy saving and equalization of fluctuating power generation will be essential. Battery storage systems, pumped-storage stations, or a transformation to hydrogen are potential solutions.

Offshore Wind Energy

A new area for the industry is the installation of WECs offshore, in the water. While offshore wind energy draws high public attention, its share in wind energy is relatively small. In 2015, only 3 percent of worldwide wind energy capacity was offshore. (This figure increased to 7 percent by 2021.) Nevertheless, offshore wind offers new opportunities, especially for regions with dense populations in coastal areas.

The great advantages of offshore installations lie in the stronger and more consistent, constant wind conditions in offshore locations. While an onshore wind farm may reach 1,800 to 2,500 megawatts at full capacity, an offshore wind site increases the number to approximately 3,700. The greater energy yield of an offshore wind farm comes with higher installation and maintenance costs. Since turbines are placed in sites with water depths of 60 to 90 feet, foundations that are deep and strong enough to withstand the elements incur greater expense. Also, cable connections to the transmission grid are higher, as are service and maintenance costs.

The Creation of a New Industry

Connected to the growth of wind energy applications, a new industry of technology suppliers has been developing since the 1970s. While big technological corporations were attracted by the government-funded programs to develop multimegawatt turbines in the early years, the successful development of small-scale turbines was initiated by grassroots activities and carried out by midsize companies after government funding declined. Since the 1970s, some midsize wind businesses in Denmark and Germany have expanded into multinational corporations. Vestas, a Danish company with roots in the agriculture machinery business, emerged as one of the foremost market leaders.

Other original and independent WEC manufacturers are the German companies Nordex, Enercon, and REpower; the Indian company Suzlon; and the Spanish company Gamesa. In a process of mergers and acquisitions, multinational technology corporations have moved into the wind business by taking over some of the original manufacturers. In 2002, General Electric became an important producer of WECs after acquiring the assets of Enron, which had previously purchased US Zond Energy and the German Tacke. Also, Siemens became a WEC manufacturer after the takeover of the Danish company Bonus. Other multinationals that have purchased small wind turbine manufacturers are France’s AREVA and Alstom, Spain’s Acciona, Korea’s Daewoo, and the United States’ United Technologies.

Wind power remained an area of focus throughout the early twenty-first century. In 2021, the US Department of Energy reported that a record 16,836 megawatts of wind capacity was constructed throughout the country the previous year. The agency also reported that wind power provided more than 10 percent of total electricity usage for sixteen states in 2020. In 2022, the Biden administration announced plans to develop deep ocean wind farms in both the Pacific and Atlantic Ocean capable of powering 5 million homes by 2035. The sites, which aim to produce 15 gigawatts of electricity, were announced as one of the major facets of President Biden's plan to both reduce greenhouse gas emissions and promote renewable energy in the US.

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