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An early attempt at large-scale commercial generation of power from the wind was the 53m diameter, 1.25 MW Smith Putnam wind turbine, erected at Grandpa’s Knob in Vermont, USA in 1939. This design brought together some of the finest scientists and engineers of the time (aerodynamic design by von Karman, dynamic analysis by den Hartog). The wind turbine operated successfully for longer than some megawatt machines of the 1980s.
It was a landmark in technological development and provided valuable information about quality input to design, machine dynamics, fatigue, siting and sensitivity. However, preceding the oil crisis of the 1970s, there was no economic incentive to pursue the technology further in the immediate post war years.
The next milestone in wind turbine development was the Gedser wind turbine. With assistance from Marshall Plan post war funding, a 200 kW, 24m diameter wind turbine was installed during 1956 and 1957 in the town of Gedser in the southeast of Denmark. This machine operated from 1958 to 1967 with about a 20 per cent capacity factor.
In the early 1960s, Professor Ulrich Hütter developed high tip speed designs, which had a significant influence on wind turbine research in Germany and the US.
In the early 1980s, many issues of rotor blade technology were investigated. Steel rotors were tried but rejected as too heavy, aluminium as too uncertain in the context of fatigue endurance, and the wood-epoxy system developed by Gougeon Brothers in the US was employed in a number of both small and large wind turbines. The blade manufacturing industry has, however, been dominated by fibreglass polyester construction, which evolved from LM Glasfiber, a boat building company, and became thoroughly consolidated in Denmark in the 1980s.
By 1980 in the US, a combination of state and federal, energy and investment tax credits had stimulated a rapidly expanding market for wind in California. Over the 1980-1995 period, about 1700 MW of wind capacity was installed, more than half after 1985 when the tax credits had reduced to about 15 per cent.
Tax credits attracted an indiscriminate overpopulation of various areas of California (San Gorgonio, Tehachapi and Altamont Pass) with wind turbines, many of which were ill-designed and functioned poorly. However, the tax credits created a major export market for European (especially Danish) wind turbine manufacturers, who had relatively cost effective, tried and tested hardware available. The technically successful operation of the later, better designed wind turbines in California did much to establish the foundation on which the modern wind industry has been built. The former, poor quality turbines conversely created a poor image for the industry, which has taken a long time to shake off.
The growth of wind energy in California was not sustained, but there was striking development in European markets, with an installation rate in Germany of around 200 MW per annum in the early 1990s. From a technological standpoint, the significant outcome was the development of new German manufacturers and of some new concepts. The introduction of innovative direct drive generator technology by German manufacturer Enercon is noteworthy. Subsequently, a huge expansion of the Spanish market occurred, including wind farm development, new designs and new manufacturers.
Over this period there have been gradual, yet significant, new technological developments in direct drive power trains, in variable speed electrical and control systems, in alternative blade materials and in other areas. However, the most striking trend in recent years has been the development of ever larger wind turbines, leading to the current commercial generation of multi-megawatt onshore and offshore machines.
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