The early wind turbines which were developed for power generation in the late 1970s and the early 1980s had generating capacities of around 30-60 kW. Hundreds of machines of this size were installed in wind farms in California.
Through the 1980s and into the 1990s, wind turbine capacities increased steadily. During the 1980s there were several pilot projects involving single wind turbines with capacities of over 1 MW but during the decade the standard turbine size tended to be between 300 and 500 kW.
During the 1990s, turbine unit size continued to increase steadily. By 1998, most new wind farms employed turbines with a capacity of between 600 and 750 kW. These modern, higher-output machines tended to provide greater efficiency than the smaller machines of the previous decade and the trend towards even larger machines continued. At the end of the 1990s, the typical wind turbine size had reached 1 MW.
As the new century dawned, manufacturers began to introduce a range of multi-megawatt machines. A unit of around 2 MW is the most common at the beginning of 2004 but larger machines are being installed and 5 MW machines are already being developed. These largest machines have blades up to 60 m in length, leading to rotor diameters of 120 m.
The largest machines are particularly popular for offshore developments where the high cost of a turbine foundation favours a large generating capacity. The end of the first decade of this century will almost certainly see wind turbines for offshore applications in the 6-10 MW range. It is not clear yet whether there is an ultimate limit to wind turbine size.
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