Wind turbines today are more complex than windmills and simple wind turbines of the past. The image below shows the major components of a modern wind turbine.
[image from: Iowa Energy Center's Wind Energy Manual]
The rotor, which consists of wood or fiberglass blades, collects the energy of the wind. It is connected to hub which is connected to the main shaft, as shown. Most new turbines work on the principle of lift. Just as air flows over an airplane wing and causes the plane to lift, turbines used for power generation have wings that are shaped to allow air to flow over them in such a way that the wings are not pushed, but are caused to lift. This causes the rotor to turn.
Turbines use the principle of lift, which allows the rotational speed of the blades to actually surpass the wind speed. This is described quantitatively by the tip speed ratio: the ratio of the rotation blade speed to the wind speed. Turbines today that employ lift technology can reach tip speed ratios of approximately 10.
The generator is where the electricity is produced by rotating a coil of wires in a magnetic field. Depending on the turbine, either alternating current (AC) or direct current (DC) electricity is generated. A more in depth discussion of AC and DC is included later in the Converting Electricity part of this section.
There is some general terminology that is useful to know when discussing wind turbine technology. The cut-in speed, typically 7 to 10 mph, is the minimum wind speed required for the turbine to start generating electricity. Rated speed, generally 25 to 35 mph, is the minimum speed required for the turbine to generate at its rated power.
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