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By extension, the efficiency of the wind turbine is a function of the tip-speed ratio. Ideally, one would like to have a turbine operating at the maximum value of C p at all wind speeds. This means that as the wind speed changes, the rotor speed must change as well such that C p = C p max.
However, very high tip speeds also increase the drag on the blades, decreasing power production. Balancing these factors is what leads to most modern horizontal-axis wind turbines running at a tip speed ratio around 9. In addition, wind turbines usually limit the tip speed to around 80-90m/s due to leading edge erosion and high noise levels.
The reason to vary the rotor speed is to capture the maximum aerodynamic power in the wind, as the wind speed varies. The aerodynamic efficiency, or coefficient of power, for a fixed blade pitch angle is obtained by operating the wind turbine at the optimal tip-speed ratio as shown in the following graph.
[100] [101] Ice accretion on turbine blades has also been found to greatly reduce the efficiency of wind turbines, which is a common challenge in cold climates where in-cloud icing and freezing rain events occur. [102] Deicing is mainly performed by internal heating or in some cases, by helicopters spraying clean warm water on the blades. [103]
An example of a wind turbine, this 3 bladed turbine is the classic design of modern wind turbines Wind turbine components : 1-Foundation, 2-Connection to the electric grid, 3-Tower, 4-Access ladder, 5-Wind orientation control (Yaw control), 6-Nacelle, 7-Generator, 8-Anemometer, 9-Electric or Mechanical Brake, 10-Gearbox, 11-Rotor blade, 12-Blade pitch control, 13-Rotor hub
In high wind speed, where the turbine is operating at its rated power, the turbine rotates (pitches) its blades to lower C P to protect itself from damage. The power in the wind increases by a factor of 8 from 12.5 to 25 m/s, so C P must fall accordingly, getting as low as 0.06 for winds of 25 m/s.
Global map of wind speed at 100 meters on land and around coasts. [12] Distribution of wind speed (red) and energy (blue) for all of 2002 at the Lee Ranch facility in Colorado. The histogram shows measured data, while the curve is the Rayleigh model distribution for the same average wind speed. Global map of wind power density potential [13]
One reason for the low efficiency of a Savonius wind turbine is that roughly only half of the turbine generates positive torque, while the other side moves against the wind and thus produces negative torque. A variant of SWT is the Harmony wind turbine [11] with helix-shaped blades and an automatic furling mechanism during high-speed wind ...