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The power coefficient [9] C P (= P/P wind) is the dimensionless ratio of the extractable power P to the kinetic power P wind available in the undistributed stream. [ citation needed ] It has a maximum value C P max = 16/27 = 0.593 (or 59.3%; however, coefficients of performance are usually expressed as a decimal, not a percentage).
Wind-turbine blades in laydown yard awaiting installation. The primary application of wind turbines is to generate energy using the wind. Hence, the aerodynamics is a very important aspect of wind turbines. Like most machines, wind turbines come in many different types, all of them based on different energy extraction concepts.
The power coefficient, , expresses what fraction of the power in the wind is being extracted by the wind turbine. It is generally assumed to be a function of both tip-speed ratio and pitch angle. Below is a plot of the variation of the power coefficient with variations in the tip-speed ratio when the pitch is held constant:
For a wind turbine, the power harvested is given by the following formula: = where is the aerodynamic power and is the density of the air. The power coefficient is a representation of how much of the available power in the wind is captured by the wind turbine and can be looked up in the graph above.
Whereas the streamtube area is reduced by a propeller, it is expanded by a wind turbine. For either application, a highly simplified but useful approximation is the Rankine–Froude "momentum" or "actuator disk" model (1865, [1] 1889 [2]). This article explains the application of the "Betz limit" to the efficiency of a ground-based wind turbine.
Turbines equipped with a diffuser-shaped shroud and a broad exit ring generate 2–5 times more power than bare wind turbines for any given wind speed or turbine diameter. [2] Further analysis concludes that the Betz's limit can be exceeded if the wind turbine were to be equipped with a diffuser. For multi-rotor turbines equipped with a ...
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
When rotor power or torque coefficient is assumed constant, the weighing function is: = and the corresponding weighted solidity ratio is known as the power or torque-weighted solidity ratio. This solidity ratio is analogous to the activity factor used in propeller design and is also used in wind turbine analysis.