Monday, July 11, 2011

Wind Turbine Swept Area

The wind turbine swept area is the area through which the wind strikes the wind turbine blades and causes the blades to spin. The wind spinning the blades causes the rotor to turn and generates power that can be used.

Wind Turbine Swept Area
Swept Area –This refers to the area swept by the blades of the wind turbine when the wind turbine rotates. It is also called the 'capture area' as seen in the diagram to the left.

Wind Turbine Radius – it is the distance measured from the center of the turbine blade (hub) to the end of one of the blades. Most if not all wind turbine manufacturers print the blade’s length on the nameplate of the rotor and/or on the manufacturer’s data sheet. The blade’s radius (or diameter which is twice the radius) is simply the diameter the blade’s cover circle wise.

For a three bladed wind turbine with radius (r) and diameter (2r), the wind turbine swept area would be the area of the circle (A) = Pi r2 as seen in the diagram. The equation for area swept by the wind turbine is employed as part of the power equation that is used to calculate the power output of a wind turbine.

The wind turbine power output is directly related to the swept area of its blades. Increasing the radius of the wind turbine or the longer the blades would result in an increase of the power that can be extracted from the wind. With larger blades, a lot of wind force will be applied on the wind turbine blades. These blades need to be built to be strong in order to withstand higher levels of centrifugal and varying gravitational loads.

Swept Area and Output Power Relationship:

So what is the relationship between the wind turbine swept area and the power output? Looking at the equation for output power you can see that the capture area of the wind turbine blades is utilized to calculate how much power can be extracted from the wind turbine.

Power Output (Watts) = ½ ρ CP A V3 = ½ ρ CP (pi r2) V3
Air density is: (ρ)
Betz limit (Cp): 35% (for a good design)
Swept area is: (A) = Pi r2
and Wind speed is: (V)

See examples on Output Power Calculations

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