The importance of: swept area.
In our second instalment we will take a look at another factor which is critical to the amount of energy that your turbine can extract – or harvest – from wind.
Swept area can be pictured as an imaginary disc that the turbine blades sweep through, this is shown in the diagram below.
Most manufacturers provide the rotor diameter (d) and this can be used to calculate the swept area using:
Using this formula, both the C&F 15e and C&F 20 have swept areas of 135 m2.
At the time of writing this is the largest swept area in this class, other models have swept areas that range from 133 m2 to 57 m2. So, how does swept area relate to the potential output of your turbine?
We need to look at the relationship the provides the theoretical power available for given conditions.
Where P is the maximum theoretical power, p is the air density, A is the swept area and v is the wind speed.
If we take the conditions of 8 m/s and air density of 1.23 kg/m3, we can compare the effect of different swept areas.
For a CF 20 wind turbine with a swept area of 135 m2:
Compared with another 20 kW turbine with a swept area of 78.5 m2:
This results in a 33% increase in the theoretical output of a CF20 when compared to a competing model.
