Calculating the Mean Wind Power Density at 50m

Windographer calculates the mean wind power density at 50 metres above ground in order to provide a basis for comparing datasets and in order to determine the wind power class. The approach that Windographer takes to calculating the mean wind power density at 50m requires the dataset to contain wind speed data for multiple heights above ground.

Single Wind Speed Measurement Height

If the dataset contains wind speed data for only one height above ground, then it contains no information about wind shear, which is the change in wind speed with height. So unless that single measurement height happens to be 50m, Windographer will not estimate the mean wind power density at 50m because it cannot estimate how the wind speed will change between the measurement height and 50m.

If the single measurement height does happen to be 50m, Windographer will simply calculate the mean wind power density of the 50m wind speeds.

Multiple Wind Speed Measurement Heights

In the case where the dataset contains wind speed data from more than one height above ground, Windographer estimates the mean wind power density at 50m in a three-step process:

It calculates the mean of monthly means (MoMM) of wind power density at each height. If two or more sensors record wind speeds at one height, Windographer calculates the MoMM of each sensor, and then calculates the mean of those MoMM values.
It calculates a least squares line of best fit to the natural logarithm of MoMM wind power density versus the natural logarithm of height.
From the line of best fit, it calculates the MoMM wind power density at 50m.

Tip: The Wind Power Class window shows the inputs to and the results of this analysis, including the MoMM wind power density for each height, the graph of MoMM wind power density versus height, and the line of best fit.