Wake effects in wind farms - Part 2

Frequency distribution of turbulences

Our last Blog article showed that turbulence intensity is particularly noticeable in wind directions where other wind turbines of the wind farm are located. From these shaded wind directions, the turbulence intensity is comparatively high (usually greater than 15%), but the wind frequency or the frequency of high wind speeds is comparatively low.

The statistical wind frequency distribution of the turbulence intensity can be viewed in a histogram plot. One then sees the frequency of the different turbulence intensities. Integrating the range higher from a turbulence intensity of 15%, one obtains the frequency of times when the turbine was mostly shadowed (in wake). From this, a percentage can be calculated that indicates how much of the time the turbine was shadowed. This gives an indication of how much time the turbine was in an unfavorable situation (mostly shaded).

Of course, this could also have been achieved by filtering the wind directions, but this method is more universal and independent of the constellation of the wind farm and also accurate enough for an estimation.

In our example, the wind turbine was shadowed about 23 % of the time. The corresponding plot of the turbulence frequency distribution can be seen below.

In the next article we will describe how to calculate the parking efficiency from an analysis of the wind direction distribution.