Wake Effects in the Wind Farm - Part I

Turbulence due to shadowing (wake effects)

As a wind turbine extracts energy from the wind, the wind speed behind the wind turbine is also reduced.

This energy extraction does not take place uniformly, which ultimately also leads to strong fluctuations in wind speed. The caused turbulences in the wake of the turbine then lead to a more irregular inflow and higher loads of the wind turbines in the wake. Turbines influenced by these wake effects produce less energy and wear faster.

When planning wind farms with several wind turbines, it is therefore very important that the wind farm constellation is designed in such a way that as few shading effects as possible are created in the wind farm from frequently occurring wind directions.

However, since the climate and the weather can not be predicted 100%, it can happen that plants are shaded more often than originally planned.

It is therefore quite exciting to investigate the effects caused by shading in a wind farm.

Turbulence rose and wind frequency distribution

In the picture above you can see a turbulence rose.

This illustration describes the average turbulence intensity from the different wind directions.

One can see, for example, that higher turbulence intensities were measured from approx. 25° and 260°. Exactly in these directions are also the neighbouring plants.

This type of display allows the average turbulence intensity from shaded directions to be directly compared with that of free flow directions.

In this case the shading causes an increase of the turbulence intensity from approx. 14% up to 30%, which corresponds to a doubling.

IInterestingly, an inverse phenomenon of the compass rose can be seen in the picture.

Read in our next post how to calculate a factor from this that describes what proportion of the operating hours the plant was shaded.