Wake effects and how they impact wind turbine performance

Wake effect refers to the phenomenon whereby turbines create a trail of slower and more turbulent air after the wind has passed through them. This trail is referred to as a “wake” and can go quite far. This not only affects the turbine itself, but any other turbine located in the area will experience lower incoming wind speeds, leading to reduced power generation. 

The turbulent airflow also makes turbines less efficient, as it can lead to mechanical stress, potentially increasing wear and tear and maintenance needs. The reduction in energy production caused by the wake effect is called wake loss.

Wake effects, or reductions in wind speed caused by turbine operation, are typically observed in two main zones: the immediate upstream area and the downstream area. These two zones effect the efficacy of the wind farm, one more than the other.

Wind starts to slow just before it reaches the rotor of a wind turbine. This area can be referred to as the“upstream” zone. Although turbulent airflow in this area does not have a great impact on the turbine, it alters the wind in the immediately adjacent area. This can affect nearby turbines and reduce the overall efficiency of the wind farm.

The upstream wake effect has a smaller impact on efficiency than the downstream wake effect.

The second zone is the area behind the turbine, where the wind has already passed through the rotor of a turbine, which experiences a “downstream wake effect”. This wake effect has the greatest effect on production, as the wind slows significantly and the airflow has more turbulence. 

The turbine blades create turbulence as they cut through the air, creating a disturbed flow pattern that continues behind the turbine. Here, the wake can extend hundreds of meters, depending on the wind speed and turbine size.

The effect of the wake decreases the further it gets from the turbine, as the wind naturally returns to free stream conditions, reaching wake recovery. The recovery depends on the wind conditions, spacing of the turbines, and the location. In offshore wind, wake recovery can occur faster as a result of more consistent wind conditions at sea.

Although there are preventative measures that can be taken, there will always be wake effects present in wind power, so the key is to minimise the impact.

One of the most important measures is to ensure ideal spacing between turbines in order to reduce the impact of wake on nearby installations. To ensure energy efficiency, turbines should be placed far enough apart while at the same time utilising the area designated for the wind farm as efficiently as possible. Wind speed and direction, turbine design, wind farm layout and environmental factors also influence the strength of the wake effect.