What Are the Causes of Yaw Misalignment?

Wind farm operators are well aware that yaw misalignment can significantly reduce turbine power output. However, despite knowing and understanding this problem, the industry is still struggling to identify and correct this effectively. Today we will discuss the most common causes of static yaw misalignment.

Static yaw misalignment is the difference between the wind direction and the turbine’s nacelle position when the yaw error from the nacelle anemometer is 0°. In a well-tuned turbine, there is no static yaw misalignment. Unfortunately, many turbines in the field are not well-aligned and suffer from power loss and increased loads. Although this static yaw misalignment is invisible to the turbine controller, it does have an observable effect for the wind farm owner through a lower than expected AEP. For this reason, it’s a critical issue to address. Where do you begin? The first step is to understand what’s causing it.

Yaw Misalignment Causes

Through our extensive work helping wind farms identify and address yaw misalignment, we have found that there is no single cause for this problem. Static yaw misalignment can arise from a variety of hardware or software issues.

Hardware Causes

Sometimes, static yaw misalignment is a result of physical issues. These may include:

• Physical misalignment between the nacelle anemometer and the nacelle neutral axis. This misalignment may occur if the anemometer is not aligned correctly during installation, or the misalignment could arise later during operation. For example, the nacelle anemometer may be moved, adjusted, or bumped during turbine service or repair. This physical shift could cause a misalignment between the anemometer 0° error and the turbine’s direction.
• Change in the wind direction due to its flow around the blades. The wind flow across the blades changes the observed wind direction downwind of the rotor. If there is no mechanism to correct for this aerodynamic behavior, then the actual yaw error will be incorrectly measured by the nacelle anemometer.
  

Software Causes

If there is no physical cause for the static yaw misalignment, the source of the problem may be your software. Common software causes include:

• An incorrect nacelle transfer function. Some turbines use a nacelle transfer function to account for wind flow around the blades. This function tries to account for the flow distortion by approximating the true wind direction. If the transfer function is incorrect or out of calibration, it can cause a misalignment. In some cases, incorrect transfer function values can make the yaw misalignment worse than it would be with no transfer function at all.
• Incorrect yaw offset parameter. Some turbine owners apply one generic offset for all turbines of a particular model, usually based on a LiDAR campaign on a few turbines. While this has the potential of addressing part of the problem, it could also make the problem worse for some turbines.

See the Process in Action

Static yaw misalignment is an issue that affects most wind farms in some way. When you’re able to pinpoint the causes of yaw misalignment in your wind plant, you can take real, actionable steps to address the issue. In a recent engagement, WindESCo worked with UPC Renewables to identify static yaw misalignment for all turbines at their wind farm and come up with real solutions to address the problem. Download the case study to see how our partnership helped UPC Renewables see a 2% increase in AEP.