Yaw error correction

Faulty turbine wind direction sensors generate power losses

The nacelle instruments measuring the wind speed and direction provide important information used by the turbine during operation. In order to deliver its maximal output, a wind turbine needs to be precisely yawing to face the wind. If the wind direction sensor (e.g. wind vane) is providing erroneous information, the turbine will be misaligned.

This misalignment, called yaw error, results in a loss of power. Yaw errors are commonly reported by O&M teams, and misalignments can be as important as 15°.

Wind direction sensors are affected by many parameters and are difficult to verify

Today, the wind direction is provided by a sensor placed on the nacelle. Due to its position, the wind direction sensor is affected by complex aerodynamics effects such as rotor blocking effect and blade passage. Usually, the sensor is initially calibrated to account for these effects and to deliver the correct wind direction to the turbine.

As for any instrument, calibration functions should be regularly checked to avoid any drift over time. Specifically, it has been observed that wind direction sensor calibration can be affected by maintenance actions or turbine upgrades. In some instances, the mechanical reference for the sensor is incorrect. Finally, the calibration function can be site dependent.

From what we have seen, it becomes clear that potential AEP can be gained by simply recalibrating wind direction sensors. In practice, there is today no reference tool to verify on-site its calibration function.

Our solution

The Wind Iris provides a direct measurement of the free wind direction in front of the rotor. By comparing this reference measurement to that of the wind direction sensor, the user can directly detect a potential misalignment.

If necessary, simply recalibrating the sensor ensures that the turbine will be facing the wind as it should be. This translates into a gain of production. Once this is done, the Wind Iris can be used on another turbine, as the wind direction sensor is now properly functioning.

On a recent study over 12 different wind turbines, we measured an average of 6.2° of misalignment, which equals to a loss of 2% annual energy production. It is easy to see the optimization potential that can be yielded by using the Wind Iris to increase this benefit turbine after turbine.

Watch the video illustrating yaw error correction: