Unlocking wind farm power potential using LiDAR campaigns

Ventus Wind Services: Nacelle based LiDAR

Unlocking wind farm power potential using LiDAR campaigns

By David Stacey, LIDAR/SCADA Data Analyst, VENTUS Wind Services GmbH

With the worldwide increase in wind turbine generator (WTG) installations, O&M is becoming an increasingly important topic to owners and operators who must manage their wind farm portfolio and make sure their lifetime and power production are maximized. Many times, it is found that the annualized energy production (AEP) of a wind farm is not as high as expected in the planning stage, or certain WTGs are not behaving well compared with neighboring turbines. These problems can appear over time but can also happen equally during the installation phase.

WTGs may not produce optimal power for several reasons. First is to check for influences of wake from nearby turbines and environment, which is called “micro-siting”. If this can be ruled out, it is often the case there is a problem of misalignment either in relative blade pitching or turbine yaw in relation to the wind direction, which can cause an imbalance in the system leading to additional fatigues and non-optimal energy production. In the case of yaw, a yaw misalignment means the turbines are not fully facing the wind. Whilst the dynamic yawing is normal behavior from the constantly changing wind direction, there is a measure called static yaw-misalignment pertaining to the cumulative averaged difference over time between the wind direction and nacelle direction. We know that the power loss from such a misalignment is related with a cos(α)³ relationship, so a misalignment of 5° can lead to 1% AEP reduction but a 10° misalignment can lead to a 4.5% AEP loss.

Illustration of yaw misalignment, and relation of angle of misalignment to power production loss.

The adoption of nacelle based LiDARs has picked up over recent years to measure true wind speed and direction in front of the WTG, and are far superior compared to sensors that are located behind the blades such as anemometers. Ventus Group has several years of experience with the use of nacelle based LiDARs to optimize wind turbine performance by performing checks on yaw misalignment, as well as verification of power curve and nacelle transfer function (NTF). Additional parameters such as wind shear and turbulence intensity are also available from the LiDAR to understand environmental and surrounding factors. These are all done in compliance with the standard IEC 61400-12-1:2017, and the recent release of the new IEC 61400-50-3:2022 further embraces the use of nacelle-mounted lidars for wind measurements.

The first step is usually to identify those WTGs in the farm which are worst performing, using big data analysis. Data sources are brought together such as SCADA data, error log data, location data, and parameter settings to get a comprehensive picture of WTGs with underperformance. It is made sure to rule out factors such as micro-siting, downtime, parameter settings, and other factors. From this list of WTGs ranked by power performance, a LiDAR campaign of two weeks can identify the yaw misalignment, and with longer term campaigns, corrections can be made alongside verification of power curves and NTFs. The LiDARs go from one WTG to another, with Ventus taking care of everything from project planning to logistics, providing wind turbine technicians for installation, IT specialists to manage automated data pipelines, and data analysts to process the data and deliver top quality reports within a quick timeframe.

Ventus approach to nacelle LiDAR campaigns in a wind farm, going from WTG to another and correct yaw misalignment.

Giving a couple of case studies, Ventus followed the approach of big data analysis across close to 100 WTGs in India and ranking the worst performing WTGs. The different available data sources were merged and streamlined together with an automated pipeline, allowing for processing of enormous datasets, and summarizing results for whole wind farms. From the list of underperforming WTGs, LiDAR campaigns were initiated in sequence and reporting provided following end of each campaign. Static yaw misalignment of between 5° to 13° have been identified throughout the campaigns, with a potential AEP gain of between 1% and 8% respectively for each WTG. Once a large static yaw misalignment has been identified, a correction can be applied during an extended campaign allowing for a pre- and post-correction analysis and verification to be performed on WTGs.

Yaw misalignment before and after correction, measured by the nacelle-based LiDAR.

For another client with WTGs in the Castilla y León region, a 12-week LiDAR campaign was implemented to identify reasons for underproduction. The long duration campaign enabled for collection of a large amount of data, allowing for a more detailed analysis of the surrounding wind profile, with parameters such as wind speed, shear, and turbulence intensity. For this campaign, a ZX TM nacelle based lidar was used with the added benefit of being able to capture wind data across several height segments. Comparing the SCADA wind speeds to the Ventus LiDAR wind speeds, it was found the NTF was underestimating the wind speed, which typically shifts the power curve to the left which can mask the underperformance of a WTG. During analysis of the power curve, it is made sure to comply with IEC standards of filtering sectors where wakes from neighboring WTGs would impact power production. A power underperformance of 15% was found when comparing the Ventus power curve with the warranted power curve. Several other issues were identified during the campaign, including yaw misalignment, earlier than expected blade pitching, as well as identifying high TI (Turbulence Intensity) and surface boundary layer along the rotor where energy conversion is a concern. To the client, the report outlined areas to help target WTG performance improvements, on which basis collaboration and discussions can be initiated with the turbine OEM.

ZX TM nacelle-based LiDAR on top of WTG in Castilla y León, Spain.

Our streamlined approach to identify WTG underperformance using big data analysis and LiDAR campaigns help our clients unlock the power potential in their wind farms. Please contact Ventus to help get your WTG optimization project off the ground.