Preprints
https://doi.org/10.5194/wes-2023-129
https://doi.org/10.5194/wes-2023-129
16 Oct 2023
 | 16 Oct 2023
Status: this preprint has been withdrawn by the authors.

The winds are twisting: analysis of strong directional shear across the rotor plane using coastal lidar measurements and ERA5

Christoffer Hallgren, Heiner Körnich, Stefan Ivanell, Ville Vakkari, and Erik Sahlée

Abstract. The change of wind direction with height (the directional shear) affects both the power production from a wind turbine, wake effects and aerodynamic loading. In this study, a climatology of the relative occurrence of strong directional shear over Scandinavia is created using 43 years of hourly ERA5 data covering the height range of a modern wind turbine and at wind speeds of operation. It is shown that strong directional shear (≥15° over the rotor) is occurring 20–30 % of the time over land and 10–25 % of the time over the extended Baltic Sea. The height of the atmospheric boundary-layer and the wind speed at hub height are identified as the most important predictors for strong directional shear, with low boundary-layer heights and weak winds being the main causes. Associated with this, a strong land–sea seasonality is observed. Furthermore, ERA5 is validated against lidar soundings from two coastal sites, both indicating a major underestimation in the distribution of the directional shear in ERA5. Especially in strongly stratified boundary-layers ERA5 struggles, with 25 % of the data having errors exceeding 24° and 28° for Östergarnsholm and Utö respectively.

This preprint has been withdrawn.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Christoffer Hallgren, Heiner Körnich, Stefan Ivanell, Ville Vakkari, and Erik Sahlée

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2023-129', Anonymous Referee #1, 27 Oct 2023
    • AC1: 'Reply on RC1', Christoffer Hallgren, 04 Feb 2024
  • RC2: 'Comment on wes-2023-129', Anonymous Referee #2, 08 Dec 2023
    • AC2: 'Reply on RC2', Christoffer Hallgren, 04 Feb 2024
  • AC3: 'Comment on wes-2023-129', Erik Sahlée, 20 May 2024

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2023-129', Anonymous Referee #1, 27 Oct 2023
    • AC1: 'Reply on RC1', Christoffer Hallgren, 04 Feb 2024
  • RC2: 'Comment on wes-2023-129', Anonymous Referee #2, 08 Dec 2023
    • AC2: 'Reply on RC2', Christoffer Hallgren, 04 Feb 2024
  • AC3: 'Comment on wes-2023-129', Erik Sahlée, 20 May 2024
Christoffer Hallgren, Heiner Körnich, Stefan Ivanell, Ville Vakkari, and Erik Sahlée
Christoffer Hallgren, Heiner Körnich, Stefan Ivanell, Ville Vakkari, and Erik Sahlée

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This preprint has been withdrawn.

Short summary
Sometimes, the wind changes direction between the bottom and top part of a wind turbine. This affects both the power production and the loads on the turbine. In this study, a climatology of pronounced changes in wind direction across the rotor is created, focusing on Scandinavia. The weather conditions responsible for these changes in wind direction are investigated and the climatology is compared to measurements from two coastal sites, indicating an underestimation by the climatology.
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