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Larwood and Simms article clarification: “Analysis of blade fragment risk at a wind energy facility,” Wind Energy, 2018;1-9. DOI: 10.1002/we.2194.

The Larwood and Simms article was intended to illustrate the process by which a site-specific analysis can be used to assess the risk induced by loss of a wind turbine blade.  The study used work done to address the safety of a unique wind energy testing facility – the National Wind Technology Center near Boulder, Colorado. The assumptions used by the authors include site-specific wind conditions and local risk factors. Assumptions of turbine blade failure rates were taken from a report over a decade old, which was considered conservative due to the continuous improvement in blade reliability in the intervening years. The study concluded that despite the proximity of turbines and research facilities, operations at the site were safe relative to blade throw risk. The assumptions and results do not apply to commercial wind energy sites and are not suitable for setback recommendations in other locations. However, some of the conclusions were summarized in a way that made them appear to be more broadly applicable than intended. Due to the possibility of misinterpretation, the authors are working to withdraw the version causing confusion and resubmit with a more clearly articulated summary.

Summary of important issues:

  1. Although the reported methodology is intended to be more generally applicable, the conclusions reached about the National Wind Technology Center should not be assumed as applicable elsewhere or for different wind turbine configurations.
  2. The authors used assumptions specific to the National Wind Technology Center that are not applicable to other wind energy sites (e.g., blade speeds of custom research turbines that are 35% greater than conventional turbines, how often trucks drive on certain access roads, occupancy schedule of buildings near wind turbines).
  3. The article was written based on the methodology used to conduct a Hazard Analysis Review for a unique federal government wind energy test facility site with extreme wind conditions – the National Wind Technology Center.
  4. The authors used a Department of Defense (DoD) safety standard to assess risk because the National Wind Technology Center is government property; however, DoD requirements do not apply in most places.
  5. The data used in this article (e.g., failure rate for wind turbine rotors) are based on a 13-year-old report on wind turbines installed in Europe in the preceding decades. The intervening years have seen significant improvements in turbine technology including enhancements in blade reliability. Since the study concluded that the operations at the National Wind Technology Center  are safe, a more recent and accurate failure rate basis was not considered necessary.