Delegates are invited to meet and discuss with the poster presenters during the poster presentation sessions between 10:30-11:30 on Thursday, 29 September 2016.

Thomas Hahm F2E Fluid & Energy Engineering GmbH & Co. KG, Germany
Co-authors:
Thomas Hahm (1) ^F
(1) F2E Fluid & Energy Engineering GmbH & Co. KG, Hamburg, Germany

Ice Throw Hazard - Experiences and Recent Developments in Germany

Introduction

In many regions of the world ice throw from wind turbines can be a serious hazard to the environment especially close to high frequented traffic ways. In Germany there is an increasing demand for independent assessments of the related risks. As there is currently no international and no German national standard for the assessments of ice throw there is some uncertainty about the correct methods and assessment criteria. The wind industry has to meet this challenge and to develop guidelines and standards to gain more acceptance for projects in icing climate.

Approach

Based on the experiences, accepted procedures and methods from the German market the presentation will give an overview of the critical points which need to be addressed and solved both in the discussions with authorities and in the more technical part of the assessment. This shall serve as a contribution for future harmonization and standardization of ice throw from wind turbines.

Main body of abstract

The assessment of ice throw risk from wind turbines can be split into several steps. The easiest because most determined step is the calculation of the trajectories of ice fragments. The size, mass and density of the ice fragments as well as the distribution of ice fragments along the rotor blade have to be defined. The main driving parameters for the calculation of the trajectories of ice fragments and their impact location on the ground are the rotational speed of the turbine and the topography of the terrain. The rotational speed depends on whether the turbine is idling (due to e.g. cut off by ice sensors) or running at full operational speed. It will be shown how both parameters affect the results.
The more difficult and controversial steps are the number of icing days and the risk criteria to be applied. The number of icing days show a very high annual variation. Long term measurements are needed which in Germany typically are only available at few meteorological station at 2m height. A high uncertainty arises from extrapolating this data to the wind farm location and to hub height. Germany's National Meteorological Service (DWD) has recently published an icing map of Germany. The DWD correlates the number of icing days to the elevation above sea level. This approach gives good results for many locations and may be useful in other European countries. Concerning the risk criteria the concept of Minimum Endogenic Mortality has been used in Germany for many years and has become well established. It is consistent with other approaches to determine a socially accepted risk level. It will be shown how both these approaches are applied in practice.

Conclusion

The demand for risk assessments of ice throw from wind turbines has increased in the German market during the last few years. The technical part of calculating the trajectories of ice fragments can be solved quite accurately and the driving parameters which determine the results are known and have been presented. There is much more uncertainty in the assessment of icing days and the risk threshold that can be applied. During the last years approaches and methods have developed within the German market to solve the mentioned uncertainties and discussions. Some of these approaches are specific for Germany while others may easily be adopted by other countries.


Learning objectives
There is a strong need for the development and standardization of methods to assess the risk due to ice throw from wind turbines. Without this the acceptance of wind projects in areas with risk potential and the acceptance of risk assessments by authorities may decrease in the future.