Risk assessment of wind turbines close to highways

Publication: Research - peer-reviewArticle in proceedings – Annual report year: 2012

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This paper describes an assessment of the minimum distance from wind turbines to highways based on risk assessments of the consequences due to total or partial failure of a wind turbine and due to ice throw in case of over-icing. Data has been collected from a large number of modern wind turbines from Denmark and abroad and with the same basic technology as new large wind turbines. These data contain information on events where parts of the turbine is
thrown / dropped at a distance from the turbine.
Based on the data, the risk is estimated that persons in car are killed because of wind turbine parts 'thrown away' from a wind turbine in events with total or partial failure. The risk is expressed as a probability per kilometer. It is assumed that a row of wind turbines is placed along a highway with a typical total height of 120m (equivalent to wind turbines in the underlying data base) and a spacing of 400-500 m along the road.
The studies show that the probability per kilometer that a person in a vehicle is killed due to total or partial collapse (damage) of a wind turbine can be assumed to be of minor importance. The probability per kilometer will be less than 5 10-12 for wind turbines that are more than 60 meters from the road. This risk is considered acceptable using the ALARP principle and comparing with the general, well-documented risk on roads in Denmark which in 2009 was 2 10-9. The analysis also shows that the height of the turbines and the distance between them is of less importance.
Assessment of risks due to ice throw in case of over-icing is also performed. This is associated with many uncertainties which are described and quantified in the paper mainly for Danish conditions. The assessment includes both situations where the turbine is in operation and situations where the turbine is stopped.
Both for pieces from the wind turbine and for ice the throwing distances are determined from ballistic computations assuming an average drag coefficient of 0.6. This number is based on results from a more elaborate model that takes into account the full 6 degrees of freedom movement of the fragments subject to detailed aerodynamic lift and drag forces.
The probability per kilometer that a person in a vehicle is killed due to ice throw from a wind turbine is determined and shown in the paper for tip heights at 150m as a function of distance to a number of wind turbines located along a highway with a spacing of 400m. As an example the generally accepted risk on highways in increased with less than 0.1% in wind turbines are installed more than 150 meters from the highway. The risk due to ice throw from a wind turbine
in operation is seen to be slightly greater than the risk if the wind turbine is parked.
It is recommended that for practical projects a proper risk assessment is performed, which also include the location in relation to the road and the prevailing wind direction.
Original languageEnglish
Title of host publicationProceedings of EWEA 2012 - European Wind Energy Conference & Exhibition
Number of pages9
PublisherEuropean Wind Energy Association (EWEA)
Publication date2012
StatePublished

Conference

ConferenceEWEA 2012 - European Wind Energy Conference & Exhibition
CountryDenmark
CityCopenhagen
Period16/04/1219/04/12
Internet addresshttp://events.ewea.org/annual2012/
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