Use of helicopters to reduce downtimes and increase production

Veith Pietsch, Matthias Henke
SgurrEnergy, Hamburg, Germany


The reduction of the cost of energy became a key factor in the offshore wind industry. The distance to shore is increasing significantly as well as the size of the WTGs and the wind farms.Several synergy effects are available considering a clustering of wind farms with similar owners and/or service operators.

An additional effect to the operation and maintenance strategies of offshore wind farms is the trend towards an energy-based availability warranty vs a simple time based availability definition. Less events are excluded from the availability calculation and higher (energy-based) availabilities are demand by the wind farm operator. Furthermore incentives for the service operator are common.

A high availability can be only reached with an optimised scheduled maintenance in low wind periods and a high accessibility to respond to unscheduled maintenance in high wind periods.

In periods of wave heights above 2.5 m the access can only be reached by the use of helicopters. Especially in winter periods with a frequency of high wind speeds and reduced weather windows for conventional access a fast access is necessary.

A presentation about the results of a weather based access modelling will be given. Focus of the presentation is, to show in the influence on the availabilities and energy yield production of a far offshore wind farm project by using additional helicopter to a conventional vessel based O&M strategy.


A modelling with historical weather data and defined failure rates was undertaken for different generic offshore wind farms in the German North Sea. Helicopters were added to the conventional vessel based strategies (crew transfer vessel or support offshore vessel concept) to show the potential of helicopter usage regarding the expected downtimes and the corresponding energy yield figures. The modelling takes the different vessel and helicopter parameter into account as well as the potential for clustering of offshore wind farm projects in the same region sharing O&M facilities and vessels.



The results of the modelling showed that support offshore vessel cannot guarantee an overall accessibility. Even with a walk to work system access in rough weather conditions is not always possible. Mainly in winter periods a helicopter can reduce the downtime of the WTGs significantly as the possibility for quick access has a huge impact when the wind speeds are high. The results of the modelling showed a significant impact of the distance to the shore when comparing the different access concept.


The high energy based availability figures require a well panned scheduled maintenance concept in low wind periods and a high accessibility to the WTGs at all times especially, in the winter periods when the WTGs can only be reached by the use of helicopters. The right O&M logistic concept does not always require helicopters, it is more dependent on several parameter including the distance to shore, the weather conditions, the WTG typ and the potential for clustering O&M activities.


The delegates will receive an overview of the modelling of different O&M concepts and the influence of additional helicopter usage, for different generic

Offshore wind farms at different distances from shore. The current development and clustering in the German North Sea has been considered as well and modelled accordingly. The delegates will get a detailed comparison of the different access strategies and how to evaluate them individually for the different offshore wind farms.