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Rob Rawlinson-Smith on wind turbine design: Innovation through integration

The most important lesson from 30 years of wind turbine design is that components work best when they work together.

The development of the modern wind turbine has been a progression from agricultural technology to offshore power station in less than three decades. Of the countless lessons learned by wind turbine designers which are relevant to offshore wind, some of the most important ones fall under the theme of integration.

The EU-funded project ‘Design Methods of Offshore Wind Turbines at Exposed Sites’ (OWTES) set out at the beginning of the 2000’s to reduce the uncertainties associated with the design of offshore wind turbines in the marine environment. By installing a comprehensive monitoring system on and around the first two wind turbines to be located in the North Sea (off Blyth harbour, UK), the project captured the wind and wave conditions along with the loads on the structure and performance of the wind turbines themselves.

This database of measurements has proved to be of immense value in the development of design standards for offshore wind turbines. Analysis of the data showed that accurate prediction of lifetime fatigue and extreme loads is only possible by modelling the turbine, its control system and the support structure as an integrated whole. In particular, the importance of the aerodynamic damping in reducing wave-induced fatigue loading on the support structure, which had only previously been predicted by theory, was confirmed by the measurements – opening up opportunities for designers to create cheaper foundations.

The results of the OWTES project gave impetus to the development of more sophisticated design tools for wind turbines and their support structures. The Offshore Code Comparison Collaboration (OC3) set up by the International Energy Agency provided a framework for the cross-verification and improvement of these design tools.

Code comparisons or benchmarking exercises allow the cross-verification of individual sub-models. It ensures that the integration of these building blocks can produce a complete and robust ‘seabed to rotor tip’ model.

The need for replacement components at early large-scale offshore wind farms such as Horns Rev demonstrated the need to use proven technology in hostile environments where maintenance and retrofit activities can be very expensive. As we start to see the emergence of wind turbines in the 5-10MW range designed specifically for offshore deployment, the need to get things ‘right first time’ is more important than ever.

There are now full-scale nacelle and drive train test facilities in the UK and Denmark. These facilities, along with factory testing by manufacturers, have the potential to aid the integration of the many components and sub-systems that make up a wind turbine drive train and control system.

The difficult, expensive, and time consuming nature of measurements, testing and the development of design codes may fail to set pulses racing in the boardroom, but we have seen how important this activity is in driving cost reduction and bringing innovation to market. It is only successful when a joined-up, integrated approach is taken: bringing the science and technology into design practices.

As the offshore wind turbine market consolidates, matures and strives to meet the increasing pressure to achieve significant cost reduction, designers’ top three priorities should be: integration, integration, integration. 

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