Over 15% of the cost of an offshore wind turbine is usually attributable to the foundations. Foundation installation and erection of the turbine constitutes one of the greatest areas of risk for an offshore development, because of the problems posed by working in an often difficult marine environment. Developing alternative foundation systems and addressing installation techniques that are less weather sensitive will have a direct and significant impact on the economic viability of offshore wind farm schemes. Results of studies for several offshore wind sites are presented in this article to demonstrate the savings that can be made by innovative thinking in terms of foundation design and construction. Relative costs of foundation systems are compared for differing seabed conditions, together with an assessment of the associated risks in terms of certainty of out-turn costs and schedule.

Optimal siting of wind farms and positioning of turbines requires a thorough understanding of local wind flow and turbulence conditions. But these can be difficult to quantify and time-averaged measurements at a few selected locations may not be fully representative. Complex sites present particular difficulties, as cliffs, buildings and trees all serve to modify the wind flow. With turbine hub heights now reaching over 100m, conventional met-masts of 50m or so cannot always provide the confidence needed to predict future wind farm productivity. A new, ground-based, remote wind lidar (light detection ­and ­ranging) system has been developed to overcome the cost and deployability issues associated with conventional laser radar systems. It has been shown to operate reliably in remote locations, and in independent tests has demonstrated accuracy comparable to the best calibrated cup anemometers in use today.

A Clear Picture?
In the early 1990s a number of test wind turbines were installed in Denmark and Sweden. The turbines were small compared to the current size and output of turbines, and the waters in which they were installed were relatively quiet. The installation could easily be managed using existing floating cranes and barges. Now that large-scale wind power plants are being installed offshore in more exposed areas such as the North and Irish Seas, more ‘rugged’ methods are needed in order to install large quantities of high megawatt turbines in a short season. In this article, Kurt Thomsen from A2SEA A/S gives his views on this matter.