The offshore wind industry has come a long way since the first wind turbines were set up off the coast of Denmark in the 1990s, but work still has to be done to make offshore wind energy more cost efficient as the challenges grow in terms of deeper water, increased turbine size, environmental loads, installation complexity, fabrication efficiency and operation stability.
The United Kingdom, Denmark and Germany are the leading nations in the development of offshore wind energy and are in the process of moving into deeper water. New innovations on turbine foundations are essential to keep the costs of deepwater wind farms from spiraling.
Dr.techn.Olav Olsen is a leading consultancy within structural and marine engineering with world-leading competence and experience in concept development and design of offshore concrete and steel structures.
Olav Olsen has teamed up with AF Gruppen, a leading Norwegian contractor, and Lyse, a Norwegian Energy company to establish a new company called Vici Ventus Technology. Vici Ventus will focus on offering foundation solutions for the offshore wind industry and will draw on Olav Olsen's expertise in construction and engineering, the AF Group's strengths within contracting and project management, and Lyse's experience in developing and implementing major energy projects. Vici Ventus will make use of competencies that have evolved over several decades in the North Sea to develop, build and install cost effective foundations for wind turbines.
The paper presents Vici Ventus' patent-pending designs that are competitive for a variety of different water depths and seabed conditions, construction sites and installation methods:
Gravity based concrete substructure (CGS) based on well proven technology from harsh environments around the world. The concrete substructure can be assembled inshore with the tower and turbine. In this way the use of expensive offshore cranes for installation is avoided. On arrival at the final destination, the base is installed through a simple ballasting operation. The concrete foundation provides a stiff and strong base for the wind turbine preventing unfavorable dynamic effects and fatigue problems. It can be designed for 100 years life or more, and require almost no maintenance. The solution is robust and durable, and significantly reduces risks and costs associated with transport, seabed preparation and installation.
The Space Frame Tower (SFT) is a unique wind turbine foundation concept combining excellent strength and fatigue properties with flexible and cost-effective fabrication. It is suitable for water depths up to 60 m. The triangular design with parallel legs and constant leg diameter enables efficient fabrication of components with equal lengths and angles – only member thickness is varied dependent on water depth and turbine type. Identical geometrical interfaces between all components make assembly simple and efficient. Fatigue is a critical issue for all offshore steel structures and for wind turbine foundations in particular. The standardized nodes – which can be mass-produced by hot-stamping and automatic welding – have excellent properties with regards to fatigue.