The turbine converts kinetic energy from the wind into three-phase AC electrical energy.

What it costs

About £20 million for a 15 MW floating offshore wind turbine. This includes components, factory assembly and some elements of installation and commissioning, plus warranty provision. The elements of installation and commissioning included in this cost are mainly the supplier’s logistics and staff costs at head office, at the construction port, on the installation vessel and on the turbine, mechanical and electrical completion, testing, and pre-handover checks and trouble shooting. These costs typically exceed £1.5 million per turbine.

Who supplies them

Western suppliers: GE Renewable Energy, Siemens Gamesa Renewable Energy (SGRE) and Vestas.

Asian suppliers: CSIC Haizhuang, Doosan, Dongfang Electric Corporation, Envision, Goldwind, Hitachi, MingYang, Shanghai Electric, Sinovel and XEMC Windpower.

Key facts

Most designs have upwind, pitch controlled, variable speed rotors with three blades. Compared to onshore wind turbines, offshore turbines are larger and there is an increased focus on reliability and maintainability and a decreased focus on noise, visual and transport constraints.

Floating offshore wind projects use the same turbine models that are used for fixed turbines, with minor variations:

  • The control system tuned to jointly optimise the loads and energy production for the particular combination of turbine, floating substructure and metocean conditions.
  • Tower stronger and heavier to compensate for the increased loads and different resonant frequencies experienced by the floating structure.
  • Downwind variants have not been developed yet by the established suppliers by the established, as there is not yet enough demand.

Up to 2030, the ratings of turbines used on floating projects may lag a few years behind the turbines used on fixed offshore wind projects. This is because suppliers will want to have greater confidence in the response of each turbine model to the dynamic loads of the floating substructure before they are used on floating projects.

Wind turbine suppliers are systems integrators. Blades are typically manufactured in-house, along with a few other components in some cases, depending on the industrial strength and breadth of the supplier.

There are fewer offshore turbine suppliers than onshore turbine suppliers. The high investment costs, large project sizes but relatively low overall sales volumes make it difficult for new suppliers to challenge the incumbents.

Typically, after a new turbine model is developed, variants of this model are offered to the market with higher ratings and/or larger diameter rotors, whilst many of the original systems and components remain unchanged. These variants become possible once the loads and factors of safety are better understood. This extends sales lifetime of a given model while minimising development costs.

Wind turbine suppliers prefer to operate just one or two nacelle assembly facilities and blade manufacturing facilities for the European offshore market, to avoid adding complication and cost to their supply chains. The choice of site depends on the size of the local market, the locations of key suppliers, skills availability, and support for local job creation.

The design life of an offshore turbine is 25 years. The trend for longer design life on all turbines is due to the maturing of the industry. Asset owners now expect to operate wind farms for such periods without the technology becoming obsolete or unsupported by suppliers. The design driver for many components is fatigue loading when generating. Extreme loads due to storms, abnormal events and faults during operation can also be critical. Typically, an offshore turbine will be turning over 90% of the time.

Asian suppliers are typically offering turbines optimised to lower average wind speed wind regimes with larger rotors for a given turbine rating.

Type certification for turbines is provided by third parties. This confirms that the wind turbine type is designed, documented and key features of performance verified in conformity with specific standards and other technical requirements. This certification also covers the suppliers of the key components.

Health and safety requirements are encouraging safety by minimising or avoiding designs where people need to be put in hazardous environments.

Guide to a Floating Offshore Wind Farm