Function
The turbine converts kinetic energy from the wind into three-phase AC electrical energy.
Who is involved
The European turbine supply market is dominated by three key Original Equipment Manufacturers (OEMs); GE Renewable Energy, Siemens Gamesa Renewable Energy (SGRE) and Vestas.
Key facts
Most designs have upwind, pitch controlled, variable speed rotors with three blades. Compared to onshore turbines, offshore turbines are larger and there is an increased focus on reliability and maintainability and a decreased impact of noise, visual and transport constraints.
There are fewer offshore turbine suppliers than onshore. The high investment costs, large project sizes but relatively low overall sales volumes make it difficult for new suppliers to challenge the incumbents. A new generation of 15 MW+ turbines is being developed, continuing the rapid increase in turbine capacity over the previous two decades. Typically, after a new turbine platform is developed, variants are offered to the market with higher rating and/or, larger diameter rotors, whilst many of the original systems and components remain unchanged. This extends sales lifetime of a given platform 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. Turbines are type certificated by third parties, confirming that the wind turbine type is designed, documented and key features of performance are 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 increasingly focused on safety by design, where the need for people to be put in hazardous environments is minimised or avoided at the design stage.
Notable differences for floating
Floating offshore wind projects use the same turbine models that are used for fixed turbines, with minor variations:
- The control system is tuned to jointly optimise the loads and energy production for the combination of turbine, floating substructure and metocean conditions.
- Towers are 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, 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.
