Standard Development for Floating Wind Turbine Structures

1. Standard Development for Floating Wind Turbine Structures EWEA 2013

2. Outline of presentation Development of a standard for design of floating wind turbine structures Certification process for floating wind turbines

3. Joint Industry Project (JIP) • Objective: Develop a (DNV) standard for design of floating wind turbine structures • 10 participants from the industry • Statoil • Navantia • Gamesa • Alstom Wind • Iberdrola • Sasebo Heavy Industries • Nippon Steel • STX Offshore & Shipbuilding • Glosten Associates • Principle Power • Kick off:September 2011 • External/internal hearing: tentatively March/April 2013 • Expected release: Q2 2013

4. Why develop a standard for floaters? Courtesy: Principle Power WindFloat, Principle Power • Until recently existing standards have been restricted to bottom-fixed structures only: • IEC61400-3 - DNV-OS-J101 • GL (IV Part 2) - ABS #176 • This forms the background for the new floater standards issued by ABS, NKK, GL and for the standard to be issued by DNV later in 2013 • The standard will contain normative requirements that shall be satisfied in design of tower and support structure • Development of this standard will lead to: • Expert / industry consensus on design principles • Experience from the industry reflected in the contents • Innovative designs and solutions • Economically optimized designs

5. Three main technologies:Spar buoys, Semi-submersibles, Tension leg platforms (TLP) Weight-buoyancy stabilized structure with large draught + Simple, inherently high stability substructure + “Proven” technology - Substructure weight - Draught implication on site flexibility Spar Free-surface stabilized structure with relatively shallow draught + Simple transport & installation + Flexible design with respect to site - Substructure weight and complexity - Motions in extreme wave conditions Semi-submersible Tension restrained structure with relatively shallow draught + Low steel weight + Small seabed footprint - Sensitive to soil conditions - Stability in intermediate phases TLP

6. Technical issues covered by the standard Photo: Knut Ronold Safety philosophy and design principles Site conditions, loads and response Materials and corrosion protection Structural design Design of anchor foundations Stability Station keeping Control system Mechanical system Transport and installation In-service inspection, maintenance and monitoring Cable design (structural) Guidance for coupled analysis

7. Safety philosophy Hywind Photo: C.F. Salicath The safety class methodology is based on the failure consequences The safety class is characterized by a target annual failure probability Safety class LOW => target annual probability of failure of 10-3 Safety class NORMAL => target annual probability of failure of 10-4 Safety class HIGH => target annual probability of failure of 10-5 In DNV-OS-J101 and IEC rules: safety class Normal Requirements for load factors to be used in design depend on the target safety level of the specified safety class

8. What shall the safety level be in large floating wind farms? Kabashima demonstration turbine Photo: Knut Ronold, DNV • The current safety class NORMAL was originally developed for small, individual turbineson land and has been extrapolated to be used also for: • Larger MW size turbines on land • Offshore turbines • Support structures for offshore turbines • Many large turbines in large offshore wind farms • Is it possible to reduce the target safety level based on having large wind farms with many turbines offshore? • The consequence of failure is primarily a loss of economic value => cost-benefit analysis

9. Cost – benefit analysis • Establish which safety level is necessary / acceptable in design of floating support structures • Find optimum between choice of safety class in design and net present value (NPV) for a wind farm development • The analysis is to be used as part of the basis for selecting target safety level • Input: • Insurance companies estimated maximum loss philosophy • Cost data for CAPEX and OPEX • Cost data for replacing turbines and support structures • Cost differences when applying different safety classes • Electricity prices

10. Cost – benefit analysis – example of results Optimum Low CAPEX, low safety level High CAPEX, high safety level

11. Structural design Kabashima demonstration turbine Photo: Knut Ronold, DNV Kabashima demonstration turbine Photo: Knut Ronold, DNV • Special provisions for the different floater types and for floater specific issues • Design rules and partial safety factors for structural components • Ultimate Limit State (ULS) • Fatigue Limit State (FLS) • Accidental Limit State (ALS) • Existing design standards from oil & gas industry has been capitalized on: • DNV-OS-C101 for offshore structures • DNV-OS-C105 for tendons • DNV-OS-E301 for mooring lines • Design Fatigue Factors (DFFs) specific for floating support structures and station keeping system have been established

12. Station keeping Demonstration turbine in Japan Photo: Knut Ronold, DNV • Develop design rules and requirements for station keeping of floating wind turbines • The JIP has received data on load/response from three developers: • Hywind (full-scale data, mooring lines) • Pelastar (analysis data, tendons) • WindFloat (analysis / full scale data, mooring lines) • Load factors for tendons and mooring lines for different safety classes are established • Capitalize on “PosMoor” rules (DNV-OS-E301) • Reliability-based calibration for validation has been performed based on received data

13. Project Certification for Offshore wind farms • Provide evidence to stakeholders that a set of requirements laid down in standards are met during design and construction and maintained during operation • DNV-OSS-901 Project Certification of Offshore Wind Farms (2012) - developed for DNV service for bottom-fixed wind farms • Phases: • Phase I – Verification of Design Basis • Phase II – Verification of design • Phase III – Manufacturing Survey • Phase IV – Installation Survey • Phase V – Commissioning Survey • Phase VI – In-Service

14. Project Certification for Floating Wind Farms • DNV is currently in the process of extending the project certification service to also cover floating wind farms • Extended scope for Phase II – Design verification: • Floater stability • Station keeping • Validation of software • Verification by model testing • Current floating wind turbine concepts capitalize on novel technology to various degrees • Technology items not covered by any standards may need to be taken through a technology qualification process to obtain documentation required for certification

15. Type Certification WindFloat Photo: Principle Power Type certification of floating units for a specific environmental class is foreseen as a possible new service in the case of mass-produced floater units The station keeping system including anchor design would need to be qualified for each site

16. Thank you Thank you for your attention

17. www.dnvkema.com