A. L. Hopstad, K. Ronold, C. Sixtensson, J. Sandberg Standard Development for Floating Wind Turbine Structures EWEA 2013

Standard Development for Floating Wind Turbine Structures Outline of presentation  Development of a standard for design of floating wind turbine structures  Certification process for floating wind turbines 2 HywindWindFloDIWETWindSea Statoil Norway Future Emerg. Tech. EU Blue H Netherlands WindSea AS Norway

Standard Development for Floating Wind Turbine Structures 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: Q

Standard Development for Floating Wind Turbine Structures Why develop a standard for floaters?  Until recently existing standards have been restricted to bottom-fixed structures only: - IEC 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 4 Courtesy: Principle Power WindFloat, Principle Power

Standard Development for Floating Wind Turbine Structures 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 5 Tension restrained structure with relatively shallow draught + Low steel weight + Small seabed footprint - Sensitive to soil conditions - Stability in intermediate phases 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 Spar Semi- submersible TLP

Standard Development for Floating Wind Turbine Structures Technical issues covered by the standard SSafety philosophy and design principles SSite conditions, loads and response MMaterials and corrosion protection SStructural design DDesign of anchor foundations SStability SStation keeping CControl system MMechanical system TTransport and installation IIn-service inspection, maintenance and monitoring CCable design (structural) GGuidance for coupled analysis 6 Photo: Knut Ronold

Standard Development for Floating Wind Turbine Structures Safety philosophy  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  Safety class NORMAL => target annual probability of failure of  Safety class HIGH => target annual probability of failure of  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 7 Hywind Photo: C.F. Salicath

Standard Development for Floating Wind Turbine Structures What shall the safety level be in large floating wind farms?  The current safety class NORMAL was originally developed for small, individual turbines on land and has been extrapolated to be used also for: 1.Larger MW size turbines on land 2.Offshore turbines 3.Support structures for offshore turbines 4.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 8 Kabashima demonstration turbine Photo: Knut Ronold, DNV

Standard Development for Floating Wind Turbine Structures 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 9

Standard Development for Floating Wind Turbine Structures Cost – benefit analysis – example of results 10 Optimum Low CAPEX, low safety level High CAPEX, high safety level

Standard Development for Floating Wind Turbine Structures Structural design  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 11 Kabashima demonstration turbine Photo: Knut Ronold, DNV Kabashima demonstration turbine Photo: Knut Ronold, DNV

Standard Development for Floating Wind Turbine Structures Station keeping  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 12 Demonstration turbine in Japan Photo: Knut Ronold, DNV

Standard Development for Floating Wind Turbine Structures 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 13

Standard Development for Floating Wind Turbine Structures 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 14

Standard Development for Floating Wind Turbine Structures Type Certification  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 15 WindFloat Photo: Principle Power

Standard Development for Floating Wind Turbine Structures Thank you Thank you for your attention

Standard Development for Floating Wind Turbine Structures