Hurricane Risks for Offshore Wind Design

1. Hurricane Risks for Offshore Wind Design Walter Musial Principal Engineer Manager, Offshore Wind National Renewable Energy Laboratory July 12, 2016

2. Uncertainties are Greater for Offshore Wind • Siting (Public commons) • Resource • External conditions • Design loading • Geo-tech • Extreme events • Reliability and maintenance • Decommissioning Offshore wind uncertainty is reduced by leveraging experience from land-based wind and oil and gas industries

3. United States Technology Challenges Addressing Challenges Will Expand Offshore Wind Resource Area Freshwater Ice Deep Water Deep Water Tropical Storms Graphic Source: NREL 3

4. Unique Site Conditions in US Waters Gulf and Atlantic Coasts Exposed to Tropical Cyclones Hurricane Sandy 2012 New Jersey Coast <100 Year Return Conditions Hurricane Katrina 2005 Central Gulf of Mexico 400 Year Return Conditions Slide Courtesy of Keystone Engineering

5. Governing Design StandardsFixed-bottom Systems Turbine and Tower International Electro-technical Commission IEC 61400-01 IEC 61400-03 IEC 61400-22 • Wind Turbines are often Type Certifiedbefore foundations & exact site conditions are known Substructure and Foundation American Petroleum Institute API-RP-2A ISO 19900 • API Standards do not address unique offshore wind turbine engineering conditions 5

6. Codes and Standards Hierarchy The Order of Document Priority AWEA OCRP IEC 61400-3 IEC 61400-1 IEC 61400-22 ISO 19902 API RP2A US UNIQUE LOADS RESISTANCE ROADMAP Slide Credit : Rudy Hall – Keystone Engineering

7. AWEA OCRP 2012 • Over 50 stakeholders/subject matter experts participated in AWEA OCRP • AWEA OCRP was published in October 2012 as a Recommended Practice Document. • AWEA OCRP was structured for relevance to BOEM 30 CFR 585 • Dozens of Standards, Guidelines, and recommended practices are mapped through development process • Does not cover floating or siting • Updates are planned for metocean, geotech, hurricanes, floating http://awea.files.cms-plus.com/FileDownloads/pdfs/AWEA%20Offshore%20RP2012%20FINAL%202012%20October%2010.pdf AWEA OCRP 2012 is a roadmap on how to use existing standards

8. Recent Activity in Offshore Standards • AWEA OCRP 2012 was published in 2012 • BOEM Standards Workshop – June 2014 • IEC-TC88 61400-1 MT – New CD out for comment CDV in 2016 • IEC TC-88 61400-3-1 and 61400-3-2 issued new CD versions • API RP 2A WSD Ed 22 issued in 2014; • API RP 2A LRFD Ed 2 expected in 2016 • Several U.S. projects have advanced to design stage – (Cape Wind, Block Island, Dominion Power, Fisherman’s Energy, Aqua Ventus - I, LEEDCo Ice Breaker Wind Standards Summit Presentations Feb 25-26, 2016 Golden Co \\nrel.gov\shared\wind\Public\Projects\Projects G-S\Standards Summit\2016

9. Hazard Curves Atlantic WEAs L-2 Structure Atlantic WEAs North Sea Slide Courtesy of Keystone Engineering

10. What is Robustness? Robustness is Reserve Strength. Reserve Strength Ratio (RSR) RSR = Ultimate Structure Resistance Design Load RSR will vary for different substructures RSR applies to the substructure design only RSR calculations for 500 year check are unfactored Slide Courtesy of Keystone Engineering

11. RSR Region B Hazard Curve 3.0 Region A Hazard Curve 2.5 2.0 DesignCapacity (IEC/ISO FACTORS) 1.5 DesignPoint 1.0 50 500 5,000 Load Return Period (Years) The Robustness Check Can Control the Design Typical L-2 Jacket Support Structure RSR Region B Robustness Check - Controls Region A Robustness Check - Satisfied Slide Courtesy of Keystone Engineering

12. Hazard Curve Examples • From Preliminary data & Oil&Gas Derived L2 Robustness Check PSF1.45 IEC (1.35) NOT SUFFICIENT DLC6.1 – normalized to 100 years (ABS); -15º wind-wave misalignment PSF1.51 IEC(1.35) NOT SUFFICIENT Alstom’s Haliade 150, at the Belwind site, Belgium DLC6.1 – normalized to 100 years (ABS); All wind-wave misalignment

13. 61400-01 Tropical Storms Sub-committee Revisions to address turbine survival in tropical cyclone conditions. • Wind conditions for tropical cyclones, e.g. wind shear exponent turbulence intensity, vertical wind shear effects, extreme direction • Does class “T” cover a significant percentage of sites in China, Japan, Korea, Taiwan, U.S. and other countries? • Can design loads be reduced enough by providing back-up battery during grid loss? • Prediction method of the extreme wind speed of tropical cyclones, • Others related to the 61400-3, site assessment, etc. Preliminary Proposal Slide Credit – Paul Veers

14. Understanding Reliability Targets - Research Needs • Reliability index (or probability of failure, Pf) for Offshore Wind should be based on cost-benefit analyses that minimizes lifecycle cost • High uncertainty associated with estimation of failure rates • Oil and gas criteria may be bias toward conservative designs • What is the correct risk balance for offshore wind (Target reliability)? • return period (RP) • partial safety factors (PSF) • minimum life cycle cost Cost Installed Cost increases Failure Cost increases Load Factor Higher and/or nominal Return Period Lower and/or nominal Return Period What is the Correct Reliability Target for Cost Optimization?

15. Summary and Conclusions • Offshore uncertainty is greater than land-based and is contributing to higher costs • Lack of a mature certification and standards process increases risk and cost on offshore wind. • Hurricane Design is not fully addressed by standards • IEC 61400-1,-3 are incorporating new design approaches (Typhoon class, Substructure Robustness check) • Mature standards will reduce uncertainty and project risk in offshore wind and help lower cost. Understanding reliability targets for offshore wind is a key research opportunity

16. walter.musial@nrel.govThank you for your attention!