Gulf of Mexico hurricane hazard assessment for offshore wind energy sites

Abstract

A feasibility assessment of offshore wind in the Gulf of Mexico conducted by the National Renewable Energy Laboratory concluded that hurricane risk was one of the major challenges that would need to be overcome for a mature offshore wind industry to develop in the Gulf of Mexico, as the hurricanes that frequent this area can potentially exceed design limits prescribed by the International Electrotechnical Commission (IEC) wind design standards. To better understand and account for these unique conditions, we target two objectives. The first is to develop a translation between the well-established Saffir-Simpson hurricane scale and the IEC design classes, which are based upon different averaging periods and reference heights and often lead to misinterpretation, speculation, and uncertainty. The conversion of wind speed averaging times between Saffir-Simpson and IEC design standards reflects the behaviour of the sea surface drag coefficient as a function of the mean wind speed, which controls the turbulence characteristics of the hurricane boundary layer near the surface. The second objective is to quantify the hurricane exposure risk for wind turbines at sites potentially impacted by hurricanes in the Gulf of Mexico using probabilistic hurricane track and wind field models. The IEC prescribes the reference wind speeds associated with Class 1A and Typhoon Class limit states to be 50 years, though model results indicate the return periods associated with the IEC Class 1A limit state range from approximately 20 to 45 years, while the return periods associated with the Typhoon Class limit state range from approximately 40 to 110 years. Ultimately, this indicates that the Class 1A limit state may be nonconservative for the entire Gulf of Mexico offshore wind energy area, while the Typhoon Class limit state may be adequate for the design of turbines in some regions of the Gulf of Mexico offshore wind energy area.