Air–Sea Interaction Challenges for Offshore Wind Energy

As of August 2019, there are 15 active commercial wind energy leases in U.S. waters representing a power potential of 21 GW. Part of the success of these projects will depend on the wind industry’s ability to accurately assess the winds and turbulence at each site in order to properly estimate the annual energy production and the design load conditions for the wind turbines. While considerable experience has already been gained through offshore wind plant developments elsewhere, especially in Europe, there are unique features in the U.S. offshore environment. Off the East Coast of the U.S., both nor’easters and hurricanes are common and generate extreme conditions that are not fully accounted for in industry standards. During the summer months, westerly offshore flow frequently results in strong stable stratification that complicates the representation of winds at hub height. In addition, the Gulf Stream not only provides energy for rapidly intensifying storms, but for easterly flow can also create near-shore stable stratification. Sea breezes and coastal low-level jets provide strong spatial variability of the wind field. Off the West Coast, where floating wind turbines are likely to be installed, upwelling and prominent coastal terrain features generate spatial complex winds and shallow atmospheric boundary layers that are often stably stratified. Because of the historic lack of offshore wind observations, especially at hub height, numerical weather prediction models, which are also used for resource assessment, have not been well validated. Moreover, there are good reasons to expect that many of the assumptions underlying model parameterizations are frequently violated in this environment. In March 2019, the U.S. Department of Energy supported a workshop to assess current research needs for offshore wind resource characterization. Building on information gathered at that meeting, this presentation will provide an overview of current physics challenges in air-sea interactions that need to be addressed to reduce current uncertainties in the characterization of offshore winds and turbulence for wind energy applications.