Observation and regional model based Gulf Stream marine hydrokinetic energy resource estimates for North Carolina

North Carolina and Florida are likely the only two states on the US east coast that have practical access to energy extraction from the Gulf Stream. After leaving the Florida Straits, the Gulf Stream in the region offshore of Cape Hatteras, NC exhibits the least variability in position of any location on the east coast, while simultaneously being closest to land. Gulf Stream current speeds exceed 2 m/s. These important characteristics have made this area the focus of observations and regional model estimates to quantify the hydrokinetic energy that may be available from the Gulf Stream for the state of North Carolina. Three types of observations to quantify the energy resource off NC began in 2013. A 150 kHz Acoustic Doppler Current Profiler (ADCP) was moored on the 225 isobath at the location estimated to be best for energy extraction, and recovered after two consecutive nineand ten-month deployments, respectively. Another ADCP was moored in nearly the same location to continue observations, and will be retrieved in August 2015. Currents from the first deployment averaged 1.15 m/s, and the power density was 779 W/m2 at a depth of 30m over the 9-month duration. Significant variability in current speed, and thus power, occurred over the deployment period. Additionally, current measurements from a vessel mounted 300 kHz ADCP were made from water depths of 100m to 1000 m on a crossisobath transect that passed over the location of the ADCP mooring. Currents measured from the vessel compare favorably with those from the moored 150 kHz ADCP in both magnitude and direction, and provide valuable information about the spatial variability of the current and its dependence on depth. In 2013, a coastal ocean radar (Codar) was added to an existing radar network that had been measuring ocean surface currents for more than a decade in the region to expand coverage over the entire study area. The radar current measurements provide consistent spatial and temporal coverage throughout the Gulf Stream cyclonic shear zone, and are being used to measure the variability in Gulf Stream position off of Cape Hatteras, NC. One method being developed using measurements from individual radars assumes the landward Gulf Stream front lies along selected maxima in the radial current shears chosen for consistency over the time period sampled, and magnitude. The locations where the Gulf Stream first enters and exits the radar coverage area are apparent in the large radial speeds measured by the radar, and the width and variability of the Gulf Stream cyclonic shear zone is estimated using maxima in velocity and velocity shears. Favorable comparisons between the three current observations will provide confidence that power estimates can be extrapolated from the radar surface currents alone over long time periods when ADCP information may not be available. Finally, observations are being compared with a regional specific Mid-Atlantic Bight and South Atlantic Bight (MABSAB) Model. Moored ADCP current measurements compared favorably with the model, demonstrating the skill of the model for power estimates in this area. Averaged current measurements 30 m below the surface from the ADCP mooring made between August 2013 - April 2014 and model estimates at the same location were nearly identical, both having average current speeds of 1.15 m/s. The model is more conservative than the observations with respect to higher frequency fluctuations in speed and direction.