Gulf Stream Marine Hydrokinetic Energy Observations for North Carolina

Abstract:

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. These important characteristics have made this area the focus of observations 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 meter isobath at the location estimated to be best for energy extraction, and recovered after a 9-month continuous deployment. Another ADCP was moored in nearly the same location to continue observations, and will be retrieved this fall. Currents from the first deployment averaged 1.15 m/s, and the average Betz Power was 0.8 kW/m² at a depth of 30 meters 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 cross-isobath transect that included the location of the ADCP mooring. Currents from the ship transects are still under evaluation and comparison with the 150 kHz ADCP mooring, and will provide valuable information about the spatial variability of the current and its dependence on depth. A coastal ocean radar was added to an existing radar network to provide hourly surface current measurements over the larger study area. Methods to use the relative vorticity in the surface currents to identify the shoreward front of the Gulf Stream are being developed and compared with existing frontal determinations such as Navy Gulf Stream frontal charts produced bi-daily. Frontal estimates are being used to determine the location of the Gulf Stream cyclonic shear zone during ADCP current measurements. Favorable comparisons between the three current observations will provide confidence that the available Betz power can be extrapolated from the radar surface currents alone over long time periods when ADCP information may not be available.