Mapping the Ocean Current Strength and Persistence in the Agulhas to Inform Marine Energy Development
The potential for energy extraction from the fast-flowing Agulhas Current along South Africa’s East Coast is examined. Potentially suitable regions are evaluated using state-of-the-art satellite remote-sensing, predictive modelling, and in situ observation technologies. A mid-shelf location (91 m depth) and an offshore location (255 m depth) at approximately 32.51°S and 28.83°E are evaluated using these tools, and it is found that the current core borders on the mid-shelf location and passes over the offshore location with mean velocities of 1.34 m/s and 1.59 m/s, respectively, at the 30 m depth. Current velocity data derived from satellite remote-sensing and predictive models were compared to in situ current measurements from Acoustic Doppler Current Profilers to determine their ability to accurately capture current velocities for future use in the evaluation of energy extraction sites. Although the modelled data’s representation of the Agulhas Current’s velocities was a better comparison than the satellite product, the predictive model was less representative of the variability in the Agulhas Current. Further examination of the data showed that both the satellite and the predictive model are only able to accurately capture variability in the Agulhas Current on time scales longer than monthly. Despite this, the data provide useful insight into the unique challenges encountered when exploiting the Agulhas Current as a resource for energy generation; in particular, the irregular occurrence of large Agulhas Current meanders (known as Natal Pulses) . The proposed energetic region is well positioned with respect to environmental, economic, and social aspects because the nearest medium voltage substation is 30 km from the point of contact at the coastline. The sites are not located within any existing or proposed marine protected areas or prime fishing grounds. If the mooring challenges in water depths of 250 m or greater are overcome, then such a turbine array can make a significant contribution to the South African electricity grid.
KeywordsAgulhas current Marine energy Ocean modelling Satellite remote sensing Acoustic Doppler Current Profiler Natal pulses
The authors would like to acknowledge the South African national utility Eskom for making available the data, without which this research would not have been possible. Dr Backeberg acknowledges joint support from the Nansen-Tutu Centre for Marine Environmental Research, Cape Town, South Africa; the Nansen Environmental and Remote Sensing Center, Bergen, Norway; and the South African National Research Foundation through the Grants 87698 and 91426. This work has also received a grant for computer time from the Norwegian Program for supercomputing (NOTUR project number nn2993 k). Special thanks to Dr Julie Deshayes for her input and guidance in analyzing the spectra. Both the GlobCurrent and HYCOM data used in this study are freely available online at http://www.globcurrent.org and hycom.org, respectively. GlobCurrent products are available for free thanks to European Space Agency funding under GlobCurrent DUE project A0/1-7472/13/I-LG.
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