Energy Postgraduate Conference 2013 Resource Assessment of the Agulhas Current to determine Feasibility for Marine Energy Extraction Centre for Renewable and Sustainable Energy Studies Stellenbosch University Presenter: Josh Reinecke Researchers: I. Meyer, J. Reinecke & Prof J. L Van Niekerk

Ocean Current Energy around South Africa Agulhas Current is South Africa’s strongest ocean current resource Viability for energy extraction?

Water mass contribution of the Agulhas Current: –Agulhas Current retroflection – largest source –Mozambique Current –East Madagascar Current Poleward flowing Under Current The continental shelf narrows between Durban and Port Edward – causing the current to flow near the shore with a high velocity – also helps stabilize the Agulhas Current in this region and no regular wide meanderings are present. Destabilizing Region: The Natal Bight – Situated between Durban and Richards Bay – This area has a wider continental shelf and the shelf’s morphology change destabilizes the current, resulting in infrequent formation of Natal Pulses Agulhas Current: Characteristics } The contributions from these two sources are mostly in the form of eddies or rings

Agulhas Current: Previous Research Mean structure of the Agulhas Current presented by Bryden et al (Bryden, et al., 2005) Velocity structure [cm/s] (Beal & Bryden, 1999) Bryden et al (2005) took the variability into account when examining the mean characteristics of the Agulhas Current through the use of composite spectral analysis It was concluded in the study that a transport of Sv ± 4.3 Sv is achieved by the Agulhas Current at 31 o S Beal and Bryden discovered that the core of the current is situated 20 km from the coastline at the surface and it is 70 km wide

Agulhas Current: Data Analysed Location of ADCP deployment of data collected Data analyses on shore due to restrictions in morning depth of available technology

Factors impacting deployment site choice External factors that can impact the depth, location and available resource: −Shipping routes −Existing infrastructure that can utilize the generated energy −Marine Protected Areas Technology specific factors: −Operational depth −Turbine Capacity factor −Array configuration and spacing −Instrumentation used for data capturing Distance from the assessment sites to closest substation

ParameterValue Mean [m/s]1.46 Median [m/s]1.6 Mode [m/s]1.76 Standard Deviation [m/s]0.59 Minimum [m/s]0 Maximum [m/s]2.82 Agulhas Current: Results from 18 month analysis Cape Morgan Probability of exceedance Velocity [m/s] P501.6 P P P990.1

Natal Pulses Agulhas Current: Results from 18 month analysis Cape Morgan

Turbine specifications SeaGen Turbine (Siemens, 2012) Numerical Turbine Cut in speed0.8 m/s0.6 m/s Cut out speed2.5 m/s2.0 m/s CpCp Diameter16 m Agulhas Current: Results from 18 month analysis Cape Morgan The capacity factor also gives a good indication of the variability of the site The achieved capacity factors are considerably lower than expected. This can be accounted for by the lower velocities experienced in ocean currents in comparison to tidal applications which the technology is designed for and the variability of the Agulhas Current. SiteCapacity factor % Cape Morgan50.9 East London location East London location 247.5

The plot shows the power plot which has averaged over a five day period. This five day averaged power presents a smoother trend plot and highlights where the distinct drop in power occurs Agulhas Current: Results from 18 month analysis Cape Morgan

Site 1 and site 2 lie 45 km and 25 km respectively from the nearest low voltage station. It can be argued that Cape Morgan is the better choice to the East London location 2 for marine turbine deployment due to the improved velocities and lower variability at this chosen site. The difference in capacity factor is approximately 3.3% between the two locations, but a techno-economic analysis will have to be carried out in order to see if the greater capacity power produced will compensate for the costs incurred for the longer distance of sea cabling. Agulhas Current: Conclusion East London 2 Cape Morgan 1 2 Distance from the assessment sites to closest substation