Abstract
This study was undertaken to assess whether the available and recoverable wave power density resource on the Agulhas Bank (South Africa) is sufficient to support a Pumped Storage Scheme (PSS). We used 5 months of insitu wave data collected in a depth of 80 m off Cape Agulhas, Mossel Bay, Tsitsikamma and Cape Recife, together with model wave data from the National Centre for Environmental Prediction (NCEP) - WAVEWATCH III which was reanalysed by the French Research Institute for Exploitation of the Sea (IFREMER) - IWOAGA. The wave power density resource (P) was estimated by calculating the wave energy flux across a unit diameter circle of the wave field, and the resource available by the lateral transfer of wave energy along a linear array of wave energy converting devices. The results showed that Cape Agulhas had the most available P (75% for 40 kW/m, 25% for 17 kW/m, with an average of 31 kW/m) followed by Mossel Bay (75% for 34 kW/m, 25% for 14 kW/m, with an average of 25.2 kW/m), Tsitsikamma (75% for 32 kW/m, 25% for 13 kW/m, with an average of 25.0 kW/m), and Cape Recife (75% for 30 kW/m, 25% for 12 kW/m, with an average of 23.7 kW/m). For the entire nearshore domain, the most frequent waves had values of P between 30 kW/m – 50 kW/m, with the dominant direction of propagation from the southwest. On average, the diurnal cycle was characterised by a peak in energy in the evening nearshore and in the afternoon offshore. The seasonal cycle was characterised by a peak in winter (40 – 50 kW/m) and trough in summer (20 – 30 kW/m). The interannual variability signal had a strong correlation with regional Sea Level Pressure (SLP), surface westerlies winds, and regional sea surface currents. It is also correlated to El Niño Southern Oscillation (NINO3) and the Southern Annular Mode (SAM). In terms of the total annual wave energy resource (P), approximately 380 TWh/yr, are available near the 80 and 128 m water depths. For the PSS, it was estimated that for a moderate flow rate of 50 m3s-1, the required power to pump sea water to an upper reservoir with a volume of 5 and 15 million m3 is approximately 43 and 150 MW. The pumping process would take between 28 and 82 hours. This study concludes that the entire Agulhas Bank has indeed sufficient wave energy resource to supply a large scale PSS.