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Marine
Wave Energy Along the Coast of Southern Africa
a report by
James Joubert
Centre for Renewable and Sustainable Energy Studies, Stellenbosch University
The southern coast of the African continent is exposed to a highly The results of this investigation can be used for the identification of
energetic wave climate due to its proximity to the storm-generation areas of high wave-power concentration within the study area for the
zone in the south Atlantic ocean. The possibility of exploiting this location of WEC units.
abundant energy resource was first researched in South Africa
(at Stellenbosch University in particular) 30 years ago by the privately Stellenbosch Wave Energy Converter
funded Ocean Energy Research Group (OERG) led by Professor Deon The SWEC consists of a pair of submerged collectors (arms) coupled in
Retief. During this time, Retief et al. designed and developed the a V-formation to an air turbine and generator mounted above the
Stellenbosch Wave Energy Converter (SWEC). The stabilisation of oil water level in a tower at the apex of the V. Each collector arm consists
prices in the late 1980s led to the wave energy research project of 12 oscillating water column (OWC) chambers in which water level
being discontinued, but current market drivers such as the oscillations displace air via inlet and outlet valves through low- and
ever-increasing cost of electricity, the need for secure energy supply high-pressure manifold systems that are connected to the air turbine in
and increasing pressure on the South African government to the tower. This is a near-shore system, thus reducing the transmission
promote renewable energy technologies have increased the distance and consequent high cost of underwater cabling. The SWEC
possibility of implementing this indigenous design as a cost-effective is founded on the seabed, which provides a fixed reference frame and
way to harvest wave energy. eliminates the need for complex mooring configurations.
An energy resource can only be successfully exploited if the resource 2D and 3D physical model studies (1:50 and 1:100 scale) were
itself is well understood, defined and harnessed. Therefore, a wave conducted in the hydraulic laboratories of Stellenbosch University and
energy resource assessment was recently conducted to quantify the by the CSIR to assess the conversion efficiency of the SWEC
wave energy conversion potential of the South African coastal waters. device and to optimise its design parameters (length of collector,
The results of this study are presented in the following section.
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orientation of device and internal geometry of oscillating chambers).
2
The structural stability and impact of the device on sediment transport
Local Meteorology and the processes were investigated in scale model tests. The cost of electricity
Resulting Wave Energy Resource for the SWEC compared favourably to that of nuclear power and
Eastward-moving low-pressure systems created in the south Indian and coal-fired power at the time, but a drop in oil price in the early 1990s
south Atlantic oceans, with their associated cold fronts and wind fields, saw the project discontinued.
are the main wave-generating mechanism off the south-western
African coast. A secondary source of high waves along the eastern Unfortunately, a full-scale SWEC prototype has never been built, mainly
extremity of the South African coast is the presence of tropical cyclones due to the high capital investment of a standalone system and the
in the western Indian ocean.
1
complexity of obtaining the required permission. To overcome these
barriers an adaptation of the SWEC called the ShoreSWEC is currently
In order to identify the South African coastal zone with the greatest being investigated at Stellenbosch University; a brief description of the
wave energy resource, wave data recorded at wave-measuring ShoreSWEC is presented in the following section.
stations operated by the Council for Scientific and Industrial Research
(CSIR) on behalf of the National Ports Authority were analysed. From ShoreSWEC
the recorded wave data analysis it was found that the south-west The ShoreSWEC is an oscillating water column WEC integrated into a
coastal zone has the greatest wave energy resource, with a mean vertical wall caisson breakwater structure. Integrating wave energy
annual average of approximately 40kW/m. The rest of the South absorption in (new) coastal structures has the main advantage of
African coast is exposed to average wave power that is between sharing cost between the breakwater and the WEC, in addition to the
approximately 18 and 23kW/m. advantages over ‘normal’ breakwaters by reducing loads and wave
heights in front of the device, as the wave energy is absorbed, not
The spatial distribution of wave power in the south-west coastal zone reflected.
3
Orientating the device at an oblique angle to the prevailing
was further investigated by modelling hindcast National Centre for wave direction ensures that the chambers operate sequentially as
Environmental Prediction (NCEP) wave data using the Simulating Waves each wave propagates along the length of the device.
Nearshore (SWAN) wave model. The mean annual average wave power
for a 10-year period over the focus area is shown in Figure 1 as an The ShoreSWEC consists of OWC chambers founded on the seafloor
example of the model output. Joubert’s MSc thesis provides a detailed and extends above the still water level (see Figure 2). Wave-induced
description of the monthly, seasonal and annual distribution of wave water-level oscillation forces air into and out of the chamber via
power in the south-west coastal zone.
1
unidirectional valves located in the top of the chamber. The valves are
© TOUCH BRIEFINGS 2010
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