South Africa’s ocean energy potential
Submitted by: Jean McKenzie, Thursday, February 5, 2015
Oceans are already a well exploited source of energy as they are a major reserve of the world’s fossil fuels. There is however also an opportunity to access renewable energy from the oceans. Speaking to the South African National Energy Association (SANEA) in Cape Town, Professor Wikus van Niekerk, from the Stellenbosch University Centre for Renewable and Sustainable Energy Studies (CRSES), explains that there are six major forms of ocean energy that have the potential to be exploited: wave energy, tidal currents, ocean currents, temperature gradients, salinity gradients, and offshore wind energy. While this sounds immediately attractive, van Niekerk however warns that “it’s a very challenging and expensive environment to operate in…you need lots of guts and big budgets to go into the ocean.”
According to van Niekerk, while South Africa has some limited potential for harnessing tidal current energy, particularly at the Knysna Heads and the Langebaan Lagoon, the country’s most promising renewable ocean energy potential lies in ocean currents and waves.
As a source of energy, ocean currents are attractive because they are generally more consistent than tidal currents and provide a large volume of flowing water, thus having base load potential. However there are a number of challenges with ocean currents as they are significantly further offshore and deeper than tidal currents making them difficult to access for the deployment, maintenance and operation of the equipment to harness the energy. As van Niekerk points out there is also the possibility that climate change may influence the way in which the ocean currents flow, raising questions about each ocean currents’ sustainability.
The Agulhas current is a major wind driven ocean current travelling from the Indian Ocean to the Atlantic Ocean along South Africa’s eastern coastline. While ocean currents are generally consistent (being one of their appealing features as mentioned above), the Agulhas current does suffer from both rogue waves (formed by the interaction between the current, tides and storm systems) and also what are known as “Natal pulses”, which are eddies that break off the main current and swirl back while moving south west with the current, effectively causing interruptions in the current flow. South Africa’s power utility Eskom has commissioned three studies on the Agulhas current, the first in 2003, the second running from 2005 to 2010, and the third in 2012. The presence of the “Natal pulses” has been observed in the studies and can affect the current for up to two to three weeks. However the frequency of the pulses is still being investigated. “We are currently working with [the University of Cape Town] to try and understand these “Natal pulses” better to try and find out if it is possible to put ocean current turbines in the Agulhas and get some measure of base load out of the current,” says van Niekerk.
Technology to harness ocean current energy
According to van Niekerk there is currently no commercial or pilot scale technology available for harnessing ocean current energy but a device such as the SeaGen produced by Marine Current Turbines Ltd that has been deployed for tidal currents is a concept which may have potential application in ocean currents. However besides the challenges of locating the equipment in such a remote location offshore, a further concern about equipment in the flow of the Agulhas current is that ships use the current to conserve fuel by drifting down the current to reduce travel time, providing the potential for collision. Thus using the Agulhas current to generate base load renewable energy still seems a long way off at the moment, with a number of challenges needing to be overcome.
Harnessing energy from waves
At this stage, from a technology point of view, wave energy appears to be a more likely first option for South Africa to take advantage of. The energy can be obtained from the ocean surface wave action by converting the wave kinetic energy into mechanical and/or electrical energy. The South African potential for wave energy is high given the fact that South Africa has an extensive coastline of over 2,500 km and a sophisticated manufacturing economy. An indicator of wave power generation is kW per m which is a measure of the amount of electricity that can be generated for a ‘metre of wave’. Research conducted at CRSES shows that the Western Cape has the highest kW/m along the South African coast ranging from 35 at the border with the Eastern Cape and 38 near Saldanha Bay to a peak of 40 kW/m off the coast of Cape Town. The KwaZulu-Natal coast near Durban has recorded an annual mean rating of 15 kW/m which is significantly less than the rest of the South African coast. A number of Wave Energy Converter (WEC) technologies are available internationally and in South Africa itself a few wave energy projects have been initiated (some of which have already come and gone such as Pelamis and AquaBuoy). One of these is the Stellenbosch Wave Energy Converter (SWEC) developed at Stellenbosch University in the 1980s as a converter that is optimised for the South African wave conditions. An extension of this has been the ShoreSWEC which would be incorporated into a breakwater (with Granger Bay at the V&A Waterfront in Cape Town having been proposed as a suitable location). In Hermanus the company Mean Sea Level (Pty) Ltd is looking to develop an overtopping device up to 5.25 MW to provide electricity for abalone farming. An initial 1MW pilot project is planned.
Cost of technology
While van Niekerk believes South Africa has promising wave energy and ocean current resources, he highlights that harnessing any form of ocean energy on a commercial scale at present is expensive. A recent UK study, he says, states a cost of the equivalent of R5.50/kWh. “To put that in context, [Solar] PV in South Africa is R1/kWh and it might even go down. Wind 74c/kWh and it might even go down. So if you want to do ocean energy you are fighting R1/kWh and 74c/kWh”. So as it stands, compared to other energy sources, the technology for ocean energy converters remains too expensive for deployment in South Africa for now.
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