SA has yet to build any large, sea-based wind farms, but the first comprehensive assessment of offshore wind energy potential suggests that large wind turbines off the KwaZulu-Natal and Western Cape coasts could generate between 15% and 800% of current electricity demand.
The lower figure is for shallow water wind farms at depths of less than 50m, whereas the higher figure includes turbines further out to sea, at depths of up to 1,000m.
Writing in the latest issue of the Journal of Energy in Southern Africa, Stellenbosch University researchers Gordon Rae and Dr Gareth Erfort say SA is under pressure to reduce climate-heating emissions after making an international pledge in 2009 to cut emissions by 42% by the end of 2025, subject to international support and funding.
[ SA is yet to] exploit
— Gordon Rae, Dr Gareth Erfort
the abundance of
offshore wind
energy
Stellenbosch University researchers
While the government had put in place a new renewable energy procurement programme for independent power producers, it was yet to "exploit or consider the abundance of offshore wind energy", they say.
"The urgency of decarbonisation, coupled with both the price reduction and abundance of wind and solar resources in SA, make investment in these technologies an obvious decarbonisation strategy," say the two researchers from Stellenbosch's department of mechanical and mechatronic engineering.
In their study, which they describe as the first site-specific study of offshore wind farms in SA's 370km-wide Exclusive Economic Zone, Rae and Erfort say the investigation is a crucial first step towards developing future markets for offshore wind energy.
After mapping water depths and modelling wind speeds for the past 30 years, they conclude the shallow-water shelf between KwaDukuza and Richards Bay is the best place in SA to build offshore wind farms.
This was largely because this section of coast has high wind speeds and is relatively shallow at between 40m and 60m, allowing for cheaper fixed-bottom foundations for wind turbines. Waters near Durban are arguably the second-best location, followed by Struis Bay near Cape Agulhas.
Their study focused on coastal areas with relatively shallow water, combined with wind speeds of at least 7m per second as winds speeds below this benchmark were considered economically unfeasible.
Though the assessment had not considered the impact of wind farms on shipping lanes, it excluded all marine protected areas.
The study also considered the likelihood that no wind farms would be built within 10km of the coastline. This was because most European offshore wind farms included a 10km "buffer zone" to prevent negative visual impacts that could affect tourism, natural aesthetics and the value of real estate.
Based on their modelling, they suggest that shallow-water wind farms could generate more than 44 teraWatt hours of electricity annually, while deeper water installations could generate up to 2,387TWh.
Based on SA's current annual consumption of about 298TWh, offshore wind energy could in theory generate between 15% and 800% of annual electricity demand.
The researchers say the global offshore wind power-generation technology is maturing and costs are slowly declining, though they do not provide specific cost comparisons with existing fossil fuel and renewable energy options.
Eskom said it had conducted studies on the potential for offshore wind but many factors led it to the conclusion it was not feasible, not least of which was the cost.
It added that SA's oceans have a significant ocean shelf drop-off, which implies additional support structures (with increased costs) are necessary for offshore plants.
And given the abundance of land in SA with the option to continue farming activities after plant construction, onshore plants are far more attractive, Eskom said.
According to the US Energy Information Administration's latest Annual Energy Outlook (2020), offshore wind farms remain one of the costliest options when measured according to the metric of levellised cost of electricity (LCOE).
But when measured according to a different metric - levellised avoided cost of electricity (LACE) - future offshore wind farm costs compared favourably, and in some cases better, than other generation options.
LCOE is the most common indicator used to compare the cost of electricity-generating technologies, while LACE uses more complex equations and is a measure of the market value of electricity.
However, critics say neither is a perfect yardstick as one-to-one comparisons can distort the complex costs and benefits of widely different technologies, including varying lifespans, region-specific issues, carbon intensity, taxes and other factors.
Senior World Bank economist Govinda Timilsina suggested recently that the limitations of the LCOE measure could be misleading to investors for several reasons and that the economics of renewable energies would improve further if investors and regulators took account of factors such as environmental externalities such as carbon taxes as well as health and climate change benefits.
Timilsina said the costs of electricity generation from a given technology varied widely across countries. "For example, the LCOE of solar PV [photovoltaics] in Japan is almost 2.5 times as high as that of India. Similarly, the LCOE of wind power in Italy is almost twice as high as that of China."
In an article in the journal Science Advances published earlier this year, three Harvard University engineering and planetary science researchers noted that the recent expansion of offshore wind plants in Europe and China indicate that the economics have changed markedly and could be cost-competitive now with present technologies.
"Offshore wind will be cost-competitive by 2030, and may already be so," they say.
