Page 53 - Energize January 2022

TECHNICAL

The South African Wind Atlas: Essential

for renewable resource planning

by Mike Rycroft, Energize features editor

Wind power is a major feature of most energy plans, South Africa’s included. Wind is a variable
resource, both geographically and chronologically, and planning of wind installations requires

reliable information on the wind resource available at a proposed site. Numerous models are
available and South Africa has completed its own reliable wind atlas (WASA).

ccurate, reliable and up to date information on wind speed height greater than 10 m above ground level (AGL).
and wind energy potential is essential for the planning of wind The Atlas provided a general wind profile for the whole country
Afarms and the co-ordination of the aggregated national wind (Figure 1) as well as information on specific recording stations.
power resource. Information for specific recording sites included seasonal and daily
Most wind farms are planned using wind models based on wind speed variations. More importantly, the Atlas included statistical
historical wind data recorded at specific sites, or other high-level data on wind speed distribution, using the Weibull distribution model.
data such as satellite and global meteorological data. Many wind Although the Atlas provided a rough guide to the potential for
installations worldwide are suffering from performance below wind power, it did not provide an accurate means of estimating the
expected standards, as well as such phenomena as onshore doldrums wind potential at a particular site. Attempts were made at establishing
and wind pattern shifts. Offshore installations suffer even worse as a method of determining the wind speed data at a particular site by
accurate data on offshore winds is not directly available and often interpolating data from nearby existing sites and making use of surface
comes from proxy sources. effects. This was hampered by the lack of detailed information on
Incorrect estimation of available wind power can be disastrous. surface topology and lack of computing power.
Britain suffered an embarrassing low level of wind power during Since the publication, several other models have been
COP26 and has on several recent occasions had to re-activate coal constructed, such as SARERD (Eskom 2001) and Hagerman (UCT
fired stations due to poor performance of wind farms. Germany, a 2009), many based on satellite data and other databases. Although
champion of wind power, suffers a regular phenomenon known as the the wind atlas proved useful in its intended application, the decision
dunkelflaute, an onshore doldrum, which causes low wind and solar to introduce utility scale wind farms on a large scale required a more
production for days on end. Both these countries are able to draw accurate and easier to use system. Accurate modelling of wind is
additional power from neighbours. We don’t have that luxury, so wind necessary when designing for wind power. A 10% error in wind speed
power planning has to take these possibilities into account. To do this can lead to a 30% error in wind power and energy.
requires accurate and reliable information on the wind resource.

Historical wind mapping
One of the first attempts at mapping the wind resource in South
Africa was undertaken by Roseanne Diab, of UKZN, and this resulted
in the publication of the “Wind atlas of South Africa” in 1995. The
publication was prepared for the then Department of Mineral
and Energy affairs. The wind atlas was compiled using data from a
number of different sources, using different recording methods. This
included stations run by the SAWB, the ARC, Eskom, Atomic Energy
Commission, Sea Fisheries, Dept of Forestry, and other parties.
One of the limitations of this method was that that wind recording
stations are located at a height above ground level (AGL) varying from
2 to 12 m, which makes the wind speed very dependent upon location
and terrain. Although results are normalised to a height of 10 m, the
data is of limited use to modern large wind turbines. The wind atlas
proved a useful means of determining the viability of the small wind Figure 1: Generalised map of wind power potential in South Africa
turbines available at the time, which were not generally mounted at a (Diab 1995)

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