Page 57 - Energize January 2022

TECHNICAL

Results
Comparison of calculated and measured wind data showed a high
correlation with small errors or differences for most sites. Several
sites were regarded as “challenging” and may require refinement of
the modelling process in those areas.

Information available from the wind atlas
In the WASA modelling domain, wind climate data is available
in grids with a 3,3 km spacing for the whole of South Africa.
This results in approximately 170 000 virtual masts. Some of the
information available is:

Wind speed graphs
Daily, weekly and monthly wind speed graphs for all the measuring
sites (Figure 7).

Figure 8: Grid points which can be accessed for data download 3

effort of doing the calculation. This grid can be accessed on the
CSIR WASA website.

Country wide aggregated wind resource
Wind is a variable resource and varies both in time and in space.
(a) Daily wind speed
Time based wind patterns differ from place to place, and studies
of the South African wind resource have suggested that wind
resources could be combined in a spatially diverse manner to
minimise time variation and give a consistent power generation
pattern across the country. The old mantra that “The wind is
always blowing somewhere” may well be true but wind sites
have to be selected carefully to take advantage of this. High level
studies of the South African wind resource have suggested that
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combining wind power from selected sites could significantly
(b) Weekly wind speed reduce the variation in aggregated wind output. One should
imagine then that these studies would have been considered
when compiling the IRP and when awarding contracts under the
REIPPPP system.
It seems though that this was not the case and no specification
other than capacity has been specified in any of the REIPPPP
windows. In addition, this factor does not seem to have been
considered when evaluating bids, and allocation was based mainly
on price.
Information on wind for individual sites is important for the
(c) Monthly wind speed site and the sizing and costing of the wind project on site, but for
Figure7: Wind speed graphs a national plan, and for performance information on each site
and the aggregated output, aggregated time-based information
Time series from measuring sites is required. An important dataset when attempting to compile
Time series of wind speed and direction at half hourly intervals a national energy plan is the real-time-based model of how all
is available for all of the established sites. Information can be potential wind sites operate together.
downloaded from the CSIR site. Many reports emphasize the maximum aggregated output
of modelled networks, but little if any information is available
Time series from established grid points on the minimum aggregated value of wind power. From a grid
Calculated time series of wind speed and direction at data, at any operators’ point of view, the crucial criteria will be the minimum
of the established grid points shown in Figure 8 and averaged over values of wind power generation and their time and frequency of
half hourly intervals, ranging from 1990 to 2020, this saves the occurrence.

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