Abstract

 
 
 Spatio-temporal dynamics of near-surface wind speeds were examined across the Northern, Western and Eastern Cape regions of South Africa. The regions assessed were geographically subdivided into three zones: coastal, coastal hinterland and inland. Wind speed data (10 m) were evaluated at monthly, seasonal, annual and zonal resolutions, with the aim to establish wind speed attributes and trends. Data from 19 weather stations with high-resolution wind records between 1995 and 2014 were evaluated. The majority of stations (79%) recorded a decrease in mean annual wind speed over the study period. The mean rate of decrease across all stations over the 20-year period equates to -1.25%, quantifying to an annual decrease of -0.002 m/s/year (-0.06% pa). The largest seasonal decline of -0.006 m/s/year (-0.15% pa) was recorded in summer. Statistically significant declines in mean annual wind speed are somewhat more pronounced for the coastal zone (-0.003 m/s/year, -0.08% pa) than over interior regions (-0.002 m/s/year, -0.06% pa) for the study period. The largest decrease (-0.08% pa) was recorded for the coastal zone, followed by the inland zone (-0.06% pa), equating to an annual reduction in available energy of 0.18% pa and 0.09% pa, respectively. When considering all stations over the study period, the mean inter-annual variability is 3.11%. Despite such decreases in wind speed, the variance identified in this study would not have posed any risk to power generation from wind across the assessed stations, based on the period 1995 to 2014.
 
 
 
 
 Significance: 
 
 
 
 Mean recorded wind speed decreases have been marginal under recent (last 20 years) climatic conditions and change, thus adding confidence to the justification by the South African government to procure additional wind-generated electricity capacity.
 Wind speed trends and variance measured over the research period (1995–2014) for the Cape stations in this study, would not have posed any risk to power generation from wind.
 Only four stations (28.6%) recorded statistically significant trends at the 0.05% level; of these 75% were decreasing trends.
 Coastal zones recorded a statistically larger decrease in mean wind speed compared to inland regions.
 When considering all stations over the period 1995–2014, the mean inter-annual variability is 3.11%.
 
 
 
Highlights
Despite uncertainty in forecasting wind speed and variance over time, wind power generation is the fastest growing form of renewable energy, and such forecasts are important considerations for the renewable energy sector
This assessment confirms that mean regional near-surface wind speeds are insignificantly declining at 10 Cape stations at an average rate of -0.002 m/s/year
Coastal zones recorded a statistically larger decrease in mean wind speed compared to inland regions
Summary
Despite uncertainty in forecasting wind speed and variance over time, wind power generation is the fastest growing form of renewable energy, and such forecasts are important considerations for the renewable energy sector. South Africa recorded its first wind-generated electricity from independent power producers incorporated into the national grid at the end of 2013. This generation had reached 1212 MW by the end of 2015, which equates to 2.66% of the national installed power capacity.. The projected outlook would see up to 4360 MW (approximately 5% of national power capacity) of wind generation installed by 2030.5 This substantial uptake in energy generation from wind requires some understanding of wind variability and trends in the South African context, so as to quantify the potential impact of wind variability and/or change over a 20-year power purchase agreement term This generation had reached 1212 MW by the end of 2015, which equates to 2.66% of the national installed power capacity. The projected outlook would see up to 4360 MW (approximately 5% of national power capacity) of wind generation installed by 2030.5 This substantial uptake in energy generation from wind requires some understanding of wind variability and trends in the South African context, so as to quantify the potential impact of wind variability and/or change over a 20-year power purchase agreement term
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