Wind Power Variability and Power System Reserves in South Africa

Poul Sørensen, Marisciel Litong-Palima, Andrea N. Hahmann, Schalk Heunis, Marathon Ntusi, Jens Carsten Hansen

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Variable renewable generation, primarily from wind and solar, introduces new uncertainties in the operation of power systems. This paper describes and applies a method to quantify how wind power development will affect the use of short-term automatic reserves in the future South African power system. The study uses a scenario for wind power development in South Africa, based on information from the South African transmission system operator (Eskom) and the Department of Energy. The scenario foresees 5% wind power penetration by 2025. Time series for wind power production and forecasts are simulated, and the duration curves for wind power ramp rates and wind power forecast errors are applied to assess the use of reserves due to wind power variability. The main finding is that the 5% wind power penetration in 2025 will increase the use of short-term automatic reserves by approximately 2%.
• Simulations are validated against observations of 30 minutes ramp rates.
• Absolute wind power ramp rates increase from 2014 to 2025.
• Normalised wind power ramp rates decrease from 2014 to 2025.
• Wind power will not impact the use of instantaneous reserves.
• Wind power will increase use of regulating reserves with less than 3% in 2025.
Original languageEnglish
JournalJournal of Energy in Southern Africa
Issue number1
Pages (from-to)59–71
Number of pages23
Publication statusPublished - Feb 2018
Externally publishedYes


  • Variable generation
  • Forecast errors
  • Ramp rates
  • Power curve estimation
  • Fluctuations

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