The study was prepared for the Department of Energy and Eskom by international engineering consultants who were commissioned and paid by the Deutsche Gesellschaft für Internationale Zusammenarbeit as part of the South African German Energy Programme. The study — “Assessing the impact of increasing shares of variable generation on system operations in SA: A flexibility study” — investigated the raised flexibility requirements of the South African power system resulting from increased levels of renewable generation up to 2030.
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The study also examined whether existing and planned power plants could cope with these requirements. In addition, the study quantified the costs associated with the raised flexibility requirements imposed by variable renewable energy sources, that is wind and photovoltaic (PV) solar.
The system has to be flexible because, with the introduction of renewable energy, generation is not constant but varies over time. This means power plants have to adjust their power output to demand, either by starting and stopping or just by varying their power output. There are operational and cost constraints to their ability to do this, which can be dealt with by forward planning; being able to predict variations in load, and having a balancing reserve to cater for a mismatch between the predicted and actual load and generation. The size of the reserve will increase as the level of renewable energy generation increases.
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Professional short-term forecasting capacity will be required to predict wind and solar energy generation if the power system is to work in a secure and cost-efficient way with high levels of renewable energy generation.
A system for short-term prediction of rooftop solar PV will also be needed
“The study presented in this report confirms that the South African power system will be sufficiently flexible to handle very large amounts of wind and PV generation, especially when considering the addition of combined cycle gas turbines and open cycle gas turbines,” as provided for in the base case of the department’s integrated resource plan which was released in November last year.
The authors note that when looking at the time frame beyond 2030 when even larger penetration levels of wind and PV are possible, the flexibility requirements of the system would increase further and additional mitigation measures would be required.