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The recently released Assessing the impact of increasing shares of variable generation on system operations in South Africa – a flexibility study, has found that the South African power system will be sufficiently flexible to handle very large amounts of variable wind and solar PV generation.

Study finds SA power grid can handle additional powerThe report, commissioned and funded by the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) under the Department of Energy (DoE) South African – German Energy Programme (SAGEN), was conducted by international engineering consultants.

The study confirms that the country’s power system will not be adversely affected by additional wind and solar PV power in any way – despite Eskom’s claims to the contrary – especially when considering the addition of combined cycle gas turbines (CCGTs) and open cycle gas turbines (OCGTs) proposed in the draft IRP 2016 Base Case. “In 2030, the addition of CCGTs will even reduce cycling requirements of coal-fired power stations, even with 20GW of additional rooftop PV,” it states.

Up to 2020, the allocated operating and emergency reserve does not need to be increased, even when adding 10 GW of additional rooftop solar PV, the study found, adding that in the case of very high PV installations (10GW in 2020, 20GW in 2030), it is recommended to move pumping operation of pumped-storage power plants from night to midday, when Residual Load is at its minimum value. This relaxes Residual Load Requirements and allows coal fired power plants to operate at higher levels. It can also help reduce the amount of curtailed PV energy.

“Up to 2030, the operating and emergency reserve will still be sufficient to balance the increased variability of wind and solar PV generation capacities proposed in the draft IRP 2016 Base Case.

When installing 10GW or 20GW of rooftop solar PV in addition to utility scale variable renewable energy capacity proposed in the draft IRP 2016 Base Case, the operating and emergency reserve must be increased to balance increased variability. However, the required additional operating and emergency reserves are in the moderate range,” the report says.

To ensure secure and cost-efficient operation of the South African power system even with very high levels of wind and PV generation, the researchers made a number of recommendations. The first was the application of professional short-term forecast tools/services for wind and PV prediction, including a system for short-term prediction of rooftop PV. In the case of very high PV installations (e.g. 27GW by 2030), there should be allocation of higher levels of Operating Reserve and Emergency Reserve in the afternoon hours. In the case of very high PV installations (e.g. 27GW by 2030) pumped-storage power plants should operate in pumping mode during mid-day (and not during night time) when Residual Load is at its minimum value.

“Other modifications to operational procedures (day-ahead planning, intra-day planning, real-time operations) are not required in the studied time frame and the studied levels of wind and PV. This study confirms that very large penetration levels of wind and PV could be handled by the system, from an active power balancing point of view, at moderate additional costs for balancing services (Reserve and increased cycling of thermal power plants), the researchers conclude.

Other aspects, like voltage issues resulting from the operation of the South African power system with very high levels of distributed PV and potentially required additional reactive power compensation equipment (and/or new strategies for reactive power and voltage control at distribution levels) was not subject to the study. However, the report recommends that this should be analysed in a follow-up study.

Image credit: Copyright: hxdyl / 123RF Stock Photo

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