Seasonal Energy Storage to Support South Africa’s Energy Transition

Variable renewable energy (VRE), in the form of wind and solar power, is poised to be the foundation of South Africa’s future decarbonized electrical power system. However, the intermittent nature of VRE poses significant challenges to reliability in this power system and is likely to result in seasonal energy imbalances. Seasonal energy storage (SES) offers a potential solution by storing excess energy generated during periods of high renewable output and releasing it when generation is low, effectively bridging seasonal gaps. This study investigates SES's technical feasibility and financial viability in South Africa's future decarbonized power system. By analyzing the country's future energy mix, this study assesses the optimal timing for deploying SES. A techno-economic analysis is performed incorporating three different SES technologies (pumped hydro, compressed air, and hydrogen energy storage) and different discharge durations (one week, two weeks and four weeks) to determine which technology and sizing characteristics are more suited for SES in South Africa, using the benefit-cost ratio (BCR) metric. The results show that, for the reference scenario in South Africa’s most recent capacity expansion plan, SES will be financially viable by approximately 2036 for a one-week discharge duration and by 2039 for a two-week discharge duration, which occur at VRE penetration levels of 48% and 54%, respectively. Pumped hydro energy storage with a two-week discharge duration emerges as the most financially viable SES. Under current technology costs, hydrogen energy storage only emerges as the most viable option towards 2060, but decreasing costs could accelerate its financial viability to the mid-2040s. The 2050 energy mix with added SES shows significant reductions in VRE curtailment compared to the non-SES scenario. This research provides valuable insights for South African and international stakeholders involved with optimizing future power systems related to the value of SES.