A techno-economic assessment of Seasonal Energy Storage in high Renewable Energy Scenarios

Tiaan Vivier (Dept. of Electrical Engineering, Stellenbosch University)
Prof. Bernard Bekker (Dept. of Electrical Engineering, Stellenbosch University)
Christina Auret (Dept. of Electrical Engineering, Stellenbosch University)

Variable renewable energy (VRE), like wind and solar, is essential for South Africa’s future decarbonized power system, but its intermittency causes significant seasonal energy imbalances. Seasonal energy storage offers a solution by storing excess generation during high-output periods for release when VRE generation is low, effectively bridging these seasonal gaps.

This study investigates the economic competitiveness of seasonal energy storage in South Africa’s future energy mix to improve the efficiency of long-term capacity expansion plans. The research introduces value stacking, where SES delivers multiple benefits simultaneously (e.g., seasonal storage, peaking support, congestion relief) to enhance its financial viability.

A techno-economic analysis was conducted across three long duration energy storage technologies: pumped hydro, compressed air, and hydrogen energy storage. Each was evaluated over one, two, and four-week discharge durations. Using a benefit-cost ratio, financial viability was assessed across scenarios reflecting various VRE penetration levels in the Integrated Resource Plan.

The findings reveal that seasonal energy storage can become economically competitive when multiple value streams are considered together. This research provides meaningful insights for policymakers, system planners, and investors supporting resilient, low-carbon energy systems through the integration of long-duration energy storage.

Energy storage systems, Generation technologies

September 2025