South Africa’s latest round of load shedding, attributed to unplanned outages at Eskom’s coal fleet, was compounded by almost depleted pump storage and diesel levels, an energy expert has told Energize.
Eskom implemented Stage 3 load shedding on February 22. It escalated to Stage 6 a day later after multiple unit failures at Majuba and Camden power stations. In the preceding week, signs of a strained system were evident, with diesel and pump storage reserves used at an unsustainable rate, leading to severe depletion, says independent energy analyst Clyde Mallinson.
“Ideally, Eskom should use pump storage and the open-cycle gas turbine (OCGT) fleet to manage peak-demand periods by storing excess electricity during off-peak hours and releasing it when needed. But, with an insufficient surplus, pump storage reserves weren’t sufficiently replenished – even at night – forcing Eskom to run costly OCGTs more often and during off-peak hours to replenish pump storage reserves.
“OCGTs are designed for short bursts of operation to address peak-time shortages rather than running for long periods, which is highly inefficient and expensive. This continuous reliance on diesel quickly depleted reserves – stretching Eskom’s capacity to replenish them.”
The first signs of a problem emerged in early December when Eskom significantly increased its diesel use – likely in an attempt to prevent load shedding and sustain its uninterrupted power supply record, Mallinson says. “At times, diesel turbines were running through the night – a tell-tale sign of an impending supply crisis and generation shortfall.”
Load shedding resumed on January 31 after 10 months of uninterrupted supply. By this time, the system had already been pushed to its limits multiple times, he says.
The recent and unexpected breakdowns of the coal fleet have forced Eskom to implement and then escalate load shedding, Mallinson says. “Had Eskom introduced controlled load shedding a week earlier, at a lower stage, it could have mitigated the need for such a rapid escalation by preserving its emergency reserves – effectively keeping its powder dry. However, by delaying the decision, the power utility scrambled to restore diesel and pump storage levels, necessitating rapid escalation to higher load-shedding stages.”
The root of the problem remains Eskom’s struggle to sustain a stable and consistent energy availability factor (EAF), Mallinson says. “Increasing the average EAF alone is not a reliable indicator of load shedding risk. Rather, the variability of the instantaneous EAF is far more critical as a low instantaneous EAF often necessitates load shedding. The unpredictability of Eskom’s coal fleet, plagued by unplanned outages, directly impacts emergency reserves.
“Even a 1 000 MW shortfall can have massive consequences, draining pump storage reserves faster than they can be replenished and pushing the country closer to load shedding.”
A long-term solution would be to ramp up renewable energy capacity, particularly solar power and battery energy storage systems (BESS), to supplement day-time generation and fill up pump storage and BESS during daylight hours, Mallinson says. “With sufficient solar energy feeding into the grid, Eskom could replenish its reserves more effectively, minimising the overuse of costly diesel-fired OCGTs. Unless Eskom improves its ability to balance supply and demand strategically, South Africa may continue to face abrupt and severe load-shedding episodes,” he warns.
