Kusile Unit 1 Returns to Grid as Power System Remains Stable Despite Constraints

South Africa's power system remains stable but constrained as the country moves deeper into the winter season, with Eskom announcing the return of Kusile Unit 1 to service today after being offline since March.

Kusile Unit 1 Back Online

Kusile Unit 1 has officially returned to service following its successful reconnection to the repaired flue gas desulphurisation (FGD) system and permanent stack. The unit had been out of service since 31 March 2025.

Once the unit reaches full capacity, it will contribute 800MW to the national grid, improving the Energy Availability Factor (EAF). With this return, Kusile Power Station will deliver its total combined output of 4,800MW to the national grid.

Additionally, Eskom expects a further 2,930MW of generation capacity to return to service ahead of Monday evening's peak demand on 2 June 2025, which should further stabilize the system.

Current Performance Metrics

The power utility reports that the Unplanned Capacity Loss Factor (UCLF) stands at 28.60% for the financial year to date (1 April to 29 May 2025). This represents a slight increase of approximately 0.2% compared to the 28.43% recorded during the same period last year. Eskom attributes this marginal increase primarily to delays in returning units from planned maintenance.

Planned maintenance has averaged 6,197MW (13.25% of total generation capacity) for the financial year so far. This reflects a decrease from the previous week but remains 2.6% higher than the same period last year. For the current week (23-29 May), planned maintenance is averaging 4,883MW, slightly above typical winter maintenance levels seen in previous years.

The Open-Cycle Gas Turbine (OCGT) load factor increased to 12.70% this week, up from 7.65% in the previous week, indicating greater reliance on these emergency generation units.

System Status and Immediate Outlook

As of today, unplanned outages amount to 13,327MW, while available generation capacity stands at 29,913MW (excluding the 720MW capacity from Kusile Unit 6, which is not yet in commercial operation). Tonight's peak demand is projected to reach 28,778MW.

The year-to-date EAF has slightly increased to 57.67%, down from 60.45% over the same period last year. This decline is primarily attributed to the 2.6% increase in planned maintenance compared to the previous year.

Eskom has spent approximately R3.54 billion on diesel fuel for the OCGT fleet so far this financial year, generating 595.33GWh—significantly higher than the 219.37GWh generated during the same period last year.

Winter Outlook

The Winter Outlook published by Eskom on 5 May 2025, covering the period until 31 August 2025, remains unchanged. According to this outlook, loadshedding will not be necessary if unplanned outages stay below 13,000MW. However, if outages rise to 15,000MW, loadshedding would be implemented for a maximum of 21 days out of the 153-day winter period, limited to Stage 2.

Currently, unplanned outages are averaging 13,871MW (from 23-29 May), which is 883MW higher than the same period last year and 871MW above Eskom's base case scenario of 13,000MW. For the financial year to date, average unplanned outages stand at 13,600MW.

Public Warnings About Infrastructure Protection

With loadshedding suspended and electricity demand rising during winter, Eskom has issued warnings about illegal connections and energy theft. These activities often lead to transformer overloads, equipment failures, and in some cases, explosions and extended outages in affected areas.

Eskom urges the public to report illegal activities impacting infrastructure to the Eskom Crime Line at 0800 112 722 or via WhatsApp on 081 333 3323.

Key Terms Explained

Energy Availability Factor (EAF): The percentage of maximum energy generation that a plant is capable of supplying to the electrical grid, relative to the maximum amount that could be supplied if the plant operated at full capacity continuously. Currently at 57.67%, down from 60.45% last year.

Unplanned Capacity Loss Factor (UCLF): The percentage of generation capacity unavailable due to unplanned events or breakdowns. Currently at 28.60%, slightly up from 28.43% last year. The higher this number, the more generation capacity is unexpectedly offline.

Open-Cycle Gas Turbines (OCGTs): Emergency power generation units that run on diesel fuel. They are expensive to operate but can be switched on quickly during periods of high demand. The OCGT load factor (12.70% this week) indicates how intensively these units are being used.

Flue Gas Desulphurisation (FGD) system: Technology used to remove sulfur dioxide from exhaust flue gases of fossil-fuel power plants, reducing air pollution.

Gigawatt-hour (GWh): A unit of energy representing one billion watt-hours. For context, 1 GWh could power approximately 650,000 homes for one hour.

Megawatt (MW): A unit of power equal to one million watts. A typical coal power station unit produces 600-800MW, enough to power roughly 400,000-500,000 homes.