Power Grid Remains Stable as Medupi Unit 4 Returns to Service, Adding 800MW Capacity

July 11, 2025

Power System Remains Stable with Medupi Unit 4 Back Online

South Africa's power system continues to show stability amid winter demand, with Medupi Power Station's Unit 4 successfully returning to service on July 6th. The unit will contribute 800MW to the national grid once it reaches full capacity in the coming weeks.

According to Eskom, no loadshedding has been implemented since May 15th, with only 26 hours of power cuts recorded in the 2025/26 financial year to date (April 1 to July 10).

Current System Status

As of July 11th, unplanned outages stand at 13,380MW, with available generation capacity at 30,195MW against an expected evening demand of 28,346MW. Eskom reports that an additional 3,470MW of generation capacity is scheduled to return to service by Monday, July 14th.

The Energy Availability Factor (EAF) has ranged between 60% and 62% over the past week, with the month-to-date average increasing to 62.07%. This represents a marginal improvement in plant performance, though still below the levels needed for long-term grid stability.

Performance Metrics Show Mixed Results

The Unplanned Capability Loss Factor (UCLF) has increased to 29.44% for the current financial year, up by approximately 2.4% compared to the same period last year (27.03%). This increase in unplanned outages remains a concern for grid stability.

For the past week (July 4-10), planned maintenance averaged 4,418MW, while unplanned outages averaged 13,628MW. This is 1,525MW higher than the same period last year and 628MW above Eskom's base case estimate of 13,000MW.

The year-to-date EAF has reached 58.83%, which is lower than the 61.74% recorded during the same period last year. Eskom attributes this decline primarily to a 2.9% year-on-year increase in unplanned maintenance.

OCGT Usage and Diesel Consumption

The open-cycle gas turbine (OCGT) load factor has marginally increased to 10.78% year-to-date, up from 5.87% during the same period last year. For the past week, the OCGT load factor jumped to 11.92%, significantly higher than the 2.41% recorded in the previous week.

Eskom has spent R5.26 billion on diesel fuel for OCGTs in the current financial year, generating 892.42GWh. This is substantially higher than the 485.39GWh generated during the same period last year, indicating increased reliance on these emergency generation resources despite the overall improved system performance.

Winter Outlook

Eskom maintains that its Winter Outlook (published on May 5th and covering the period until August 31st) remains valid. According to this outlook, loadshedding will not be necessary if unplanned outages stay below 13,000MW. If outages increase to 15,000MW, loadshedding would be limited to a maximum of 21 days out of 153 days and restricted to Stage 2.

Currently, unplanned outages (13,380MW) exceed the 13,000MW threshold, placing the system in a precarious position despite the current suspension of loadshedding. The margin between available capacity and demand remains tight, particularly during evening peak periods.

Call to Protect Transformers and Avoid Illegal Connections

Eskom has issued a warning about illegal connections and energy theft, noting that these activities often lead to transformer overloads, equipment failures, and extended outages. The utility has urged the public to purchase electricity only from accredited vendors and report illegal activities 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, after accounting for planned and unplanned outages. A higher percentage (closer to 100%) indicates better performance. Eskom targets 70% EAF for stable grid performance.

Unplanned Capability Loss Factor (UCLF): The percentage of a plant's maximum possible energy generation that is lost due to unplanned outages (breakdowns, trips, etc.). Lower percentages indicate better reliability. Currently at 29.44%, this figure represents nearly one-third of Eskom's generation capacity being unavailable due to unexpected problems.

Open-Cycle Gas Turbines (OCGTs): Emergency power generation units that run on diesel fuel. These are expensive to operate (approximately R4.50-R5.00 per kWh compared to R0.40-R0.60 for coal) and are meant to be used only during peak demand or emergencies. Higher usage indicates system stress despite the absence of loadshedding.

Load Factor: The ratio of average power to peak power over a specified time period. For OCGTs, a higher load factor means these emergency units are being used more intensively.

Megawatt (MW): A unit of power. For context, 1MW can power approximately 650 average South African homes.