There is a low likelihood of a total blackout, or collapse of the power system, Eskom said on Wednesday.

The power utility provided a system update as Stage 4 load shedding persists.

Planned outages were at 5 787 MW, with unplanned outages at 15 147 MW, an improvement from about 15 600 MW on Tuesday.

During a virtual briefing from Duvha power station, CEO André de Ruyter said teams were "working hard" to bring units back online. Eskom expects to return six units to service on Wednesday. Three are already online.

Eskom lost units at Majuba and Arnot on Wednesday morning.

However the power utility made progress in replenishing diesel reserves at Ankerlig power station - to 76.7% from 67% previously.

The Drakensberg Pumped Storage Scheme, which generates electricity, has 38 hours of pumping left to replenish the dam to total capacity, while Ingula Pumped Storage Scheme needs 15 more hours of pumping to restore its upper dam, De Ruyter said.

Eskom's executives also said that a total blackout - where there is no electricity available - is unlikely, given that load shedding is in place to reduce demand and keep the system balanced.

De Ruyter said load shedding is a tool to limit the chances of a blackout. "We still have headroom in the system to allow us to avoid a total blackout." 

"The likelihood of a blackout is low," added Segomoco Scheppers, Eskom group head of transmission. Scheppers explained the power system is designed with protection measures.

The power system operates at a frequency of 50 Hz - an indication that electricity demand matches supply. The system operator makes sure the 50 Hz is maintained. But once supply drops, to keep the system balanced, demand must drop, and that is when load shedding is implemented - as it curtails power use by consumers. "If we lose generation, we take measures to reduce demand," Scheppers said.

Even at Stage 4, the power system is still in the balance, Scheppers said. He added that a system recovery plan is in place, and Eskom is not too concerned about the risk of a blackout.

Eskom spokesperson Sikonathi Mantashantsha said a blackout would only become possible after Stage 8 load shedding - which reduces demand by 8 000 MW  - is reached.

If there happens to be a blackout, the country has the capability to restore the system using the pumped storage scheme in Drakensberg as well as Kendal Power Station and Tutuka Power Station. De Ruyter assured that Eskom does not believe a blackout is a "credible risk".

Eskom's latest weekly system status report (from 11 April to 17 April) indicates a high-risk scenario of not being able to meet electricity demand for the rest of the year. This means it will have to implement load shedding.

In response to questions about this, De Ruyter said that as part of its planning, Eskom communicates probabilities of various load shedding scenarios, but these are just scenarios. "The very fact that we talk of unplanned outages means we do not anticipate, we do not plan for them. They occur when there are unplanned plant trips and failures and these result in the loss of generation capacity and will necessitate the need for load shedding."

He likened it to a weather forecast for rain. "If there is 60% chance of rain, you can't say with certainty that it will rain. But neither can you say with absolute certainty that it will remain dry."

De Ruyter said that load shedding would likely reduce once Koeberg Unit 2 comes back to service in June and as the power utility ramps down its maintenance programme for the high-demand winter period.

"We have better performance from power stations during the colder and drier winter season."

De Ruyter reiterated the need for new generation capacity to be added to the grid. He noted the Department of Mineral Resources and Energy is expediting Bid Window 5 and Bid Window 6 of the Renewable Energy Independent Power Producer Procurement Programme (REIPPPP) to get enough capacity on the grid as soon as possible.

Eskom is also working on making available grid access to private producers, relying on the 100 MW licence exemption.

"We are aware that our grid access unit will need to do more to expedite applications," he added.

He reiterated that between 4 000 MW and 6 000 MW of power is needed to address the risk of load shedding.