There can be as many as 101 days of load-shedding this winter, in the "extreme case", according to an Eskom official.

Eskom on Tuesday provided an update on the state of the power system, this after load-shedding escalated to Stage 4 in the morning due to failing generating units.

In its assessments for the winter period, Eskom expects between 37 and 101 days of load-shedding, said group head of transmission, Segomoco Scheppers. The 101 days is "far in the extreme" scenario, he added.

Eskom has to contain unplanned breakdowns below 12 500 MW to avoid load-shedding entirely.

Planned maintenance has taken out over 5 000 MW of capacity. However, unplanned losses are in excess of 15 600 MW. Eskom chief executive André de Ruyter said this is "unacceptably high" and has led to the implementation of Stage 4 load-shedding to manage demand and avoid a total blackout.

The heavy rains over the Easter weekend were not in Eskom's favour. It contributed to wet coal which is difficult to handle. It tends to stick and causes blockages at units leading to load losses, he explained.

Group head of generation Philip Dukashe echoed concerns that persistent rain affects the ability to manage coal. "We have plans to curb rain to manage the risks imposed by the rain, particularly on coal stockyards … but if the rain is persistent for more than five days and even after that, it is not dry, and you continue to have some rain, it poses a major issue."

Units impacted by rain had to be supported with fuel oil. Often power stations lose combustion due to the wet coal, and there are also problems with the flow of coal in the system.

Dukashe also said that, over the weekend, demand was higher than forecasted. On Friday, demand was 700 MW higher than forecasted, and this increased to 1 687 MW on Saturday and 1 200 MW more on Sunday. These significant changes impacted Eskom's planning, he explained.

Eskom had hoped to take some units out for planned maintenance, but had to run them to meet demand. "So the units queuing up for maintenance to be done were not able to be taken off," he said." Eventually, some of those units took themselves off due to various reasons, such as tube leaks.

Eskom has units in excess of 11 000 MW that are at risk of giving in or failing at any stage, Dukashe said. This is a concern for Eskom as it has not been able to reduce the risk.

Dukashe assured Eskom plans to bring more generation capacity online this week.

"We are hoping to be in a better position by Thursday evening, based on the units that will be coming back over this week," he said. By Thursday evening or Friday, Eskom plans to reassess the situation and possibly lift load-shedding.

No Stage 6 foreseen

Eskom does not foresee load-shedding escalating to Stage 6 this week, Dukashe said. "In terms of where we are, we do not see that happening this week. We expect some units to come back tomorrow and some big units coming online on Thursday."

As to whether the damage caused to infrastructure in KwaZulu-Natal due to flooding will impact Eskom's access to fuels, Dukashe said that the power utility is currently not getting enough fuel oil supply, but contingency plans are in place. The ability to replenish diesel is also slower than the norm, but he assured there were contingency plans for diesel supplies.

Diesel supplies at Ankerlig power station are around 67%, said De Ruyter. "This is not ideal. We would like the number to be north of 80%," he said. Eskom expects delivery from 129 diesel trucks during the day to replenish reserves.

Gourikwa power plant does not have the same logistical constraints as Ankerlig. Its diesel levels are at around 82%. "We are running Gourikwa to supplement the generation shortfall, but we are not running Ankerlig to preserve our capacity there," said De Ruyter.

The Drakensburg Pumped Storage Scheme has not recovered its reserves as well as expected. However, Ingula Pumped Storage is in a better position in terms of the replenishment of its reserves, De Ruyter added.