South Africa's power system is severely constrained with a high risk of increased stages of loadshedding as the nation heads into winter, Eskom said this week. Unit 1 at the Koeberg nuclear power plant is expected to return to service in September.

Calib Cassim presents Eskom's winter plan (Image: South African Government News Agency)

In its State of the System and Winter Outlook briefing on 18 May, the state utility said that loadshedding might be predominantly implemented at Stage 5 for the winter period, with breakdowns or capacity unavailable due to unplanned maintenance at 15,000MW. But should unplanned outages reach 18,000 MW, Eskom said, loadshedding might be required "every day and might be implemented up to Stage 8 … an ultimate worst-case scenario that Eskom is working tirelessly to avert at all cost; by all means necessary".

Loadshedding involves shutting down parts of the electricity network in a controlled way to prevent the electricity system becoming unbalanced when there is not enough supply to meet demand, avoiding the risk of a country-wide blackout. Eskom has provided for eight stages of loadshedding, from Stage 1, shedding 1000 MW of load, to Stage 8, when 8000 MW would be shed. Loadshedding is implemented on a rotational basis - so Stage 8 loadshedding could mean customers having their supply interrupted throughout the day for a total of about 12 hours.

The current situation is exacerbated by the loss of four major units which are on extended outages, the company said: three at the Kusile coal-fired power station, plus Koeberg 1, which is currently on a long-term outage for maintenance and refuelling as well as the replacement of the steam generators, and is expected to return to service in September. Together, the unavailability of the three Kusile units and Koeberg 1 has removed 3080 MW of capacity from the grid, equivalent to three stages of loadshedding.

"We are striving to reduce plant breakdowns to 15,000 MW or below for the winter period to keep loadshedding at lower stages. We, however, concede that this will be extremely hard given the unreliability and unpredictability of the power generating fleet and that we are already about 3000 MW worse off this winter compared to the same period last year," Eskom Generation Group Executive Bheki Nxumalo said.

"It is going to be a difficult winter," Eskom Acting CEO Calib Cassim said, adding that the company was confident that the control measures that it has in place, including loadshedding, mean a national blackout will not occur.

June, July and August are South Africa's winter months.

Eskom's update came two days after South Africa's Minister of Mineral Resources and Energy Gwede Mantashe told the National Council of Provinces (NCOP) - the upper house of the South African Parliament - that the government intends to issue a request for proposals for the procurement of 2500 MW of nuclear energy in the fourth quarter of this year as part of its electricity procurement plans.

"Grid availability is critical to securing electricity supply in the future. It impacts not only on the public procurement programmes, but also on private embedded generation initiatives," he said in a budget vote speech to the NCOP.