Eskom has blamed the severe power constraints in South Africa, and which is triggering Stage 2 load-shedding, on a broken coal conveyor belt at the Medupi power station.

In addition, five electricity generating units are unavailable due to boiler tube leaks. The utility also said that there are delays in the return to service of units that are on planned maintenance and it is struggling with a limited diesel supply.

The utility said in a statement on Wednesday that a conveyor belt supplying the Medupi power station with coal failed on Saturday. This cut the station's power output by half.

Since Saturday, Eskom has used pumped storage and open cycle gas turbines "extensively" to make up for this electricity shortfall, but now dam and diesel levels are running low. 

In a statement on Wednesday morning, Eskom warned that Stage 2 load-shedding could be implemented from 9:00 to 23:00 today.

Stage 2 load-shedding allows for 2 000 MW of power to be shed on a rotational basis. Stage 1 is the "lightest" load-shedding schedule, while during Stage 4, 4 000 MW of power will be shed. 

Last month, Eskom warned that plant maintenance, which often takes place during the summer time, may trigger outages.

"Most of our power stations are in need of maintenance to improve reliability... we do our best to strike the right balance between plant maintenance and keeping the lights on," said Eskom chairperson and acting CEO Jabu Mabuza.

Last month, Eskom warned that in order to avoid load-shedding, unplanned breakdowns needed to be contained at below 9 500 MW.

In the event generator breakdowns are experienced beyond 10 500 MW there will be high usage of emergency resources (diesel and pumped storage generators) which may lead to load-shedding. Unplanned breakdowns have now exceeded this limit, Eskom said on Wednesday.

It also "unreservedly" apologised to South Africans.

South Africa last saw load-shedding in March this year, after a cyclone in Mozambique affected power imports from the country. Eskom also didn't have enough diesel.

The energy availability of Eskom’s generation fleet is supposed to be as high as 80%, but was last month as low as 69%, an Eskom board member warned recently.

Even a 0.1% rise in economic growth could result in outages, Nelisiwe Magubane, an Eskom director, told an event last month.

A new plan to deal with Eskom, which will probably be split into generation, transmission and distribution units, is supposed to be discussed in cabinet today.  

Earlier this week, President Cyril Ramaphosa said government will announce its plan to deal with Eskom's R450-billion debt pile in the next days.

"I think Moody's and others will be happy with the announcements made," Ramaphosa said.

More than 270 hours of load-shedding contributed to South Africa’s economy shrinking by 3.2% in the first quarter of this year. While avoiding a recession in the second quarter, the economy has been struggling. 

Click here to find your load-shedding schedule.