JOHANNESBURG (Reuters) – South Africa’s state utility Eskom cannot say how long a new round of power cuts that began on Friday will last, its spokesman Sikonathi Mantshantsha told Reuters.

Eskom implemented planned power outages for the first time since March on July 10, ending a period of unusually stable power supply thanks to reduced demand during a coronavirus lockdown.

The company generates more than 90% of South Africa’s power but has battled to meet demand for years because of faults at its coal-fired power stations, which have interrupted power supplies, hampered economic growth and deterred investment.

“The reality is we don’t know which of the coal units are going to fail on any given day, that is true for both the old and the new units,” Mantshantsha said.

He said Eskom was sending a team led by one of its senior engineers to try to improve the performance of problem power stations. Morning peak power demand on Wednesday was at its highest this year because of extreme cold weather, compounding the generation shortfall, Mantshantsha added.

Eskom said on Wednesday that it would step up load-shedding to “stage 2” from “stage 1” from 1200 GMT, requiring more supply interruptions.

Stage 1 allows for up to 1,000 megawatts of the national load to be shed, and stage 2 up to 2,000 megawatts.

Despite assurances from the government that it would expedite procurement of new generation capacity late last year, when Eskom implemented some of the worst power cuts on record, additional capacity has not yet been procured.

“Once this bout of load-shedding is over, it would be naive to think we are done with load-shedding,” Mantshantsha said. “We don’t have a single extra megawatt since we implemented stage 6 load-shedding during summer.”