South Africans had better bone up on their load-shedding schedules as Eskom is forecasting a winter with rolling blackouts.
Yesterday , it was Eskom's expensive gas turbines that kept the nation's lights on, only by a whisker.
But it lost the battle and load-shedding began by 5.30pm.
The power utility declared an emergency as the grid remained under pressure.
During the day, several Joburg suburbs experienced power failures as did the City of Johannesburg's head office in Braamfontein. The reason for these outages was said not to be load-shedding.
Usually, explained Eskom spokesman Andrew Etzinger, there was a 10% reserve margin. Last night, it was hovering at between 1% and 2%.
"We are going to be at risk from time to time this winter," said Etzinger.
"If we need to protect the grid we will implement load- shedding."
The reserve margin fell to 0% on Wednesday night, causing the first load-shedding.
The reason for this was tripping at the Duvha and Kendal power stations, coupled with reduced capacity from the hydroelectric power station at Cahora Bassa in Mozambique.
"It has become a fine balancing act, making daily calls to keep the lights on," he said.
The threat of planned power cuts coincides with the start of the soccer World Cup, watched avidly on TV, and as pupils prepare for exams.
To ensure that the national grid does have enough capacity, gas turbines in Mossel Bay and in Atlantis in Western Cape are powered up during peak demand periods. They provide 5% to the grid, adding to the safety margin, said Etzinger.
The grid comes under pressure between 6pm and 8pm.
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