Eskom chief executive Brian Dames said on Tuesday more maintenance was done during this year's winter period, which runs from May to August, compared to the same period in the three preceding years, but more work was needed.
"Summer is typically maintenance season, but this summer maintenance will increase as most of the maintenance cannot be deferred," Dames said at a news conference.
"With the maintenance that needs to be done, the system will remain tight."
Eskom has been walking a tightrope for five years as it tries to bring long-overdue power plants online after the grid came close to collapse in 2008.
The utility said in July that the first power from its new Medupi plant would hit the grid in the second half of next year, a delay of at least six months caused by labour unrest and "underperformance" by contractors.
Cabinet last month gave Eskom a go-ahead to build another coal-fired power station. The size and costs of this project have yet to be determined. – Reuters