Johannesburg - Eskom's power system is expected to be constrained for the next two weeks while generators are being maintained, the parastatal said on Monday.
"The likelihood of a shortfall in capacity is higher than normal. This means our reserve margins are inadequate compared to where we'd want them to be," said acting spokesperson Andrew Etzinger.
"When we analysed the power system, we took into account the risk of unexpected power failures and demand being higher than anticipated, and based on these we can estimate the possibility of shortfalls."
He said summer was a difficult time for Eskom, as most maintenance was being done during this time. In summer, demand remained high throughout the day because of the use of air conditioners.
"In summer, demand is driven by our industrial and commercial customers. During summer we also do most of our maintenance," said Etzinger.
The capacity available to meet Monday's night peak demand was 31 200MW while demand was forecast at 30 934MW.
This meant there was only about 200MW in reserve.
"This means our ability to cope with higher than expected demands or unexpected demands or unavailability is far less then it should be.
"In order to manage the situation we need the support of the public, because if we can get demand down to a manageable levels... we will be fine, but right now we are not," said Etzinger.
The power constraint was at a national level.
Peak demand for the rest of the week was forecast at 30 888MW on Tuesday, 31 073MW on Wednesday, 30 897MW on Thursday, 30 287MW on Friday, 29 167MW on Saturday and 28 476MW on Sunday.
He said Eskom expected demand to drop after two weeks, when the two large generators, which were undergoing maintenance, returned to service.
Demand was also expected to drop over the festive season as businesses wound down.