Eskom said 18 of its 79 power generation units have broken down and nine more are undergoing planned maintenance.
Rolling blackouts are expected to be lifted by the weekend.
The utility also warns some power stations may be affected by rain this weekend.
Eskom general manager Rhulani Mathebula said: “We have got 79 power generation units and 18 of those are at the moment off due to breakdowns and eight of those are on planned maintenance. That obviously includes Koeberg which makes them nine units.”