Eskom says Stage 2 load shedding will continue from 9 am again on Friday morning until Monday morning 6 am.
The power utility says it had been using pumped-storage schemes and open-cycle gas turbines on Thursday to maintain capacity during the day.
It said it would replenish these overnight.
Eskom says the system operator will continue to monitor the power grid closely and will give an update on Saturday morning, once the overnight performance of the power system has been reviewed.