Eskom said in its twice-weekly capacity update service that unplanned outages were 3,881 Megawatts (MW) on April 16 compared with a recent peak of 5,737 MW on February 6 and this year's low of 2,807 MW on March 22 and its own benchmark of having a maximum of 3,600 MW offline in unplanned maintenance.
The electricity generating capacity available to meet peak demand on April 16 was 35,029 MW (including open cycle gas turbines), while demand is expected to be 32,323 MW as cooler weather raises demand from 31,770 MW on April 12. Current planned maintenance eased to 4,320 MW on April 16 from 5,074 MW on April 12, 6,573 MW on April 9 and this year's peak of 7,473 MW on April 5.
As many businesses closed for the Easter long weekend, demand dropped to only 25,440 MW on April 9 before rising to 31,559 MW on April 10, when businesses reopened.
On March 12, Unit 1 of the Koeberg nuclear power station was shut down for a scheduled refuelling, inspection and maintenance outage. The unit is scheduled to return to service at the beginning of June 2012. Unit 2 of Koeberg will continue to operate at full power output during this period.
Each of the two units at Koeberg is shut down for refuelling, inspection and maintenance approximately every 16-18 months. These routine shutdowns are scheduled so as to avoid having both units out of service at the same time and to avoid the winter months in each year.
During these routine planned outages, one third of the used nuclear fuel is replaced with new fuel, statutory inspections and maintenance are performed, and modifications that will improve safety or the plant performance are implemented.
The scheduled shutdown of Koeberg Unit 1 is part of Eskom's overall maintenance programme for its fleet of power stations. The shutdown has therefore been taken into account into Eskom's plans to keep the lights on, and is not expected to result in a shortage of supply to the Western Cape or the rest of the country.
Eskom continues to make progress with its programme of planned maintenance but the system remains tight. Eskom has moved to twice a week updates instead of the previous quarterly updates in line with its commitment to regular and transparent communication on the power system, which is expected to be constrained for at least the next two years.
On January 9 peak demand of 30,282 MW was met by available capacity of 30,742 MW or a margin of only 460 MW (less than one generating unit at a modern coal generating plant) or only 1.5%. The internationally accepted safe margin is 15%.
The reason for this low margin in SA is that Eskom carries out planned maintenance on its power stations during the seasonally low demand summer months, so that the power stations are ready to handle the peak winter demand months of June and July, when service delivery protests also peak.
On January 12, capacity taken offline for planned maintenance was 4,461 MW or around nine generating units, but unplanned outages were 3,678 MW or around seven generating units. Last year in February, a 600 MW generating unit at Duvha failed during tests as it was being returned to service, while in January 2003 a similar event took place.
This year and next year Eskom does not have the spare capacity to be able to have a large generating unit fail, as the first unit of the new Medupi power station will only come on line in late 2013. - I-Net Bridge