Eskom has been benchmarking its coal fired power stations against a comparablefleet of a similar age in Europe and the results are favourable. However, it should benoted that the capacity factor of its power stations has dropped.
The first half of 2008, marked by rolling blackouts acrossSouth Africa, represented the end of many decadesduring which the country took for granted the comfortgiven by its power generation fleet. It is now over half a decadelater, and no further rotational load shedding has occurredsince it was suspended on 5 May 2008. Coal stockpiles, whichled to the initial problems in 2008, have increased from 12days’ worth then to 45 days’ worth in 2013. But no sense of theprevious comfort has returned.
Part of the reason is that the end of the blackouts cameabout after an appeal by Eskom to energy intensive users ofelectricity to cut their power usage by 10%. Secondly, the rapidslowdown of the global economy provided breathing space,and Eskom says it has seen lower than expected electricitydemand over the past five years.
Following the blackouts of early 2008 Eskom undertookplant performance recovery initiatives for its fleet of coalfired power stations. This was effective in reducing generatorunavailability from over 5% to less than 4.5% for a year.However, sustaining these superior performance levels hasbecome significantly more challenging, Theo Govander,Eskom’s generation group executive, says.
In 2009, the reserve margins of some 14% to 15% dueto the slowdown in electricity demand gave some level offlexibility. At the same time, though, the condition of thegenerating plant had adversely begun affecting the outagescope at Eskom’s power stations.
By 2010, the year South Africa undertook the massiveglobal marketing campaign of itself, otherwise known as theFifa soccer world cup, the national demand for energy hadstarted to recover to 2007 levels. At the same time it becamenoticeable that several of Eskom’s power stations are in theirmid-life and this means significant refurbishment work isneeded. The oldest two power stations, barring the returnto service plants, are Arnot (2,352 MW) and Hendrina(2,000 MW). Both approach their 40 year milestones. Kriel(3,000 MW) is well past 30 years old, while Matla (3,600 MW)and Duvha (3,600 MW) are at about the 30 year mark.
However, maintenance was a kept at a minimum to ensuresufficient capacity during the world cup, as having any instance of blackouts during this tournament would have been a publicrelations disaster for the country. As it turned out, the systemremained healthy between 11 June and 11 July 2010, despitethis being one of coldest winters the country has experienced. An orange line that demarcated interruptible load shedding from the electricity system was barely crossed during thetournament. A red line, which meant use of peaking open cyclegas turbines, was never crossed during that time.
During 2010 and 2011, the generation fleet was run closerto this red line, and it was able to provide less reserve tothe system operator. In 2008 maintenance done was 8.8%(3,370 MW) and this went up to 9.5% (3,733 MW) in 2009,but with the world cup and thinner margins it dropped to 8.6%(3,458 MW) in 2010, and 8.14% (3,315 MW) in 2011. Whilethe system was run much closer to the red line comparedwith 2009 to deal with plant maintenance requirements, thetotal amount of maintenance was insufficient and a backlog developed.
The supply demand situation has not remained entirelystatic since 2008. Since 2008, South Africa has added2,000 MW of capacity on the supply side in the form of the return to service power station initiative and theaddition of open cycle gas turbines. Eskom has signed up 1,000 MW of capacity from independent power producers andmunicipal generators. The utility has undertaken demand side management initiatives that have led to more than 1,500 MWof verified savings since 2008. In addition, an interruptibledemand agreement exists, whereby for up to two hours a week 2,100 MW of supply to BHP Billiton smelters can be interrupted to help manage the frequency on the system.
There has also been the approval of a load sheddingcritical load management protocol. And finally there have beenawareness campaigns to get people in the residential sector toreduce their consumption during the critical peak period of 5pm to 9pm. During this period peaks can jump by up to 3,000 MW in an hour as households switch on lights, heatersand cookers. The nature of coal fired power stations is thatthey don’t just switch on and off, thus the equivalent of fiveunits of a large power station is kept on load all day to meet that peak demand.
Eskom predicts the 2013 winter peak will be 36.8 GW,which is slightly lower than that of 2012, but this is the average for an hour. What is called the peak within the peak can go ashigh as 37 or 38 GW.
In the summer of 2013, usually a period when demand islower and Eskom ups its maintenance, it was unable to do soto the extent it had hoped for a variety of reasons. Flooding thataffected a transmission line as well as the failure of a smoothingreactor at Songo substation reduced supply from CahoraBassa from 1,500 MW to 650 MW (with occasions when supplydropped to zero) during the early part of 2013.
The capacity ofthe link was back at 1,300 MW as of 22 April 2013.Further exacerbating the difficulties Eskom faced duringthe summer was an unplanned outage at one of the 900 MWKoeberg units, Unit 1, with this returning to service also on the22 April 2013. When South Africa loses a Koeberg unit twofossil fuel units have to compensate for this, since you don’tjust lose 900 MW, but up to 1,200 MW as line losses have tobe factored in with power transferred down to the Cape fromthe north.
The need to manage the impact of strike action at Exxarocoal mines also cost the utility 1,000 MW during that period. Inaddition, power station performance is described by Govanderas having been volatile. This saw planned non-safety criticalmaintenance being deferred and it saw the extensive use ofthe open cycle gas turbines. During January, February andMarch of 2013, the open cycle gas turbines were run harderthan in any month during the past four years, with average loadfactors of close to 20%. In other words the red line was welland truly breached.
Eskom has benchmarked itself against other utilities, andin particular a reference case is German power utility VGB whose 108 unit fleet is comparable in age to Eskom’s. The benchmarking of the energy availability factor, which measuresplant availability including planned and unplanned unavailability as well as energy losses not under plant management control,has been done since 2000. In the early years, Eskom’s fleetoutperformed that of VGB in terms of worst, median and bestquartiles for this energy availability factor. However, from about2011, the performance of Eskom’s fleet relative to VGB’s hasdeteriorated, with its best and median quartile performancenow below those of VGB. Its worst quartile fleet performanceremains above that of VGB, but in both cases there has been asignificant downward trend.
However, Eskom’s fleet has been running much harderthan that of VGB with its load factor, which indicates theextent to which the generation fleet was loaded on averageto produce the energy demanded, being much higher. Forexample, during 2011, in its lowest quartile the load factorof Eskom’s fleet was at or above 60%, while that of VGBdropped to well below 30%. In terms of another benchmark,that of energy utilisation factor, which indicates the extent towhich available capacity is utilised, Eskom’s fleet has trendedupwards to 80% or more for all quartiles. VGB has seen lesspressure on its fleet, with periods when the energy utilisationfactor dropped to about 50%.
Govander says unplanned outages have become veryunpredictable, and the first four months of 2013 saw volatilityin unplanned outages increase. “When you lose 800 MW,the existing fleet has to run flat out and defer maintenance.”It is a vicious circle as more maintenance is required toimprove reliability of the hard running fleet. Hence Eskom’sunprecedented decision to continue with planned maintenanceduring winter. During June and July 2013, the plan was toundertake 2,000 MW of planned maintenance that cannot bedeferred any longer.
There is also an intense focus by Eskom to reduce thelevel of unplanned outages to 4,500 MW. This requiresmore planned maintenance. Over Eskom’s past financialyear that closed at the end of March 2013 the utility did 8%of maintenance on its generation fleet. Only 2% of that wasplanned maintenance though.
All this means that while Eskom’s maintenance backlog was reduced from 36 units in January 2012 to 23 units at the end of March 2013, it has become impossible to further delay maintenance until the next summer. Some units will be out for up to 120 days for planned maintenance during the winter, and Govander says a minimum of nine units will undergo planned maintenance during this period. These units reached technical or statutory limits in terms of maintenance, which cannot be deferred.
The focus will be on the heart of Eskom’s fleet, to sustainits life. The plans regarding what are called category threepower stations are more flexible. These include the threereturn to service power stations with Camden (1,510 MW) andKomati (1,000 MW) having a planned life of 15 years, of whichCamden is already halfway through its allotment. Grootvlei(1,200 MW) is planned to operate for 20 years. These powerstations in addition to the older Arnot and Hendrina powerstations get running maintenance, but not project overalls.This is because plans to extend their lives beyond 50 yearsdepends on finding gaps of time and funding, neither of whichare available at this stage.
The plan for the next five years is for Eskom to achieve afleet availability of 80%, with 10% planned maintenance and10% unplanned maintenance. Of the planned maintenance,8% is to be made up of maintenance that is fixed in itsschedule, while 2% will be short term maintenance.
In terms of new capacity, Medupi and Kusile could providesome breathing space once they are fully operational, but atthis stage Eskom has no plans beyond these stations. Therenewables when they come online could take some of burdenoff the existing fossil fleet. The variability of the renewablesremains a big problem for Eskom as the old fleet will haveto run in parallel to provide security of supply. However, anymegawatts available as soon as possible will be welcome,to provide breathing space and allow for the much needed maintenance. MRA