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Eskom has shut down Koeberg’s unit one ahead of schedule for scheduled maintenance, after “an increasing leak rate was observed in one of the three steam generators.” The unit had been scheduled to go offline for refueling and routine maintenance starting in February. Eskom says it expects the unit to “be operational again during May 2021.”
Read: Eskom not prepared as generator leak accelerates nuclear shutdown
Koeberg supplies stable and predictable base load power generation of just over 1,800 megawatts (MW), which was halved after 6pm Sunday night when the unit went offline (yellow in box a continuation). Of concern is the fact that it now has to replace the ± 900MW deficit, especially during the afternoon peak.
Source: Eskom Data Portal
It continues to use pumped storage schemes, designed for peak periods, for base load power generation. On Sunday, for example, it used them to generate between 500MW and 1,800MW throughout the day. Once Koeberg 1 was removed from the grid, their use peaked at 2,071MW (at 7pm). Pumped storage schemes are net energy consumers in the sense that they use more electricity to operate than each unit of energy they produce. This is what makes them so effective peak plants: The “surplus” energy is used to pump water uphill at night when demand is low.
Last week, historically the lowest demand period of the year (lockdown level five, excluded), the utility was forced to implement Stage 2 load shedding overnight. He said this was to “preserve his emergency generation reserves.” From its publicly available control panels, it is clear that Eskom simply did not have enough free space at night to use base load power to replenish its pumped storage schemes (which it was using to increase base load power to throughout the day).
Source: Eskom Data Portal
From its dashboard of unplanned outages, it is clear that these outages increased from around the 9,000MW level to 12,000MW between December 28 and December 30. Typically you could cope with this many plant breakdowns (and partial losses), but you have deliberately increased your planned maintenance to the highest level in at least a year. A total of more than 9,000 MW of capacity was taken out of service last week as the utility continues to catch up with maintenance that has simply not been performed in recent years.
As plant breakdowns increased, it can be seen from its own data that Eskom was forced to run its open cycle gas turbines (OCGT) overnight on Monday (December 28). Their use peaked at more than 1,300MW before he made the record-breaking call to implement load shedding. During the evening peak on December 29, it also made use of interruptible load supply (ILS) where it cut almost 700MW from its large industrial clients. Did this again during the evening peaks of December 30 and 31. On December 30, it asked the independent operators of the peak gas plants to increase supply (in addition to its own OCGT use of around 1,000MW).
Another cause for concern is that Eskom has relied on approximately 1,000 MW (and up to 1,300 MW) of so-called “non-commercial generation” capacity since December 23. These are units in Kusile (units 2 and 3) and Medupi (unit 1) that are not yet in commercial operation. In the past week, you did not use any of these drives. The two Kusile units are expected to reach commercial operation this month (unit 2,800MW) and in March (unit 3,800MW), which will help in some way to alleviate the generation deficit. However, all this capacity is not really available. The utility company identified design flaws at both new power plants in November 2018 and work has begun to remedy them.
Now, with a shortfall of 900MW to take down a unit in Koeberg, Eskom will be forced to recalculate its generation plan. He always planned to have these additional units available in early 2021 (plus, this doesn’t really change the supply picture as he has been able to draw on these units in a similar way to other plants in his fleet).
You actually only have two levers to work with – some of the planned maintenance can be deferred (although this is why the utility has such an unreliable coal fleet to begin with), and you can use emergency generation capacity (OCGT) to meet peak demand.
This is the balancing act you will need to perform over the next several weeks as demand increases from the 25,000/26,000 MW level now to 29,000 MW by mid-month. By the end of this week, these figures are expected to be between 26,000 and 27,000 MW (the difference between the so-called residual demand and the contracted demand is offset by renewables).
Before Koeberg’s forced blackout, Eskom’s official three-month perspective seemed manageable. At its planned risk level, with unplanned outages of 12,000MW plus an operating reserve of 2,200MW, it can be slightly short at certain peaks of the week. It is able to solve this with its available emergency generation resources (pumped storage schemes, its own OCGT, as well as IPP and ILS diesel / gas peak plants).
Source: Eskom system status report week 52 2020
The only way Eskom prevents loss of head is by giving yourself more headroom (doing less planned maintenance, which is unlikely) or by ensuring (read: waiting) that you can keep unplanned breakdowns well below the level of 12,000 MW. We’ll know if you chose the former once your weekly system health reports are released for this week and next.
It will be a difficult few months.
