Stage 3 as Eskom loses control of breakdowns

Eskom was forced into the unusual situation of pre-announcing Stage 3 load shedding scheduled for the evening peak on Monday and Tuesday this week, as breakdowns have spiralled beyond 17 500 megawatts (MW) of coal generation capacity.

Due to the demand profile in winter, Eskom has trouble fulfilling demand in the morning and evening peaks (versus in summer where elevated breakdowns mean load shedding all day).

On Friday, it said capacity had recovered to a point where it made a late change to the evening load shedding level (from Stage 2 to Stage 1). In truth, breakdowns ‘improved’ from 16 305MW at noon to 15 997MW after 16:00.

Of course, the 300MW helped – but all Eskom did to reduce load shedding to Stage 1 was invoke 897MW of interruptible load supply to large industrial customers (effectively the aluminium smelters) during the peak.

The utility said on Friday evening that “barring any significant breakdowns, there is a low probability of load shedding being implemented during the weekend”.

Less than an hour before the evening peak on Saturday – at short notice – Eskom announced Stage 2 load shedding. It had lost units at its Arnot, Majuba, Hendrina and Kusile power stations, and two units at Lethabo since Friday night. The units at Majuba and Hendrina were returned to service by Sunday, but by then the utility had lost a further unit at Majuba, along with units at Tutuka and Camden.

That’s nine units lost in 48 hours, of which two were put back into service.

To put this in perspective, from lunchtime on Thursday where it had 15 365MW of plant out of service not due to maintenance, Eskom lost a further 2 400MW of coal generating capacity by Saturday afternoon. This is equal to half the normal output from Medupi (before an explosion in August last year left Unit 4 out of service until 2024). This is over and above the 15 000-odd megawatts of capacity already offline.

In the past week, its coal fleet was only able to produce more than 24 000MW once (24 061MW) – at 18:00 on Thursday.

With an installed capacity of around 40 000MW – excluding imports, nuclear, open cycle gas turbines (OCGTs) and so on – this equates to an energy availability factor (for coal) of 60%.

The problem is that Eskom has only managed to produce more than 23 000MW for 16 hours over the last seven days. It is not certain that this is going to improve meaningfully.

This means Eskom has to enforce load shedding during the evening peak and use its diesel-burning OCGTs to match supply and demand.

Peak (MW)	Mon May 9	Tue May 10	Wed May 11	Thu May 12	Fri May 13
Demand	32 701	31 946	32 487	32 106	29 961
Eskom capacity	29 753	29 676	31 154	32 252	30 143
Loadshedding	2 043	2 100	2 100	2 100	1 057
VPS/ILS*	261	227	447	179	897
Eskom OCGTs	1 938	1 901	1 498	984	675
IPP OCGTs	792	762	0	0	224
Renewables	449	689	556	794	648

* Virtual power station and/or interruptible load supply

From this data, one can see that in addition to the ±2 000MW of load shedding on Monday and Tuesday nights, Eskom used as much as 2 730MW of supply from OCGTs.

It also relied on the virtual power station mechanism to interrupt load to large customers. In total, this meant 5 034MW of emergency ‘generation’ on Monday at 18:00 (including the demand-side cuts). And this excludes another 1 801MW from its pumped storage schemes at the peak.

That Eskom believes the situation will ‘improve’ to Stage 2 by Wednesday night’s peak suggests that the second of the Kusile units that have been undergoing planned maintenance may return to service.

The current 2 094MW of planned maintenance comprises Koeberg Unit 2 (±900MW set to return in June), a unit at Kusile (±600MW) and Unit 4 at Medupi (±600MW), which exploded in August.

It has to include the last of these in planned maintenance for its capacity planning models (in other words, it can’t count on this returning to service until 2024).

Eskom executives believe that bringing back the two Kusile units that had been out for maintenance (one of which is believed to have returned) and the unit at Koeberg will ensure that load shedding is “limited” in the winter months.

For now, the sky-high breakdowns have edged the transmission unit’s ‘winter plan’ to the worst-case scenario – which sees breakdowns at above 15 000MW and requires Stage 3 load shedding.

In this scenario, there are as many as 104 days of load shedding between April and the end of August.

Diesel costs in this scenario run at between R1.2 billion and R1.5 billion a month for the rest of winter.

Things are not looking good.