How Eskom kept the lights on for Christmas, but not New Year’s

Contrary to what many assume, Eskom didn’t burn a single litre of diesel on Christmas Day to avoid load shedding. In an announcement on December 24, the utility said that the “suspension of load shedding [was] only possible due to the lower demand for electricity”.

This is only half of the equation. It is true that actual demand was about 1 500MW lower than on Christmas Eve. In fact, demand was a full 4 000MW lower than the previous Sunday (December 18) – equivalent to Stage 4 load shedding. Moreover, peak demand on the 25^th was almost 1 000MW lower than Eskom’s own forecast for the day.

Still, the supply side of the picture is revealing…

On Christmas Day morning, the coal fleet ramped up from overnight lows of 15 600MW to exceed 17 000MW of output by 07:00. Output remained above 16 500MW until after 13:00 and by 18:00 it had declined to below 16 000MW.

This is vastly different to the load profile – and therefore Eskom’s coal fleet output – on a ‘typical’ day. Normally, output is ramped up in the morning and then this drops until a higher peak in the afternoon into the evenings, when demand is at its highest. In recent months, Eskom has struggled to maintain this profile of output from its coal power stations as it battles constant plant breakdowns (and partial load losses). At times, its output in the evenings (dark grey on the chart below) is only barely higher than in the mornings – sometimes, it’s actually lower.

Abnormal coal output

The reason why the steep ramp-up of capacity from the coal fleet on Christmas Day is strange is because Eskom had not managed to achieve output from these baseload power stations of anywhere above 17 000MW for at least a week prior to that Sunday.

In the week that followed, it managed to just about get to that level once – at 18:00 on Friday, December 30, where it hit 16 940MW. In fact, until that day, it scarcely achieved coal output of over 16 000MW.

The context here is important. Maintenance is running at higher-than-normal levels (around 8 000MW), and there had been a catastrophic level of breakdowns (above 16 000MW) leading up to the festive season.

The only plausible way that Eskom managed to achieve output from its coal power stations that was a full 1 000MW higher than it was demonstrably capable of was to have run units that it knew needed repairs, were unreliable, and had a strong chance of breaking down.

One could easily theorise that political pressure – whether implicit or explicit – resulted in this decision.

The consequences are plain to see with even maximum use of its pumped storage schemes on Boxing Day not enough to stave off load shedding. Things got worse as the week progressed, with higher stages of load shedding and near-constant use of its open cycle gas turbines (OCGTs) for more than 48 hours from the morning of December 27. Recall, the diesel for these “emergency” resources had long been ‘depleted’. Government is still “urgently” working on a solution to this.

New Year’s Day

On the last day of 2022, Eskom used its OCGTs as well as those from the two IPPs at Avon and Dedisa for the entire day – from 08:00 until around 23:00. For most of that day, output from these diesel generators was above 1 000MW, peaking at 1 700MW at 13:00. These have a total installed output of 2 400MW, so this is a material amount of usage.

This was likely an attempt to reduce the impact of load shedding on New Year’s Eve festivities, given that it had been constant since the anomaly of Christmas Day. This wasn’t enough and, combined with the erratic output from coal above 15 000MW,

the country entered the new year with load shedding for the first time ever.

And renewables?

Supply from renewables played a big role in there not being load shedding on Christmas Day (and a worse stage of this on January 1). Solar (from PV and CSP) peaked at around 2 400MW at midday on December 25, with the contribution from wind cresting at just under 2 000MW that evening. The solar contribution was higher-than-average.

This meant Eskom could take units offline – either by proactively shutting off those in need of repair or by them just tripping and making that decision for the utility – without coming anywhere near falling short of meeting demand. At peak on December 25, Eskom had an operating reserve margin of 22% – multiples higher than it typically has (in recent months, it has had a negative reserve margin due to load shedding).

On December 31 and New Year’s Day, the supply from solar was approximately 2 000MW, with wind’s contribution peaking at over 2 000MW on New Year’s Eve itself.

Of note: Eskom has been running its two hydroelectric power stations, at the Gariep and Vanderkloof dams, almost constantly. Usefully, high rainfall has made this possible. Together, these two plants provide 600MW of capacity – critical, when Koberg Unit One (900MW) has been offline since early December for a steam generator unit replacement, expected to take “approximately” six months.