How Eskom kept the lights on for Christmas but not for New Years

Contrary to what many assume, Eskom did not burn a single liter of diesel on Christmas Day to avoid load shedding. In a Dec. 24 announcement, the company said the “suspension of load shedding [was] it is only possible because of the lower demand for electricity”.

This is only half of the equation. It is true that the actual demand was about 1,500 MW lower than on Christmas Eve. In fact, demand was a total of 4,000 MW less than the previous Sunday (December 18), equivalent to stage 4 of discharge. Also, peak demand on the 25thth it was almost 1 000 MW lower than Eskom’s forecast for the day.

Still, the supply side of the picture is telling…

On Christmas Day morning, the coal fleet rose from overnight lows of 15,600MW to over 17,000MW of output at 7am. Output remained above 16 500 MW until after 13:00 and by 18:00 it had fallen below 16 000 MW.

This is very different from the load profile – and hence the output of Eskom’s coal fleet – on a “typical” day. Production typically increases in the morning and then declines to a higher peak in the afternoon and evening when demand is highest.

In recent months, Eskom has struggled to maintain this output profile from its coal-fired power plants as it battles constant plant breakdowns (and partial load losses). Sometimes their output in the evening (dark gray in the graph below) is only barely higher than in the morning; sometimes it’s actually lower.

Production of Eskom’s coal fleet. Source: Eskom data

Abnormal output of coal

Why the sharp increase in coal fleet capacity on Christmas Day is strange is because Eskom had failed to get output from these baseload power plants above 17 000MW for at least a week before that sunday

The following week, it managed to reach this level almost once: at 6 pm on Friday 30 December, where it reached 16 940 MW. In fact, until that day, it barely managed to produce more than 16,000 MW of coal.

The context here is important. Maintenance is running at higher than normal levels (around 8,000MW) and there had been a catastrophic level of outages (over 16,000MW) before the festive season.

The only plausible way in which Eskom managed to achieve an output from its coal-fired power stations that was 1,000MW higher than it was demonstrably capable of was by running units that it knew needed repairs, were unreliable, and had many chances of breaking. . .

It could easily be theorized that political pressure – whether implicit or explicit – led to this decision.

The consequences are clear, even with peak use of its pumped storage schemes on Christmas Day not enough to avoid 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 27 December. Remember, the diesel for these “emergency” resources had been “used up” for a long time. The government is still working “urgently” on a solution to this.

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New Year’s Day

On the last day of 2022, Eskom used its OCGTs as well as those of the two IPPs Avon and Dedisa throughout the day from 8am until around 11pm. For most of that day, output from these diesel generators was over 1,000 MW, peaking at 1,700 MW at 1:00 p.m. These have a total installed capacity of 2 400 MW, so this is a substantial amount of material use.

This was probably an attempt to reduce the impact of loadshedding on New Year’s Eve, as it had been constant since the Christmas Day anomaly. That wasn’t enough, and combined with erratic coal output above 15,000 MW, the country entered the new year with a first-ever offload.

And renewables?

The supply of renewable energy played an important role in there being no discharge on Christmas Day (and a worse stage of this on January 1st). Solar power (from PV and CSP) peaked at around 2 400 MW at midday on 25 December, with the wind peaking at just under 2 000 MW that evening. The solar contribution was above average.

This meant that Eskom could take units offline, either by proactively shutting down those in need of repairs or simply hanging on and making that decision for the utility, not being close to meeting demand. At its peak on 25 December, Eskom had an operating reserve margin of 22% – higher multiples than it usually has (in recent months, it has had a negative reserve margin due to load shedding).

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On December 31 and New Year’s Day, the solar supply was approximately 2,000 MW, and the wind contribution reached more than 2,000 MW on New Year’s Eve itself.

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

This article originally appeared on Moneyweb and has been republished here with permission. Read the original here.

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