Independent energy analyst Pieter Jordaan has been compiling in-depth data on Eskom’s power supplies and load shedding – and he’s found a trend among the chaos: load shedding always seems to get worse on Tuesdays.

Following the trends in the data, it’s apparent that a week typically starts on stronger footing – but when Tuesday rolls around, the grid comes under strain and load shedding is usually intensified.

The graphs below show the trend in action over the past few months:

While not the case every single time, it’s clear that if load shedding is going to get worse, chances are that it will be on a Tuesday.

According to Jordaan, the reason for this trend isn’t that mysterious.

He said that this happens because the national grid System Operator “defends” the network against peaks on Mondays by using maximum peaking capacity.

“However, the peaking capacity is drastically reduced by this action and the System Operator must call on load reduction (load shedding and -curtailment) to lessen or attenuate the peak in the following days. This buys time to replenish diesel and water stocks,” he said.

What is peaking capacity?

Eskom has to defend a surge of power demand every morning as households prepare for the day and every evening as they prepare to go to bed.

“The utility has special power generating stations that can ramp up output in minutes or even seconds to deal with the peaks,” Jordaan said.

These stations are called peaking stations, consisting mainly of diesel/gas generators (3,400MW), pumped hydro (2,800MW) and local hydro (600MW).

The national grid System Operator uses the maximum peaking capacity of around 7,000MW to keep the grid stable during the peaks. However, the last 2,200MW may only be used in an emergency and is called the emergency (Operating Reserve) margin.

“Therefore, the System Operator generally only has 4,800MW with which to defend the peaks,” Jordaan said.

Because of this capacity, the System Operator has some room to work with in dealing with load shedding, and very rarely breaches the margins or goes over what was announced.

Reporting on megawatts removed from the grid has caused some confusion about this, with Eskom often reporting over 6,000MW being shed when only stage 6 load shedding has been announced.

Jordaan said that contrary to reports stating that Eskom has hit stage 7 or 8 load shedding, the System Operator has not shed more load than announced.

“In the following graph, apparent load reduction breaches (09.13, 09.14) are in fact due to load curtailment measures that helped the System Operator with an additional 1,000MW of peak attenuation.

“The System Operator did, however, breach the emergency margin (grey zone) on Monday, 11 September 2023 with less than 1,000MW to spare for at least an hour. It is far safer to ‘over-shed’ than to ‘over-peak’,” he said.

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Read: Double trouble – South Africa heading for a new load shedding record