It’s 16:30 on Thursday July 25, 2013 – an unseasonably mild winter’s afternoon in Gauteng, South Africa’s most populous and industrialised province.

The six engineers and technicians working a 12-hour shift at Eskom National Control, situated alongside Germiston Lake, in Ekurhuleni, are exuding a quiet confidence that they will be able to manage the network through the evening peak.

A multistorey video wall – located in a control room at the heart of a complex so critical that it has been designated a National Key Point – is ablaze with colour.

The six individuals are positioned behind desks, supporting multiple large-screen terminals and computer keyboards. Each desk controls a different aspect of the country-wide network, from transmission and dispatch, to frequency and even events such as fires and lightning.

The names of each of South Africa’s 27 power stations feeding into the national grid are displayed in a column on the left hand side of the video wall.

Alongside each name are square blocks, each representing a generating unit. Counterintuitively, solid red indicates that a unit is operating, while the outline of a green square shows it is not. There are also some solid cyan blocks indicating that digital communications have broken down and that generation information from those stations should be confirmed offline.

By 17:00 just over 33 000 MW of capacity is available, primarily from Eskom’s coal-fired fleet, as well as some imports from Cahora Basa, in Mozambique. Only a few of the open-cycle gas turbines (OCGTs), which are hugely expensive to run, are shown to be operating, along with some of the pumped-storage units.

System operator GM Robbie van Heerden explains that, while South Africa’s installed generation base is around 44 000 MW, a number of units are out for planned winter maintenance, while there are also some unplanned losses.

Despite earlier weather forecasts warning that the working week of July 22 to 26 was likely to be Gauteng’s coldest, temperatures have remained well above expectations. Thus, barring any major unforeseen generation losses, Van Heerden is relatively confident Eskom will beat the Thursday evening peak, which will officially endure from 17:00 to 21:00.

But it is really the ‘peak within the peak’ that preoccupies the minds of those working at the Simmerpan campus, and all eyes are either trained on the video wall or on individual terminals so that a real-time assessment can be made about the state of supply and demand, while ensuring that the frequency is not falling precipitously.

By 17:00, demand has breached the 31 000 MW level and is rising rapidly. Ten minutes later there are indications that some more OCGT and pumped-storage capacity is being introduced.

At 17:27, demand breaches the 32 000 MW mark and frequency levels begin to fall. The 33 000 MW level is surpassed less than 15 minutes later, by which time just about all the OCGT generators are shown to be operating.

Once all the diesel generators and pumped-storage units are operational available capacity on this Thursday evening rises to nearly 34 500 MW, with demand closing in fast. In fact, by 17:55, the 34 100 MW level is breached.

However, National Control senior manager Al’Louise van Deventer is sanguine, noting that some reprieve will arrive at 18:00. At this time, a number of energy-intensive industries begin to switch off either in line with contracts concluded with the utility, or to avoid the higher winter peak tariff.

Demand does indeed begin to fall and is back below 33 900 MW by 18:01. “It looks like we will comfortably get through the evening peak,” Van Deventer muses.

However, Van Heerden stresses that the system will not be out of the woods for a few hours yet, given the tight operating parameters and Eskom’s limited levers to switch off load. However, its interruptible contract with BHP Billiton’s aluminium smelters, which draw up to 2 000 MW, remains an option – one which is exploited from time to time.

So is Eskom conducting rotational load shedding? Van Heerden dismisses the assertion.

He explains that, while load shedding remains a possibility in light of the constraints, the utility has no immediate plans to resume implementation, most of which will be conducted with the help of municipalities, which have load-shedding schedules.

Van Heerden acknowledges, though, that it would be he and his team at National Control that would be required to make any load-shedding call. He also stresses that the risk of load shedding is arguably more pronounced in the high-maintenance summer months than during winter, when Eskom is geared to meet an evening peak that rises by around 4 000 MW when compared with loads experienced during the course of the day.