How Eskom avoided more load-shedding this winter

Fewer unplanned unit losses and better wind generation during evening peak usage hours have helped Eskom avoid load-shedding for almost a month, despite colder temperatures in South Africa keeping overall electricity demand high.

Eskom’s last day of load-shedding was on Sunday 13 June, following a full week of load-shedding at various stages during which it appeared as though the country should brace itself for more severe power cuts.

With further maintenance work on ageing units scheduled for later in that month, energy experts expected the power cuts to possibly worsen to stage 5, but this did not come to pass.

While stage 4 load-shedding was implemented at one point during the last full week of load-shedding, it was only required for eight hours on a single day.

Since 14 June, the only scheduled power cuts the utility has implemented were for load reduction, preventing overloading of transformers in areas prone to illegal connections.

The power utility told MyBroadband the main reason for load-shedding not being required was an improvement in the performance of its generation fleet.

“The energy availability factor (EAF) of the fleet during load-shedding was in the low 60%, and this has since improved to a high 60% and even over 70% last week,” Eskom stated. “This is, however, still below Eskom’s aspiration for EAF.”

Eskom said the higher EAF and fewer unplanned losses indicated a reduction in losses due to unavailable units and a drop in partial load losses, where units could not operate at full capacity.

The utility said the return of Koeberg unit 1 on 22 June, in particular, had a significant impact as it added approximately 900MW of capacity to the grid.

The unit was out of action for more than five months after being taken offline for repairs and routine maintenance in early January.

Koeberg Nuclear Power Station near Cape Town

Eskom’s biggest challenge is keeping the power system from being overloaded during peak usage hours, typically occurring in the evenings between 18:00 and 21:00.

One noticeable trend in the evening peak feedback statistics shared by spokesperson Sikonathi Mantshantsha over the last few days was a big increase in the capacity provided by wind generation.

In the last full week of load-shedding – between 7 June and 13 June – the average contribution of wind generation during peak evening usage stood at 525MW.

In the most recent week of 28 June to 4 July 2021, the figure was more than double that – at 1,272MW. The week before that, wind generation’s contribution averaged at 1,077MW during the evening peak.

This was even though no new wind farms were connected to Eskom’s grid since the last rounds of load-shedding.

The utility explained that wind generation during the winter months tended to be erratic and less predictable than summer beyond a 7-day weather forecasting window.

“Wind generation in winter is generally impacted by cold fronts moving through the Western and Eastern Cape where many wind turbines are situated,” Eskom said.

“The strong winds associated with these cold fronts increase the wind generation as they move across the country.  As the cold front passes these areas, we often experience a sudden drop in wind  generation.”

“The high wind generation over some evening peaks over the past weeks has been due to these weather conditions,” it explained.

Eskom currently has nearly 5,350MW of renewable generation capacity, including more than 2,700MW of installed capacity at independent power producer (IPP) solar plants and 2,600MW of wind generation from both its own Sere project and private sectors farms.

The table below shows a breakdown of its installed renewable capacity.

Current installed renewable capacity
Power source Capacity
Concentrated Solar Power (CSP) 500.0
Photovoltaic (PV) Solar Plants  2 211.1
Wind (Eskom + IPPs)  2 612.7
Total (including other renewables, such as hydro)  5 349.4

The improved energy availability also reduced the need to use emergency generation reserves in the form of open-cycle gas turbines (OCGTs) operated by Eskom and IPPs.

Last week, for example, Eskom only used OCGTs during the evening peak demand period on one day, with four units in total being utilised.

In the last week of load-shedding, it was forced to use many more of these units on five days while they were depleted for the other two.

In total, these units were running on 83 occasions during the evening peak demand.

OCGTs are powered by diesel, which means that running them over long periods can be incredibly expensive.

Gourikwa OCGT Power Station

Eskom also told MyBroadband it was still expecting significantly improved plant performance by September.

“It should be noted, however, that many units are running with risks, and the outage programme is impacted by limited resources, especially Capex funding, while the country needs additional capacity.

The utility warned that despite the improvement in recent weeks, the performance of the generation fleet remained unreliable and unpredictable.

“Eskom has numerous plans and programmes in place to improve the situation, but these, such as catching up on all the reliability maintenance, will take time and until then, or until significant additional capacity comes online, the risk of load-shedding remains.”

The utility also said it did not yet have a clear picture of how much capacity is likely to be installed for self-generation by private businesses and individuals in the wake of government lifting the threshold for private power to 100MW.

It said it could therefore not make a clear assessment on how it will impact its ability to meet demand.

Now read: Real reason behind load-shedding in South Africa

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How Eskom avoided more load-shedding this winter