Eskom producing too much electricity

Eskom is facing a strange new challenge – it is producing too much power. This puts pressure on the system operator to shut down some units to maintain grid stability. 

Typically, the electricity grid is at risk of collapse from an unstable electricity supply, with wild swings in available capacity potentially creating a cascading trip. 

Eskom has six ‘defensive barriers’ to prevent a national blackout of this type. For a complete blackout to occur, all six barriers would have to fail. 

The general manager of Eskom’s system operator, Isabel Fick, explained that the chances of a blackout are extremely low in South Africa. 

A grid collapse does not stem from a lack of generation capacity but rather from the transmission network failing, typically from overloading it. 

South Africa has previously had two regional blackouts. One is in the Western Cape due to a transfer limit issue, and another is in KwaZulu-Natal due to extreme snowfall. 

Eskom has at least six barriers that prevent a national blackout, ranging from equipment design and operation to emergency response. 

One barrier is a permanent reserve margin of 2,200 MW. Others include equipment design, operational procedures, and emergency responses should the transmission network experience an issue. 

“If a blackout occurs, we must restore the grid. We have many plans in place because it will depend on exactly what state the network is in,” she said.

“We estimate that it will take between six and 14 days to restore the grid should we ever have a national blackout.”

Fick said Eskom’s grid is monitored in real-time to ensure the utility can react quickly to any failure. 

However, Fick’s explanation of why a grid collapse is unlikely was based on the threat to grid stability brought about by the erratic performance of Eskom’s coal fleet in 2023. 

The fear was that wild swings in available capacity from this fleet would overload transmission infrastructure, resulting in a regional blackout or worse. 

Now, the threat is coming from a completely different direction – Eskom is producing too much power. 

The head of generation at Eskom, Bheki Nxumalo, explained to Newzroom Afrika how this creates a problem for the system operator managing the grid. 

Nxumalo said the performance of Eskom’s coal fleet has greatly improved since last year, with its output stabilising and increasing. 

Many of Eskom’s worst-performing power stations have been successfully turned around after a period of intensive maintenance. 

This has boosted the fleet’s energy availability factor (EAF) to above 70% for the past two weeks. 

On 23 July, Eskom achieved 35,000 MW of available capacity. This level of generation capacity was last seen six years ago. 

This improved performance has enabled its supply to meet demand relatively comfortably over the past few months, with South Africa not experiencing load-shedding for over 120 days. 

However, Nxumalo said a new problem has emerged. During off-peak periods during the day and the weekend, the grid now sits with over 10,000 MW of excess power. 

Not only is this effectively wasted, as the power is not used and thus no revenue is generated, but it also poses a risk to grid stability due to the possible overloading of transmission infrastructure. 

Thus, the system operator must shut down some of Eskom’s units and place them in cold reserve to ensure the grid remains stable. 

Nxumalo said this is a much better problem than managing a highly unstable coal fleet and the corresponding swings in load-shedding stages. 

Another problem both Nxumalo and Fick pointed out was the rapid growth in renewable energy generation across the country. 

Both said more needs to be built out and that these projects contribute meaningfully to the electricity grid. 

However, output from renewable energy sources is inconsistent, and thus, it poses a substantial risk to grid stability. 

Renewable energy sources are inherently variable as they can only generate electricity when the weather conditions are right. Solar needs the sun to shine, and wind turbines need the wind to blow.

This makes Fick’s job of managing Eskom’s network much more difficult, as sudden weather changes can radically alter the supply and demand of electricity.

For example, in Gauteng alone, the combined effects of load-shedding and the variable output of rooftop solar can cause a sudden increase in electricity demand of 2,000 M