MATSHELA KOKO
Durban — In my letter to Minister Gwede Mantashe on September 9, 2022, I wrote, “The only short-term solution other than resorting to electricity blackouts is a co-ordinated government effort to improve Eskom’s energy availability factor to at least 72%.”
I gave this advice to Minister Gwede Mantashe because the power system stability builds on the laws of physics, not ideology. Alexander Stahel (2022) said: “One such law states that the alternating current that flows through the grid needs to match generation with consumption 525 960 minutes per year because electricity cannot be stored in the grid.”
The three dimensions of power system stability are voltage stability, rotor angle stability and frequency stability.
Voltage stability is the ability of a power system to maintain a steady acceptable voltage at all buses in the system under normal operating conditions and after being subjected to a disturbance. Voltage stability is about reactive power balance.
Rotor angle stability is the ability of interconnected synchronous generators to maintain synchronism after being subjected to a contingency. Rotor angle stability is about the torque balance of synchronous machines.
During my tenure as a group executive of technology and generation at Eskom, voltage stability and rotor angle stability were the least of my worries. Gav Hurford, and later Bernard Magoro, were system operators during my tenure. They never bothered me about the power grid’s voltage and rotor angle stability.
The frequency stability kept both Magoro and Hurford awake at night. In turn, they both kept me awake at night. It got so bad that I demanded a grid frequency meter in my office. I wanted to see the grid frequency in real time so I could respond to generation capacity challenges before Hurford calls. Magoro and Hurford’s calls were painful.
Magoro and Hurford’s calls were like a kiss of death. I learnt a lot about the performance of the power system from Magoro and Hurford. When I became Eskom’s interim group chief executive in December 2016, I ensured that the office of the chief executive at Eskom had a functioning grid frequency meter. I want to believe it is the best gift I left for Andre de Ruyter.
The frequency stability of a power system depends on three factors: the amount of active power imbalance, available reserves, and inertia.
The amount of power imbalance refers to the difference between generation and load after a contingency. The index employed to represent the balance between generation and load is frequency.
The power system’s frequency is maintained close to its nominal value of 50Hz. The South African grid code defines the frequency limit values and the remedial actions to take if the frequency is outside those limits. The corrective actions include over-frequency generator shedding and under-frequency load shedding, among others.
The more significant the power imbalance, the greater the instantaneous frequency deviation the power system suffers. The disturbance of the highest importance to Magoro and Hurford was an instant rapid loss of 2 000MW from generation units under my control.
In January 2016, the generation operations team and I met with Hurford to create the winter plan. The mandate from the board and President Zuma was that load shedding was not an option and that the planned maintenance should not be compromised.
Hurford wanted 2000MW of operating reserves in his pocket. He projected 35000MW of peak demand for the winter. A total of 37000MW of dispatchable generation capacity was required to get through the winter peak.
The actual peak demand for the winter of 2016 was 34900MW. We met Hurford’s targets, and he was happy. The diesel and kerosene usage for the emergency gas generators was 1248 million litres for the year.
The extensive utilisation of the emergency gas generators in 2016 created the much-needed maintenance headroom for the planned capability loss factor of 13%.
The forecast used by Hurford was the latest operational weekly residual peak forecast, which excluded the expected renewable energy generation. Therefore, I find it very strange that De Ruyter keeps telling South Africans to build more renewable energy projects to stop the blackouts when the system operator excludes the expected renewable energy generation in his forecast.
My conclusion is that the incomplete or inadequate reporting by Meridian Economics has misled De Ruyter and his team. Meridian Economics (2022) has published that the empirical data unequivocally shows that adding renewable generators to the existing South African power system will result in a disproportionate reduction in load shedding and an increase in system reliability.
The context for Meridian Economics is essential. Meridian Economics is funded by the Children’s Investment Fund Foundation (CIFF). The scope from CIFF (2021) shows that Meridian Economics is funded to support the “life after coal coalition in South Africa and to show that gas is uneconomical and unrequired”. Meridian Economics is a pressure group and it is getting paid for that.
I explained in my letter to Minister Mantashe why scholars with more extraordinary expertise in power system engineering would disagree with Meridian Economics. The power system stability can only be built based on physics laws, and no amount of lobbying will change that.
My advice to the new board of Eskom is to embrace renewables but know they are not a reliable energy source from a grid perspective. Europe has 236GW of installed wind generation capacity.
The hourly wind data in Europe for March 22, 2022 – September 21, 2022, shows a maximum wind generation of 122GW, a minimum wind generation capacity of 10.2GW, and a mean wind generation capacity of 41GW. That’s a dismal capacity factor of 17%.
Germany had nine days in September 2022 with little wind power generation. The capacity factor for Germany’s wind power plant for September was 4.5%. The mean wind generation capacity was 2.7GW against the installed base of 62GW.
It is now making perfect sense why Hurford did not include renewable energy in his projections. The energy availability factor of at least 72% is the system operator’s top of mind. The first order of business for the new Eskom board of directors is to get the energy availability factor right.
With the gift that I left De Ruyter, surely there must be a step change in the right direction in the next 90 days. Already, it is positive signalling that Eskom suspended stage 3 blackouts, on Saturday morning, for the first time in 32 days.
Matshela Koko is the MD of Matshela Energy
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