RENEWABLE ENERGY & ELECTRIFICATION
Optimising energy
SUPPLY AND DEMAND
Load-shedding has become a frustrating problem that requires workable solutions. Bruce Munnings talks about the challenges and the search for answers.
Noupoort Wind Farm
Bruce Munnings, engineer: Electricity & Energy, iX engineers
T
he first time I remember loadshedding happening in South Africa was in January 2008. The bulk of electricity generation at the time was from coal-fired power stations. Electrical demand had been growing faster than new generation was being built, which led to a supply/demand imbalance. Despite the warnings on climate change, Eskom decided to build new coal-fired power stations to increase base generation. A pumped storage hydro system, Ingula, and fossil fuel generators were built to manage the peaks. Around the same time, the Renewable Energy Independent Power Producer Procurement Programme started. Between 2008 and 2022, additional new generation has been added to the South African grid. However, from Eskom’s weekly system status report, it can be calculated that at least a third and sometimes more of Eskom’s coal-fired power stations are unavailable due to planned or unplanned maintenance. Due to capital, operational and maintenance costs, climate change and corruption issues, building more coal-fired power stations is no longer considered a good option.
Breaking down the complexity of the load-shedding problem The need for load-shedding has been created for various reasons: • maintenance of coal-fired power stations • peak demand exceeds generation capacity available • environmental and climate change considerations
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IMIESA May 2022
• renewable energy not always available and currently limited in capacity • new nuclear power stations have not been built due to cost, corruption and other concerns • demand-side management (DSM) has not shifted enough demand out of peak demand times • energy-efficiency initiatives have not reduced demand sufficiently. Each of these items needs to be addressed in depth. However, due to the focus of this article, only some will be covered here.
Peak demand exceeds generation capacity available Figure 1 illustrates the weekly electricity demand profile. The morning peak and evening peaks are noted. The evening peak is at present higher than the morning peak. On Saturdays, FIGURE 1
FIGURE 2
Sundays and public holidays (Monday in this week), the curve is lower. Balancing supply and demand must be achieved at all times in order to keep the grid stable.
Generation: pumped storage and peaking power plants Pumped storage hydro is one of the means of balancing supply and demand. Water is pumped up during the night and used to generate electricity during the morning peak and evening peak times to balance the grid. Figure 2 provides a weekly profile of pumped storage hydro over the same period. In addition to pumped storage, liquid fossil fuels and gas peaking generators are used to meet the morning and evening peak demands. Figure 3 provides the weekly curve of generation from peaking power plants over the same period ending 6 May 2022.
