Eskom’s next biggest challenge

The biggest challenge Eskom faces is the variability of its power supply from renewables and, to a greater extent, its coal fleet. 

This is according to Eskom’s general manager for system operations, Isabel Fick, who spoke at an event hosted by UCT’s Energy Systems Research Group and the Presidential Climate Commission this week. 

While coal-fired power stations usually provide a stable electricity supply throughout the year, Eskom’s have proven tremendously unreliable, making their output highly variable. 

“Variability on the coal fleet far outweighs the variability we are seeing on renewables at this stage,” Fick said. 

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. 

Fick said this is a unique challenge, as coal power stations should provide more reliable power than renewables and thus be able to smooth out variable output from renewables. 

That is not the case in South Africa, with variability from renewables hovering around 150 MW, while the variability of the rest of Eskom’s fleet is around 4,000 MW. 

Fick said the uncertainty this creates, exacerbated by load-shedding, is one of the utility’s biggest challenges. 

The exponential growth of rooftop solar to about 4,800 MW of capacity has further complicated this. 

“Rooftop solar has overtaken generation from large solar PV plants and is now the biggest variable and uncertainty we have to deal with on a daily basis on our network,” Fick said. 

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

There is roughly 1,000 MW of rooftop solar in Gauteng, explained Fick. During overcast conditions, this 1,000 MW has to be drawn from Eskom’s grid. 

“During continuous, higher stages of load-shedding, batter inverter systems recharge from the grid after load-shedding, adding an additional 1,000 MW burden to the grid.” 

“This often happens simultaneously, adding 2,000 MW of additional demand to the grid, just in Gauteng,” Fick said. 

Wind power has its own challenges. While wind generation coincides almost perfectly with the evening peak demand in summer, wind generation increases significantly in winter in the Western and Eastern Cape. 

This can lead to an oversupply of electricity in some areas and shortages in others, adding yet more uncertainty and variability to Eskom’s network.