Solar saving the day in South Africa – but not the night

Power utility Eskom says that solar is making a huge contribution to energy generation and sparing the country from load shedding, but it has a huge drawback: it only helps during the day when the sun is shining.

Eskom has managed to avoid load shedding for the entirety of April so far, marking 30 consecutive days without outages.

Questions have been asked why this is, with politicians lauding improved generation performance, analysts saying it’s thanks to lower demand, and critics positing that diesel burning is doing the trick.

In reality, it’s a mix of all of the above. Eskom’s generation has improved – and there is a significant drop in typical demand patterns thanks to increased private generation. But both of these factors have their limits, and when needed, diesel has to be burned to keep the lights on.

This was explained rather succinctly by Eskom’s System Operator, Isabel Fick, at the group’s Winter Outlook briefing this week (26 April).

Commenting on the contribution of private generation and solar to the grid, Fick said that around 2,800MW of photovoltaic solar is directly connected to the Eskom grid.

Solar not connected to the grid—which would include rooftop solar and smaller plants—is estimated to be around 5,440MW installed.

Fick said that solar is the biggest part of private generation and makes a significant contribution to operations. However, this is only after 09h00 and before 18h00 when the sun is shining—which leaves the morning and evening peaks up to Eskom to manage.

This is why Eskom must resort to emergency measures—like burning diesel with open-cycle gas turbines (OCGTs)—during these peaks.

Despite this major caveat, Fick said that Eskom can at least use the boost from solar to pump during the day because more power is available, ensuring that emergency resources are available when needed.

Burning diesel

Eskom has been criticised for burning excessive amounts of diesel to keep the lights on in the country. Critics have attributed the recent reprieve from outages to this diesel burn.

But Eskom said that its OCGT use has actually been declining. The group noted that diesel use in April 2024 was 50% less than the same time last year.

In a recent parliamentary response, Public Enterprises minister Pravin Gordhan revealed that Eskom has spent R64.78 billion in the last five years on diesel to power its Open Cycle Gas Turbines (OCGTs) to plug the electricity generation gap.

The utility’s diesel expenditure for each financial year is broken down as follows:

• 2020 – R5.8 billion;
• 2021 – R5.75 billion;
• 2022 – R8.6 billion;
• 2023 – R21.25 billion;
• 2024 – R23.38 billion.

Eskom’s diesel spend for 2023 was far above regulator Nersa’s capped output for Eskom’s OCGTs, at 1,266 GWh or R8.4 billion, set for the 2023/24 financial year.

Read: Stage 6 load shedding not on the cards for winter: Eskom