Eskom’s rooftop solar numbers and peak demand decline explained

Eskom has provided more details on how it calculates the amount of rooftop solar installed in South Africa and why it can meet evening peak demand without load-shedding despite the sun not being available.

The utility recently started including a statistic for “behind-the-meter” solar capacity installed by households and businesses in its weekly system status outlooks.

According to Eskom’s latest estimates, there was about 5,440MW of rooftop solar capacity not directly connected to Eskom’s grid in March 2024.

However, determining the amount of private power installed in South Africa would be a monumental task, requiring a national audit of all private solar panel installations.

Eskom said the estimates were based on historical provincial demand data during noons over a 3-month rolling period.

“This is correlated against cloud cover data to analyse the difference in demand behaviour during cloudy and sunny days,” Eskom explained.

“Comparison is done on similar days of the week, where there is a significant change in cloud cover from one day to a similar day.”

The utility added that any other variables that could influence the demand, like temperature, were also considered to ensure that only days with similar conditions were included.

“A range of additional logical checks and parameters are incorporated to remove any outliers,” it added.

Unfortunately, Eskom said it could not distinguish between the amount of rooftop solar capacity added by households and businesses.

“The methodology used to estimate the behind-the-meter PV cannot distinguish between types of customers,” Eskom said.

The table below shows Eskom’s estimates for rooftop solar capacity in South Africa from July 2022 to March 2024 and how it compared with utility-scale renewables.

Eskom’s rooftop solar numbers and peak demand decline explained
Click to enlarge

Eskom’s System Operator Isabel Fick recently explained how this capacity and a further 2,800MW of solar supplying power to the grid were helping the utility avoid load-shedding.

Fick said the additional power, which is around 2,100MW more than the same time last year, enabled Eskom to replenish its emergency generation capacity including water levels at pumped storage dams and diesel supplies for open-cycle gas turbines during the day.

Eskom can then dispatch power from these “peaking” generators as required during the evening peak periods.

At the same last year, it had to rely more on these sources during the day, which meant they could be depleted by the peak periods, resulting in the need for higher levels of load-shedding.

Several solar sceptics were not satisfied with Fick’s explanation, arguing the emergency reserves were not enough to meet the shortfall during peak periods.

It should be noted that the utility’s peaking power stations have a combined capacity of 5,894MW, equal to around six stages of load-shedding.

For further clarification, Eskom told MyBroadband that there has also been a slight continuous decline in the evening peak demand since 2007.

The graph and tables below show how Eskom’s peak electricity demand in 2024 has mostly been lower than in 2023.

Eskom’s rooftop solar numbers and peak demand decline explained
Click to enlarge

Eskom said a variety of factors could be to blame for this peak demand drop, including:

  • Households using backup battery power during peak periods
  • Warmer-than-usual weather
  • Higher electricity prices
  • More energy-efficient appliances and lighting
  • Use of alternative energy sources, including gas for cooking and solar for heating water
  • Use of alternate fuels for space heating

However, the utility said that there was no empirical evidence to support that the above could be blamed for the reduction.

Eskom said that industrial activity, including mining, was still the dominant energy consumer at all times of the day.

“The evening peaks are a result of the overlap between commercial, residential and industrial demand,” the utility said.

“This is particularly pronounced in winter when the evening peak is earlier and higher, driven by earlier sunset and cold weather.”

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