Midlands Exergy owner Sydney Zeederberg has proposed fitting some of Eskom’s coal power stations with thermal batteries. He said the systems could help South Africa cope with high electricity demand at peak times.
Zeederberg said these heat batteries could supply power far more cheaply than lithium-ion batteries. This would only work if they were linked to generation and transmission equipment that is already in place, he said.
“Where a unit is kept at minimum load through the middle of the day so it is available for the evening peak, it burns coal to stand still,” Zeederberg said.
“A thermal store charged from midday surplus could keep the boiler and turbine warm with the unit off, and supply steam for a faster restart,” he said.
The idea comes after the Ministry of Electricity and Energy announced the first energy storage bid window under the 2025 Integrated Resource Plan. The programme wants 4,600MW of battery storage and 5,000MW of gas power.
The batteries are meant to store extra power that would otherwise be cut off. This waste has become a big problem for renewable energy producers.
In a LinkedIn blog post, Zeederberg asked why thermal storage in the form of Carnot batteries was left out of the bid. A Carnot battery stores electricity as heat. It then turns that heat back into power using a heat engine.
The battery can be charged with an electric heater or a heat pump. At a coal plant, it could be charged at times of day when solar power is strong and the plant runs on low power.
Zeederberg pointed to a 2026 design study by Novotný, Vocel and Špale in the Journal of Energy Storage. The researchers changed a combined-cycle plant so it could store 959MWh of energy.
They did this by heating a packed bed from 100°C to 600°C with a 78.7MW electric heater. “The bed discharges through the plant’s existing heat recovery steam generator and turbine,” Zeederberg said.
That system was about 33% efficient, so only around a third of the power was returned. A lithium-ion battery returns about 85% to 90%.
The thermal system was cheaper because the turbine, generator and grid link were already paid for. The paper put the cost at about $41 (R674) per kWh of returnable energy. Lithium storage costs about $105 (R1,726) per kWh.
Zeederberg said the latest battery bid window had an average cost of about R3,860 per kWh of capacity. His own figures showed the retrofit could supply power at about R0.33 per kWh over 30 years, if cycled 300 times a year.
He said the idea only made sense at a site that already owned a turbine and bought power at a generator’s price, not a customer’s price.
Zeederberg also suggested large thermal storage at industrial sites in his comments on the draft Electricity Pricing Policy. He said the heat made there could be used when needed by both the power system and the factory.
Other sites that could gain include a ferrochrome smelter that burns off-gas in a boiler and turbine, or a cement plant with a waste-heat turbine.
Zeederberg said tests on steam conditions, the cycling life of old turbines and the grid code would first be needed to confirm the idea works at specific plants.
Source: this article is based on reporting by MyBroadband. Image: MyBroadband. Written with the help of AI and published by the Tzaneen Voice Business desk. See our Editorial Standards.
Anelisa Nkuna covers business and money news for Tzaneen Voice. Anelisa reports on the rand, fuel prices, interest rates, jobs, Eskom, Transnet, farming and company results. The aim is simple: explain what the numbers mean for household budgets, small businesses and workers in South Africa.