Rondo and Rio Tinto Start Engineering on 360-MWh Yarwun Heat Battery

• Rondo Energy and Rio Tinto started front-end engineering on a 360-MWh, 30-MW heat battery at the Yarwun alumina refinery in Queensland.
• It would cut about 67,000 tonnes of CO2 a year, roughly 3.3% of Yarwun's 2.05 million tonnes of covered emissions in 2024-25.
• ARENA pays A$3.6 million for the study; up to A$38 million for construction depends on a final investment decision by Rio Tinto.

Rondo Energy and Rio Tinto have started front-end engineering and design on a 360-megawatt-hour heat battery at the Yarwun alumina refinery near Gladstone, Queensland. The Australian Renewable Energy Agency (ARENA) said on Oct. 21 it will fund the project in stages.

The unit stores electricity as heat; it is not a concentrated solar power plant. Resistive heaters will charge refractory bricks to about 1,100 degrees Celsius. Hot air from them will raise steam, ARENA's project page shows.

Three coal boilers and a gas-fired cogeneration plant now make Yarwun's digestion steam. The battery could replace about 5% of it and cut about 67,000 tonnes of CO2 a year, Rio Tinto said. The refinery reported 2.05 million tonnes of CO2-equivalent emissions under the Safeguard Mechanism in 2024-25, Clean Energy Regulator data show.

ARENA pays A$3.6 million ($2.5 million) for the study, and Rio Tinto will match it. Up to A$38 million ($26.6 million) for construction follows only if the project proceeds. A further A$33.3 million ($23.3 million) in conditional contingency covers risks such as cost overruns and electricity costs.

The project in numbers

• 360 MWh of heat storage, with 78 MW of electrical charging and 30 MW of thermal discharge.
• 12 hours of steam at 30 MW from one charge (list.solar calculation).
• About 4.6 hours to charge at 78 MW before losses, within the 4-6 hours of midday solar surplus Rondo cites (list.solar calculation).
• 3.3% of Yarwun's 2024-25 covered emissions equals the expected annual cut (list.solar calculation).
• A$74.9 million ($52.5 million) in total ARENA commitments, against a project cost of A$125.19 million ($87.8 million).
• 36 months of trial operations after commissioning, with the project ending by April 30, 2033.

Rondo, a California-based energy storage company, says its heat batteries have served fuel and cement plants in the U.S. and Asia since 2023. A 100-MWh unit is under construction for a European chemical plant, Rondo said in a statement.

"Reducing emissions from alumina refining is complex, particularly when it comes to generating the high-pressure steam needed for our operations," said Armando Torres, Rio Tinto's Pacific Operations managing director.

Rio Tinto said in November 2025 it would cut Yarwun's alumina output by 40% from October 2026, to extend the refinery's life to 2035.

The study should take about 12 months. Construction then needs an ARENA stage-gate review and a final investment decision by Rio Tinto.