Holmes Western Heat Battery

At Holmes Western, Rondo deployed a 100 MWh Rondo Heat Battery (RHB), its largest industrial heat battery system to date, powered entirely by an on-site off-grid solar PV array. Solar charges the battery during daylight hours, and the RHB discharges heat around the clock, delivering continuous high-pressure steam into the existing plant alongside traditional gas boilers, with no changes to facility operations. Rondo states storage temperatures above 1,000 °C and round-trip efficiency above 97 %, with drop-in integration into existing steam flanges and boiler systems. The storage medium is only brick and wire, so there is no combustion, no emissions and no new air permits are required. The system has been in commercial operation since September 2025, and Rondo describes it as the world's largest industrial heat battery in commercial operation.