Thermal Batteries Power Clean Industrial Heat

For the last 12 weeks, California start-up Rondo Energy has been operating what it’s calling the world’s largest thermal battery. Rondo’s system converts cheap renewable electricity into heat that can be discharged on demand into industrial processes.

This differs from most next-generation energy storage strategies, which provide electricity to grids in the absence of sun or wind. Instead, Rondo’s system aims to help decarbonize emissions-heavy sectors like steelmaking and cement.

The system works like a toaster crossed with a blast furnace. Electricity from solar arrays heat iron wires similar to those in a toaster oven. These warm hundreds of tonnes of refractory bricks to temperatures up to 1,500 °C. After four to six hours of charging a day, the heat can be discharged as air or steam, without combustion or emissions.

To discharge heat, a circulating air blower is turned on, pushing air up through the brick stack and heating it to over 1,000 °C before releasing it through an outlet. The heat delivery rate can be controlled by adjusting the air flow. The battery can discharge steam instead of heat by injecting water into an attached chamber that the heated air passes through before leaving the battery through the outlet.

The real challenge in thermal energy storage is not storing heat; it’s being able to charge rapidly and then deliver heat continuously at the same temperature, says John O’Donnell, Rondo Energy’s chief innovation officer. The structure of Rondo’s heat battery, which O’Donnell describes as “a 3D checkerboard of brick and open chambers,” keeps temperatures uniform and enables rapid charging. “We can turn charging circuits on and off as fast as you can turn your toaster on and off,” O’Donnell says. “So we can be agile.”

In Rondo’s first project, its 100-megawatt-hour battery is supplying heat for an enhanced oil recovery facility operated by Holmes Western Oil Corp. in Kern County, California. The battery, which is about the size of a small office building, is powered by an off-grid, 20-MW solar array built for this purpose. It converts the clean electricity into heat, and then generates steam that is injected into oil wells, heating the oil so that it thins out and flows more easily, increasing production.

Holmes Western Oil previously accomplished this with a gas-fired boiler. Cutting it will save Holmes just under 13,000 tonnes of CO₂ emissions annually while also lowering costs, according to Rondo. “This oil field uses the second-largest portion of industrial heat in the state,” says O’Donnell.

Rondo’s choice to deploy its first commercial-scale, emissions-reducing battery for the extraction of a fossil fuel stirred some controversy.

Thermal Batteries for Clean Industrial Heat

Several other companies are developing thermal batteries with industrial heat applications. Antora Energy makes modular carbon-block heat batteries that can reach over 1,500 °C and are being deployed at pilot…