Thermal energy storage could connect cheap but intermittent renewable electricity with heat-hungry industrial processes. These systems can transform electricity into heat and then, like typical batteries, store the energy and dispatch it as needed.

Rondo Energy is one of the companies working to produce and deploy thermal batteries. The company’s heat storage system relies on a resistance heater, which transforms electricity into heat using the same method as a space heater or toaster—but on a larger scale, and reaching a much higher temperature. That heat is then used to warm up carefully engineered and arranged stacks of bricks, which store the heat for later use. Air blown over the hot bricks can then be used to generate steam, or delivered directly to heat up equipment. 

By using common materials and designing equipment that can work with existing facilities, Rondo is working to show that its technology can integrate into a sector where cost is key. “We’re proving this is economical right now,” says John O’Donnell, the company’s CEO.

Rondo has been running its first commercial pilot at an ethanol plant in California since March 2023. The company is also scaling up, manufacturing equipment in a factory in Taiwan that it’s already announced plans to expand.

A recently announced project with the beverage company Diageo will see Rondo’s heat batteries installed in a Kentucky whiskey distillery where Bulleit bourbon is made, along with one of Diageo’s other facilities. In March, the project got a boost from the US Department of Energy, which selected it to receive $75 million in funding as part of a larger push to clean up industrial emissions. 

Rondo is far from the only contender in the thermal battery space, which now includes companies using everything from molten salt and metal to crushed-up rocks to store heat.