This fall, the thermal storage company Rondo Energy switched on a 100 megawatt-hour heat battery. It is its largest yet, and Rondo believes it to be “the largest industrial heat battery” in the world. “It’s a really big deal for us,” the company’s chief innovation officer John O’Donnell told Latitude Media.
The battery converts renewable energy from an off-grid solar array into heat, which is then stored via the company’s signature “hot bricks” and used to provide steam to a Holmes Western Oil’s facility in California. (The enhanced oil recovery system also relies on gas-fired boilers.) It has storage temperatures of over 1000°C and can provide heat 24 hours a day.
It is the first heat battery Rondo has brought online since the company installed its first two-MWh commercial-scale demonstration project at Calgren Renewable Fuels’ California ethanol production facility in 2023.
The fact that it has now been in commercial operations for 10 weeks proves Rondo’s ability to deliver projects on a large scale, according to O’Donnell. “The validation of our computational models at 100 MWh scale means that now we can go forward and build out other things, because we know that the whole product works,” he said.
It’s the result of years of work. The company has been developing the now-operational battery with Holmes Western Oil since before the Calgren demonstration got started. So a lot has been riding on its successful outcome. “There are a number of investors who’ve been tracking this unit step by step for a while,” O’Donnell said.
In July 2024, Rondo secured $80.6 million in non-dilutive funding, including infrastructure financing from the European Investment Bank for the development of three units in Europe, something that wouldn’t have happened without the Holmes Western project, according to O’Donnell.
“This unit we just turned on is exactly the same as those,” he said, adding that the “proof point” of its construction is key to de-risking the European units. (While Holmes Western Oil owns and operates its heat battery, Rondo has lined up storage-as-a-service customers for its European projects, with the kind of long-term contracts that are favored by infrastructure finance.)
This readiness — both for operation and for infrastructure finance — is a milestone for the thermal storage technologies more broadly, which have the potential of displacing “the equivalent of [roughly] 30% to 40% of current global gas use,” by 2050, according to a 2024 report by climate strategy firm Systemiq.
“Once infrastructure finance got to solar PV, the market exploded, and we’re seeing that with other kinds of battery storage right now,” O’Donnell said. “That’s our journey as well.”
Learning curve
Last December, O’Donnell sat down with The Green Blueprint’s Lara Pierpoint to discuss the many challenges the company had encountered while deploying its Calgren facility, from figuring out how many bricks it could lay in a day, to assessing the pros and cons of using cranes over forklifts. The process was a learning experience that informed how Rondo went about building the Holmes Western Oil unit, which is in turn facilitating the construction of its European units.
“You only get down the learning curve by building and building our first full-size unit taught us a ton,” O’Donnell said. “We had at least a 60% labor-hour-per-megawatt-hour [difference] between Calgary and this, and we’re doing that again, learning to repeat.”
Listen to John O’Donnell’s whole interview on The Green Blueprint:
One of the hundreds of things Rondo learned while deploying the Holmes Western Oil unit, for example, was how to make it resilient to earthquakes. The project is located less than 10 miles away from a faultline, which meant that Rondo had to work closely with county engineers to obtain permits, building physical models and putting them on shaker tables to see if they’d withstand seismic shocks.
“We had things to learn on the design side, and we had massive amounts to learn on how to work with outside engineers and permitting authorities,” O’Donnell said, noting that now, Rondo is well-prepared to tackle projects in seismic zones. The company also has more clarity on its costs and timelines, which is essential for unlocking infrastructure financing.
“Investors care…very strongly that you will deliver [a project] with date certainty and cost certainty, and the only way you ever get there is by building, which is why early full-size projects are so valuable for every technology,” he said.
