The World’s Largest Battery Made of Bricks Turns On in California
(Bloomberg) -- A Bay Area startup has turned on the world’s largest industrial heat battery.
Rondo Energy is helping power Holmes Western Oil Corp.’s enhanced oil recovery system. Holmes replaced one of its natural gas-fired boilers at a project in Kern County, California, with a 20-megawatt solar array paired with Rondo’s 100-megawatt-hour battery, which heats up clay bricks with electricity to generate steam that’s then used to force oil from the ground.
Critics argue that deploying clean tech to produce fossil fuels prolongs the life of carbon-emitting infrastructure. Rondo investor Andy Lubershane, a partner at Energy Impact Partners, views it differently.
For clean tech startups like Rondo, “it’s hard to find a customer to do your first commercial project,” he said. “Having a partner like Holmes that has an interest in decarbonization” is critical to scaling technology. Using renewables and a heat battery lowers the carbon footprint of the project.
Holmes also benefits from California’s Low Carbon Fuel Standard, which regulates oil and gas producers in the state. By replacing natural gas with the solar and battery system, the oil company avoids 13,000 tons of carbon dioxide emissions annually while also lowering costs, according to the battery startup’s founder and Chief Innovation Officer John O’Donnell. Those avoided emissions allow the company to generate environmental credits, which can be sold or used to offset its own excess emissions. Holmes declined to comment.
“It is absolutely a moral necessity to decarbonize every single part of our economy,” and producing oil locally produces fewer emissions than shipping it in tankers across the ocean, O’Donnell said. California Governor Gavin Newsom has recently started championing the state’s beleaguered oil industry.
The fuel standard has helped companies producing some of the most carbon-intensive oil in the US to continue operating, though. It includes a carve-out for local drillers to generate credits for using “innovative crude oil production methods” that cut emissions at the well site.
Other climate tech startups have also partnered with oil companies for early-stage support. Occidental Petroleum Corp. acquired a direct air capture startup in part so that it could use the captured carbon dioxide for enhanced oil recovery. Meanwhile, oil majors, including Chevron Corp. and Shell Plc, have experimented with using solar to boost their oil output.
Rondo sees applications of its technology beyond the fossil fuel sector, including for the production of green cement, aluminum and other industrial processes. The company has also partnered with Portugal-based energy company EDP to install 2 gigawatts of heat batteries across Europe, though that represents a vast increase in scale. Other technologies, notably hydrogen, are also competitors to heat batteries.
The startup is also focusing the bulk of its future development efforts outside the US, partly because the Trump administration’s policy boomerangs have created a difficult business environment, according to O’Donnell, a trend mirrored by other climate-focused startups. A spike in natural gas prices after Russia’s invasion of Ukraine has also made renewables paired with storage more appealing in Europe.
“Uncertainty is the enemy of infrastructure,” and developers building long-term projects need consistent business conditions, O’Donnell said.
©2025 Bloomberg L.P.
