$150 million investment injected into thermal battery maker Antora

Antora Energy, a thermal battery maker, said on Thursday it had secured $150 million in funding from BlackRock, the world's largest asset manager, and Singapore's state investment firm Temasek. The partnership, called Decarbonization Partners, is a new venture capital arm of an investor group led by Emerson Collective, GS Futures, The Nature Conservancy, Lowercarbon Capital, Breakthrough Energy Ventures and top global mining company BHP Billiton (BHP.AX).

The new financing will support the company in increasing production of its batteries, which are solid carbon blocks heated by renewable energy.

The energy produced by these cells could be used in industrial processes in industries ranging from chemicals to concrete, which use heat to melt and alter raw materials.

Antora or its customers will buy renewable electricity at the time of day when prices are lowest to heat the batteries to 2,400 degrees Celsius (4,352 degrees Fahrenheit). Consumers can tap into that heat throughout the day, potentially decarbonizing sectors of the economy that are particularly dependent on fossil fuel use.

Thermal batteries combined with cheap renewable energy represent an opportunity to decarbonize industrial emissions in a way that is cost-competitive with fossil fuels, Antora co-founder and Chief Executive Andrew Ponec said in an interview.

The heat can also be converted into electricity through Antora's thermophotovoltaic technology.

Blocks made of graphite or ceramics, similar to the concrete blocks shown here, could be a promising medium for thermal energy storage from renewable sources such as intermittent solar and wind power.

Justin Briggs, Antora’s co-founder and chief scientific officer, said he and co-founders Andrew Ponek and David Bierman, who founded the company in 2018, considered several energy storage technologies to achieve this goal. That included today’s mainstream approach, pumped hydro, where water pumped to higher altitudes spins turbines as it falls, and a similar new approach, gravity storage, which lifts 35-ton bricks and lets them fall.

Ultimately, the heated carbon blocks won out with their impressive energy density, simplicity, low cost and scalability. Briggs says their energy density is comparable to lithium-ion batteries at a few hundred kilowatt-hours per cubic meter and hundreds of times higher than pumped hydro or gravity batteries, which “require two reservoirs separated by a dam the size of a mountain or a skyscraper.”

Antora uses the same graphite blocks that are used as electrodes in steel furnaces and aluminum smelters. “There are 100 million tons of these materials already produced, so we can tap into the supply chain,” he says. Briggs imagines blocks about the size of a dorm fridge , packaged in modular units and wrapped in common insulation like rock wool.

“The real trick, after you heat it with electricity, is how to recover the heat,” he says. One option is to use the heat to drive a gas turbine. But Antora chose thermophotovoltaics, a device similar to solar cells that converts infrared radiation and light from glowing hot carbon blocks into electricity. These semiconductor devices fall dramatically in price when manufactured at scale, so they cost less per watt than turbines. And, unlike large turbines, thermophotovoltaics perform well regardless of power output.

Antora Energy’s graphite blocks store renewable energy at temperatures exceeding 1000ºC, ultimately converting it into electricity through its proprietary thermoelectric thermal engine.

Thermophotovoltaics have been around for decades, but Antora has developed a new system. Richard Swanson, one of the company’s advisors, was an early pioneer of the technology in the late 1970s. The efficiency of these devices in converting heat into electricity had been stuck in the 20-plus percent range until the Antora team set a world record of 30 percent in 2019. They did this by switching from silicon to higher-performance III–V semiconductors, and using tricks like harnessing low-energy infrared light that would otherwise pass through the semiconductor and be lost. Antora’s system recycles the heat by placing a reflector behind the semiconductor to bounce the infrared light back into a block of graphite.

The technology is already catching on. Antora received early funding from ARPA-E and is an alumnus of the Activate startup fellowship program and the Shell/NREL GameChanger accelerator program. They recently received funding from venture capitalists and the California Energy Commission (PDF) to scale their technology and will have a pilot system in place at an undisclosed customer site in 2022.

Electricized Thermal Solutions, part of the Activate 2021 team, was founded in 2020, which makes it much younger. The company's co-founders, Joey Kabel and Daniel Stack, chose ceramic blocks as their thermal storage medium. Specifically, honeycomb-shaped ceramic blocks are used today to collect waste heat from steel plants. Since ceramics don't conduct electricity, they coated the bricks with a coating to make them conductive so they can be electrically heated to 2,000°C.

Stack said they plan to target a broad market for this stored heat. They could use it to drive gas turbines to generate electricity, or run any other high-temperature process, such as producing cement and steel.

Rondo Energy, another California startup that takes a similar approach using bricks to store heat for later use, has raised $85 million, according to PitchBook data.

Antora’s funding would make it the sixth-largest Series B climate tech round of 2023, according to PitchBook, and brings the company’s total funding since its Series A in 2022 to $230 million.

(Source: Antora Global Energy Storage Network, New Energy Network Comprehensive)