Iron rusts. Most engineers spend careers trying to prevent that. Form Energy has spent eight years making it useful. The Cambridge, Massachusetts company has built a rechargeable battery that runs on iron, water, and air , stores electricity for 100 hours or more, and costs a fraction of what lithium-ion systems charge per kilowatt-hour of usable capacity. Founded in 2017 and backed by over $1.2 billion in private and public funding , Form Energy has moved from sub-scale lab cells to a 550,000-square-foot factory on the site of a former steel mill in Weirton, West Virginia. Its commercial pipeline now exceeds 75 GWh of contracted projects , including what would be the largest grid battery ever built. AI-generated image Form Factory 1, built on the 55-acre site of the former Weirton Steel mill in Weirton, West Virginia. $1.2B+ Total funding raised 100+ Hours of discharge duration 75 GWh Commercial pipeline under agreement 550K sq ft Form Factory 1, Weirton WV $405M Series F raised (Oct 2024) 750+ Projected WV jobs at full capacity Five Founders, One Very Old Element Form Energy came together in 2017 through a combination of MIT lab access and a shared conviction: the electricity grid needed storage that could last days, not hours. Lithium-ion, the dominant chemistry at the time, was proving excellent for four-hour applications but economically impractical for the multi-day storage that would be needed as solar and wind generation expanded. The five co-founders each brought distinct expertise. Mateo Jaramillo , who became CEO, had led Tesla's energy storage products and programs as Vice President at Tesla Energy. Ted Wiley , now President and COO, handled operations from the start. Billy Woodford took the role of Chief Technology Officer, focused on battery engineering. Yet-Ming Chiang , an MIT professor and one of the most cited materials scientists working on electrochemistry, became Chief Science Officer. Marco Ferrara , Chief Digital Officer, rounded out the team with software and digital systems expertise. The group launched with seed funding and early lab space from MIT's The Engine, a venture firm spun out of the institute to support companies with long development timelines and genuine technical risk. That origin shaped Form Energy's approach: patient, science-first, and skeptical of shortcuts. Why Not Lithium? Lithium-ion batteries are exceptional at what they do, but their cost structure works against multi-day storage. A four-hour lithium-ion system might run $200 to $300 per kilowatt-hour. Stretch that to 100 hours and the economics collapse: you need 25 times more energy capacity for the same power output, multiplying the hardware cost proportionally. Form Energy's target cost for iron-air is under $20 per kilowatt-hour of energy capacity , which is what makes the math work for week-long storage at grid scale. Early R&D moved quickly. The company validated its core iron-air chemistry by 2019 and produced its first full-scale cell in 2020, the same year it announced its first customer agreement with Great River Energy, a Minnesota electric cooperative. A Series A of $9 million led by Breakthrough Energy Ventures had grown into a Series B of $40 million by 2019, funding the chemistry work and initial manufacturing research. How a Battery Built on Rust Actually Works The iron-air battery operates on a chemical reaction that anyone who has left a bicycle outside in the rain has witnessed. During discharge, iron pellets inside the battery cells react with oxygen drawn in from the surrounding air, forming iron oxide, more commonly known as rust. That oxidation reaction releases electrons, generating electrical current. During charging, electricity reverses the process: the iron oxide sheds its oxygen back into the air, returning the material to metallic iron. The battery breathes in oxygen when working and breathes it out when refueling. The electrolyte is a water-based alkaline solution, non-flammable by nature. There is no lithium, no cobalt, no nickel, and no rare-earth material anywhere in the active chemistry. Iron is the fourth most abundant element in Earth's crust. It is cheap, widely mined in the United States, and fully recyclable at the end of a battery's life. Iron-Air Battery: Key Technical Specs • Discharge duration: 100+ hours at nameplate power output. • Round-trip efficiency: Approximately 40 to 60 percent (lower than lithium-ion's 85 to 90 percent, but acceptable at this price point for multi-day applications). • Active material cost: Less than $1 per kilowatt-hour, the lowest of any rechargeable battery chemistry. • Safety certifications: UL 1973, UL 9540, and UL 9540A (fire propagation test). No thermal runaway risk. • System footprint: Approximately 2 megawatts per acre at standard density. • Materials sourcing: More than 80 percent U.S.-sourced materials. The physical architecture scales in layers. Individual cells, roughly a meter tall, stack into flat modules about the size of a large cutting board. Multiple modules combine into shipping-container-sized enclosures, each holding 4.5 megawatt-hours. Those enclosures group into power blocks of 2.5 to 4 megawatts, and power blocks aggregate into multi-megawatt project sites. A 300 MW / 30 GWh installation would cover roughly 150 acres at standard density. The tradeoff most often raised by analysts is round-trip efficiency. Where lithium-ion returns about 85 to 90 cents of electricity for every dollar put in, iron-air returns closer to 40 to 60 cents. For applications that cycle daily, that inefficiency is a real cost. For applications that might discharge fully eight to thirteen times per year during multi-day low-wind or low-solar events, the cheap energy capacity more than compensates. The system is designed for depth, not speed, and the two chemistries serve different parts of the grid. Building the Balance Sheet: Six Rounds and a Government Partner Form Energy's fundraising history tracks almost exactly with its technical milestones. Each round came as the team hit a new proof point, and each enabled the next phase of scale. Round Year Amount Key Milestone Series A 2018 $9M Led by Breakthrough Energy Ventures; initial iron-air prototypes Series B 2019 $40M Chemistry validated; cumulative funding exceeded $50M Series C 2020 $76M First full-scale cell; Great River Energy pilot announced Series D 2021 $240M Led by ArcelorMittal; first module tests completed Series E 2022 $450M Weirton factory announced; Georgia Power agreement signed Series F 2024 $405M Led by T. Rowe Price; GE Vernova joins as strategic investor The October 2024 Series F brought in $405 million with T. Rowe Price leading and GE Vernova joining as a new strategic investor alongside a memorandum of understanding for product collaboration. Existing backers including TPG Rise Climate, Breakthrough Energy Ventures, Temasek, GIC, Coatue, Energy Impact Partners, and MIT's The Engine Ventures all participated. The round closed with Form Energy's cumulative private funding at over $1.2 billion. On the public side, the U.S. Department of Energy selected Form Energy in September 2024 for an award of up to $150 million through its Office of Manufacturing and Energy Supply Chains under the Bipartisan Infrastructure Law. The program, called Project RAPID (Realizing Advanced Production of Iron-Air Batteries for Commercial Deployment), targets manufacturing expansion at Form Factory 1 with a goal of reaching 20 GWh of annual production capacity by 2027 and hiring up to 600 additional workers at the Weirton site. A separate DOE award of approximately $147 million supported grid infrastructure upgrades tied to an 85 MW / 8.5 GWh Form Energy project in Maine, one of the larger near-term deployments in the company's pipeline. Form Energy has also received smaller ARPA-E grants totaling several million dollars for iron powder production research and regenerative metal fuel applications. For