In the push toward a fully renewable energy grid, a Massachusetts-based startup is betting on an unlikely hero: rust. Form Energy’s iron-air battery, which harnesses the reversible process of iron rusting to store and release energy, promises to deliver ultra-long-duration storage at a fraction of the cost of traditional lithium-ion systems. As detailed in a recent Fast Company report, this technology could enable grids to rely entirely on clean sources like wind and solar without fossil fuel backups, addressing one of the thorniest challenges in the energy transition.

The battery operates on a simple electrochemical principle. During discharge, iron anodes react with oxygen to form rust (iron oxide), releasing electrons that power the grid. To recharge, an electric current reverses the reaction, converting rust back to iron while storing energy. This cycle can last up to 100 hours—far exceeding the four to eight hours typical of lithium-ion batteries—making it ideal for bridging multi-day lulls in renewable generation.

The Rise of Reversible Rust

Form Energy, founded in 2017, has raised over $800 million from investors including Bill Gates’s Breakthrough Energy Ventures. According to insights from Scientific American, the company’s approach leverages abundant, inexpensive materials like iron and air, slashing costs to potentially $20 per kilowatt-hour of storage—about a tenth of lithium-ion equivalents. This low price point stems from avoiding rare earth metals and volatile supply chains that plague conventional batteries.

Pilot projects are already demonstrating real-world viability. In June 2025, Form Energy announced plans for a 1.5-megawatt iron-air system in California, capable of 100-hour discharges, as reported by Yahoo News. Meanwhile, Dutch startup Ore Energy connected a similar rust-based battery to the grid in the Netherlands last month, marking a global first, per updates shared on X from sources like New Scientist.

Scaling Up Amid Grid Demands

Industry insiders note that as electrification surges—driven by electric vehicles, data centers, and AI—the need for long-duration storage is acute. Form Energy’s batteries, with their water-based electrolytes and non-flammable design, offer safety advantages over lithium-ion, which have faced fire risks and recycling challenges. A post on X from BIS Research highlighted how these systems provide “multi-day storage using reversible oxidation,” underscoring their role in achieving net-zero goals without lithium dependence.

Deployment timelines are accelerating. Form Energy aims to have commercial-scale facilities operational by 2026, including a massive plant in Maine backed by federal incentives. As Interesting Engineering explored in a 2022 piece that foreshadowed these advances, the technology could “revolutionize the industry” by enabling cost-effective seasonal storage, such as banking summer solar for winter use.

Challenges and Competitive Edge

Yet hurdles remain. Iron-air batteries have lower energy density than lithium-ion, requiring more space for equivalent output, which could limit urban applications. Efficiency is another focus area, with round-trip rates around 50%, though ongoing R&D aims to improve this. Competitors like flow batteries and compressed air systems vie for the long-duration niche, but rust’s material abundance gives Form an edge, as noted in a 2021 ClearPath analysis.

For energy executives, the implications are profound. Widespread adoption could stabilize wholesale power prices, reduce curtailment of renewables, and facilitate decarbonization in hard-to-abate sectors. As one X post from ESS News observed, these innovations are pivotal for “long-duration energy storage” in a smart energy future.

Looking Ahead to a Rusty Revolution

Form Energy’s co-founder Mateo Jaramillo, formerly of Tesla, envisions a grid where rust batteries handle the “heavy lifting” of extended outages. With global investment in clean tech topping $1.7 trillion last year, per International Energy Agency data, the stage is set for rust to rustle up a new era. If scaled successfully, this could not only lower costs but also democratize energy access in developing regions, where lithium scarcity poses barriers.

Critics argue the tech is still nascent, but early grid integrations suggest momentum. As The North Bay Business Journal reported in June, a Mendocino County project exemplifies how rust batteries might integrate with local renewables, offering a blueprint for broader rollout. In an industry hungry for breakthroughs, rust may prove to be the unassuming alloy that powers tomorrow’s grid.