Form Energy pulls in $750 million to scale 100-hour iron-air batteries

Form Energy has raised $750 million in a Series G round led by T. Rowe Price, lifting its cumulative equity past $2 billion. The company said the money will go toward manufacturing scale-up in Weirton, West Virginia, and commercial deployments of its iron-air battery systems, which are designed to store electricity for up to 100 hours.

ESG Today reported the financing on August 13. The raise lands in a busy month for clean-energy finance. Copenhagen Infrastructure Partners closed a $3 billion growth markets fund. Sonnedix borrowed €730 million for solar and storage across four countries. Form Energy's round is part of that trend. The money is chasing the grid's weakest link: the hours when the sun is down and the wind is calm.

Form Energy was founded in 2017 in Somerville, Massachusetts. Its iron-air battery does not compete with lithium-ion on power density; it competes on duration. The company says its systems can deliver stored electricity for up to 100 hours, covering extended stretches of low wind and solar output, grid stress, and extreme weather events. The typical grid battery holds four hours.

The round comes with commercial agreements attached. Form Energy named Xcel Energy, Google, Crusoe, and FuturEnergy Ireland as counterparties to new deals. Crusoe is the telling one: the company builds data centers and pairs compute with clean firm power. Google's presence on the customer list shows how hyperscale demand is changing what utilities buy. Renewables alone cannot cover a data center's load through a windless stretch; the financing exists to pay for the multi-day gap.

T. Rowe Price led the round, repeating its role in the $405 million Series F closed in October 2024. Existing backers — Prelude Ventures, Engine Ventures, TPG Rise Climate, Breakthrough Energy Ventures, Coatue, Energy Impact Partners, GE Vernova, and M&G Catalyst Fund — were joined by Sequoia Capital, Janus Henderson, Franklin Templeton, and PEAK6 Investments. The mix spans climate-focused venture funds and public-market asset managers. Multi-day storage is no longer a specialist-only bet.

What the $750 million buys is a chance to prove the economics. Iron-air batteries are large and heavy; the cost case depends on manufacturing them at volume and on utilities contracting for a resource that will sit idle much of the year. The competing option in most utility resource plans is a natural gas peaker. Form Energy must ship its systems at a price and reliability that beat that comparison. The Weirton factory is the test.

The size of the raise does more than fund a factory. With cumulative equity past $2 billion, Form Energy can carry receivables, self-finance early deployments, and hold inventory through the multi-year sales cycle of a utility. That is the kind of balance sheet flexibility that smaller storage startups cannot match.

For transition finance, the raise is a marker. Early capital concentrated on solar, wind, and vehicles; the current cycle is funding the parts that make those assets dependable. Storage was long an afterthought in renewable project finance, an add-on battery sized to the solar farm's output. A dedicated manufacturer of 100-hour batteries, backed by more than $2 billion of cumulative equity, treats firming capacity as a standalone industry, with its own factories, its own off-take agreements, and its own capital stack. That is a shift from the past decade.

Delivery is the open question. Form Energy has a factory, a customer list, and a treasury above $2 billion. The next proof is the cost of a stored megawatt-hour and whether utilities keep signing. The equity is in place; the factory has to do the rest.