Investment Surges Into Multi-Day Energy Storage as Form Energy and Antora Raise $1.3 Billion

Investment in long-duration energy storage is accelerating as developers seek alternatives to lithium-ion batteries for applications requiring electricity or heat to be stored for days rather than hours.

Two US companies have raised a combined $1.3 billion within weeks of each other. Form Energy secured $750 million in Series G financing for its iron-air battery technology, while Antora Energy raised $550 million in Series C funding to expand its solid-carbon thermal battery business. The two transactions underline growing investor interest in storage technologies designed for periods when renewable electricity production falls short of demand for extended periods.

Form Energy's latest financing round was led by T. Rowe Price and takes the company's total equity funding to more than $2 billion. New investors included Sequoia Capital, Janus Henderson, Franklin Templeton and PEAK6 Investments, alongside existing investors such as Breakthrough Energy Ventures, TPG Rise Climate, Capricorn Technology Impact Funds, GE Vernova and Energy Impact Partners.

The company intends to use the capital to increase manufacturing at its factory in Weirton, West Virginia, and accelerate the deployment of commercial projects.

Form's technology is based on iron-air chemistry. During discharge, oxygen from the air reacts with iron to produce iron oxide, effectively rusting the metal and releasing electricity. Charging reverses the process, converting the iron oxide back into metallic iron.

The company's first commercial product is designed to provide approximately 100 hours of energy storage. That gives it a fundamentally different role from most lithium-ion battery installations, which are generally designed to shift electricity over shorter periods such as several hours.

The distinction becomes increasingly important as power systems install greater volumes of wind and solar generation. Short-duration batteries can manage fluctuations between daytime solar production and evening demand, for example, but multi-day periods of low renewable output can require substantially greater storage capacity.

Form says its commercial backlog has increased from around 20 GWh to approximately 80 GWh this year. Projects include agreements involving Xcel Energy and Google, data centre developer Crusoe and renewable energy developer FuturEnergy Ireland.

One of the largest planned projects involves Xcel Energy and Google in Minnesota. A 300 MW Form Energy installation designed for 100 hours of discharge would provide approximately 30 GWh of energy storage capacity, illustrating how multi-day systems can reach energy capacities far beyond those normally associated with conventional grid batteries.

Form is also expanding its manufacturing capacity. Its approximately 550,000-square-foot Form Factory 1 facility in Weirton employs nearly 400 people and produces the company's iron-air systems.

Antora Targets Electricity and Industrial Heat

Antora Energy is addressing the storage challenge using a different physical process.

The California company closed a $550 million Series C financing round on July 30. G2 Venture Partners and Eclipse co-led the investment, with participation from Ribbit Capital, Salesforce Ventures, Activate Capital, John Doerr, Westly Group, StepStone Group and Liberty Mutual Strategic Ventures.

Existing investors including Breakthrough Energy Ventures, Lowercarbon Capital and Decarbonization Partners also participated.

Antora plans to use the funding to expand project deployment, increase manufacturing capacity, establish a second US manufacturing hub and strengthen its domestic supply chain.

Rather than storing electricity through an electrochemical reaction, Antora converts electricity into heat. Its thermal batteries use inexpensive electricity to heat insulated blocks of solid carbon. The stored thermal energy can later be supplied directly as industrial heat or converted back into electricity.

This dual capability potentially gives the technology a role in sectors where high-temperature heat remains difficult to decarbonize, including chemicals, food processing, steel and other industrial operations. The same technology is also being positioned for data centres and electricity grid applications.

The carbon blocks can be heated to temperatures of up to around 2,400°C. Antora has also developed thermophotovoltaic technology that converts light emitted by the hot material into electricity.

The company recently deployed a 5 GWh thermal storage project in South Dakota, which Antora says progressed from the start of construction to energy delivery in less than 12 months. The project provides heat to POET Bioprocessing under a long-term offtake agreement.

Storage Requirements are Becoming More Diverse

The simultaneous funding rounds demonstrate that the rapidly expanding battery market is becoming more technologically diverse.

Global additions of battery storage capacity reached 108 GW in 2025, around 40% more than in 2024, according to the International Energy Agency. Battery storage was the fastest-growing power technology globally during the year.

Most installed systems still use lithium-ion technology, which has benefited from declining manufacturing costs and the rapid expansion of the electric vehicle battery supply chain. Lithium-ion remains particularly competitive for applications requiring rapid responses and frequent charging and discharging over relatively short durations.

However, systems increasingly need to perform different functions. The IEA reports that storage deployment is moving towards energy shifting and renewable integration, while a growing proportion of utility-scale projects provide four hours or more of storage.

Technologies capable of operating for ten hours, several days or potentially longer could complement rather than directly replace lithium-ion systems.

The US Department of Energy has historically classified systems providing at least ten hours of storage as long-duration technologies under its Long Duration Storage Shot programme, which set a target of reducing storage costs by 90% from a 2020 lithium-ion baseline by 2030.

Data Centres Add Another Source of Demand

Rapid growth in electricity consumption from data centres is also changing the economics of storage.

New data centres can be developed considerably faster than major electricity transmission infrastructure. The IEA estimates that new grid infrastructure can require five to 15 years to plan, permit and complete, while data centres can typically be built within one to three years.

That mismatch is encouraging technology companies, utilities and developers to investigate generation and storage combinations that can add reliable capacity without waiting for major grid upgrades.

Both Form and Antora are explicitly targeting this market alongside traditional renewable integration.

For utilities, the significance of multi-day storage is its potential to provide firm capacity during prolonged grid stress while absorbing surplus renewable electricity during periods of high production.

For industrial companies, thermal systems could offer an additional route for replacing fossil fuels used to generate process heat.

Neither technology has yet achieved anything close to the deployment scale of lithium-ion batteries. Manufacturing performance, operating costs, financing conditions and reliability across large commercial fleets will ultimately determine how large a role they can play.

The scale of the latest financing rounds nevertheless suggests that investors increasingly view long-duration storage as a commercial infrastructure opportunity rather than solely an emerging clean technology.

As renewable generation, industrial electrification and data centre demand expand simultaneously, electricity systems will require flexibility across timescales ranging from seconds to multiple days. The $1.3 billion raised by Form Energy and Antora Energy represents a substantial bet that abundant materials such as iron and carbon can help fill the longest part of that storage spectrum.

Source: www.forbes.com