What Flatiron’s $850 million deal means for US battery storage
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Flatiron Energy has secured approximately $850 million in financing commitments for a 1.2 GWh battery energy storage project in Massachusetts, marking a major investment in the US energy storage market.
The Energizar project, located in Chelsea near Boston, is expected to begin commercial operations in the fourth quarter of 2027. Once operational, Flatiron says it will be the largest battery energy storage system (BESS) on the US East Coast.
Announced on Oct. 15, the financing package includes construction loans, bridge loans, term loans, letters of credit, preferred equity and investment tax credit transfer commitments.
Nord/LB, Santander and Société Générale served as coordinating lead arrangers, while Investec and East West Bank acted as joint lead arrangers. Siemens Financial Services also participated as a lender.
The investment comes as Massachusetts expands its energy storage capacity to improve electricity reliability and reduce pressure on the grid during periods of high demand.
The agreement also shows how developers are attracting substantial private investment to bring large battery storage projects into commercial operation.
Large-scale batteries are becoming a bigger part of grid planning
Energizar is designed to provide electricity capacity and support the Boston-area grid during periods of peak demand.
Battery energy storage systems charge when electricity is available and discharge it when demand rises. This allows grid operators to manage short-term changes in electricity supply and consumption without relying entirely on conventional power plants.
The technology can be particularly useful in urban areas, where electricity demand is concentrated and building new power infrastructure can be difficult.
By storing electricity for later use, large battery projects can reduce pressure on existing infrastructure and help grid operators manage changes in renewable electricity generation.
Massachusetts has made energy storage a growing part of its electricity planning.
In December 2025, the state selected four battery storage projects totaling 1,268 MW through its first Section 83E procurement process.
The selected developments included Flatiron’s Energizar and Salt Cod projects, alongside Jupiter Power’s Trimount project and Rhynland Energy’s River Mill Storage project.
In July 2026, Massachusetts utilities submitted long-term contracts for Energizar, Salt Cod and Trimount for regulatory review. The agreements form part of the state’s efforts to secure additional energy storage capacity.
Energizar was listed as a 250 MW project in the original procurement records. Its announced energy capacity of 1,200 MWh refers to the amount of electricity the facility is designed to store.
The distinction matters when assessing battery storage performance.
Power capacity, measured in MW, determines how much electricity a system can deliver at any given time. Energy capacity, measured in MWh, determines how much electricity it can store.
For utilities, both figures are important when assessing how battery projects can help meet demand.
The value of storage will also depend on when electricity is available and how reliably it can be delivered.
These factors are becoming more important as changes in electricity demand, renewable generation and the retirement of older power plants place additional demands on grid planning.
Financing deals show how the battery storage market is maturing
The size and structure of Energizar’s financing illustrate the substantial capital required to develop large battery storage projects.
The approximately $850 million package combines commercial lending, preferred equity and commitments linked to federal investment tax credits.
These arrangements provide developers with several sources of capital to support construction and long-term operations.
Construction loans cover costs during development, while longer-term debt can support a project once it begins operating. Letters of credit provide financial assurances, while preferred equity offers another source of investment.
Tax credit transfers can also help finance battery storage developments. They allow eligible project owners to sell certain federal tax credits to other companies in exchange for cash.
For investors, battery storage projects offer opportunities linked to electricity markets and the need for flexible grid capacity.
However, financial returns depend on several factors, including operating costs, market revenues, long-term contracts and construction schedules.
Flatiron has already secured substantial financing for another battery project in Massachusetts.
In September 2025, the company announced approximately $540 million in financing commitments for its Taft battery storage development in Uxbridge.
The facility, rated at 200 MW and 800 MWh, was scheduled to enter commercial operation in late 2026.
Together, the Taft and Energizar agreements represent approximately $1.39 billion in announced financing commitments for two Massachusetts battery projects.
The transactions demonstrate Flatiron’s ability to attract backing from financial institutions across multiple developments.
They also indicate that lenders and investors are prepared to finance large battery storage projects where commercial arrangements and expected returns meet their requirements.
However, securing financing does not guarantee that a project will be completed on schedule or achieve its expected financial performance.
The success of these investments will depend on whether the facilities can provide reliable grid services while generating enough revenue to meet operating costs and financial obligations.
Project delivery will test the value of major storage investments
With financing secured, Energizar’s next challenge is moving through construction and into commercial operation.
Large battery storage projects require coordination across equipment supply, grid connections, construction, safety systems and regulatory compliance.
Delays in any of these areas can increase costs and affect when a project begins generating revenue.
For Energizar, the planned fourth-quarter 2027 opening will be an important milestone.
Its location near Boston places the project close to an area with substantial electricity demand. However, the benefits will depend on how the facility operates and the services it provides to the grid.
Developers and investors must also account for battery performance over time, including maintenance requirements, equipment degradation and the costs of maintaining storage capacity.
These considerations matter because grid-scale batteries are expected to operate for many years in electricity markets where prices and demand can change significantly.
Massachusetts’ wider procurement program will provide further evidence of how large-scale storage can support electricity reliability.
As more projects enter operation, utilities and grid planners will be better placed to assess the role of batteries in meeting peak demand and reducing reliance on conventional power plants.
Flatiron’s financing agreement represents a major step toward completing Energizar and expanding the company’s Massachusetts storage portfolio.
The project’s longer-term significance will depend on whether it enters operation as planned and delivers reliable electricity services to the Boston-area grid.
Source:
Energy Storage News
