US energy storage developer Flatiron Energy has closed on approximately US$850 million for its 1,200MWh Energizar energy storage project in Chelsea, Massachusetts, US.
Announced 15 October, Flatiron closed on the US$850 million financing, spanning construction and bridge loan facilities, term loan facilities, letter of credit facilities, a preferred equity commitment, and a tax credit transfer commitment.
The construction loans, term loans, bridge loans, and letters of credit were provided by a consortium of banks with Nord L/B, Santander, and Societe Generale serving as coordinating lead arrangers; Investec and East West Bank serving as Joint Lead Arrangers; and Siemens Financial Services serving as lender.
Flatiron stated the 1,200MWh battery energy storage system (BESS) project will reach commercial operations in Q4 2027. It will be the largest BESS facility on the east coast and provide capacity and peaking energy resources for local communities relying on the Boston, Massachusetts grid.
Try Premium for just $1
- Full premium access for the first month at only $1
- Converts to an annual rate after 30 days unless cancelled
- Cancel anytime during the trial period
Premium Benefits
- Expert industry analysis and interviews
- Digital access to PV Tech Power journal
- Exclusive event discounts
Or get the full Premium subscription right away
Or continue reading this article for free
Flatiron Energy has the project’s power capacity listed at 250MW though notably this seems to be from when the project had a planned capacity of 1,000MWh. While unconfirmed, the project could have a power capacity of 300MW to keep in line with the previously planned 4-hour duration.
Flatiron also stated that the preferred equity commitment was provided by funds managed by a premier global credit asset manager with more than US$350 billion of assets under management. Additionally, two Fortune 500 corporations provided a commitment to transfer a portion of the project’s investment tax credits (ITCs).
In late 2025, Massachusetts’s Department of Energy Resources (DOER) completed the evaluation of bids received in response to the Section 83E Storage request for proposals (RFP), selecting projects totalling 1,268MW of energy storage capacity.
One of the selected projects was Energizar, another selected project, also from Flatiron was the 168MW Salt Cod BESS, which was proposed to be located at the former coal-fired Montaup Power Plant.
Last month, the DOER awarded funding to 36 projects through its Advancing Massachusetts Power Energy Storage Grant Programme.
The agency is distributing approximately US$40 million, primarily to BESS, at critical community facilities in the state.
Recently, the state Governor Maura Healey released a comprehensive framework establishing principles and expectations for responsible data centre development in Massachusetts and the month prior, DOER issued an RFP seeking 1,000MW of BESS.
It includes a 250MW-300MW procurement target for distribution projects in addition to the 1,000MW of mid-duration BESS.
