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Flatiron closes $850M financing for East Coast's largest battery storage project

Flatiron closes $850M financing for East Coast's largest battery storage project

Built World

Energizar, a 1,200 MWh battery in Chelsea, Mass., targets Q4 2027 operations.

Yesterday: Flatiron closes $850M financing for Energizar

Overview

Updated 1 hour ago

Flatiron Energy closed roughly $850 million in financing on October 15 for Energizar, a 1,200 MWh battery storage facility in Chelsea, Massachusetts. When it starts operating in late 2027, it will be the largest battery storage facility on the East Coast and one of the largest urban battery installations in the world.

The project sits in an industrial waterfront neighborhood that the Commonwealth of Massachusetts classifies as an Environmental Justice population, meaning residents are more vulnerable to climate impacts. Energizar is part of the state's effort to deploy 5 GW of storage by 2030, and the financing structure shows banks and corporate tax-credit buyers now underwrite large batteries like infrastructure.

Why it matters

At 1,200 MWh, Energizar can carry Boston through peak-demand hours without firing fossil-fuel peaker plants, and its financing proves large storage is now bankable.

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Key Indicators

$850M
Total financing committed
Construction and bridge loans, term loans, letters of credit, preferred equity, and tax credit transfers.
1,200 MWh
Battery storage capacity
Largest BESS facility on the East Coast once operating.
Q4 2027
Target commercial operations date
Per the financing announcement; earlier project materials cited Q2 2027.
5 GW
Massachusetts storage target by 2030
Energizar emerged from the state's first solicitation under that mandate.

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People Involved

Organizations Involved

Timeline

2025 October 2026

3 events Latest: Yesterday
  1. Flatiron closes $850M financing for Energizar

    Latest Financing

    Closed construction and term loans, bridge loans, letters of credit, preferred equity, and tax credit transfer commitments. Nord/LB, Santander, and Societe Generale led.

  2. Utilities file contracts for 4.5 GWh of storage

    Regulatory

    Eversource, National Grid, and Unitil filed long-term contracts with the DPU for the three projects, covering 1,068 MW/4,472 MWh.

  3. Massachusetts selects Energizar in storage solicitation

    Procurement

    Energizar and Salt Cod, both Flatiron projects, were selected alongside Jupiter Power's Trimount in the state's first storage solicitation.

Scenarios

1

Energizar Reaches Commercial Operations in Q4 2027

Likely Resolves by Jan 31, 2028

Discussed by: Flatiron Energy and the financing announcement

Construction proceeds on schedule and the 1,200 MWh facility comes online by December 2027, becoming the largest BESS on the East Coast. It would provide peaking capacity to the Boston grid and begin the 20-year commitment of $15 million toward workforce development programs in Chelsea.

2

Construction Delays Push COD Into 2028

Possible Resolves by Q1 2028

Discussed by: DealFlow.energy and project finance observers noting complexity

Supply chain or interconnection issues delay the project beyond Q4 2027. The financing package was structured to reach COD in Q4 2027; a slip would extend construction borrowing and could trigger renegotiation of offtake contracts with utilities.

3

Flatiron's Salt Cod Project Reaches Financial Close Next

Possible Resolves by Q2 2027

Discussed by: DealFlow.energy coverage of the Massachusetts storage pipeline

Energizar's successful financing de-risks Flatiron's second Massachusetts project, Salt Cod (168 MW/672 MWh), also under contract with utilities. A similar financing package would follow using the same lender relationships and tax credit transfer model.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

December 2017

Hornsdale Power Reserve (2017)

Tesla built a 100 MW/129 MWh lithium-ion battery beside the Hornsdale wind farm in South Australia in under 100 days, after a statewide blackout triggered political pressure. It was then the largest battery in the world.

Then

The battery responded to grid frequency events in milliseconds, faster than gas plants, and earned revenue through frequency regulation markets.

Now

It demonstrated that grid-scale batteries were reliable money-makers, helping launch the global BESS boom.

Why this matters now

Hornsdale proved the grid-services business case for large batteries. Energizar applies the same logic at roughly 10 times the capacity, in an urban setting.

December 2020 through 2022

Moss Landing Energy Storage Facility (2020)

Vistra commissioned a 300 MW/1,200 MWh battery at a retired natural gas plant in Moss Landing, California, then the world's largest. Two thermal incidents in 2021 and 2022 forced shutdowns and raised safety questions.

Then

The facility was temporarily taken offline after overheating events triggered sprinklers and evacuation orders.

Now

California tightened thermal-runaway safety standards for BESS, and operators added fire suppression systems.

Why this matters now

Moss Landing showed large batteries can scale in dense areas, but also flagged thermal safety as the key operational risk. Energizar, an urban facility, will face the same scrutiny from Chelsea residents and regulators.

Sources

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