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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.

October 15th, 2026: Flatiron closes $850M financing for Energizar

Overview

Updated Oct 16

Flatiron Energy closed about $850 million in financing on October 15 for Energizar, a battery storage plant in Chelsea, Massachusetts. The project is designed for 250 megawatts and 1,200 megawatt-hours, and Flatiron says it will be the largest battery plant on the East Coast when it opens in late 2027.

The plans have changed since summer. Utility contracts filed in July described a 1,000 megawatt-hour project starting in mid-2027; the October announcement gave the larger figure and pushed the start to the fourth quarter of 2027. Chelsea's planning board also approved a redesign in February that moved the batteries from inside a building to outdoor enclosures, and the city's fire chief has told councilors the site falls in the Mill Hill station's response area.

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; up from 1,000 MWh in the July utility contracts.
250 MW
Planned power capacity
Figure given in Foley Hoag's account of the financing; the October announcement itself did not restate it.
Q4 2027
Target commercial operations date
Per the financing announcement; the July utility contracts cited Q2 2027.

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People Involved

DM
Dan Myers
Chief Financial Officer, Flatiron Energy
Leads financing for the Energizar project
 Andrew Platt
Andrew Platt
Managing Director, Santander
Worked on the Energizar financing as lender
JQ
John Quatieri
Fire Chief, Chelsea, Massachusetts
Told city councilors the battery site falls in the Mill Hill station's response area

Organizations Involved

Flatiron Energy
Flatiron Energy
Private energy storage developer
Financing closed for Energizar; construction contractor not yet named

Denver- and Boston-based developer focused on standalone battery storage projects.
Massachusetts Department of Public Utilities
Massachusetts Department of Public Utilities
State Regulatory Agency
Reviewing long-term contracts for storage projects

State body reviewing utility contracts for the three storage projects selected in the 2025 solicitation.

Timeline

2025 October 2026

5 events Latest: October 15th, 2026 · 4 weeks ago
Tap a bar to jump to that date

  1. Flatiron closes $850M financing for Energizar

    Latest Financing

    Closed construction and bridge loans, term loans, letters of credit, preferred equity, and tax credit transfer commitments. Nord/LB, Santander, and Societe Generale were coordinating lead arrangers, with Investec and East West Bank as joint lead arrangers and Siemens Financial Services as a lender.

  2. Chelsea fire chief flags response coverage for battery site

    Public safety

    Fire Chief John Quatieri told a City Council public safety subcommittee that the Eastern Avenue site sits in the Mill Hill fire station's response area, not the Central station's.

  3. Chelsea planning board approves outdoor battery design

    Regulatory

    The board voted 5-0 to treat the change as minor, letting Flatiron replace a battery building with separate outdoor enclosures behind a wall.

  4. 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.

  5. 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.

4

Fire-Safety Review Delays or Reshapes Energizar

Possible Resolves by End of 2027

Discussed by: Chelsea city councilors and Fire Chief John Quatieri

Councilors have raised concerns about the Eastern Avenue site, and the fire chief has said it falls in the Mill Hill station's response area. A demand for added fire suppression, setbacks or a different station assignment could slow permitting or construction before the Q4 2027 target.

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

(11)
+5
Business Wire Energy Storage News Renewables Now Utility Dive DealFlow.energy Energizar project site Construction Review Chelsea Mass Foley Hoag LLP Energy-Storage.News Project Finance International