Chelsea Creek and the Tobin Bridge in Chelsea, where the Energizar battery storage project broke ground

Flatiron Breaks Ground on 1,200-Megawatt-Hour Battery Plant in Chelsea, Billed as the East Coast’s Largest

Flatiron Energy broke ground on its Energizar battery storage plant in Chelsea, a 1,200 MWh, $850 million project due online in late 2027.

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Featured photo: Chelsea Creek, with the Tobin Bridge in the distance (file photo). Photo: ArnoldReinhold, Wikimedia Commons, CC BY-SA 4.0.

CHELSEA, Mass. — Flatiron Energy has broken ground on Energizar, a large battery energy storage system on a former industrial site on Eastern Avenue in Chelsea, the Boston Business Journal reported Thursday, Nov. 13.[1] The story is part of our Boston news coverage.

1,200 MWh
Planned storage capacity
~$850M
Financing Flatiron lined up
Q4 2027
Target start of operations
Eastern Ave.
Site in Chelsea

Related: Vineyard Wind Reaches Full Commercial Operation.

The project

Energizar is designed to store 1,200 megawatt-hours of electricity. Flatiron says it will be the largest battery storage facility on the East Coast when it opens and one of the largest urban battery systems in the world.[2] Jonathan Poor, Flatiron’s chief operations officer, spoke at the groundbreaking.[1]

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Flatiron expects commercial operation in the fourth quarter of 2027.[2]

The money

In October, Flatiron said it had closed about $850 million in construction and long-term financing commitments. The package includes construction and bridge loans, term loans, letter-of-credit facilities, a preferred equity commitment and a tax credit transfer commitment.[2]

Why it matters

The company says the batteries will supply peak power and reliability to the Boston-area grid and cut local reliance on fossil-fuel plants.[2] Batteries store power when it is plentiful and release it when demand peaks.

Massachusetts is adding clean power at the same time: Vineyard Wind is now fully operating, and the state is exploring Canadian offshore wind.

More Boston business news and the latest Boston local news.

Sources

  1. NBC Boston (Boston Business Journal): Largest battery power storage site in region breaks ground near Boston
  2. Construction Review Online: Energizar Battery Project Secures $850M Financing for East Coast’s Largest Energy Storage Facility

About the reporter: Elena Park is an AI reporter covering business, markets and the economy for The Boston Report. This article was produced with AI under our editorial policy. Read our AI and media disclosure.

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