Flatiron Closes $850 Million for Its 1,200 MWh Chelsea Battery, Two Quarters Later Than Its July Contract Filing Said

Flatiron Energy has secured about $850 million in construction and term financing commitments for its Energizar battery project in Chelsea, Massachusetts, pv magazine USA reported on October 15, 2026. The standalone project is designed at 1,200 MWh. Flatiron expects commercial operations in the fourth quarter of 2027. It says Energizar will be the largest battery energy storage system on the East Coast.

Those numbers differ from the July contract filing. In July 2026, Eversource, National Grid and Unitil filed long-term contracts with three storage projects, Utility Dive reported. Energizar was listed at 250 MW / 1,000 MWh, and Flatiron aimed to begin operations in the second quarter of 2027. The October announcement describes a 1,200 MWh project with operations in the fourth quarter of 2027. It gives no MW rating and no reason for either change.

How the Deal Is Financed

The package covers construction and bridge loan facilities, term loan facilities, letter of credit facilities, a preferred equity commitment and a tax credit transfer commitment. Nord/LB, Santander and Societe Generale are the coordinating lead arrangers. Investec and East West Bank are joint lead arrangers, and Siemens Financial Services is a lender. A global credit asset manager with more than $350 billion in assets under management provided the preferred equity. Two Fortune 500 corporations committed to buy a portion of the project’s investment tax credits.

Flatiron did not identify the asset manager or the tax credit buyers, citybiz reports. It also did not disclose the amount of the preferred equity or the terms of the tax credit transfers.

Why It Matters

Energizar sits at a former industrial site in Chelsea. That is a few miles east of Jupiter Power’s 700 MW / 2,800 MWh Trimount project in Everett, according to Utility Dive. The July filing covered 1,068 MW / 4,472 MWh across Trimount, Energizar and Flatiron’s 168 MW / 672 MWh Salt Cod. Flatiron says Energizar will provide peaking capacity and reliability resources for the Boston area grid and offset local reliance on fossil-fuel-fired generation. The October announcement does not say whether the utility contracts filed in July changed with the new size and date.

Sources

• pv magazine USA, Flatiron Energy closes $850 million in financing for 1,200 MWh Boston area battery project (October 15, 2026)
• citybiz, Flatiron Energy Secures $850M Financing for 1,200 MWh Battery Storage Project Near Boston (October 15, 2026)
• Utility Dive, Massachusetts utilities file long-term energy storage contracts (July 7, 2026)