Flatiron Energy closes $850m for a 1,200 MWh battery project near Boston
Victoria Shinder2 min readUS energy storage developer Flatiron Energy has closed about US$850 million of financing for its 1,200 MWh Energizar battery storage project in Chelsea, Massachusetts, Energy-Storage.news reported. Announced 15 October 2026, the financing spans construction and bridge loan facilities, term loan facilities, letter-of-credit facilities, a preferred equity commitment and a tax-credit transfer commitment. Flatiron says the project will reach commercial operation in Q4 2027 and will be the largest BESS facility on the east coast, providing capacity and peaking energy for the Boston grid.
The lenders. The construction loans, term loans, bridge loans and letters of credit came from a consortium of banks, with Nord LB, Santander and Société Générale as coordinating lead arrangers, Investec and East West Bank as joint lead arrangers, and Siemens Financial Services as a lender. The preferred equity came from funds managed by a credit asset manager the report describes as having more than US$350 billion under management, and two Fortune 500 companies committed to take a portion of the project's investment tax credits.
On the capacity figure. Flatiron lists the project's power capacity as 250 MW, but the report notes this appears to date from when the project was planned at 1,000 MWh; at the current 1,200 MWh and a four-hour duration the power rating would be around 300 MW. Energy-Storage.news flags the 300 MW as unconfirmed, so the firm figures are the 1,200 MWh of energy and the $850 million financing, not an exact power rating.
State context. Energizar was one of the projects selected in late 2025 under Massachusetts' Section 83E storage RFP, which picked 1,268 MW of storage; another Flatiron project, the 168 MW Salt Cod BESS at the former Montaup coal plant, was also selected. The state's Department of Energy Resources has since awarded about US$40 million to 36 projects through its Advancing Massachusetts Power Energy Storage grant program and issued a further RFP seeking 1,000 MW of BESS.
Source: Energy-Storage.news, "Flatiron Energy closes US$850 million financing for 1.2GWh Massachusetts BESS project" — https://www.energy-storage.news/flatiron-energy-closes-us850-million-financing-for-1-2gwh-massachusetts-bess-project