The company building a giant battery storage plant at 284 Eastern Avenue in Chelsea says it has lined up about $850 million to pay for it, and that the project, called Energizar, will be the largest battery storage system on the East Coast when it starts running at the end of 2027.
Flatiron Energy announced on October 15 that it had closed the financing for the 1,200-megawatt-hour project, according to pv magazine USA and other energy trade publications. The money is a package of construction and bridge loans, term loans, letters of credit, a preferred equity investment and an agreement by two Fortune 500 companies to buy part of the project’s federal tax credits. Nord/LB, Santander and Societe Generale led the lending, joined by Investec, East West Bank and Siemens Financial Services.
Flatiron says the batteries will store electricity and send it back to the grid when demand peaks, cutting the Boston area’s reliance on fossil fuel power plants at those times. The company is aiming for commercial operation in the fourth quarter of 2027.
Bigger, and later, than in July
The numbers have changed since the summer. In July, Eversource, National Grid and Unitil filed long-term contracts with three battery projects, and those filings listed Energizar at 250 megawatts and 1,000 megawatt-hours, with operation starting in the second quarter of 2027, according to Utility Dive. The October announcement puts the project at 1,200 megawatt-hours, gives no megawatt figure and pushes the start back two quarters. It does not explain the changes or say whether the utility contracts changed, as the trade site mgrid.org pointed out.
The same round of contracts included a far larger battery nearby: Jupiter Power’s Trimount project in Everett, at 700 megawatts and 2,800 megawatt-hours.
What Chelsea approved
The project came to Chelsea’s boards as Energizar Storage LLC in 2024. The original plan put the batteries inside a building. In February, the Planning Board took up a change that eliminated the building and instead placed the battery units in separate outdoor enclosures behind a wall. The Zoning Board of Appeals and the Conservation Commission had already found the change minor.
Hunter Prange of Flatiron told the Planning Board on February 24 that the wall would be 20 feet high, that a living green wall had been ruled out because it could catch fire, and that the company was considering murals and landscaping to break it up. He said the gate would open only with a badge, the Fire Department would get a key, and the company was talking with a camera supplier about giving police access. One or two people would be on site for maintenance, he said, but not around the clock.
Board member Sarah Ritch raised concerns about the side facing the commuter rail tracks, where Prange said there would be a 10-foot chain link fence, and about the site having no roof. Prange said the batteries sit in metal containers, so stray embers should not be a problem, and that the company would train regularly with the Fire Department. Asked what happens when the batteries reach the end of their life, he said the land is not contaminated, the batteries would not contaminate it and the only liquid on site would be transformer oil, with pits built to catch any leak. He said a substation next door makes the site attractive for energy companies.
Member Eric Czernizer said he supported the project but called it “an extremely different change” and argued it should count as a major one. He changed his vote, and the board approved the change as minor, 5-0, with a lattice design for the wall and an opaque wall along the railroad side. No one from the public spoke.
Several city councillors have raised concerns about the site, according to the minutes of the council’s Public Safety subcommittee in April. Fire Chief John Quatieri told the subcommittee the battery site is in the response area of the Mill Hill fire station, not Central Station.
Graphic: chelseamass.net.