Northfield Mountain LLC - Franklin County - ISONE
Northfield Mountain is an operating four-unit, 1,168 MW pumped-storage plant built underground beside the Connecticut River in Massachusetts. FirstLight operates the facility, which can generate at full output for about 7.5 hours. The plant continues to operate under annual federal licenses while relicensing is pending.
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Canonical EIA plant baseline.
plant-547
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Operating generator records and technology attributes reported through EIA-860.
| Generator | Capacity | Technology | Operation | Status |
|---|---|---|---|---|
| 1 | 292 MW 292 MW summer | Hydroelectric Pumped Storage Water · PS | Feb 1973 | Operating |
| 2 | 292 MW 292 MW summer | Hydroelectric Pumped Storage Water · PS | Oct 1973 | Operating |
| 3 | 292 MW 292 MW summer | Hydroelectric Pumped Storage Water · PS | Jul 1973 | Operating |
| 4 | 292 MW 292 MW summer |
Monthly EIA generation history and recent market-resource behavior where linked telemetry is available.
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Source-backed project transactions, agreements, land records, permits, and environmental disclosures. Portfolio and adjacent-project facts remain explicitly scoped.
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Project milestones and public references behind the asset profile.
FERC issued the original license for the Northfield Mountain Project (Project No. 2485).
| Nov 1972 |
| Operating |
EIA-923 reports gross generation and net grid exchange for storage plants. Gross generation is shown as a discharge proxy; it is not a cycle count or conventional capacity factor.
| Largest reported plants | Capacity | State | |
|---|---|---|---|
| Northfield MountainCurrent | 1,168 MW | MA | |
| Cabot | 61.8 MW | MA | |
| Turners Falls | 5.7 MW | MA | |
| NFM Solar Power LLC | 1.9 MW | MA |
Portfolio membership follows the latest EIA-860 reporting entity. It does not imply ultimate ownership.
View full reporting portfolioEIA-860 lists generator 4 with this operating date.
EIA-860 lists generator 1 with this operating date.
EIA-860 lists generator 3 with this operating date.
EIA-860 lists generator 2 with this operating date.
Energy Capital Partners agreed to purchase Northeast Utilities' competitive-generation portfolio of 15 plants (14 sites, 1,442 MW total), including Northfield Mountain (1,080 MW), for $1.34 billion, assuming $320 million of debt. Transaction expected to close by end of 2006.
Units 2, 3, and 4 began efficiency improvements with turbine-runner replacement and motor-generator rewinds, continuing through 2014.
PSP Investments announced a definitive agreement to acquire ENGIE Group's (formerly GDF SUEZ) New England hydroelectric portfolio (1.4 GW total) for US$1.2 billion enterprise value, including the 1,168 MW Northfield Mountain facility.
Original FERC license for Northfield Mountain (Project 2485) expired. Facility continued operating under annual licenses pursuant to Section 15 of the Federal Power Act during relicensing proceedings.
FERC approved transfer of the Northfield Mountain project license from FirstLight Hydro Generating Company to Northfield Mountain LLC.
Northfield Mountain LLC and FirstLight MA Hydro LLC filed amended final license applications for the Northfield Mountain and Turners Falls projects.
FirstLight and stakeholders entered into an Agreement in Principle covering relicensing measures for Northfield Mountain and Turners Falls projects, which had been operating on annual licenses since April 30, 2018.
FirstLight filed a Flows and Fish Passage Settlement Agreement with FERC for Northfield Mountain and Turners Falls projects, committing to over $350 million in combined environmental and operational measures, including approximately $152 million for state-of-the-art fish-passage facilities.
Answered from the published record above. Questions whose inputs this profile does not carry are omitted rather than estimated.
Northfield Mountain has a reported capacity of 1,168 MW. Source: EIA Form 860M.
Northfield Mountain is a Hydroelectric Pumped Storage facility in Franklin County, MA, participating in the ISO-NE market.
Northfield Mountain is in Franklin County, MA, inside the ISO-NE balancing area.
Northfield Mountain is operated by FirstLight Power Resources, Inc. - MA according to the EIA generator inventory. Reporting membership does not by itself establish ultimate ownership.
Northfield Mountain reported 887.4 GWh over the twelve months to 2026-04. For a storage plant this is reported gross generation — a discharge proxy, not a cycle count or a conventional capacity factor.
By capacity, Northfield Mountain ranks #6 of 39 operating plants of the same technology nationally. It ranks #1 of 2 in MA.
Plants within 25 km, nearest first, regardless of technology. Proximity is straight-line distance between mapped plant coordinates; it does not by itself establish a shared point of interconnection.