New England utility closes import-dependent gas-fired power plant, keeps LNG import option

On May 31, Constellation Energy retired the natural gas-fired Mystic Generating Station it owned and operated. Mystic was one of the oldest U.S. electric power plants, located in Charlestown, Massachusetts, on the north side of Boston.

Constellation also owns and operates the adjacent Everett liquefied natural gas (LNG) terminal, which supplied 100% of Mystic’s natural gas. Constellation will keep the Everett terminal open through winter 2029–30 to serve other customers in New England under new six-year supply contracts. Excelerate Energy’s Northeast Gateway, located 13 miles offshore of Massachusetts, can also receive LNG for delivery into New England.

With 1,413 megawatts of combined-cycle gas turbine (CCGT) capacity, Mystic was the largest natural gas-fired power plant operating in the region managed by the Independent System Operator New England (ISO-NE). Mystic has delivered electricity to the Boston metropolitan area since the 1940s with simple-cycle petroleum- and natural gas-fired units. When the simple cycle units retired in 2003, the Mystic facility generated power from two CCGT units.

In 2018, Mystic’s then-owner Exelon filed plans with ISO-NE to retire the plant by June 1, 2022, stating that the plant could no longer operate profitably. In response, ISO-NE established that the CCGT units at Mystic were critical for fuel security and system reliability in the Boston metropolitan area and required that the plant remain available from June 1, 2022, through May 31, 2024.

After its initial filing for retirement in 2018, the Mystic CCGT plant operated at low levels, generating only around 20% of its rated capacity. For the past five years, Mystic served as a peaking plant, running mainly during peak-load periods in the winter and summer when there was the most demand for space heating and air conditioning.

Constellation Energy had planned to also close the Everett LNG regasification terminal along with the Mystic plant because it was built to supply Mystic’s natural gas needs. The Everett facility can also supply other customers with both LNG by truck and as regasified natural gas delivered to the Algonquin Gas Transmission and Tennessee Gas Pipeline interstate systems.

The possible loss of natural gas from the Everett facility concerned ISO-NE and others about the availability of supply around Boston, particularly during the winter and other peak periods of natural gas consumption, and about the potential for high natural gas prices. Natural gas and electricity price spikes in New England in the winter are common because pipeline constraints often limit deliveries of natural gas into the region and to power plants.

In May, the Massachusetts Department of Public Utilities approved new long-term supply contracts with three New England utilities—National Grid, Eversource, and Unitil—to supply natural gas from June 2024 through May 2030. These new contracts permit Constellation Energy to keep the Everett facility open. The agreements provide each company with seasonal (November–March) natural gas supply through the Everett LNG terminal.

The United States imports less than an average of 0.1 billion cubic feet per day (Bcf/d) of LNG a year, and almost all of those imports are delivered into New England between November and March. In 2023, all of the 13.3 Bcf of LNG imports into New England were delivered to the Everett terminal. The other terminal that can supply New England, Northeast Gateway, last received LNG during winter 2021–22, with two cargoes that totaled almost 3 billion cubic feet (Bcf).