The Mystic Generating Station really is the grande dame of the Boston area power plants and is a major feature of the Boston area skyline. Almost all I-93 commuters know this plant as a major landmark and there are many hilltops in the Northern and Western Boston suburbs that offer a great view of this plant (like near the top of the hill on Rt. 2 in Arlington Heights). This plant is particularly interesting given its history and unique fuel arrangement.
In the late 1950s, Boston Edison constructed three ~ 156 MW natural gas fired units, named Units 4-6. Prior to this, Boston Edison operated three small units at the site, named Units 1-3, but these were decommissioned long ago. In 1975, Boston Edison built Unit 7 which is a 577 MW load following dual fuel (gas/No.6) unit. Unit 7 can be identified by the tallest smokestack at the site and its construction began after the adjacent Distrigas Liquefied Natural Gas (LNG) facility came online in 1971. The entire facility was sold off by Boston Edison during deregulation and was purchased by merchant generator Sithe Energies.
Sithe Energies commenced a major investment in the plant in 1999 and contracted with Raytheon Engineers & Constructors to build a new 2,000 MW combined cycle natural gas generating facility at the site. In 2000, Raytheon sold their EPC business to the Washington Group, who subsequently declared bankruptcy. The project was mired in controversy, but Raytheon was contractually responsible for the completion of the project despite the Washington Group bankruptcy. Raytheon delivered on their contractual obligations and in 2003, Units 8 & 9 went into service. Both units consist of two combustion turbines mated to a steam turbine which recovers the waste heat. Units 8 & 9 are easy to spot because they have the shortest smokestacks and the warning lights for aircraft on these stacks are white, not red.
In 2003, Sithe Energies was acquired by Exelon. Unfortunately, Exelon soon ran into serious financial difficulties with its financing of the plant and transferred ownership to its lenders. The consortium of lenders, led by BNP Paribas, took ownership of the plant and subsequently sold it to US Power Generating. In 2010, US Power Generating's subsidiary, Boston Generating ran into major financial difficulty and was forced to declare Chapter 11 bankruptcy. Its capital structure had become completely untenable after ISO-NE power prices crashed in 2009 due to the large increase in natural gas supplies attributable to fracking. In 2010, the plant was sold to Constellation. Constellation and Exelon subsequently merged in 2012 and the plant is now back in its former owner's hands.
Although Units 4-6 were retired in 2003, Units 7 - 9 are a critical component of the grid in the NEMA zone. There is also a tiny 10 MW distillate fired jet engine at the facility, but it only turns on a few hours a year when power supplies are extremely tight. Unit 7 tends to run around 10% of the time, generally when power prices are high. Units 8 & 9 currently have a capacity factor around 60%, but they can be expected to be running as much as possible during the summer and winter months when demand is highest. In higher priced ISO-NE environments (e.g., 2008), Units 8 & 9 have had capacity factors near 90%.
The economics of Units 7-9 are very unique in that they are cut off from the New England natural gas pipeline network. Their sole source of gas supply is from the LNG delivered to the Distrigas facility. This gas is procured under a long term contract that runs through 2027 and therefore, these units have very different economics than their peers in the ISO-NE market. This dependence on LNG as a fuel source does carry some risk, as many were worried in the summer of 2012 about the impacts to the ISO-NE grid caused by LNG shipment disruptions due to unrest in Yemen. In essence, if Distrigas can't get LNG, then the Mystic Generating Station can't get gas, and the NEMA zone on the ISO-NE grid won't have enough power. In summary, not only is this plant a key part of the Boston skyline, its also a vital source of supply for the NEMA zone in the ISO-NE grid and is one of the more unique plants in the region.