Exelon works 200-MW West Medway II project through Massachusetts siting process

Two Exelon Corp. (NYSE: EXC) subsidiaries on Sept. 30 filed with the Massachusetts Energy Facilities Siting Board a Draft Environmental Impact Report covering the gas-fired, 200-MW West Medway II Project, which would involve expansion of an existing power plant.

Exelon West Medway LLC and Exelon West Medway II LLC had filed in March for approval of this project, which would be a fast-starting peaking plant located at the existing West Medway Generating Station property located in Medway, Massachusetts. The new facility would operate during times of peak energy demand and would run primarily on natural gas, but could also run on ULSD fuel oil, ensuring fuel diversity and reliability. Use of ULSD will be limited to an equivalent of 30 days/720 hours per year.

Exelon’s existing 135-MW West Medway power plant is located on the northeastern portion of the Summer Street site. The western half of the Summer Street site is occupied by two Eversource switchyards (one 345 kV, one 115 kV) and associated transmission rights of way.

The proposed project will include:

  • Two simple-cycle General Electric LMS100 combustion turbine generators (CTGs);
  • Pollution control equipment including Selective Catalytic Reduction (SCR) and carbon monoxide (CO) oxidation catalysts in modules downstream of each CTG;
  • Two 160-foot-tall exhaust stacks;
  • Natural gas compressors;
  • Aboveground storage tanks for ULSD, service/fire water, demineralized water and aqueous ammonia, including unloading areas;
  • Transformers and electrical interconnection facilities;
  • Combined ~15,000 square foot building for control room, administrative and facility services, maintenance and warehouse area, water treatment area, and associated systems;
  • 450 kW emergency diesel generator;
  • 147 kW emergency diesel fire pump engine;
  • Gas pipeline interconnection (3,080 feet); and
  • Stormwater management system.

Project will meet ISO New England needs

Said the draft report: “The Proposed Project is intended to provide additional needed capacity to the Southeast Massachusetts–Rhode Island (‘SEMA/RI’) load zone in the ISO New England electric grid, to help meet energy demand during peak times. The Proposed Project will also enhance the region’s overall electric system and support the growth of renewable energy in Massachusetts by providing a quick-starting back-up for intermittent renewable energy sources such as solar and wind.

“One of the markets that ISO-NE operates is the Forward Capacity Market (‘FCM’). The Forward Capacity Market is a long-term wholesale market that assures resource adequacy, locally and system-wide. The market is designed to promote economic investment in supply. Critically, in exchange for capacity payments, a generating resource has an obligation to be ready to run and produce power when called upon. Long-term capacity markets such as the FCM provide economic incentives to attract investment in new and existing resources to achieve power system reliability requirements. In the FCM, ISO-NE holds an annual auction in which suppliers compete for the opportunity to meet New England’s projected electricity demand three years out. Suppliers with the lowest price offers ‘clear’ the auction and will receive capacity payments, which resources rely on for a stable revenue stream to maintain their viability.

“In the 2018-2019 forward capacity auction that occurred in February of 2015 (FCA # 9), ISO-NE introduced a modification to help to ensure a more reliable and more flexible fleet of power supply resources. The principal change made to the FCM is called ‘Pay-for-Performance’. ISO-NE determined that the market was not providing sufficient incentives for resource performance (i.e., availability) during the winter when natural gas delivery is constrained. This resulted in resources that sometimes failed to produce energy when it was needed most by the region, which posed a serious threat to the electricity grid’s reliability.”

Natural gas for the project will be delivered via an interconnection to the Algonquin Gas Transmission Co. (AGT) pipeline.

To interconnect with Eversource, Exelon will construct one approximately 1,200-foot, three-phase 115 kV overhead circuit from a circuit breaker at a GSU transformer to be connected to Eversource’s 115 kV SEMA/RI switchyard (Station #65) to the southeast of the project site. Eversource will distribute this power through its existing yard and into its bulk transmission system. At present, it is Exelon’s understanding that no off-site changes or upgrades need to be made to the Eversource transmission system to accommodate the project.

The draft study said that project construction is scheduled to begin in fall 2016 and continue for 17 months. The project is required to commence commercial operation no later than June 2018. The physical lifespan of the project is anticipated to be 40 to 50 years (or more).

About Barry Cassell 20414 Articles
Barry Cassell is Chief Analyst for GenerationHub covering coal and emission controls issues, projects and policy. He has covered the coal and power generation industry for more than 24 years, beginning in November 2011 at GenerationHub and prior to that as editor of SNL Energy’s Coal Report. He was formerly with Coal Outlook for 15 years as the publication’s editor and contributing writer, and prior to that he was editor of Coal & Synfuels Technology and associate editor of The Energy Report. He has a bachelor’s degree from Central Michigan University.