The Expansion

What is the Medway expansion?

Exelon is expanding its existing Medway generating station by adding two new highly efficient electric generating units which will be capable of producing an additional 200 megawatts of electricity to meet New England’s energy needs in times of peak demand. The units, which are scheduled to begin operating in 2018, will be dual-fueled, meaning they can run on either natural gas or ultra-low sulfur diesel fuel. Natural gas will be the primary fuel. Ultra Low Sulfur Diesel will be used when natural gas is not available or only available at very high prices.

What’s currently in Medway?

Exelon Generation currently owns and operates the West Medway electric generating facility in Medway – a 3-unit oil-fired peaking power plant that produces 117 megawatts of energy. The plant began operating in 1970.

What equipment is being added at the Medway site?

The expansion will include the construction of two new electric peaking generating units. Specifically the units being added are General Electric LMS100 models – the most efficient electric generation peaking technology available. The GE LMS100 is the most efficient simple cycle technology available today. The units burn less fuel per megawatt hour than any other peaking machine on the market, and can start-up and begin producing electricity to meet demand in less than 10 minutes.

Why build it here?

The existing Medway site is an ideal location to add energy generating capacity for a number of reasons. There is already an energy facility at the site that’s been operating since 1970. In addition, the site has access to water, sewer and natural gas lines as well as existing access to transmission lines.

What are the advantages to the local community?

In addition to enhancing the region’s overall electric system, by providing a quick-starting generation source using the latest and cleanest technology available, the local economy will benefit significantly from the expansion of the Medway facility. The expansion will mean up to 200 jobs during the peak of construction, and four to six full-time positions once the plant begins operation. The expanded facility will also have a significant positive impact to the Town of Medway’s property tax base, moving the Medway facility from the second largest property tax payer in the Town to the largest. Exelon is also working with the Town of Medway on a Community Host Agreement that can provide economic benefits to the Town.

What’s the project schedule?

We are still in the early stages of project development. Currently Exelon is applying for the numerous permits required from state and local agencies which includes the Massachusetts Environmental Policy Act (MEPA), the Department of Environmental Protection (Mass DEP), the state’s Energy Facilities Siting Board (EFSB) and the local Conservation Commission. As part of the permitting process, residents will have numerous opportunities for input. Our plan is to begin construction as soon as Fall 2016 and have the new units in operation by June 2018.

Who is Exelon Generation?

Exelon Generation is a business unit of Chicago-based Exelon Corporation, a leading U.S. competitive energy business. Exelon Generation operates one of the nation’s cleanest and lowest-cost power generation portfolios totaling more than 32,000 megawatts across the US. We also own and operate a balanced mix of generation sources across the U.S. including nuclear, natural gas, oil, hydro, wind and solar. Exelon Generation also owns and operates generating plants in Framingham and the Boston area.


Why do we need more power?

Due to upcoming closures of older, less efficient power plants, there is a need for future new electricity generation during peak demand times in New England. The Medway expansion will help ensure that energy will be there to turn on lights and computers and heat and air conditioning and avoid brownouts.

How much energy will the Medway expansion produce?

The two-unit expansion at the Medway facility will be able to produce 200 megawatts of electricity. Generally speaking, that’s enough power to meet the energy needs of about 200,000 homes.

What does peaking mean?

Plants such as the one in Medway are called “peakers” because they only run when demand for electricity is unusually high – during “peak” demand times such as very cold winter or very hot summer days. Both the existing Medway facility and the new Medway expansion are peakers, so they do not run often.

How do peaking plants support renewable energy?

As renewable energy becomes more available in Massachusetts, peaking plants provide a reliable back-up energy source. Because renewables such as solar and wind are intermittent, another source needs to be available when renewables cannot produce power. Peaker plants react quickly to meet demand and provide energy to customers when renewables are unavailable.

Where does the energy generated in Medway go?

Power generated by the Medway facility, like power from most New England generating facilities, is sold to the New England ISO (Independent System Operator) which manages bulk electric power and transmission in New England.

Sound and Visuals

Won’t you be able to see the stacks and expansion from miles away?

No. The noise wall and stacks will not be visible to most neighbors due to topography and wooded buffer areas. The fact is that you can’t see the existing transmission towers on the Medway property now, you will not be able to see the new stacks after the expansion.

Will Exelon have to buy more land for the expansion?

The expansion will be built on the existing Medway plant site. The overall site is 94 acres, with 54 acres operated by Eversource under easements for its transmission and switchyard facilities. The expansion will be built on approximately 10 of the remaining 40 acres on the existing site.

Will there be increased noise as a result of the expansion?

While it’s been in operation for more than 40 years, the existing Medway facility has been a significant but relatively quiet member of the community. With the two-unit addition that will not change. To ensure the project meets all state and local standards, the expansion will include the addition of a 55-foot sound wall around the new units as well as the addition of sound reduction equipment.

How tall with the new emissions stacks be?

The two new emissions stacks will be 160 feet tall – the same as the existing Eversource transmission towers adjacent to the Medway plant.

How does that compare with the existing stacks?

The existing emission stacks at the West Medway plant are approximately 65 feet tall. The new stacks will be taller in order to meet both emissions and noise regulations.


What is the fuel source for the expansion?

The primary fuel source for the new units is natural gas. As a back-up, the new units can also run on ultra-low-sulfur-distillate fuel oil, which is the same oil currently used as a fuel source for the existing Medway generating units and used in oil furnaces in many homes. Having two possible fuel sources means the plant will be more reliable since if one fuel source is not available or overpriced, there’s a back-up alternative.

Is Exelon required to have back-up oil capability?

Rules governing the New England regional power grid, as approved by the Federal Energy Regulatory Commission (FERC), require “peaker” power plant owners such as Exelon, to produce and deliver electricity when it’s called upon by the Independent System Operator (ISO), which runs the New England grid, when it’s needed to meet peak energy demand.

This obligation to produce electricity when called upon (called a “performance obligation”) is not excused when our fuel of choice (natural gas) is unavailable. Failure to meet this performance obligation results in the imposition of severe penalties.

To assure compliance with this performance obligation, and to avoid penalties, Exelon has chosen to use oil as the back-up fuel for the proposed expansion.

Why oil as a back-up?

From time to time, the availability of gas may be constrained. For example, during periods or severe cold weather, limited natural gas supplies will generally first be allocated to heating homes and businesses. By switching to oil at such times, the Medway facility can continue to provide reliable electric power while helping to make more natural gas available for heating use.

Wouldn’t it be more cost-effective to make the plant natural gas only?

The Medway facility will have an obligation to provide power when called upon and to help meet the region’s power needs. To effectively meet its obligations it is important to have more than one fuel source. In addition, the systems that safely handle oil are already in place at the facility, and will be expanded to accommodate the new tank.

How often will the new units run on oil?

Because the existing and new units are “peaking plants,” they only run at times of peak demand. As a result, permits Exelon is seeking for construction and operation of the plant will allow the additional generating units to run a maximum of 60 percent of the available hours in any given year. Of those days, Exelon is proposing the units could run a maximum of 30 days per year using oil.

When would the units run on natural gas versus oil?

Natural gas is the primary and preferred fuel source to run the plant. During times of high natural gas demand the supply of gas can be constrained and Exelon may exercise the option to switch to oil. To reduce impact on air quality, Exelon is committed to not run the new units using oil during the ozone season months of May 1 to Sept. 30.


What’s being done to reduce emissions for the expansion?

The equipment to be added for the expansion will feature clean-air technologies including water injection, Selective Catalytic Reduction (SCR) and oxidation catalyst, to control emissions of Nitrogen Oxide (NOx), Carbon Monoxide and volatile organic compounds (VOCs). The units at Medway will comply with all state and federal emission regulations.

Will Greenhouse Gases increase?

By displacing older, less efficient generating facilities, the Medway expansion will help reduce greenhouse gas emissions in New England and will be one of the cleanest peaking plants of its kind in the nation. Again, to reduce impact on air quality, Exelon is also committed to not run the expanded units using oil during the ozone season of May 1 to Sept. 30.

The expanded plant will include a million gallon oil tank – what protections do you plan to ensure that oil is being safely stored?

The new oil tank will be surrounded by an impervious berm, extending roughly fifty feet from the tank in all directions, to provide full secondary containment. The tank itself will need a construction permit and a periodically renewed use permit under Mass Department of Public Safety regulations and will require inspection every five years in accordance with state standards. The Town of Medway Fire Department also issues annual renewals of permits for any flammables at the site including oil tanks.

Doesn’t adding a plant with oil as a possible fuel source run counter to the state’s efforts to move to renewable energy sources?

On the contrary, peaker units fueled with natural gas or backup oil in winter are the perfect complement to renewable sources of energy. The Medway expansion project will participate in the Regional Greenhouse Gas Initiative (RGGI) and will be required to purchase allowances for each year of operation for each ton of CO2 emitted.

What is water for the expansion being used for?

The new units are designed to minimize water use, and water will primarily be used just for controlling emissions. The plant’s equipment will be cooled using fans.

Will water for the expansion come from Medway?

No Medway municipal water will be used for the expansion. Water for the expansion will come from a combination of onsite wells and backup water sources from neighboring municipalities.

How does the expanded Medway plant compare to other fossil-fuel technology options?

As part of studies conducted for the proposed expansion, the LMS100 technology proposed at the Medway site was compared with other fossil-fuel generating technologies. Based on reliability, cost, diversity of supply and environmental impact, it was concluded the Medway expansion contributes to a reliable, low-cost, diverse regional energy supply with minimal environmental impacts.

Additional Information

How do I get more information?

Please contact Mark Rodgers, Communications Manager, Northeast Region, at 617-699-6327.

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