Community Public Forum: Questions and Answers

Charlton was not chosen so much as the Carpenter Hill Substation was. The 345 kV and 115 kV transmission lines meet there, and it connects eastern and western Massachusetts. We described it as an interchange on a highway, where voltage can be stepped up or down to serve the region. Battery storage fits best at a substation like this one. When we find a suitable substation, we reach out to the surrounding landowners to see whether any are willing to lease land to host a project.

We looked at substations across the market. A site has to meet three tests: a substation that can support storage, land that can actually be built on (many sites are wetlands or otherwise unbuildable), and a landowner who is willing to lease. Very few sites passed all three.

ESA did. We start by looking at the grid. When electricity prices swing up and down, that signals a need for storage to smooth them out. We are all part of one New England grid, so that need is regional. The substation here is also close to where the power lines already are, so it needs very little new infrastructure.

ESA develops the project. We find the site, design it, get the permits, and do the community engagement. We will not be the long-term owner. A company that can build and operate it will take it over, and no owner has been chosen yet. The permits, bonds, and agreements go with the project to that owner.

An owner could be a utility, an infrastructure fund, or an energy company. We cannot name any, because none has been selected. Owners earn money in three main ways: charging the battery when power is cheap and selling it when power is expensive, payments for being available when the grid needs backup, and services that keep the grid balanced second by second.

The leased project area would be about 15 acres, on a 47-acre parcel. The fenced equipment area inside it would be about 5 acres. The rest of the parcel is not part of the project area. We have not published lease terms.

The project is planned on leased land, not purchased land. Lease terms are not published.

A 150 megawatt battery energy storage system with about 600 megawatt-hours of storage, which is about four hours at full output. The latest design uses 136 battery units, down from 156 in July. It stores electricity from the grid and sends it back. It does not generate any power, and there is no solar or gas. It is not backup power for homes in an outage. It adds capacity to the grid, which matters most when supply is tight, such as during major storms or peak demand, and it helps keep voltage and demand steady.

No. Batteries can overheat in a chain reaction called thermal runaway. Early projects, built with older designs and chemistries before current fire standards, had more problems. The Electric Power Research Institute keeps a public database of failures at battery sites. It shows failures per unit of energy installed fell about 99 percent between 2018 and 2025, and the 2023 rate was comparable to the failure rate of utility transformers. The batteries proposed here use lithium iron phosphate, which has no cobalt or nickel. That chemistry is safer, not safe. Tesla's data sheet states the Megapack 3 has built-in fire detection, thermal management, and automatic shutdown, and Tesla has not yet published its test report. These features lower the risk, but they do not remove it. That is why the Emergency Action Plan matters.

Battery systems are tested to UL 9540A, the standard test method for thermal runaway fire propagation. It runs at four levels: the cell, the module, the full unit, and the installed layout. In the larger tests, a fully loaded unit is forced into thermal runaway, and the neighboring units, placed at the real spacing, are monitored to confirm the fire does not spread to them. NFPA 855, the national standard for installing these systems, uses these test results to set requirements such as the spacing between units.

The Megapack 2 and 2XL were tested this way, and the results are in the Fire Protection Engineering report in the Document Library. The test reports for the newer Megapack 3 are still being collected, and we will post them as they are released.

The most extreme fire test in the report on the Megapack 2 and 2XL, the earlier models, put a fully loaded unit into forced thermal runaway with its battery management and cooling systems turned off. Visible flames lasted 6 hours and 40 minutes, and flame intensity peaked about 60 to 90 minutes after flaming began. The fire stayed in one cabinet and burned about half of it. The report's fire modeling shows it would not spread to neighboring cabinets at the clearances studied. The unit was watched for several hours afterward, and no further fire was observed. The full report, Tesla Megapack 2/2XL Fire Protection Engineering (FPE) Report, is in the Document Library under Safety & Emergency Response.

This project is planned to use the Megapack 3, and its test reports are still being collected, so burn-time figures for this site have not been published. The Emergency Action Plan, being built with Charlton Fire, is where the response is written down. An independent reviewer the town selects will check it.

Fire experts advise against spraying water on a burning battery unit. The response being planned is defensive: keep people back, protect the surroundings, and monitor the air while the unit burns out. It is not "doing nothing." Firefighters would work to keep the fire from reaching anything else, and the test reports show why a unit can be left to burn out. In the most extreme test on the Megapack 2 and 2XL, the fire stayed in one cabinet.

Water is still used. It can cool equipment next to the burning unit. It is kept off the burning unit itself, because water that touches it can pick up contaminants. Any firefighting water used is captured on site.

Smoke from a battery fire can contain carbon monoxide and hydrogen fluoride, and even small amounts of hydrogen fluoride can be harmful. It is a real hazard close to the fire, mainly for firefighters and anyone nearby.

What has been measured at other fires is reassuring but limited. A September 2026 report by Fire & Risk Alliance, a fire engineering firm, reviewed air monitoring at seven U.S. battery fires. At the fires where air was sampled, including in nearby communities, nothing was found above public health limits. The report also explains why: hydrogen fluoride dissolves in water, sticks to surfaces and smoke particles, and is diluted by air as smoke travels. The incident review it draws on was commissioned by the American Clean Power Association, the industry trade group. These were other sites with other equipment, and the sampling covered air only, so this does not tell us what would happen here.

We have committed to publish a gas plume analysis, which looks at where smoke and gas could travel. We have not published it yet, so we cannot tell you that any road or home would be unaffected.

The Emergency Action Plan is where evacuation and shelter-in-place decisions belong. It is not published yet. Residents raised two specific problems at the public meeting: Route 20 backups on holidays and in snow that could slow fire trucks from other towns, and narrow rural roads with one way out. We wrote both down for the plan.

Three things are in progress. The Emergency Action Plan covers the response. The draft Community Benefits Plan proposes testing private wells within 1,000 feet of the work limit at the project's cost, with bottled water within 48 hours if a test shows a change linked to the site. It also proposes a payment if a home within 1,000 feet sells for less than an independent appraisal says it is worth without the facility. These are drafts and not promises yet.

The project's position is that fire equipment and training are a cost of the project, not something the town pays for. It is listed in the draft Community Benefits Plan for transparency. The plan is still a draft, so it is not a final commitment yet.

No equipment decision on suppliers has been made, and details will be confirmed in the filing with the state.

These were specific asks from a Planning Board member, and they are on our list. Testing each unit to the fire standard is routine. We told the committee member that testing the whole site as a system is best practice and should be in the plan. Replacement parts and recalls are also tied to the equipment warranty, which gives the owner a reason to stay with the maker. None of this is a commitment yet.

Since July, we have looked at two ways. One is moving the equipment on the site, which has mostly not worked for several reasons. The other is a different technology. We are watching sodium-ion batteries, which are promising on safety but are not yet available at scale. Any change in the battery technology would have to go back through approvals. Nothing is decided.

No study yet answers this for a fire. We have committed to a groundwater monitoring program with terms in writing before construction starts, and to publish the hydrology and stormwater studies. A well inventory within one mile is complete, and a door-to-door survey within half a mile is next. If you rely on a private well, send us your road so we can check it against the site plans, and we add wells to our list each time someone notifies us.

Trees slow and store water during a storm. Part of the area is already inside National Grid's easement. We have committed to no net increase in runoff and to no wetland fill. Soils on the site drain poorly, so water tends to run across the surface, and water also flows onto the site from the north. The design being developed uses basins on both the north and south sides, sized for storm events. We have not published the engineering numbers. Our mapping shows rain that lands on the equipment area draining south into a chain of wetlands. That covers surface water only. It does not tell us about groundwater.

Containing all of the site's runoff would have to be part of the filing. Staff also said we could show it in the site plan sooner. Firefighting water is already a commitment to capture on site on a hard surface, and so is runoff along the southern boundary. Whether the site needs a full liner is an engineering question for a geotechnical survey and is not answered here.

No. That spill is a different location and is not in the area this project is part of. We are sorry that your well was affected.

The state noise policy sets the limit. Sound from the facility may not be more than 10 decibels above the existing background sound at the property line and at the nearest homes. Meeting that limit is a condition of the state permit, and it binds any owner.

The first screening found that the two closest property lines, along the transmission line, would be above that limit. The closest dwelling to the equipment is the home of the landowner who is leasing the site to the project. The screening used stand-in equipment data, because sound data for the Megapack 3 is not available yet. The project is testing design changes to bring those property lines within the limit, including a sound wall. The full sound study will measure background sound at nearby homes and predict the sound level at each. It will be published, and its results, not the screening, set the design. Decibel figures mentioned at the meeting came from preliminary data and varied. The figures to rely on will come from the full study.

Three sources: the cooling heat pump in each battery unit, the inverters that convert the electricity, and the transformers that raise the voltage. Each cabinet has all three.

Construction is temporary, about 12 to 18 months, during the day. We will plan truck routes with the town.

Residents pointed to another town's storage project that has a sound barrier built in. This has been recorded as feedback. A sound wall is one of the fixes being tested.

The state looks at this directly. The census block group around the site scores 80.9 out of 100 on the state's burden measure, and anything over 75 is considered burdened. Drivers include the power plant, the gas storage, a closed landfill, a small spill, and the impaired Cady Brook. Our aim is for the project to add no burden, or to help reduce it. That is part of why the Community Benefits Plan exists.

There is no single score. The tool looks at several criteria, and the results are provisional until it is re-run on the full area. Two points matter most: there is no farmland within the project footprint, and the main tradeoff is trees, which store carbon and provide habitat. We are looking at clearing fewer trees or adding habitat elsewhere.

Each project is considered on its own merits, and we take cumulative burden into account. It is high for this census block. Storage is different from solar: it does not produce new power, but makes more efficient use of power already on the grid.

No. National Grid planned and carried out those upgrades for future use, and not for this project. National Grid does have to approve our connection, and it studies whether we can connect safely under its standards.

Three things bind any owner to this project. The conditions of approval attached to the state permit are legally binding on whoever owns the project. Each condition is enforced by the agency that covers it, and an owner who breaks one can be ordered to fix the problem and fined. A decommissioning bond is required before construction. And the Community Benefits Plan, plus any signed agreement with the town, goes with the project. Anyone who buys it sees all of this before they buy.

The owner is responsible, and the decommissioning bond is there so that money exists even if an owner fails. The bond is required before construction, and the amount is not set yet. A third-party engineer works out the cost of removal, with the town's review. Battery systems are modular, so removal is relatively simple. The site would be restored toward forest.

The bond is meant to be reviewed on a schedule, with an engineer reassessing the cost, and the owner is responsible for keeping it adequate. We have not published the review schedule.

Not decided. Residents asked, and we have written it down.

A resident asked whether ESA would put money in escrow for legal enforcement. We said it goes on the list. It is not decided, and anything that is committed will be in the Community Benefits Plan.

We cannot speak to other projects. We can say that the new state process we are following requires a community benefits plan, and our plan is a draft that you can comment on.

That is what the Community Benefits Plan is for. It is a draft with open decisions, and your comments can change it. Topics under discussion include payments to the town, fire equipment and training, senior center support, tree replanting, local hiring, and road bonding. The draft is at carpenterhillpower.com/benefits/plan, and comments are open into 2027.

PILOT stands for payment in lieu of taxes. A battery project loses value on paper as the equipment ages, so ordinary property taxes shrink over time. A PILOT sets a predictable payment each year instead. Developers like it for the same reason towns do: both know what to expect. The town negotiates it, usually through the town administrator, with the Select Board and Planning Board having a say. Other towns have agreed to 20-year terms.

We do not have a Charlton figure. Four Massachusetts agreements shown at the meeting, in Carver, Revere, Medway, and Chelsea, work out to roughly $8,500 to $11,300 per megawatt per year. That range is only for context, and it is not a promise or an estimate for Charlton. Our tax and assessment research is still open.

We have not promised any share of a household's electric bill. Rising electricity prices are a national trend driven by higher demand. Charlton buys power in bulk, so a benefit tied to bills would have to be negotiated with the town and with National Grid. At the public meeting this was raised as one idea. Nothing is agreed.

The regional grid operator decides, not ESA and not the state, and electricity goes to the nearest demand. The project is built to support the grid as a whole. It is not built to back up individual homes.

The state does not enforce it. The plan binds the project's owner. We are discussing putting some items into a community benefit agreement between the owner and the town, which would be legally binding on the owner.

The state does not require it. We expect a supplemental meeting before it goes to the state, so that Charlton has substantial input and a way to sign off. That is not decided.

Residents proposed solar and batteries for the senior center and the police and fire stations, ongoing well testing, an escrow for takedown and failures, property value protection, extending town water lines, and replanting 15 acres of trees elsewhere in Charlton. All of these are logged as input. None is decided, and the draft has 34 open decisions.

Residents in the 12:30 PM session picked their top benefit topics by phone. Money for the town budget drew the most picks, followed by fire equipment and training, conservation land and habitat, and help with home energy costs. The full results are in the session summaries at carpenterhillpower.com/documents/public-forum-sept-30-summary. The 6:30 PM session ran out of time for the activity. The activity is advisory only. It is not a budget and not a commitment.

No. This project has not been approved, and no permit exists. We are in the pre-filing phase, which is the best time to shape the design. The state's Energy Facilities Siting Board makes the final decision, with public comment and hearings.

Charlton's bylaw limits battery projects to 5 megawatts, and this one is 150. Because of its size, the project is reviewed by the state board, which can issue a consolidated approval covering some local permits. We know many residents object to that, and we have written it down.

The state's Intervenor Support Grant Program funds attorneys, expert witnesses, and other participation costs for eligible community groups, nonprofits, and towns, up to $150,000 per group for each proceeding. The state decides eligibility, and the process starts after the application is filed. Details are at mass.gov/info-details/intervenor-support-grant-program. We have also been asked to support the cost of a negotiator for the town, which is not decided.

The current proposal is 150 megawatts. A larger project, or a second one, would need its own state review with public comment and hearings.