Crews in Kendall Square are putting the finishing touches on the shell that will house what developers say will be the country’s largest underground substation when completed in 2029. The 35,000 square-foot substation will be the centerpiece of the $1.84 billion Greater Cambridge Energy Program (GCEP) infrastructure project led by the utility company Eversource to increase both the reliability and capacity of the city’s electrical grid.
Showing members of the media around the structure July 22, Eversource officials said the project was intended to support Cambridge’s long-term electrification targets. “The goal [of the GCEP] is to have the capacity for all residents to convert to electric heat pumps, as well as to provide for EV charging and the electrification of commercial development,” said Maija Benjamins, director of strategic planning development at Eversource.
Electric heat pumps provide both heating and cooling through the use of electricity, reducing the environmental impact of non-electrical HVAC units that release carbon into the atmosphere. Benjamins envisioned 2050 as a target horizon for achieving the ambitious electrification goals.
Substations act as buffers between high-voltage electrical sources, like transmission lines from the regional power grid, and the lower-voltage distribution lines that deliver electricity to homes and businesses.
There are currently three active substations in Cambridge, with the Union Square Substation in Somerville also serving parts of central Cambridge. As East Cambridge’s commercial base continues to grow, the new substation will work to feed the increasing electrical demand.
Beyond expanding capacity, Eversource Program Manager Ken Roberts explained that the GCEP will create a far more interconnected system that would allow stations to balance their electrical load and provide flexibility if problems arise at any one station.
The Putnam and Somerville substations, for instance, have both had to add additional transformers in recent years as interim measures to relieve the overburdened East Cambridge substation, but they are both now out of space to add more capacity.
The substation, 105 feet below the surface at its deepest point, will be housed within the shell, already mostly built by real estate-giant BXP. BXP’s Jeff Lowenberg added that the station would also help meet the needs of Kendall Square’s expansive and growing “life science research” community. Already, BXP’s mixed-use project, which sits atop the new substation, includes an AstraZeneca life sciences building that has recently begun welcoming employees. The space will eventually also include a public park and a clean-energy residential tower that, at 37 stories tall, is set to be the tallest building in the city.
Eversource will receive the shell from BXP next spring, and the work will transition to bringing online three transformers and connecting them with the city’s grid. A fourth transformer is planned to be introduced around 2040. In practice, one transformer will always be on standby to fulfil needs as required, so the active capacity for the near future will be 180 Mega Volt-Amperes, the measure of apparent electrical power in an electrical system.
That would make it the city’s second largest substation by active capacity, behind only the Putnam station, whose capacity is currently at 211 MVA. A 2025 Eversource report to the city’s Planning Board projected that by 2031, the demand on the Kendall Square Station will be equivalent to 120 MVA of capacity, with a lessened demand on surrounding substations.
Robert Simha, vice president of the East Cambridge Planning Team and former director of planning at MIT, said that Cambridge is not a city that “plans on an integrated basis.” This to him is the reason for the new site – a response to years of overburdening the city’s current electrical grid.
Construction has also begun across the city on the duct banks that will house 8.3 miles of new transmission lines being installed to link the Kendall Square substation to surrounding electrical stations in Cambridge, Brighton and Somerville.
The transmission routes became the project’s main source of contention during the approval process. MIT challenged the preferred alignment near its campus on Vassar Street, arguing that alternative routes would reduce impacts on the university’s operations. The state’s Energy Facilities Siting Board ultimately approved Eversource’s proposed routes.
Roberts said construction on these new lines was “25 to 30 percent complete,” with the Kendall Route — running from the station to the East Cambridge substation — “significantly complete.” Duct bank work, which has already disrupted several roadways in the city, will run through 2028.
No less of a source of controversy was the originally planned location for the station, above ground in a residential neighborhood at 135 Fulkerson Street and right beside the Kennedy-Longfellow school. BXP proposed the current underground space in response to the controversy, winning approval from the Cambridge Redevelopment Authority and the City for 800,000 square feet of additional space for commercial development in Kendall Square’s mixed development zone.
“The [new] location was a function of the fact that, in desperation, [BXP] bought this property on Fulkerson Street, and that just started a very hot war with the neighborhood,” said Simha.
Benjamins confirmed that the 135 Fulkerson space will be open in the future to new development, but that it would be held by Eversource to keep its construction materials and tools for its Kendall Square work until it is finished.
While the work excavating the pit was no different than it would be for an underground parking lot, the process of building out the structure was flipped on its head. Instead of digging the space out and building from the bottom up, BXP first installed 120-foot-deep steel columns and steel-reinforced concrete slurry walls into the ground before digging the rest out and adding four “major” floor slabs. This technique was used to mitigate the pressures of the dense urban environment surrounding the buildout.
Maintenance will be a bit more expensive than it would be for an above ground facility, said Roberts, but to him it was a trade-off for having less of a “visual impact” on the city around the station. While representatives did not have an exact number for how much more it will cost, Roberts pointed to a far more complex HVAC system and an elevator to transport building materials and equipment as examples of additional infrastructure that would not be necessary in above-ground facilities.
A maintenance hatch and two large intake and exhaust air shafts will also be added, with the latter designed to blend into the planned park above the station.
Benjamins said that Cambridge residents served by the new substation in parts of South and East Cambridge will likely see a short-term spike in their electric bills as the station goes operational, though she also stated that the “ultimate goal,” given the additional buildings that will offset the potential rate impact, was to have rates come down in the future. Exact costs will be decided by a regulatory committee once the project has been completed.
Simha has spoken with residents who are starting to sound the alarm over energy bill increases, so he believes the rate increases will both be a short- and long-term problem for residents. “It is going to be a mess here for a very long time.”
John Hawkinson contributed reporting to this article.
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