Submarine cable installations make landfall

After years of work — from civic engagement and environmental discussions to construction and underwater drilling — a two-part cable installation project to deliver more power to the Island is almost complete. 

Installation of the cables was finished this week, though the new cables aren’t expected to come into service for a few months.

Called the Martha’s Vineyard Reliability Project and 91 Replacement Cable Project, the initiatives promise to deliver cleaner energy and substitute on-Island diesel generators, as well as increase resiliency and reliability in the Island’s energy service. Advancement of the work was encouraged by faults in one of four submarine cables that run from Falmouth to the Island and power Martha’s Vineyard, as well as by a countrywide increase in energy demand.

The project for the Island are being carried out by Eversource, Martha’s Vineyard’s utility company, and barges at work to lay new cables on the sea floor have been visible off Tisbury Harbor over the past few weeks. The Island is currently powered by four submarine cables, but through the project, Eversource replaced the 91 Line, which was built in 1986 and experienced multiple faults over the years — one as recently as July 2021 — and added a fifth, 23-kilovolt cable to meet forecasted energy demand. 

“It’s a major step toward a modern, resilient, and sustainable energy future on the Island,” Matthew Biron, director of transmission project management and construction at Eversource, said.

Between the two new cables, there’s an additional 37 megawatts of energy for the Island; the new cable adds 25 megawatts of new capacity, and the replacement cable, which also has a 25-megawatt capacity, is an upgrade from the old 13-megawatt cable.

Part of the goal of the project is to deliver clean power to the Island, and so the addition of the fifth cable also allowed Eversource to decommission diesel generators in Oak Bluffs, which were more than 80 years old, and were used to supplant increased energy demand in the summer months. The contract for the diesel generators, which use fossil fuels, was terminated on Sept. 31, and enabled the utility company to transition the Island away from old fossil fuel equipment. The Island instead can be further supported by the regional grid and the energy purchased by Eversource from the grid.

“Those are completely shut off,” Biron said about the generators. “All five have been fully retired, removed, and sold, and the sites have been remediated.”

And not only do the new 23-kilovolt cables equalize the loss of the diesel generators, but Biron said the project promise to increase capacity based on forecast energy needs, such as from an increase in electric vehicles, heat pumps, and people.

The project is part of a larger effort by Eversource, buoyed by the energy goals of both states and communities like Martha’s Vineyard, to increase energy capacity and reliability as well as utilize clean sources. “We’ve also made significant upgrades across the Island to support this transition, including reconductoring and pole replacements, particularly in Oak Bluffs,” Olessa Stepanova, communication director for Eversource, said in July in an email to The Times.

“Additionally, a new underground cable supply is being installed from Edgartown–Vineyard Haven Road to State Road,” she added at the time.

Plans took years to develop — eight years, in fact. Onshore construction started in 2023, and further underwater work and drilling took place last winter, but the actual cable-lay between Falmouth and Martha’s Vineyard took only about two days. Physical installation of the new 6.1-mile cable across the seabed from Falmouth to East Chop in Oak Bluffs was completed Dec. 9, and the plan was to have the 5.5-mile replacement cable, connected at Eversource facilities in West Chop in Tisbury, also installed a week later. Weather delays, however, hampered their efforts for a few weeks, and installation was planned for this past Tuesday. Around midday Tuesday, Eversource started to pull the old 91 Line, and the final landing in Falmouth is set to take place on Jan. 9, Stepanova said on Tuesday. The most recent update, Stepanova gave Wednesday night, was that the old line was officially pulled in.

Though barges were offshore for the past few weeks, there wasn’t much to see from the land, as most of the work takes place underwater. A jet is used to blast water and dig a trench about six feet in the sea floor, which Biron said is the most environmentally efficient method. Then the cables are laid in the trench and buried below the sea floor to protect marine life and fishing gear. And to get the cables to shore, since the barges can’t go that close to land, the Eversource team uses horizontal directional drilling — which Biron said is a method that protects shorelines and coastal ecosystems — to install pipes that they pull the cables through. The cables onshore then can carry power to various substations or end-user locations.

This project was not an easy feat, nor a quick one, and required coordination at the federal, state, and local level to ensure minimal environmental impacts. Biron said this is eight years’ worth of civic engagement, environmental studies, and sign-offs from state and federal agencies, such as the Army Corps of Engineers, the Island towns, the Martha’s Vineyard Commission, environmental groups, and local fishermen.

To have the physical infrastructure laid is a major milestone, but there are still a number of steps to take before Eversource can “make an interconnection” and feed this additional energy to the Island, Biron said. That is expected to be done in the first few months of the year. If they do the job right, Biron said, there won’t be impact to any Islander’s day-to-day life.