PROVIDENCE – The electric cables for the Block Island Wind Farm were supposed to be buried in trenches at least four feet below the seabed, but workers couldn’t get down as far as they wanted, and over the last four years waves have exposed portions of the transmission lines that run to and from a beach on the island.
Now, Orsted, the Danish company that owns the five-turbine offshore wind farm that is the first in the nation, plans to rebury one of the two cables starting in the fall. Orsted, which has offices in Boston and Providence, says it should be able to do all the work at Crescent Beach in the off-season and wrap up the project by Memorial Day in 2021.
But for an indeterminate amount of time during construction, the 30-megawatt wind farm, which cost hundreds of millions of dollars to build, will have to go offline.
Orsted says it will be “solely responsible for paying for this work,” according to a statement from the company.
“Ratepayers will not bear any of these costs,” the company said.
It would not disclose the project’s price tag.
Orsted’s cable runs from the wind farm to the island. The second cable, which connects the island to the mainland electric grid, is owned by National Grid, the main electric utility in Rhode Island. National Grid is also working on plans to rebury its cable, which is expected to happen around the same time, but the company has yet to release details to the public.
At a hearing last week before a state Senate commission, Grover Fugate, executive director of the Rhode Island Coastal Resources Management Council, attributed the problems with the cables to a combination of the technology used to bury them and natural forces.
“The area that they’re in is a very dynamic area – a lot of waves, a lot of sediment movement – so there’s a lot of potential for uncovering the cables,” Fugate told the Special Senate Task Force on Fisheries.
National Grid installed both cables in 2016 with a jet plow, a device that is towed along the seafloor and uses high-pressure water jets to dig trenches. It works well in sandy environments but couldn’t get deep enough in the rocky area off Crescent Beach.
Fugate said the coastal council recommended that National Grid use horizontal directional drilling equipment to install the cables because of the tough environment. Such equipment was necessary in Narragansett, where the cable connects to the mainland power system, and there have been no problems with exposure there.
“The complexity of the environment that they’re in is a mixture of sand, boulders, cobbles, those types of things, and not really conducive to the technology that they ended up using,” Fugate said of Crescent Beach.
This time around, Orsted says it will use a horizontal directional drill and will aim to bury the cable between 10 and 30 feet beneath the seafloor. The work will entail replacing a section of cable stretching from underneath the Town Beach parking lot to a point about 3,100 feet offshore. Equipment is set to arrive on the island in September.
The company has to replace the section because the cable is currently under tension; there’s not enough slack in the line to allow it to drop into a deeper trench. The new length of cable would be spliced into the older line.
National Grid had suggested simply covering the exposed cables with heavy concrete mats, but Fugate said the council rejected that proposal because Crescent Beach is so popular with swimmers.
While Orsted has promised to pay for repairs to its cable, National Grid has yet to do so with its cable, Fugate said. The state Public Utilities Commission is currently considering the issue and whether some costs will fall on ratepayers, he said.
The coming work will require permits from the coastal council, the state Department of Environmental Management, the Town of New Shoreham, the U.S. Coast Guard and the Army Corps of Engineers. Orsted expects to secure its permits in the next few months.
The repairs to the two cables would temporarily cut Block Island off from power from the wind farm and from the mainland. The island would have to rely on diesel generators that were the only source of power until the wind farm and cables were installed.
“We are working together with National Grid and Block Island Power Company to limit the amount of time that the Block Island Wind Farm will need to be offline to accommodate this work,” Orsted said.
|Wind Watch relies entirely
on User Funding