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Block Island Cable Problem Highlights Vulnerabilities With Offshore Wind Transmission

  • Block Island Wind Farm, the first offshore wind installation in the United States, will briefly go offline in the spring to shore up transmission cables
  • This issue highlights how the transmission cables are one of the more vulnerable components in offshore wind farms
  • In addition to developments to protect cables, efforts are underway to create a more coordinated approach to connecting offshore turbines with the electric grid

Four years after the first offshore wind farm in the United States went online off Block Island, a multimillion dollar effort is underway to rebury the installation’s high-voltage transmission cables. The problem, which will necessitate a temporary shutdown of the 30-megawatt wind farm in the spring, highlights how the transmission infrastructure is one of the more vulnerable aspects of offshore wind facilities.

The problem at the Block Island Wind Farm stems from a shortcut approved for the project to bury the cables under just four feet of seabed, rather than the recommended eight to 10 feet. The tides off the island helped erode the seabed and expose the cables within months of the wind farm’s completion, and after several attempted solutions failed to fix the problem the decision was made to dig a deeper trench and re-splice the cables to accommodate the longer length.

The reburial comes at a cost of $30 million for National Grid, Rhode Island’s main energy utility. Orsted, the developer of the Block Island Wind Farm, is reportedly contributing a similar amount.

The repair or upgrade of transmission cables for offshore wind farms can not only be expensive, but also lead to turbine downtown that diminishes output and reduces revenues. The cables are also one of the more vulnerable parts of offshore wind farms’ infrastructure. The line may extend a significant distance before it is buried, increasing the risk of fatigue or over-bending due to shifts caused by tides and currents.

The cables are also vulnerable to saltwater corrosion and damage from causes such as natural disasters or fishing operations. Options for protecting these transmission lines include anchoring them or encasing them in cast iron shells.

Connecting offshore turbines to the shore has been a separate challenge, as the installations need to be integrated with existing mainland grids. Current plans involve connecting the wind farms to the grid as they come online, but there have also been calls for wind energy advocates to create a coordinated approach and develop the transmission infrastructure before the turbines are erected.

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