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The Planning and Implementation of Offshore Wind Grid Connections

An array of turbines is no use without cables, substations and grid connections. Planning and permitting for these infrastructure developments can be complex. Project developers and supply chain companies need to negotiate a web of different organisations and authorities to ensure that all the licensing is in order. In addition, the authorities themselves are moving into new territory as the US does not have a developed OW sector yet, so some delays in projects permitting should be expected by developers as the regulatory authorities create new systems and procedures.

The most important organisations include the NorthEast Planning Organisation and their NorthEast Data Portal, the US Corps of Engineers (USACE) which is often a lead organisation involved in civil engineering projects – this is unlike the usual situation in Europe where the military is rarely involved.

The USACE will almost always be involved in project review and permitting under RHA (Rivers and Harbors Appropriation Act) or CWA (Clean Water Act). The Bureau of Ocean Energy Management (BOEM), Federal Energy Regulatory Commission (FERC), and state public service commissions are likely to have roles depending on the type and location of electricity transmission projects.

The US Coast Guard is also the lead authority for maritime protection and safety, and so will need to be brought in on projects at an early stage to ensure safety at sea and deconfliction of turbine installation and cable laying with fisheries and sea transportation. They have regulations on what safety procedures and equipment are to be utilised on vessels in US waters.

Block Island Connections Case Study

The connecting of the turbine array off Block Island is an interesting early exercise in how offshore power grid connections will be realised. The project was called sea2shore. It is located right at the heart of the local community the wind farm was built to serve. And this 'green transmission' project is helping unlock the potential of offshore wind power as a new source of energy. It is part of their commitment to bring clean, renewable energy to local customers. But one of the biggest challenges is connecting customers to energy sources that are often found in difficult locations. BOEM did a post-first phase installation study on the Block Island scheme which repays reading.

Tim Horan, President and COO National Grid Rhode Island says, “The sea2shore project was a combination of many different parties coming together: National Grid, the legislature, Deepwater Wind and various others.” The National Grid agreed to purchase and build the export cable and other transmission assets. It paid for the property options, permits and engineering and other studies.

Inter-array Cabling

The cabling between the turbines was made by LS Cable & System, South Korea, and installed by Durocher Marine, with the Teklink Cable Protection system.

The Export Cable

The export cable is bidirectional from LS Cable & System. Under normal usage is transmits power from the turbines to the mainland, but in the event of the wind not blowing or generator failure it can transmit power in the other direction, from the mainland to the offshore power system.

Three Major Contracts for Transmission Work

The project was broken up into three major contracts: all of the substation work; the land cable construction, of about four miles on the mainland and one mile on Block Island itself; and the third was the submarine cable contract of 20 miles of 34.5kV underwater cable from Block Island Town Beach to Scarborough State Beach (Narragansett).  Two substations were built – one on Block Island and one on the mainland. This was an improvement for the residents of the island who did not have a grid connection and had to rely on diesel generators for power.

The submarine cable was laid from the beach to Block Island using an underwater plough which carved the tunnel for the cable using water jets – the sediment naturally buries the cable as it solidifies again, leaving it around 2 Metres below the surface. By using the specialised cable laying vessel The Big Maxx the operation was completed efficiently. Afterwards the beaches were restored to their previous state. There is manhole access to the cable on the shore for inspection and maintenance. The underground cable tunnels on land were horizontally drilled to minimise disruption to the environment.

Stakeholders and Community Involvement

The approval of local stakeholders was important to the project. New England has a significant commercial and recreational fishing sector, water sports, and other tourist activities such as yachting and whale-watching, which are a major part of the New England economy. This made it imperative that disruption was kept to a minimum. The US National Grid worked closely with many key marine-related organisations and individuals prior to and during construction. Their goal was to facilitate open dialogue, ensuring their actions are coordinated with key stakeholders at all times and keeping communications links open after the construction of the project has finished. There was a safety exclusion zone and construction corridor while the cable was being laid – and all ships were notified in a Daily Notice to Mariners. Fishing was permitted at a safe distance behind the plough after the cable had been laid, to ensure that there was the minimum disruption to commercial activities.


The complexities of grid connection and cabling were discussed at the 4th Annual US Offshore Wind Conference in Boston on June 10-11, 2019. More details here.

By Julian Jackson


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