Offshore wind generation is becoming a reality along the U.S. Atlantic Coast, but exactly how that electricity will make it to shore is currently up for debate. Up and down the coast, states and developers are working out whether each project should be responsible for its own offshore transmission or if centralized transmission networks connecting multiple projects to a single, onshore landing point makes more sense.

This question is at the forefront as projects move from the drawing board to construction. The first of the large projects is now in the planning and engineering stages. This project is the 800-megawatt (MW) Vineyard Wind that will be constructed 14 miles off of Martha’s Vineyard. Onshore construction is expected to start later this year, with operation to begin by 2021. Soon after, turbines will be spinning off the coasts of Maryland, New York, New Jersey, Rhode Island and Virginia. With developers in each state potentially building out multiple wind farms, some think consolidating offshore transmission lines to minimize landing points is the right economic and environmental choice.

“It would make sense to look into the future and try to anticipate the volume of wind beginning to be developed,” said Judy Chang, a principal with the Cambridge, Mass.-based consulting firm The Brattle Group. “From a grid perspective and a public policy perspective, it makes sense to look forward and try to understand what the needs are.”

Chang and fellow Brattle Group principal Johannes Pfeifenberger co-authored a study last year that analyzed the trade-offs between individual and networked transmission ties. In “U.S. Offshore Wind Generation and Transmission Needs,” the two estimated the 8,000 MW of then-committed offshore development in Massachusetts, New York and New Jersey would require 600–1,200 miles of offshore transmission. And using single high-voltage alternating current lines for every 400 MW of wind generation would mean 20 landing points, along with associated onshore grid interconnection reinforcements. Looking further out at the 15,000-24,000 MW of proposed—but not yet approved—offshore capacity, the pair see a potential need for approximately 3,000 miles of undersea lines. An alternative, Chang and Pfeifenberger suggest, would be the model of offshore grids Germany, the Netherlands and Belgium are now using to integrate multiple plants. The result could be economies of scale and fewer onshore grid connections. Such an approach could help the offshore wind industry build out even further, Chang said.

“Once you have a grid, the development of offshore facilities will become streamlined,” she said. “Eventually, you want a grid that the offshore wind can just plug into.”

This is also the argument that the Wakefield, Mass.-based transmission developer Anbaric is presenting in its proposals for what it calls OceanGrids. The company also is working on the studies and environmental permitting that would be required for similar offshore transmission systems in New Jersey and New York.

While current Massachusetts regulations prohibit independent transmission developers from bidding into wind-energy procurement auctions, that could change soon. A May 2019 report from the state’s Department of Environmental Resources recommended a 2020 solicitation for a single, offshore transmission system that future projects would be required to tie into. A single, primary transmission system, the report states, “has the potential benefit of minimizing impacts on fisheries, optimizing the transmission grid, and reducing costs.”

Anbaric has begun making significant investments with hopes of winning this solicitation. It has signed a $650 million agreement to turn the former site of the Brayton Point coal generating station in Somerset, Mass., into the rechristened Anbaric Renewable Energy Center. Central to these plans is a 1,250 MW high-voltage DC converter, which would be the interconnection for its Massachusetts OceanGrid and the existing transmission infrastructure once used by the coal plant. The company’s plans also include a 400 MW battery storage system.

The first generation of large offshore wind developments likely will be up and running before offshore grids can be in place. This includes Vineyard Wind. However, even developers with projects further down the proposal pipeline express hesitation over offshore grids. Their concern is that such networks won’t be in place by the time they are ready to begin operations, and that the grids’ placement might not match their locational requirements. So, with an industry developing as quickly as offshore wind, it’s likely a mix of offshore transmission approaches will prevail in the short term.

Offshore grid proponent Chang approves of this diversity. The worst approach, she said, would be to call a halt to rapidly proliferating offshore turbines until a unified plan could be developed.

“It’s possible that for the first projects that are closer to the shore, [individual connections] could make sense—so there’s a short-term and a long-term,” she said. “Maybe the question becomes, if you run out of landing points, you start developing the network. The way we’re heading, that’s what we’re looking at.”