US Offshore Wind Energy: Moving Power to the People

April 13, 2022Debra K. Rubin and Mary B. Powers

For the last six years, five yellow-based turbines lined up in shallow water off the coast of Rhode Island with just 30 MW in total power capacity have been the visual icon of U.S. offshore wind energy.

The Block Island Wind Farm was completed in late 2016 to link the 110-sq-mile island to the state power grid for the first time via one 25-mile underwater cable that no one paid much attention to—other than 1,000 full-time residents and thousands more summer visitors who gained a clean and more price-stable energy alternative to a polluting and expensive diesel system, and fast internet service thrown in for a bonus.

The tiny project’s connection, which now allows excess power sales to other state users, made its mark in enabling startup of the nation’s first commercial offshore wind energy producer.

The scale of U.S. offshore wind energy projects now proposed, with turbine capacity at 13 MW (left) and soaring more than 850 ft, is rising dramatically.                          Photo: GE Renewables

The stakes now are much higher for U.S. offshore wind as new technology and politics, demand for power and climate change urgency push states and the Biden administration to scale up plans for dramatically larger systems that will be built much farther offshore—as far as 84 miles—creating bigger challenges not just to connect electricity to the closest users, but also to create transmission links that can move it efficiently across regions.

“These projects are right up on the edge of physics, with the largest turbines farther out to sea and using the highest voltage cables, and most have never been put in service before,” says Kent Herzog, a senior managing director at Burns and McDonnell. “That makes transmission more difficult.” 

With a record 14 offshore wind farms in early development or recently approved by the U.S. Interior Dept. along the east coast, four set for approval in the next year and new Administration efforts last year to open the West Coast and Gulf of Mexico to projects, the connection challenge has grown by orders of magnitude.

On April 11, news surfaced that Washington state could get its first offshore wind farm, with developer Trident Winds announcing its unsolicited proposal to build a very large 2-GW project 43 miles off the coast of Grays Harbor County, with two transmission routes planned. Construction of the floating wind turbine project would begin in 2028 if approved, said Trident CEO Alla Weinstein, who also is active in California project development.

Interior also is set to hold its latest ocean tract lease auction on May 11 of sites off the North Carolina coast totaling 110,000 acres. The agency now is doing an environmental review of the state’s first offshore wind farm, a 69-turbine, 800-MW facility proposed by Avangrid Renewables off Kitty Hawk. Local officials have voiced opposition to it.

Sector advocacy group Business Network for Offshore Wind says if all offshore wind farms proposed by just five East Coast states are built, transmission costs could range between $15 billion and $20 billion. “Turbines capture the imagination, but interconnections make the world turn,” said Doug O’Malley, director of advocacy group Environment New Jersey, at a recent stakeholder meeting on New Jersey’s ambitious program.

The five-turbine Block Island Wind Farm project just off the Rhode Island coast, just 30 MW total, was completed in 2016. Going forward, much larger turbines, ultra-high voltage cables and greater project distance from shore present new transmission challenges.
Photo: Deepwater Wind/Orsted

Global Wind Links

Europe—and more recently and quickly, China—have developed larger programs than the U.S. As of 2020, there were 5,400 wind turbines in European waters generating more than 25 GW of power, as well as “advanced forward-looking offshore grid concepts such as the North Sea Wind Power Hub,” said the Center for American Progress, a progressive think tank, in a March report. 

Another is the privately-financed NeuConnect, set to be the first power transmission link between the UK and Germany that would enable 1.4 GW of electricity exchange between the countries, particularly of offshore wind and other clean energy sources. It announced award earlier in April of $2 billion in contracts to two firms to install 725 km of high-voltage, bidirectional undersea cable, and to design and build UK and German converter stations. Construction could start later this year, with operation projected for mid-decade. said NeuConnect, whose investors include Meridiam, Allianz Capital and Kansai Electric.

But for the US, the construction launch late last year of the 800-MW Vineyard Wind project off the southern coast of Massachusetts, America’s first offshore wind farm at utility scale, adds focus and urgency to domestic transmission planning.

The project will include 62 GE Renewables power turbines, each generating 13 MW and more than 850 ft high. Trade group American Clean Power expects 12 offshore wind projects totaling 10.3 GW to operate by 2026. This includes Dominion Energy’s 2.6-GW project off the Virginia coast, set to be the nation’s largest, although the state already deployed last year a smaller two-turbine demonstration project.

“Scaling up from Block Island represents approximately $100 billion of new investment and the opportunity to build new U.S. supply chains with tens of thousands of jobs,” says Eric Hines, a Tufts University structural engineering professor, who directs its offshore wind energy graduate program. “This rapid increase has helped to sharpen U.S. focus on our grid infrastructure as a whole … as states and regions begin to reimagine what it will mean to work together to deliver the energy transition.”

Hines says he now is researching transmission expansion “for 30 GW, 60 GW, and 100+ GW offshore wind build-out scenarios for the East Coast.”


Wind Projects: New Fixtures Along US Coasts

The U.S. offshore wind project pipeline grew to 35.3 GW of potential power generating capacity in 2020, including operating and permitted projects and those seeking approvals along the East Coast—a 24% increase over the previous year, says the U.S. Energy Dept.

New areas also are set for development in the Atlantic Ocean, as well as off the coasts of California, and along the Gulf Coast (not pictured below). Industry participants, grid operators and government regulators are creating, debating and researching new approaches to connect generated power to land-based grids and to link project outputs to other systems, where needed.

*Click on the maps for greater detail

U.S. offshore wind pipeline as of May 2021, National Renewable Energy Laboratory, U.S. Energy Dept
Maps: National Renewable Energy Laboratory, DOE

Meshed Is the Word

Grid operators, government officials and industry players now are weighing the technical, financial and regulatory impacts of moving from a simple project-specific “radial” transmission link approach, which combines generation and transmission by one developer, to a “meshed” network, which connects multiple turbines, projects and even systems built by different entities into a “backbone” offshore grid that can reduce cable congestion, environmental impacts and conflicts with ocean users. The approach could cut project costs by 10% to 18%, says the U.S. Energy Dept.  

The network of state, federal and independent U.S. grid managers has begun to address broader and longer-range transmission planning for offshore wind—as well as for other clean energy sources and overall power delivery needs—but not soon enough to meet fast-closing development targets, some activists say. 

“Let’s figure out how to minimize the need for onshore transmission to accommodate offshore wind and build a cost effective grid,” says Johannes Pfeifenberger, principal of the Brattle Group, which last year produced with engineer Hatch Group and turbine maker Siemens, a cost-benefit study on meshed transmission for the New York State Energy Research and Development Authority.

“Where are the cheapest points to connect? That planning is not being done. Building out the offshore wind grid is not a field of dreams.” He says California built a transmission loop to enable 4.5 GW of onshore wind to be built. The same could be done for offshore wind. 

But John Dalton, president of Power Advisory LLC, a North America power market consultant, points to risk. “A planned transmission would be designed in a certain way based on what you think will happen,” he says. “But if development is not as expected, there will be facilities not being used.”

Eric Runge, energy attorney at Boston law firm Day Pitney noted in a March 3 webinar that “interconnection queue delays can impact [power purchase agreement] milestones for commercial operation. These that don’t always consider the challenges of transmission and interconnection.” He added that “large projects coming ashore also can raise big issues when the shore is unused to large injections of power.” 

One industry participant says regional grid managers, known as independent system operators (ISOs), have insular cultures attuned to the interests of their region and ratepayers, and have not engaged in substantial long-term planning or inter-regional collaboration.

He and others say a more cohesive government and operator approach awaits findings of a landmark two-year federal study, begun in 2021, of east coast offshore wind transmission needs and challenges through 2050, also focusing on gaps identified in previous research. 

Data Driven

“Previous studies were looking at a single state or ISO. We’re interested in integrated transmission planning,” says Melinda Marquis, U.S. National Renewable Energy Laboratory offshore wind integration lead. She says a similar study of North Sea offshore wind found networked transmission saved about 60% in project costs and cut environmental impacts.

The study, which Marquis says also will weigh costs of both offshore and onshore infrastructure upgrades, is supported by a technical review committee that includes ISOs, developers and federal entities such as the U.S. Coast Guard and U.S. Army Corps of Engineers. “We need to be data-driven and well-informed,” says Margaret Czepiel, also a Pitney Day energy attorney.  

Some states are moving ahead on major transmission efforts to meet their own clean energy goals. New York, which has set a U.S.-leading 9-GW offshore wind energy target by 2035, recently mandated that all proposed offshore wind farms be designed “mesh-ready” in transmission, while the Massachusetts House last month passed a bill that requires independent transmission procurement for the next 2.4 GW of wind it seeks to integrate. 

NJ and NY: Clean Energy Transformation Nexus

Source: PJM and New Jersey Board of Public Utilities, State Agreement Approach, Sept. 2021; courtesy Day Pitney
*Click on the maps for greater detail

Of about 40 GW of offshore wind energy that eight East Coast states have targeted by 2040, goals set by New Jersey and New York—7.5 GW and 9 GW, respectively, by 2035—are the most aggressive.

A February federal auction in the New York Bight ocean area south of Manhattan, which netted a record $4.4 billion in lease sales to develop 500,000 acres that could produce 5.6 GW illustrates the need for a regional grid link approach, says Cullen Howe, Natural Resources Defense Council senior attorney.  “If you use wind in the New York Bight to flow back and forth between New York and New Jersey it would add reliability and resilience,” he says.

In a unique agreement, New Jersey and its regional grid operator, PJM, will incorporate the state offshore wind target infrastructure needs into overall planning and now seek developers to propose the best mix of onshore and ocean transmission and shore interconnections.

“Instead of planning for one offshore wind project at a time, the most common approach used for generator interconnections, the [agreement] contemplates what facilities are needed to support the entire deployment goal, as well as risk and uncertainty strategies,” says Jocelyn Brown-Saracino, offshore wind lead for the US Energy Dept.’s Office of Energy Efficiency and Renewable Energy. “It  also provides clarity on cost allocation.”   

New York, in its latest RFP to procure at least 2 GW and up to 4.6 GW of offshore wind, stipulated inclusion of “mesh-ready” transmission designs in proposals to expand connection and boost wind power into the New York City area.



Studies show this system could save the state $55-60 million per year by increased power deliverability, reduced need for out of state purchases and the ability to add new projects, says a March 31 analysis by law firm Perkins Cole. “Developers need to be thinking ahead from a technology perspective and considering future interconnection with other offshore wind generation, as states demonstrate this importance in their RFPs,” says the firm.

Perkins Cole adds that the Interior Dept. has indicated it “may condition approval of an offshore wind project Construction and Operations Plan on the incorporation of cable corridors, regional transmission systems, meshed systems and other mechanisms into the plan.” 

Source: Long Island Power Authority, 2021; courtesy Day Pitney

‘Optimal Mix’

The outcome of the New Jersey procurement, with bids binding, is being closely watched in the US, as the state seeks to proactively and competitively develop transmission integrating generated offshore wind with fewer line beach crossings and more connection options developed by multiple sources.

Proposals would upgrade and extend onshore infrastructure, build new offshore structures and connect both—seeking an “optimal mix” of cost-efficient and reliable strategies, the New Jersey Board of Public Utilities said. 

The solicitation last year attracted interest from 13 proposers—utilities, wind farm builders and separate transmission developers that submitted a total of more than 80 proposals. PJM said 57 of these include commitments to cap costs, 45 would upgrade existing onshore transmission, 26 propose new offshore transmission link facilities and 8 outline offshore transmission networks.

Proposal presentations last month did not disclose cost figures, but highlighted competition among wind farm builders such as Danish giant Ørsted—which is developing New Jersey’s first two major projects, totaling 2.2 GW, and also seeks to control their grid connections—and merchant transmission developers such as Anbaric Development Partners, which aims to build a communal power delivery system. 

Ørsted already is facing NIMBY pushback on its Ocean Wind 1 project, to be built by 2024 about 15-20 miles off Atlantic County, where it seeks to site a transmission line 50 ft below an Ocean City, NJ, beach to be linked to a decommissioned power plant in a nearby town. The firm has said in filings that the approach is best technically and environmentally, with no surface area disturbed. But local officials have delayed easement approvals, forcing the firm to seek state override authorized by law last year to allow the right-of-way to enable the project to stay on track. The state has not yet made a decision, according to

Local pushback through petition and state and federal lawsuits also has occurred in East Hampton, N.Y,, on Long Island, related to transmission link construction for the state’s first offshore wind farm, the 132-MW South Fork project underway by Ørsted and utility firm Eversource Energy about 35 miles east of Montauk Point. France-based manufacturer-installer Nexans S.A. will produce 110 kilometers of high-volage AC subsurface cable to connect to the 12-turbine project at its plant in South Carolina. Each turbine is set to generate 11 MW of power.

Among other issues, some residents claim high-volage AC subsurface cable installation will disturb PFAS chemicals in groundwater. It is not clear how the legal battles will delay onshore connection work for the project, set to operate at the end of 2023. “This case is yet more proof for the proposition that action by Congress and the Executive Branch may be necessary to … get renewable energy from there to here,” said attorney Jeffrey Parker of law firm Mintz In an April 14 analysis.


Who Builds Transmission?

Troy Patton, COO of Ørsted North America, which is teamed up with state utility company PSEG on seven proposals, touted the firm’s global offshore wind experience last month in airing its New Jersey proposal, including the success of 10 GW of U.K. transmission “designed, procured and built by generators at the same time that led to a very quick build-out and a well-integrated system.”

He said the firm “recognizes challenges of moving beyond” the radial approach, but “project complexity could jeopardize evolving these solutions if not managed by very experienced hands, especially when it’s not been done before.” 

Anbaric, which submitted 19 proposals, says its approach would cut costs by up to 30%. “We want to build out the ocean grid and give solutions for generators,” says Peter Shattuck, Anbaric New England president. “The move to separate transmission from generation will make it cheaper for all projects.” The firm is already contracted to handle transmission for the 1.2-GW Mayflower Wind offshore wind project in Massachusetts, which is being built separately by Europe-based Royal Dutch Shell, EDP and ENGIE.

Atlantic Power Transmission, a unit of private equity giant Blackstone, proposes a transmission approach of up to 3.6 GW through three 1.2-GW underground cables set to cross land at a non-beach location in South Amboy, NJ that will connect to an existing substation 20 miles inland. CEO Andy Geissbuehler says the approach requires only one easement. He says the firm’s team includes sector veterans, including Hitachi/ABB for facility design, Abel for offshore platforms and Nexans for offshore cable installation, as well as agreements with key construction unions. “It’s all about production capacity,” says Geissbuehler. Atlantic Power also will invest in local training and in upgrades to South Amboy pier infrastructure.

In its proposal, Rise Light & Power also would land its transmission underground in South Amboy, further routing it along a Conrail frieight line to connect inland, but the firm, a unit of LS Power, also announced on April 14 that it would build the first submarine cable manufacturing plant in the state if it wins.

The 30-acre facility would be at a planned $450-million, 1,600-acre Delaware River port site, the former location of a DuPont explosives plant. Rise did not disclose the cost of its plant but said “it is prepared to invest millions.” The firm and port developer Delaware River Partners LLC are proposing the cable project, which they say would generate 500 construction jobs and 100 for operation.

“Developers can routinely build transmission assets at a lower cost than a third party, especially when they may cover additional assets under a single large contract,” says Scott Phillips, Tetra Tech vice president and global energy lead. “But intense competition for decreasing amounts of real estate needed for onshore landing sites favors a backbone system offshore … using fewer export cables.”

PJM will evaluate proposals, but New Jersey is not obligated to implement its preferred approach in making a final selection in October. 

Meanwhile, linked transmission proponents hope the New Jersey action spurs others. “Leadership from ISOs is required,” says Brattle Group’s Pfeifenberger. “Things are clearly moving forward.

Suzanne Glatz, PJM director of strategic initiatives, notes the operator has “rules for planning and no reliability drivers” for offshore wind generation. “It’s up to the states if they want to sponsor more transmission. PJM isn’t going to take a position but will work with states to get more information about what works best for them.” 


States Step Up

In comments to the Federal Energy Regulatory Commission, Massachusetts Attorney General Maura Healey said ISO New England’s 10-year planning window is inadequate, considering the “energy system transformation already is underway.” The operator now is conducting longer-term planning based on system need projections through 2050, says Alan McBride, its director of transmission strategy.  

While coastal resident opposition wrecked Massachusetts’ Cape Wind offshore wind project a decade ago, more communities are making peace with, and actually embracing, project transmission. Italy-based cable manufacturer Prysmian Group won a contract to install Vineyard Wind’s 35-mile cable at Barnstable, Mass., on Cape Cod, where fees will help the town upgrade its wastewater system.

The firm also will link the Commonwealth Wind offshore wind project, set to deliver 1.2 GW to the state, at the retired 1,124-MW Brayton Point coal-fired power plant site in Somerset, Mass. The Mayflower Wind project also will use the site for power connection. As a result, Prysmian has agreed to build there a $200-million subsea cable manufacturing plant. The firm also will install cable for the 804-MW Park City Wind project, which will connect to Connecticut.

In Maryland, where Ørsted is building the Skipjack Wind 1 and 2 offshore wind projects, set to operate in 2026, the firm is partnering with Hellenic Cables SA to build the nation’s first fully-integrated array cable manufacturing facility. Ørsted also will construct a separate steel fabrication center in the state.. The Skipjack transmission line is likely to come ashore in Delaware, expected at the Indian River Power Plant, which has the infrastructure in place.

Delaware has yet to announce an offshore wind goal although it has committed to 40% clean energy generation by 2035. A new University of Delaware study shows that projected offshore wind power prices are within the range of wholesale electricity costs of its current supply, and would be less than half when the social costs of health and climate impacts are included.

Virginia’s Dominion Energy is laying nine cables bundled at a central location and connecting to an existing substation, says Jason Meidinger, director of renewable energy construction projects. “Dominion is designing, building and operating” its transmission, he says. “PJM is reviewing how our project will affect the overall grid system to see if network upgrades are needed.” 

Dominion will build 176 turbines and three offshore substations, 880 MW each, on a 112,000-acre lease area. “It’s a meshed system to provide power in multiple ways,” says Meidinger, adding that the firm is partnered with Europe-experienced engineers and contractors. 

Workers install the single 25-mile cable in state and federal waters to link five offshore wind energy turbines generating 30 MW in Rhode Island, completing the first U.S. commercial offshore wind project.
PHOTO: Caldwell Marine International LLC

High Voltage

Offshore wind transmission is set to introduce widespread use of high-voltage direct current (HVDC) cables, although some technology, such as DC circuit breakers, has not yet been deployed commercially.

While high voltage alternating current technology is much more prevalent, HVDC technology has attributes that make it attractive for offshore wind. It a much higher power transfer capacity. High voltage alternating cables are limited to 400 MW and transmission efficiency falls over long distances and cables must be recharged, industry experts say. HVDC cables can handle 1,200 MW per cable. and have no distance limitations.

Dominion Energy has opted to use multiple HVAC cables for its offshore cabling because of the high cost of HVDC, specifically the cost of the converter stations, says Meidinger. The cost of a pair of offshore and onshore HVDC converter substations capable of transmitting over 1 GW to shore ranges from $600 million and $850 million.

ISO-New England found in a 2019 study that because of their efficiencies over long distances, HVDC lines could take power from wind farms directly to load centers as far away as Boston without major onshore transmission upgrades, says operator manager McBride.

Current federal research on offshore wind transmission is looking at multi-thermal HVDC breaker technology and its impacts to resilience and reliability, as well as the cost and impact to marine environment and coastal communities.


Deep Water Challenge

California has transmission planning underway for an offshore wind program that only launched in earnest last year in a siting deal with the Biden administration. The California Independent System Operator (CAISO) estimates that 5-6 GW of capacity may be available on the central coast for offshore wind and other energy resources, but says there is very little infrastructure to deliver power from its north coast. 

CAISO estimates a cost of $8.1 billion to develop transmission for offshore wind to help meet the state’s 2045 zero-carbon goal.

One proposed alternative to cut onshore infrastructure costs is use of undersea cables to transmit power directly from central coast projects to Los Angeles. However, the deep west coast offshore ocean floor that mandates use of newer floating turbines adds transmission complexities.

“Additional electrical system innovations are necessary for projects in very deep waters and further from shore, including R&D focused on dynamic array cables, floating sub-stations and advancements in HVDC technologies,” says DOE’s Brown-Saracino.

“California coastal geography presents deepwater challenges to turbine placement, inter array cable networking, export cable routing and point of interconnection selection,” says Tetra Tech’s Phillips. “With cables carrying higher voltages, engineers will be required to develop a thin and flexible barrier that will flex with the cables’ continuous movement while providing 100% watertight protection.” 

He adds, “the inter array and export cable capacity, strength, floatation, flexibility and temperature regulation will be key to the success of any project developed off the California coast. Other considerations include the current distance from onshore cable landing sites to existing onshore transmission assets and environmental impacts.

Going forward, project connections may benefit from last year’s infrastructure bill, which authorizes DOE to spend $2.5 billion to contract for up to 50% of a proposed transmission line’s capacity. 

But cost allocation remains “the thorny issue,” says Burns & McDonnell’s Herzog. “Participant funding versus a socialization of transmission costs will always be a debate in the US,” adds Tetra Tech’s Phillips. “Also, the needs of one state being met through impact to another will face backlash, just as we have seen with terrestrial transmission projects.”

FERC also has launched rulemaking to address who pays for billions in new transmission infrastructure and to better connect state and regional power officials. A bill introduced in March by Sen. Edward Markey (D-Mass.) and three other Democrats addresses transmission cost allocation, grid interconnection and competitive generation procurement.

Proponents of an effective transmission network remain optimistic. “We need to view these massive projects as our future energy infrastructure,” says Hines of Tufts. “Let’s build them to last. We are making a down payment on our future economic health and global competitiveness.” 

UK Boosts Offshore Wind, Streamlines Transmission

Grid connection for the 1, 075-MW UK Seagreen project, set to operate in 2023, will be auctioned to a separate developer.
Photo: Petrofac

Even before the Ukraine war boosted British interest in renewables, nearly $30 billion in offshore power transmission work was projected by 2030. The government on April 7 hiked its offshore wind capacity target to 50 GW by 2030, from 40 GW.

With 10.5 GW now operating, UK capacity trails just China. But at 86 GW, the British project pipeline exceeds China’s by 11.5 GW, says trade group RenewableUK.

The UK was quick to mobilize offshore resources, but a piecemeal approach to transmission development now is seen as an impediment, so the government may introduce a more centralized approach for wind farm siting and transmission network design.

“It’s got huge potential to accelerate offshore wind development,” says Mayure Daby, until recently U.K. head of energy networks in the Atkins unit of SNC Lavalin Group Inc. “If there is a more coordinated offshore network that is run by, let’s say, an energy system architect … it might reduce the risk for a developer.” 

But individual developers still install turbines and land links piecemeal. Before any U.K. wind project operates, however, “unbundling” rules to boost competition require transmission assets transferred to a separate owner. Having fixed their value, the energy regulator auctions an Offshore Transmission Owner contract. The successful bidder pays the field developer for assets and earns annual fees from the national grid operator.

One consortium paid $580 million for the Hornsea Project Two’s transmission system to earn availability and inflation-linked fees for 23 years.

The regulator has since launched its latest auction—for Scotland’s 1,075-MW, $3.9-billion Seagreen wind farm, its largest, being developed by SSE Renewables and TotalEnergies and due to operate in 2023. Its 4,800-ton offshore substation topside was installed in March, following construction by EPC contractor Petrofac Ltd. of its six-leg supporting jacket in 55-m-deep water earlier this year.

As the market grows, cable manufacturers lead in technology advances, says Paul Fletcher, a Mott MacDonald technical principal for power systems engiheering. With longer transmission distances, the industry is reaching the limit for alternating current (AC) cable and is turning to more complex direct current (DC) technology.

When Fletcher began work in the sector a decade ago, most U.K. connections were 132-kV AC cable, each typically carrying about 150 MW. For AC, “the industry now is starting to introduce 275 kV cables [carrying] around 500 MW per cable,” he says.

Dutch utility TenneT announced a new extruded subsea cable system, not currently available, which raises transmission capacity to 2 GW, says Fletcher. As high-voltage grid manager in the Netherlands and in parts of Germany, it “can afford to take a little bit more [development] risk than in the U.K. where the risk tends to be carried on a project by project basis,” he adds.

 By Peter Reina