Power and renewables

Everything you wanted to know about onshore and offshore transmission grid planning and did ask

Offshore transmission grid planning

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Cornelis Plet

Cornelis Plet

Principal Consultant

Janice Fuller

Janice Fuller

President, Mid-Atlantic at Anbaric

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This blog is a follow up of the webinar "Planned Offshore Grid – An American Dream Come True".

DNV and Anbaric recently participated in a webinar, Planned Offshore Grid – An American Dream Come True, where experts discussed coordinated transmission planning, infrastructure and supply chain, technology compatibility and interoperability, and stakeholder communication for offshore grid development. The webinar generated many questions related to onshore and offshore grid, which prompted this blog post.

Electrically, there is little difference between onshore and offshore grids. There are, however, a few notable differences between onshore and offshore transmission planning.

First, an incumbent and highly standardized AC transmission grid already exists onshore. Offshore, HVDC technology must be used for many projects, for which the same degree of standardisation does not exist, leading to incompatibilities which impede transmission planning. AC cables cannot, for example, be used for DC.  Some standardization for HVDC cables already exists[1][2]. Other basic aspects to be coordinated through standardization are the choice of rated voltage and vendor interoperability. Choosing the appropriate rated voltage will depend on the amount of power to be transported, the available cable technology (currently 525 kV is highest for cables with extruded insulation, 640 kV in development), and the allowable loss of infeed limits of the onshore AC grid. It is costly to connect HVDC systems with different voltages, so it is recommended to minimize the number of different voltage levels used in an HVDC grid.

Second, in contrast to the onshore grid, the offshore grid does not directly connect residential or industrial loads, which translates into potentially different requirements for its operational characteristics, availability, and ownership. Multiple different models are possible for construction, operation, and ownership of offshore transmission links. Assets could be owned by transmission system operators (TSOs) or by third parties. Assets could be constructed by third parties and operated by an independent system operator (ISO), or assets could be constructed by a TO, then transferred to a third party and operated by an ISO. The offshore grid could be split into system zones which are operated by the adjacent onshore ISO, or a separate offshore ISO could be formulated. The required investment volumes will be enormous, so all models need to be evaluated against their ability to deliver an economic benefit, ensure sufficiently fast build-out and attract third party investment, and requires appropriate regulation[3]. The British OFTO model may be one of the “construction, operation, ownership” models for the U.S. to consider, although it tends to be less suitable for coordinated offshore grid development unless standardized electrical system ratings can be imposed. For this reason, the UK may be moving away from its OFTO model to enable coordinated offshore grid deployment.

Third, offshore transmission links do not pass through as many different jurisdictions and user spaces as onshore links—thereby potentially greatly reducing the permitting burden and improving public acceptance. Onshore connections between grids aren't technically difficult. There are 13, for example, between ISO-NE and NYISO. What has been difficult is for two regions to plan those connections together in regional planning processes. This is because the planning process looks primarily for in-region solutions to reliability or congestion issues. Regions can agree to work together on public policy projects that interconnect two different regional transmission organizations (RTOs), or states can work on those types of transmission projects through direct solicitations. For example, New York (NY) and Connecticut (CT) could issue a joint transmission request for proposal (RFP) that seeks transmission for offshore wind and provides for additional interconnections to better share the resource between the two grid operating areas. Cost allocation could be worked out among the sponsoring states.  In the CT/NY example, the two states could share costs to interconnect more wind into Connecticut and build additional transfer lines into New York with cost allocation reflecting how much capacity credit each state will claim. Cost allocation should be based on fair and transparent quantification and where possible monetization of costs and benefits to ensure costs are born by those who benefit[4].

States will need to be incentivized to work together—for cost reasons, through a regulatory process, or via other means. The federal government has clearly demonstrated an interest in the need for energy infrastructure and the planning for that infrastructure, and there will be significant federal investment. BOEM has stated that transmission planning will be part of their future COP reviews. You can also look to the planning study being conducted currently by PJM, for example.

There are roles to be played here by multiple federal departments/agencies. BOEM through their permitting process, DOE through regulation and administration of federal funding programs, and the Federal Energy Regulatory Commission (FERC) through its regulatory and oversight functions. Amongst others, these agencies will have to coordinate the offshore space use and the strategic aspects such as security. The ocean floor is already home to significant infrastructure—energy infrastructure (gas, electric), telecom infrastructure, etc. While the scale of power that will now travel through the ocean will vastly increase, heightening the need for security, the framework for that is in place.

BOEM has taken steps in the direction of coordinated offshore planning already under the leadership of the Biden Administration. In fact, in the New York Bight Final Sales Notice, BOEM noted it “is continuing a planned approach to transmission and is evaluating options including the use of cable corridors, regional transmission systems, meshed systems, and other mechanisms. Therefore, BOEM may condition COP approval on the incorporation of such methods where appropriate.” There is much work to be done on this front, but this language certainly indicates a positive move in this direction.

Political drive can speed up the adoption of high-level standardization needed to maintain the option value of future networking. The first initiatives are seen within states, and some movement towards inter-regional alignment is seen in the regional coordination committees between ISOs or between states in the same ISO. Examples are the “Northeast Coordinated System Plan” between PJM, NYISO, and ISO-NE, or the “Offshore Wind Transmission Study” by PJM.

The key to speeding up the deployment of offshore transmission grids and offshore wind farms is the development of an adequate supply chain for all necessary components. On May 31, 2021, the National Offshore Wind Research and Development Consortium (NOWRDC) announced the offshore wind supply chain roadmap project. The project aims to present the benefits of domestic supply chain and facilitate the establishment of offshore wind industry in the U.S. The report is not out yet, but we expect to see it in near future. So, this could be a very helpful resource that we can expect in near future (Supply-Chain-Study-Release-NOWRDC-May-13.pdf (nationaloffshorewind.org))[5][6][7].

References

[1] IEC 62895:2017 High voltage direct current (HVDC) power transmission - Cables with extruded insulation and their accessories for rated voltages up to 320 kV for land applications - Test methods and requirements

[2] Cigre TB852 - Recommendations for testing DC extruded cable systems for power transmission at a rated voltage up to and including 800 kV"

[3] PROMOTioN Deliverable D7.6 Financing framework for meshed offshore grid investments

[4] PROMOTioN Deliverable D7.11 CBA Methodology

[5] U.S. Offshore Wind Manufacturing and Supply Chain Development, 2013 Link: U.S. Offshore Wind Manufacturing and Supply Chain Development (energy.gov)

[6] Supply Chain Contracting Forecast for U.S. Offshore Wind Power, 2019, Link: SIOW-White-Paper-Supply-Chain-Contracting-Forecast-for-US-Offshore-Wind-Power-FINAL.pdf (cpb-us-w2.wpmucdn.com)

[7] Power Sector, Supply Chain, Jobs, and Emissions Implications of 30 Gigawatts of Offshore Wind Power by 2030, 2021, Link: Power Sector, Supply Chain, Jobs, and Emissions Implications of 30 Gigawatts of Offshore Wind Power by 2030 (nrel.gov)"

Contact us:

Cornelis Plet

Cornelis Plet

Principal Consultant

Janice Fuller

Janice Fuller

President, Mid-Atlantic at Anbaric

Phone: