Europe is betting big on offshore wind to meet its ambitious climate and clean energy goals of fully decarbonising its economy by 2050. Majority of the offshore wind potential of 450 GW by 2050 will be located in the North Sea (at 200 GW). At the end of 2019, 90 per cent of offshore installed capacity of 22.1GW was concentrated in the North Sea. In order to ensure a coordinated approach to harness offshore wind energy at the European level, the European Union (EU) funded the research project PROMOTioN [Progress on Meshed HVDC (high voltage direct current) Offshore Transmission Networks] through its Horizon 2020 (H2020) Research Program. The project concluded recently and its findings were presented in September 2020 at a concluding online conference, ‘North Sea Grid for the European Green Deal: How to Unlock Europe’s Offshore Wind Potential – A Deployment Plan for a Meshed HVDC Grid’.

During the four and a half years of the project, 34 partners from 11 countries from various fields such as manufacturers, suppliers, transmission system operators (TSOs), offshore wind (OWF) developers as well as academic and consulting institutions worked together to investigate the future evolution of Europe’s offshore energy grid. The project took a holistic approach to address the design, development and deployment of the meshed offshore HVDC transmission networks from a technical, financial, regulatory, managerial and policy perspective.

Presently, most of the offshore wind generation is transmitted to the onshore grid via point-to-point high voltage alternating current (HVAC) connections. As the distance to the shore increases and with the large-scale deployment of offshore wind farms (OWFs), a meshed or multi-terminal offshore grid is proposed as a solution where several wind farms are connected to offshore transmission assets, which may also operate as interconnectors between countries—also known as hybrid assets.

The PROMOTioN project has advanced the HVDC technology required to design, build, operate and protect meshed HVDC transmission grids such as HVDC grid and converter control systems, direct current circuit breakers (DCCBs), HVDC grid protection systems and HVDC gas-insulated switchgear (GIS). Further, recommendations have been made for the legal and governance frameworks needed for a meshed offshore grid (MOG), the necessary economic and financial rules required to attract sufficient investment and just remuneration for owners, operators and users of the grid, and the market and governmental actions necessary to facilitate an ordered roll-out.

In the Final Deployment Plan released in September 2020, which is one of the several deliverables, the programme findings and recommendations have been structured into a roadmap to 2050, elucidating the next steps required to develop an offshore grid capable of integrating offshore wind farms and evacuating huge quantities of wind generation to shore as well as providing interconnection between countries surrounding the North Sea and providing onshore AC grid reinforcements by means of offshore DC connections. The broad level findings of the research project indicate the following:

  • Hardware-based technologies such as HVDC circuit breakers and HVDC GIS are ready for use and can be manufactured industrially immediately.
  • Software-based technologies such as HVDC system control and HVDC system protection have been proven to work and to be interoperable, and are considered ready for a real-world pilot.
  • Further research is outlined to improve performance and whole system integration.
  • The next step is to develop full-scale pilot projects at sea. Such a development would accelerate the much-needed uniform DC grid code and specify system operation guidelines and agreement on high-level technical system characteristics (such as operational configurations, voltage levels, system earthing and converter configurations).
  • Clear support and affirmation from politicians regarding the regulation and market models of the MOG and more cooperation at a European political level as well as at the level of network operators is imperative.
  • UK and Norway ideally should be included in the development of joint offshore wind transmission grids in the North Sea and Irish Sea.
Figure 1: Overview of elements incorporated in the Deployment Plan
Source: PROMOTioN’s Final Deployment Plan

PROMOTioN findings and recommendations: Final Deployment Plan summary

In the plan, four offshore grid governance scenarios (concepts) were analysed under three offshore wind deployment scenarios to produce 12 grid topologies showing development of the grid from 2020 to 2050 in five-year time steps. Three dimensions were explored starting from point-to-point grid connection:

  • Integrate multi-terminal and meshed grids
  • Small 2 GW hubs to grids centred around artificial islands
  • Comparison of evacuation within national Exclusive Economic Zone (EEZ) to grids where evacuation is to the nearest landing point. A concept called European meshing is relevant here, which is reliant on intense international cooperation.

Initially, the results from a cost-benefit analysis (CBA) of the four different grid configurations were reported in another deliverable under the programme—Optimal Scenario for the Development of a Future European Offshore Grid. Based on this, a proposal for establising an offshore grid was elaborated, based on the development of different technologies within PROMOTioN, identification of short-term projects to test novel technologies and analysis of non-technological recommendations as well as market and governmental requirements.

The four PROMOTioN grid concepts are as follows:

  • Business as usual (BAU): The OWFs are connected to the grid point-to-point, either in separate connections or in some cases OWFs may be bundled to reach 2 GW critical size for power evacuation via standardised ±525 kV bipole cables, which have not yet been deployed.
  • National Distributed Hubs (NAT): Under this, the national offshore grid is the first priority for evacuation of wind power generation from each country’s EEZ to its onshore grid. The national grids may be strategically connected to each other. During low wind conditions these connections provide trading capacity between the national onshore grids.
  • European Centralised Hubs (HUB): This concept involves the creation of several AC central hubs to which several OWFs are connected. Power evacuation to shore is done via strong DC connections connecting different countries. These hubs also provide trading capacity between countries during low wind periods.
  • European Distributed Hubs (EUR): The concept proposes small, platform-sized hubs that are spread out across the North Sea and connected to each other via DC connections and to the nearest landing points independent of EEZ. These hub connections provide interconnection between countries during low wind generation.
Figure 2 – PROMOTioN Grid Concepts
Note: Top left: BAU; Top right: NAT; Bottom left: HUB; Bottom right: EUR
Source: PROMOTioN’s Final Deployment Plan

Key findings

The costs and benefits of these concepts were analysed based on a CBA methodology developed within PROMOTioN. The results indicated that when constraints on meshing are relaxed, specific multi-terminal configurations arise early on in each concept, such as establishing offshore interconnectors between wind farms. For the analysis, PROMOTioN assumed that the next generation of offshore HVDC transmission systems would settle on a voltage level of ±525 kV, with 2 GW transmission capacity and the configuration of an HVDC bipole with fixed return. The analysis indicated a cost saving when islands with large power concentration are used in place of platforms. The advantages of reduced cable length on removing constraints on evacuation of wind generated in one EEZ to a landing point in another is negated by increased complexity and cost of hub equipment for European and national solutions. Meshing of grid, wherever possible, leads to lower curtailment and a higher security of supply. However, this would require a change in the market set-up around bidding zones or a new regulatory approach besides application of novel technologies.

Although the analysis focused on four different grid development concepts, the offshore grid is ultimately expected to be comprised of elements of all four PROMOTioN concepts, depending on their applications across geographies and time based on political preference and increased benefits.

The development of each topology is split into three periods, namely, 2020-2030, 2030-2040 and 2040-2050. The first period marks the start of the roll-out of the multi-terminal and meshed grid. In this period, point-to-point connections will continue to dominate and the meshed topology of the grid will be concentrated in small areas. It will be characterised by the deployment of the first 525 kV 2        GW HVDC components and construction of simple, multi-terminal grid topologies. These will be limited to national topologies and potential cross-border synergies will be realised with the establishment of the first hybrid assets located between OWFs close to the border of the EEZs. Implementation of a small bidding zone market model may be considered. The Ten-Year Network Development Plan (TYNDP) process must be aligned with longer term system planning.

In the second period, grid development takes off and more of the PROMOTioN topologies become prevalent. Once the industrially proven protection devices are deployed in this period, interoperability between different vendors will be essential, introducing increased technical complexity into the grid. Artificial islands will be established during this period.

The final period is the end of the analysed timeframe where experiences gained in the previous periods can be applied to complete the integration of a large amount of offshore wind, and to encourage the repowering of the offshore transmission corridors decommissioned by that time.

Figure 3: Roadmap to a meshed offshore grid
Source: PROMOTioN’s Final Deployment Plan

Key recommendations

Strong cooperation between countries at both the political and operational levels will be essential to develop consistent legal, regulatory, economic and financial frameworks for the MOG. This may be formalised through a mixed partial arrangement in the form of an international law agreement between EU member states and other countries connected to the MOG, and the EU. It would set out the common interpretation of the international and EU laws related to offshore assets.

Splitting offshore grids into several bidding zones is recommended for an offshore electricity market providing efficient economic incentives. However, further studies need to be carried out on the division of offshore grids into small bidding zones and on mechanisms that could be put in place before a decision is made on the implementation of market schemes used for offshore grids.

In the short term, PROMOTioN recommends that the definition of offshore hybrid asset should be advanced by adopting it in the operative part of the EU electricity regulation, and that the legislation should specify the legal and regulatory framework for offshore hybrid assets in more detail. In the long term, international consensus on the definition of an offshore hybrid asset and the extent of the jurisdiction countries have for hybrid assets will provide greater legal certainty to all MOG-connected countries.

Given that planning and permitting procedures are perceived as a key risk in large infrastructure projects, a streamlined and preferably aligned permitting process will be necessary to deliver and connect these offshore wind projects in a timely manner.

The MOG will need to be regulated by a single entity or through cooperation of relevant NRAs. The latter will be a more politically acceptable solution.

Further research, development and demonstration will be required through the initiation of a full-scale multi-vender, multi-purpose, multi-terminal HVDC network pilot, exploring the need for flexibility in the system, integrated AC/DC system studies, offshore wind farm advanced capabilities, HVDC hub topology, DC switchgear development, interoperability of controls and protection and research on the need for DC/DC converters in the system. 

Broadly, the recommendations for stakeholder actions are grouped under four specific periods of grid development when it is necessary. The group-wise key suggested actions are as follows:

The Period 2020-2030

  • The roll-out of offshore transmission largely follows the current practices, except for the use of 525 kV 2 GW HVDC components and the need for anticipatory investments. A set of explicit technology and purpose-agnostic minimum requirements need to be formulated, which all participants in the MOG development must adhere to. For example, the establishment of an offshore HVDC network code and alignment on HVDC system ratings can facilitate meshing of the grid in later periods.
  • Many of the existing regulations can continue to apply in this period. However, a pilot project to test the small bidding zones model should be established and a decision made about its wider roll-out.
  • The development of offshore wind generation sites will require more extensive planning and coordination to gain maximum benefit from potential meshing or large hub or islands.
  • Bilateral agreements will be required to agree on the regulatory framework and the support scheme for the connection of some OWFs that are not connected to other countries other than the EEZ in which they are located. This could be achieved smoothly if the key principles of MOG regulation and how regulatory decisions will be made across the North Sea are agreed upon in the North Sea treaty.
  • Government and industry should be investing in supply chain and personnel development to facilitate the increased rate of deployment expected in later years.

The Period 2030-2040

  • As the rate of grid development increases over this period, the solutions for the control systems and DCCBs necessary for protection should be ready for deployment. Additionally, interoperability issues and multi-vendor integration of infrastructure should be understood.
  • The period also marks a large increase in the deployment rate of offshore wind capacity, which means that a dedicated supply chain should be established by this time.
  • During this period, governments must ensure the availability of quality skilled personnel in sufficient numbers.
  • Development of grid-wide support schemes for OWFs and aligned permitting should be implemented by the end of the period.

The Period 2040-2050

  • The offshore HVDC grid should be well established by this point. As the complexity of the grid increases, the benefits of connecting smaller multi-terminal and meshed grids to create a highly complex multi-terminal and meshed grid may be explored.
  • Research on decommissioning impacts should lead to the development of guidelines for OWFs and transmission infrastructure.

The Period 2020-2050

Some recommendations run from the start till the end of the period, such as research on protection systems and recommendations related to technology, which require further research, development and demonstration.

Conclusion and the way forward

The conclusion of the PROMOTioN project provides a kickstart to the coordinated development of the meshed HVDC offshore wind transmission network in Europe. It confirms the general viability of a MOG based on HVDC. Besides recommending a full-scale cross-border pilot, the project calls for political will and greater European cooperation to develop the regulatory and technical frameworks that are key for their implementation. The emphasis on a long-term view (up to 2050) in the project should give the industry the confidence to make large-scale investments in the required equipment, components and solutions.

Given the involvement of several countries and the wide-ranging players, the evolution of the regulatory and financial frameworks will be a complex process. The final deployment plan as well as a roadmap for implementation until 2050 presented in the project provides a broad guideline for the next steps in each period. The large-scale deployment of offshore wind generation and transmission energy will aid in improving energy security, reducing environmental impact as well as spur needed investments in the sector during the COVID-19 pandemic.

The article has been sourced from Global Transmission