Subsea interconnectors as protagonists of offshore renewable grid story

As the world puts more gumption into its energy transition journey, subsea interconnectors open new opportunities for sharing the access and use of renewable energy, such as offshore wind power, between countries while upping the decarbonization ante and strengthening the security of electricity supply.

The role of subsea cables in energy security and transition to clean sources is becoming more pronounced within the energy industry, as this is the main component of powering transmission to interconnect terrestrial grids, feed the power from offshore renewable sources – encompassing wind, wave, and tidal energy – into terrestrial grids, and supply power to offshore assets to enable their electrification and slash their greenhouse gas footprint.

While explaining that there is no transition without transmission, Alessandro Blasi, Special Advisor to the IEA Executive Director, pointed out: “While we are trying to electrify everything, we forgot to look at networks, ‘the highways of electricity.’ Grids are a key enabler of energy transition. We need to build more of those and to modernize in order to accompany a power system that changes radically. Some concepts are almost trivial once explained, but we tend to forget those.

“With more and more renewables in the mix, the model changes dramatically. It is not only more distributed and less centralized. But also in terms of locations change completely. Before it was possible to bring the power plant – the center of electricity generation – close to the consumption center, a city for instance. But it is not possible – or at least only rarely – to bring the city closer to the cleaner sources of electricity, as those can be offshore wind farms in the middle of oceans or huge solar panels in a desert.”

Therefore, Blasi underscores that more and more networks need to be upgraded and built to unleash “the massive potential” of renewables and put them at people’s disposal. This is where subsea interconnectors come into play. Europe is the frontrunner in the creation of offshore hubs, taking full advantage of high-voltage direct current (HVDC) electric power transmission systems in a bid to plug in green power to the grid.

To this end, the European Commission has identified various projects of common interest, including three hybrid interconnector projects – TritonLink, Bornholm Energy Island (BEI), and Elwind – in the North Sea and the Baltic Sea, which will enable Denmark, Germany, Belgium, Latvia, and Estonia to enrich their green electricity arsenal.

With the zest for a coordinated roll-out of future energy highways with multiple energy connections between North Sea countries on the rise, one or more hubs with interconnectors to bordering North Sea countries – Denmark, the Netherlands, and Germany – are also expected to be bankrolled by the EU.

Many are convinced that an uptick in offshore wind is needed to achieve net zero by 2050 ambitions. With this at the forefront, enabling cost-effective, optimized solutions for green electricity superhighways will require offshore power grids with advanced technologies, throwing meshed grid systems, energy islands, and HVDC development into play. Currently, subsea interconnectors are mostly used to connect only two separate national transmission systems, but the number of countries that want to combine transmission assets with offshore wind farms is growing fast, as nations work on saving money and space while bolstering energy flows.

A report from WindEurope and Hitachi Energy, published in 2023, noted: “A shift away from point-to-point offshore connections towards offshore hybrid projects and ultimately offshore grids will deliver on multiple socio-economic benefits. Offshore hybrid projects and offshore grids in Europe’s sea basins will provide benefits such as optimizing infrastructure build-out and on-land beach crossings, increasing infrastructure utilization rates and improving the ability of the power system to match supply and demand. More clarity is needed at the European level however to mitigate investment risks and to accelerate the deployment of such offshore projects.

“The technologies are available to meet our near- and medium-term goals – now we must deploy them at speed and scale. These clean energy technologies, including enabling technologies for the evolution from point-to-point connections to offshore hybrid projects and ultimately to meshed offshore grids, already exist. While the industry must innovate to improve efficiency and reduce cost, coordinated deployment of these technologies at ‘speed’ and ‘scale’ will now be critical.

“A full-scale offshore grid project deployment, combined with amending the existing network codes to make them fit-for-purpose for such deployments, is now necessary to respectively enable and highlight the benefits of meshed offshore grids. In addition, the continued efficient development and modernization of Europe’s onshore grids will also be crucial to ensure that the power generated and transported offshore can reach its final destination – homes, industries, and businesses.”

Since the possibility to manage the interoperability of multi-terminal HVDC transmission network development was demonstrated through projects like the EU Horizon 2020 funded project PROMOTioN, the report emphasized that the implementation of a meshed offshore grid into a full-scale high-voltage project should be on the agenda. Both the €69 million EU-funded InterOPERA project and UK-funded Aquila project plan to deliver full-scale HVDC multi-terminal, multi-vendor, multi-purpose real-life applications by 2030.

While Europe aims to build around 450 GW of offshore wind by 2050, the EU wants to have 300 GW by then. With €50 million in EU funding, InterOPERA got its hands on one of the highest slices of funding from the Horizon Europe Framework Programme, which is the EU’s key funding program for research and innovation and comes with a total budget of €95.5 billion.

The development of energy islands is seen as a steppingstone for meshed offshore grids, however, cross-border and cross-sector coordination and cooperation are expected to be crucial in addressing the challenge of developing such grids while initiatives like the North Seas Energy Cooperation agreement between governments are perceived to be the key to promote and cultivate such collaboration.

The EU’s electricity interconnection target, aiming for at least 15% by 2030, is set to encourage countries to interconnect their installed electricity production capacity and integrate the large volumes of renewables being developed. The report from WindEurope and Hitachi underscores that offshore hybrid projects optimize infrastructure build-out, boost infrastructure utilization rates, and improve the ability of the power system to match supply and demand.

These projects are forecasted to stand for one-third of all offshore wind capacity by 2050 and will include the Triton Link project – a connection between the artificial energy islands of Denmark and Belgium that will transmit 2 GW over 773 km with HVDC technology – and the Nautilus interconnector between Belgium’s artificial island and the United Kingdom, which is expected to transmit 1.4 GW over a 140 km distance.

“The natural evolution beyond offshore hybrid projects will be the creation of meshed offshore grids in Europe’s sea basins, likely through the connection of multiple offshore hybrid projects,” underscored the report.

The interest in subsea interconnections is growing. TAQA recently inked a memorandum of understanding to explore the possibility of becoming one of the shareholders in the Great Sea Interconnector project to develop a 900-kilometer HVDC electricity interconnection between Greece and Cyprus.

This came days after all key regulatory approvals were put in place for NeuConnect, the first-ever energy link between the UK and Germany, following the second partial approval for the construction and operation of the converter station on the German side.

In November 2023, the European Union signed a grant agreement for the first direct current interconnection between Europe and Africa, initiating a €307 million financing from the European Commission for the subsea power line between Italy and Tunisia.

In addition, TotalEnergies added a new project to its international portfolio by acquiring a minority stake in Xlinks. This Morocco-UK power project, powered by solar and wind energy, will supply over 7 million British homes with green electricity through the installation of 3,800 km high-voltage direct current subsea cables, along with a large battery energy storage.

Bearing in mind the importance of subsea cables, the International Marine Contractors Association (IMCA) revealed in October 2023 a new code of practice to improve subsea power cable installation by preventing cable failure and enabling savings for the offshore wind industry.

Following threats to subsea energy and telecommunication infrastructure, the Joint Expeditionary Force (JEF) embarked on a joint exercise in the Baltic Sea region to strengthen its presence and develop the capability for the surveillance and protection of subsea infrastructure.

This follows a rapture and shutdown of the Balticconnector gas pipeline between Finland and Estonia after seismic signals were recorded in its vicinity, indicating a possible explosion had occurred around the time a pressure drop was observed approximately 40 kilometers north of Paldiski, Estonia, close to where the Balticconnector pipeline crosses the Nord Stream 1 pipeline.