Interconnectors are key to meeting the net-zero challenge
Maxime Toulotte, Head of Technical Marketing, Nexans Subsea & Land Systems Business Group (SLS), explains why subsea connectors will play a vital role in facilitating the growth of renewable energy.
Electrification and the development of renewable resources such wind and solar are critical to meeting the net-zero challenge. However, major changes are also needed to upgrade the world’s electricity networks to ensure that we can accommodate these new forms of generation while maintaining the quality and reliability of supplies. In particular new interconnectors will be vital to promote energy trading and energy security. So, for example, if the wind is not blowing in one country the grid operator can make up the shortfall by importing electricity from a country that has a surplus of hydroelectric power. And at other times, when there is an excess of wind power, it could be exported to another country that is then able to shut down its fossil-fuelled power plants
What are interconnectors?
High-voltage cable interconnectors run under the sea or underground to connect the electricity networks of two countries. This allows them to trade and share surplus energy. They can carry a great deal of electricity. For example, the Nordlink (between Germany and Norway) has a capacity of 1,400 megawatt (MW) – enough to supply 3.6 million households with climate-neutral energy.
Some interconnectors are very long, such as the North Sea Link, currently under construction, that will stretch 720 km between the UK and Norway. This presents a technical challenge as traditional alternating current (AC) transmission technology starts to become very inefficient at distances approaching 100 km.
The solution is to use high-voltage direct current (HVDC) technology. This uses converter stations at each end of the interconnector to convert the AC supplied by the grid to DC and then back again. Once the electricity is converted to DC, at a very high voltage (typically 525 kilovolt,kV), it can be transmitted very efficiently over long distances with minimal losses.
Interconnectors have a long history
The world’s first commercial HVDC transmission link entered service between Sweden and the island of Gotland as far back as 1954. Currently, there are around 170 HVDC interconnectors worldwide either in operation, under construction or in planning. To show their growing importance, by 2024 the UK will have at least six interconnectors, capable of transferring up to 7.8 gigawatt to and from other European countries. That will be sufficient to supply around 25% of the UK’s electricity requirements.
Nexans cables provide the connection
Subsea interconnectors are a technical challenge for cable manufacture and design, especially as some are installed in very deep waters. This is where Nexans has a great depth of experience, not only in the design and manufacture of HVDC cables but also in their installation.
HVDC Interconnectors usually use two cables in parallel (a bipole). Two main types of cable technology are used: extruded cross-linked polyethylene (XLPE) insulation and mass impregnated (MI) insulation. Currently, MI cables are favored for higher voltage projects eg 525 kV.
Our first project was in 1977, when we installed the Skagerrak subsea link between Denmark and Norway. The cable system has been in service for 40 years and is still in operation. Currently, we are taking our installation capability to the next level with our new cable ship, the Aurora, scheduled to begin operations this year.
Other European interconnectors to feature Nexans turnkey cable projects include: Sweden–Finland (Fenno-Skan), Estonia–Finland (EstLink 2), Italy-Montenegro (Mon.Ita), the Greek Cyclades (Lavrion-Syros). Further afield, in the Phillipines there is the Mindanao-Visayas project and the Maritime Link in Canada.
Two important interconnectors to support the energy transition
Nexans has just completed the Nordlink, the 1400 megawatt (MW) 525 kV power connection between Norway and Germany with a total length of around 700 km. The NordLink project is an important step towards the development of the climate-friendly energy market of the future. It is a collaboration between Statnett, TenneT and the German promotional bank KfW. The link now makes it possible to export surplus wind and solar power produced in Germany to Norway. At the same time, Norway is able to export its surplus hydroelectric power to Germany.
North Sea Link
Currently, Nexans is providing cables for the North Sea Link that runs from Blyth in Northumberland on the northeast coast of the UK to Kvilldal in Rogaland on the Norwegian side. The interconnector is being created in collaboration between Statnett, the state-owned operator in the Norwegian energy system and the UK’s National Grid. It is designed to help increase opportunities for shared use of renewable energy.
When wind power production in the UK is high, Norway will be able to import power at a lower price than in the Nordic market, helping conserve the water in the country’s hydropower reservoirs. At times when there is little wind in the UK, then it can import Norwegian hydropower at a lower price than in the UK while helping to ensure the security of power supplies.
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