The start of production at LS Cable in Donghae (South Korea) yesterday marks the beginning of a new technological chapter for TenneT's offshore grid connection systems. The new cables with a voltage of 525 kilovolts (kV) raise the transmission capacity for offshore wind energy to a new voltage level. They make it possible to transmit two gigawatts (GW) of direct current over long distances with low losses. Up to now, 320 kV cables have been used for offshore grid connections, for example in TenneT's 900 MW projects.
The start of cable production is part of the framework agreement that TenneT concluded with the consortium consisting of the Jan De Nul Group, LS Cable & Systems and Denys in May 2023. The contract covers the production and installation of four 525 kV DC cable systems for the TenneT grid connection projects in the North Sea. The first DC cables produced by the South Korean cable manufacturer LS Cable are intended for the BalWin4 and LanWin1 grid connection projects. In addition to a positive and negative pole, an additional cable - a so-called metallic return conductor - will be laid for both grid connections in future, which will ensure that electricity can continue to flow in the event of maintenance or repair work. The three cables will be supplemented by an additional communication cable.
A total of 1,650 kilometres of cable will be produced for the BalWin4 and LanWin1 projects (route length per project: 275 kilometres, of which 165 kilometres are submarine cables and 110 kilometres are land cables). The inner conductor is made of copper, which makes the cables real heavyweights. The submarine cables alone weigh around 76 kilograms per metre. The total weight for the submarine cable (plus/minus pole) is therefore around 25,000 tonnes per project - a logistical challenge.
Production of the cables will be completed in 2028. Cable laying at sea is expected to begin in the second half of 2026. The Jan De Nul Group will use the extra-large cable-laying vessel ‘Fleeming Jenkin’, which was specially designed and ordered for the transport and laying of the 525 kV DC cables on the seabed.
The Construction of the land cable is also scheduled to start in the second half of 2026 by the construction company Denys, with work being carried out as usual using the open trench method with a cable trench and the closed trench method using horizontal drilling. These will be used to cross bodies of water and existing infrastructure such as railway lines, dykes, roads and the like.
BalWin4 is scheduled to go into operation in 2029, LanWin1 in 2030.
Background
TenneT is one of the largest investors and operators of grid connections for offshore wind power from the North Sea. Together, TenneT's grid connection systems and interconnectors transmit around 16 gigawatts of electricity. In purely mathematical terms, this means that more than 20 million households in Europe can be supplied with clean energy from the North Sea. By 2031, TenneT plans to realise a further 19 offshore grid connection systems with a total capacity of 32.2 gigawatts (GW) in the North Sea region: 14.8 GW of this in Germany and 17.4 GW in the Netherlands. In order to achieve the expansion targets, TenneT signed contracts with co-operation partners for the development of the North Sea as a distribution hub for sustainable and independent European energy production. The long-term framework agreements are the largest contract award for energy transition infrastructure in Europe to date - they ensure a strategic long-term partnership with producers and secure long-term market capacities.
TenneT
TenneT is a leading European grid operator. We are committed to providing a secure and reliable supply of electricity 24 hours a day, 365 days a year, while helping to drive the energy transition in our pursuit of a brighter energy future – more sustainable, reliable and affordable than ever before. In our role as the first cross-border Transmission System Operator (TSO) we design, build, maintain and operate over 25,000 kilometres of high-voltage electricity grid in the Netherlands and large parts of Germany, and facilitate the European energy market through our 17 interconnectors to neighbouring countries. We are one of the largest investors in national and international onshore and offshore electricity grids, with a turnover of EUR 9.2 billion and a total asset value of EUR 45 billion. Every day our 8,300 employees take ownership, show courage and make and maintain connections to ensure that the supply and demand of electricity is balanced for over 43 million people. Lighting the way ahead together.