The NordLink cable is rolled up in a cable drum on the ship NKT Victoria.
Renewable energy

Renewable energy

A live wire

The NordLink cable will directly connect the German and Norwegian energy markets for the first time. Electricity from wind and hydropower will be exchanged to ensure supply reliability, stable prices and a higher share of renewables in the energy mix. KfW Stories reports on the technologically unique project.

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Stations on the NordLink journey

Svartevatn dam (1), where water begins its cascade above Tonstad. Sira-Kvina (2), hydropower plant in Tonstad. Generates energy for NordLink. Substation (3) in Tonstad and where the cable begins. NKT Victoria (4), loaded in Karlskrona, Sweden, it laid the German section of cable. Büsum (5), this is where the NordLink cable was pushed through the dyke to begin its journey on land. Nortorf (6) in Wilstermarsch is the site for the substation at the other end of the cable. Lehrte (7), this is where the German power grid is monitored.

At an elevation of around 900 metres, the Svartevatn dam in southern Norway's granite massif holds back vast amounts of water. At first glance, the 1.4 billion cubic metres of water look peaceful and smooth behind the spectacular structure, which contains more stones than the Great Pyramid of Giza in Egypt so they say. Upon closer inspection however, you can see a maelstrom at a spot near the edge where water plummets downward. It is the starting point of a cascade that is over 75 kilometres long and drops 850 metres down through subterranean pipelines connected to reservoirs.

This network leads to Sira-Kvina's Tonstad power plant. The plant was carved into the stone at the end of the 1960s and equipped with four turbines. It has the highest hydropower output in all of Norway with 3.9 billion kilowatt hours. Green electricity produced here will soon also flow into the German power grid.

On a high plateau a few hundred meters above the Tonstad hydropower plant, a new substation has been constructed to facilitate transport of a formidable 1,400 megawatts – this can supply 3.6 million households – through the sea to Wilstermarsch in northern Germany. It is part of one of Europe's most important electricity hubs. Hydropower from this region has already been sent to Denmark or the Netherlands in subsea cables for years, and also through the AC power grid between Norway and Sweden and connections throughout the Nordic countries. In spring 2021, the longest 1400 megawatt power cable to date will be completed: NordLink. From then on, hydropower from Tonstad and other Norwegian hydropower plants will be available for German consumers as flexible backup power when there is little wind power in Germany.

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KfW IPEX-Bank finances projects all over the world in the field of power, renewables and water.

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A more sustainable energy mix

KfW, represented by KfW IPEX-Bank, has become a co-investor to finance this approximately two-billion-euro Herculean project that will enable Norway to send hydropower to Germany and Germany wind power to Norway. NordLink was initiated around ten years ago. “At that time we had a really critical situation here in Norway,” says Stein Håvard Auno, Project Director for NordLink at Statnett, the system operator of the Norwegian power system. “We had hardly any rain fall in the fall, and the reservoirs were nearly empty in the winter. We needed to import electricity, which caused the energy prices to rise. In that way NordLink is important to Norway's energy security in dry years. It will also help us keep our electricity prices more stable even during dry seasons. NordLink will contribute to a more sustainable energy mix. In this way we are making an important contribution to the energy transition in Europe.”

Supply security, stable prices, a faster energy transition – this triad also applies at the other end of the 623-kilometre-long double cable made of positively and negatively poled cables. The counterpart to the substation in Tonstad is in Schleswig-Holstein in the town of Nortorf near Wilster. Converters manufactured by ABB, which convert the alternating current obtained into low-loss direct current for transporting it through the cable and change it back into alternating current at the end, are at the heart of the two substations which count among the most powerful substations in the world.

They convert the generated alternating current into low-loss direct current for transport via the cable, which is then converted back to alternating current again at the other end. Around three metres above the ground of the converter facility, the silver valves hang on steel cables like precious shrines. They contain the newest generation of a technology that experts call VSC-HVDC: high-voltage direct current power transmission in self-commuted power converters.

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Illustration about cable history of NordLink

Video: a film about the mammoth project produced by the system operator TenneT.

The key to a successful energy transition

On the German side, the power grid is maintained by the Dutch-German electricity provider TenneT. “To successfully implement the energy transition, we need appropriate infrastructure. For us as transmission system operators, this means systematically expanding the grid because this is the key to a successful energy transition”, says Gunnar Spengel, longstanding Project Manager for NordLink, as he explains the specific mechanics behind it. “NordLink connects two renewable energy sources that optimally supplement each other. Depending on the market situation, a surplus of wind energy can be exported to Norway. Or, if the wind calms in Germany, we can import hydropower from Norway. NordLink thus also contributes to reciprocal supply security.” However, Spengel goes on to say, the direction the electricity flows is largely determined by the electricity market. It can be assumed that the exporting party is the one with the cheaper price at the time.

“To successfully implement the energy transition, we need appropriate infrastructure.”

Gunnar Spengel, project manager for NordLink

profile wire NordLink

Cross-section through the 13 centimetre NordLink cable. Inside the copper core, next to it the insulation with a thick layer of oiled paper.

The team at TenneT is able to see how much power flows from point A to point B from the control room in Lehrte near Hanover. Powerful electricity meters in the Tonstad and Nortorf substations record the amount of energy and report it to Lower Saxony. TenneT's entire German power grid is controlled from there, whereby energy flow is automated to a great extent during normal operation instead of being manually controlled. The final destination of the Norwegian power coming from the NordLink cable, whether it is used in Hamburg, Frankfurt or Dresden, cannot even be identified in Lehrte. Shortly after its arrival within a matter of seconds in Nortorf, the power generated by Norway's cascading waters is used in the German electricity grid. And the same applies in the other direction: it is impossible to specify which of the approximately 30,000 German wind turbines produced power for Norway. The wind energy and hydropower go into the German electricity mix.

A special type of cable makes this exchange technically possible. The 13-centimetre thick and 50-kilogram-per-metre cable consists of tailored components that make it particularly robust and conductive. The electricity itself flows through a massive core made of copper. This is insulated and protected by a wide layer of paper saturated with oil. It also has a casing of steel wire and different plastics. The cable is made in the production halls of two companies. The French company Nexans manufactured in Norway and then laid the Norwegian section of NordLink; NKT from Karlskrona in southern Sweden contributed the cable for the German side.

“This is a task where I fall asleep happy every day.”

Gerd-Wolf Balk, Senior Vice President at NKT

NordLink Büsum

516 kilometres of cable were laid through the North Sea, in part through the mud flats.

Video: A video of network operator TenneT shows how the NordLink cable was laid through the North Sea near Büsum.

Staff are proud of the forward-looking project

“This is a task where I fall asleep happy every day,” says Gerd-Wolf Balk, Senior Vice President at NKT. “There is a lot of pressure on the project, to be sure, because this is the first time we are doing some things in these dimensions and there is a lot of attention on us. But I feel good about working on a future-oriented project, on a new generation of energy and energy transmission. Also, our cables symbolise that our future will only be a success if we work towards it together. This is also why staff pride plays such a large role here.”

850 people work at NKT in Karlskrona, half of them in cable manufacturing. Per shift 25 people were involved in around-the-clock production for the NordLink cable. From the summer of 2016 until February 2019, 208 kilometres of the mass-impregnated 525-kilovolt cable was produced. 54 kilometres of it are in the ground in Northern Germany, 154 kilometres are underwater in Germany's territorial waters; Nexans laid an additional 362 kilometres in the Danish and Norwegian parts of the North Sea.

NKT Management needed to obtain many more approvals for the land route than the sea route. In Schleswig-Holstein, the interests of nearly 100 affected parties needed to be taken into account between the landing in Büsum and the substation in Nortorf, and countless authorities needed to be consulted. Laying the cable in the sea, which was associated with environmental requirements, only required one permit. But the underwater cable was more difficult to lay. Once the Norwegian part in the open sea was completed by the Nexans special ship, Skagerrak, NKT relied on their ship, the NKT Victoria, Offshore Construction Manager Tony Collins and a team of 75 experts. According to Collins, this type of ship does not work like a Swiss army knife that can do all sorts of things. Everything on board both boats is designed with one intention: to lay submarine cable. Everything is adjusted to the type of cable and its extremely sensitive handling. The most important aspect: the ships must be able to maintain their positions to minimise straining forces even in rough seas. Interpreting several weather forecasts daily was a fundamental aspect of planning the cable-laying trips.

Nortorf substation
Manfred Boll

Nortorf's mayor Manfred Boll talks about the new substation in the small community, and about its importance for the inhabitants.

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The NKT Victoria transported two NordLink sections measuring 60 kilometres each from Karlskrona in its slowly rotating cable carousel, cautiously lowering the cable over the curved stern into the water. The laying takes place at a very low speed of less than half a knot (about 0.9 km/h) - depending on weather and current conditions. The greatest risk to the power connection on the bottom of the North Sea is anchors and otter trawls. So the sea floor of the NordLink corridor, which is made up of sand and clay and has a maximum depth of 410 metres, was flushed out by one and a half metres. Five crossings with cable running from East to West also needed to be protected.

When the NordLink sections laid by NKT and Nexans were connected on 23 July 2019 in the middle of the North Sea, the large-scale project that began ten years ago in Norway came to a preliminary climax. Hundreds of people in three countries worked five million hours during NordLink's construction phase. Word gets around about something this special – according to Statnett it has even made its way into the Norwegian palace.

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All United Nations member states adopted the 2030 Agenda in 2015. At its heart is a list of 17 goals for sustainable development, known as the Sustainable Development Goals (SDGs). Our world should become a place where people are able to live in peace with each other in ways that are ecologically compatible, socially just, and economically effective.

Published on KfW Stories: 8 September 2020.