Longest Land, Subsea Interconnector Will Transform Renewable Energy Sharing

January 15, 2024 by John Nieman

The Viking Link, the longest interconnector traversing both land and sea, will help Denmark and the U.K. share renewable energy economies, lower carbon emissions, and reduce costs.

Energy from renewable sources is rarely consistent in its energy output. Fluctuations can cause sudden drops in power availability when energy demand abruptly increases, thus jeopardizing utility grid functionality and putting the safety of citizens in peril. The Viking Link, the world’s longest interconnector spanning land and sea, promises to transform the sharing and distribution of renewable energy resources.


A subsea interconnector cable running along the ocean floor.

A subsea interconnector cable running along the ocean floor. Image used courtesy of the PNNL


The Viking Link connects the U.K. and Denmark through a complex web of cables, substations, and converter stations. Running 475 miles over land and under sea, the Link began operations in December 2023.


Interconnectors and Energy Instability 

It is simple enough to intuit how renewable energy sources will naturally rise and fall throughout the year—summer seasons offer unique solar opportunities, wet seasons provide hydropower, and various weather system changes generate wind. But developing scalable solutions that can create steady power supplies from these unstable sources is not a simple endeavor.  

In 2021, Europe experienced record-breaking power prices in part because of an unexpected drop in the power generated from wind resources. This effect was widespread across the continent, which only worsened the impact.  

That year, the largest wind energy producers could not capture much power from the installed wind farm infrastructure. Denmark, Germany, and the U.K., the three biggest wind energy producers in Europe, could capture only 14% of what the infrastructure is set up to secure. Germany, typically the top wind energy generator, experienced a 16% drop in 2021.


Wind farm near Copenhagen, Denmark.

Wind farm near Copenhagen, Denmark. Image used courtesy of Wikimedia Commons


As a case study, 2021 shows the dangers of energy instability when renewable sources are subject to unexpected decreases and surges. 

Interconnectors address unforeseen clean energy variations that can destabilize the energy economy of an entire continent. Interconnectors are high-voltage power cables connecting large energy economies, typically those of different countries. The interconnectivity rate is critical for energy sustainability, and the EU has set a goal of 70% reserved energy for cross-zonal capacity by 2025.


The Viking Link’s Path

The Viking Link travels from Denmark across the North Sea to Great Britain. In Denmark, two high-voltage direct current (HVDC) cables connect the nation’s west coast to a 400 kV substation near Vejen, where DC is converted to AC.

In the North Sea, 625 km of HVDC cables are buried beneath the seabed between Denmark and Great Britain.

In Great Britain, two HVDC cables travel 66.5 km from the coast to a DC-AC converter station. High-voltage alternating current cables carry the power to a substation in Lincolnshire.


Viking Link’s path.

Viking Link’s path. Image used courtesy of Energinet


The Viking Link caps out at 800 MW of power because of Danish utility grid limitations. Ultimately, the link can handle 1400 MW of power, leaving room for growth and expansion. 

National Grid and Energinet led the development of the Viking Link. The initial permits for the Viking Link were granted in 2018, so in just five years, the project was completed for launch.

The U.K. is just beginning to build its interconnector energy infrastructure. The country already plans to partner with the Netherlands and Belgium to build extensive interconnectors to benefit all parties. These collaborations show a glimpse of a renewable energy future of redistributing global energy sources to reduce costs, improve safety, and minimize carbon emissions.   


The Viking Link’s Impact on the UK and Denmark

The Viking Link marks a significant stride toward supporting the electricity needs of 2.5 million homes in the U.K. The improvement improves the stability of the grid and passes down benefits to consumers. Since the energy from Denmark is more abundant and cheaper than in the U.K, British citizens will save up to $637 million in electricity costs over the next 10 years.

The 475-mile cable also brings dramatic environmental impacts in reducing the region’s carbon footprint. The Viking Link will prevent the emission of 600,000 tonnes of carbon, essentially equivalent to the carbon created by 280,000 vehicles.