The next time you switch on the lights, take a moment to ask yourself where the electricity comes from. You may be surprised to find that the source is hundreds or even thousands of kilometers away.
As electrical grids span greater distances across sea and land and reach impressive water depths, electricity generation is becoming more renewable and more interconnected.
But that wasn’t always the case.
Without advancements in power cable technology, transportation of energy was limited. The farther electricity traveled along a cable, the greater the loss, which made the transition to renewable energy challenging.
Today, thanks to continued advances in high-voltage direct current (HVDC) cables, renewables are outpacing fossil fuels in the generation of electricity.
Renewable energy grids today – onshore and offshore – require transmission lines capable of transmitting larger amounts of power over longer distances, more efficiently (lower energy loss), at greater sea depths, and able to withstand harsh environmental conditions.
And it is a key driver in the industry’s shift to 525 kV XLPE HVDC (high-voltage direct current) cable technology for large renewable projects – especially commercial offshore wind farms.
The transition to renewable energy requires a new approach to balancing demand and supply of power. Today, the interconnection of neighboring grids is solving this problem. For example, the grid interconnection between Norway and Germany is a perfect example of balancing complementary energy sources for better grid reliability.
HVDC systems make it all possible. In the future, hybrid interconnections and HVDC meshed grids between countries and offshore wind farms will be a reality.
While up-front investment costs and complexity may favor HVAC, the lower transmission loss levels, ultimate power flow control capability, and black start capability may favor the new HVDC alternative.
According to the January 2024 ENTSO-E report – Offshore Network Development Plans, European offshore network transmission infrastructure needs – 14% of the offshore renewables could be connected via dual-purpose hybrid infrastructure in Europe by 2050.
Now, let’s delve deeper into the heart of four innovations allowing long-distance connections.
The German TSOs, TenneT, Amprion, and 50Hertz, have pioneered developing and constructing offshore wind farm connections to the grid with HVDC technology.
The latest example is the standardization of 2 GW grid connections of offshore wind farms to the grid using 525 kV subsea and land cable systems. First, a qualification phase was launched for the cable contractors to develop and qualify the technology. Once qualified, projects were awarded for the start of deployment by the end of the decade.
The viability of commercial renewable energy projects is reliant on robust and highly reliable 525 kV cable systems. Achieving this requires increasingly higher quality levels throughout the manufacturing and installation value chain. For cable suppliers, this has meant the expansion of manufacturing facilities, new extrusion towers, creating high-voltage labs, and building advanced cable-laying vessels.
This feat necessitates building upon existing high technology readiness level (TRL) processes and solutions and improving them. At Nexans, cable system know-how plays an integral role in expansion plans and steers the company’s quality control (OC). Examples include:
Nexans’ Surface Inspection and Control Algorithms (SURFICAL) are tailored to maximize downstream quality control during on-site installation processes. Using 3D scanning and cable-tailored algorithms, SURFICAL overcomes past cable joint reliability and quality limitations. Whereas in the past on-site crews checked joints visually, SURFICAL ensures defect-free installation.
In 2023, Nexans achieved the world’s first electrical Type Test on a 525 kV HVDC cable system with SF₆-free accessories. The main benefits of using SF₆-free high voltage accessories include:
By eliminating the use of SF₆ gas, cable terminations reduce their potential greenhouse gas emission by 99% and contribute to a more sustainable power grid.
While the majority of the 525 kV systems are built upon yesterday’s expertise, new learnings will ensure better grid reliability.
While the 525 kV cable transmission level may seem daunting, qualification testing where compressing 40 years of operational stress in one year has shown impressive results. Testing indicates that the insulation system ages very little, and the intrinsic system margins are massive.
The transition to renewable energy relies on interconnected grids transmitting renewable energy across greater distances and at higher power flows. This will reduce the cost per megawatt (MW) and further advance the economic viability of large commercial projects, especially large interconnector projects.
For instance, the same transmission power could be increased in a single circuit rather than two at a lower voltage; dramatically reducing the CAPEX required for a project while having a positive sustainability impact by reducing the use of scarce materials.
Increasing cable voltage will also reduce energy wastage – the higher the transmission kV, the lower the cable conductor losses. Less energy lost to transmission means that remote renewable generation sites will be even more competitive in the future.
The transition to renewable energy is essential to reaching global climate targets. At the backbone of this transformation sits the HV power cable.
Advancements in HVDC systems capable of transmitting renewable energy at greater power levels with less loss per MW at greater distances will drive the economic viability of large-scale renewable energy projects, notably offshore wind.
Espen Doedens was born in Diever, Netherlands in 1988. He received the M. Sc. and Ph. D. degrees respectively in 2012 and in 2020 from Chalmers University of Technology in Gothenburg, Sweden. His main research interests are extruded HVDC cable interfaces and DC phenomena. At present he works at Nexans as Product and System responsible for HVDC extruded cable technology.