Optimised high voltage underwater cable design to support growing use of renewable energy

Researchers at the University of Southampton are running a series of interlinked projects and consultancy to optimise the design of high voltage underwater cables.

The multidisciplinary team, including high voltage engineering experts in the School of Electronics and Computer Science (ECS), are driving findings that will maximise power transfer and save money in the delivery of future energy.

The research could also lead to a much better understanding of how climate change may be affecting ocean bottom temperatures and, in turn, biological and geochemical processes at the seabed – which are critical to the health of the oceans.

Marine High Voltage Cables (MHVCs) are buried under seabeds around the world. MHVCs for a typical 1 gigawatt windfarm cost about £400 million to design and install, with operation and maintenance costs of several millions of pounds every year.

Professor Justin Dix, of Ocean and Earth Science, explains: "MHVCs primarily operate two ways. Either transferring power between one country and another, for example, hydroelectric power from Norway to Denmark or nuclear power from France to England, or to bring power from our proliferation of windfarms to land. As we explore other sources of renewable energy like tidal power and wave power, the power will need to be brought to land in the most efficient manner.

"If you can better understand the environment the cables are in, and therefore effectively model how heat dissipates away from the cables, you can optimise cables and reduce costs significantly."

The research team has established that, in many cases, cable designs can be changed whilst maintaining a healthy margin of safety.

Dr George Callender, Lecturer in ECS, says: "The current approach to cable rating is effectively based on decades of research into land-based cables. How the seabed environment would alter conventional rating approaches was poorly understood."

The insight is helping to inform the design of SOFIA Windfarm, being built in the central North Sea by RWE. On completion this will be RWE's largest windfarm, providing 1.4GW to 1.2 million homes. The team’s expertise is also being employed in the construction of Inch Cape Windfarm, which will be one of Scotland's largest sources of renewable energy producing 1GW for up to a million households.

Professor Paul Lewin, Head of ECS, says: "We're working with a large number of windfarm companies who want to use our approach rather than just the standard land-based method. We're also working with AP Sensing, a fibre optics company, integrating our ideas into burial-depth prediction software, and most recently we have entered discussion with cable manufacturers such as Nexans."

Looking to the future, the research is also taking a different turn – to understand temperatures at the bottom of the ocean.

Professor Dix says: "The cables strongly record the seasonal variation in ocean bottom temperatures. We think we can back-calculate ocean bottom temperatures from the catalogue of data we have from the last few decades. Ocean bottom temperature is one of the least studied ocean parameters on the planet."

The projects came about thanks to an event organised by the Southampton Marine and Maritime Institute (SMMI).

Professor Damon Teagle, Director of the SMMI, said: "Bringing together academics and researchers from across the University and putting them in a room with a wide range of cable stakeholders, including windfarm developers, cable manufacturers and representatives from the National Grid, was an essential and hugely successful early step.

"As has now been clearly established, the combination of expertise from both earth scientists and electrical engineers is crucial: knowledge of cable design needs to be aligned with knowledge of the ocean floor."

Read the full article in the latest edition of Re:action, the University's research and enterprise magazine.