For subsea power cables, offshore wind industry can benefit from oil and gas experience

Electric infrastructure is a hot topic these days, and for good reason. That infrastructure is needed to power daily consumption and meet future demand. Power and electricity demand will only continue to increase over the coming years given population growth, emerging markets, and the expected growth of the electric vehicle market. In the US and in other areas of the world, there is a significant opportunity to create new industries and build new infrastructure that can support sustainable electrification, including offshore wind.

Applications for power generation in offshore oil and gas, and offshore wind, have come a long way; and innovations continue to be made in the technologies that power each industry.

As offshore wind moves into deeper waters, the equipment used to bring the power from the turbine to shore will need to become more sophisticated. Designing, fabricating and installing subsea power cables can be a complex task, and supply chains can be intricate. In some emerging offshore wind markets, such as the United States, the supply chain is still being developed.

Traditionally, offshore wind turbines have been installed in relatively shallow water. But for this market to achieve its full potential, large wind turbines must be built far from shore, where winds are both stronger and more consistent. As the industry moves into deeper waters, the construction of fixed foundations will become more challenging, and floating wind turbine foundations will be needed.

To date, most offshore wind farms have used electric static subsea cables to connect the turbines to one another and the offshore substations to the land. But for floating wind turbines, the cables that connect to them will need to traverse long distances along the seabed and be installed in deep waters. They will be subject to significant and varying dynamic loads due to the waves, currents, and the movements of the floating facility. Thus, dynamic subsea power cables will be needed to withstand both hydrodynamic movement and its own weight from the floating platform to the seabed.

And there will be other important considerations. Many of these deepwater wind farms will consist of enormous turbines that will eventually reach power levels of around 20 MW. Offshore wind turbines installed today are about 7 to 10 MW, whereas 15 MW wind turbine are already available commercially. The thicker cables required for such high-voltage levels cannot tolerate any water penetrating the insulation. They need a water barrier which, in static subsea cables, comes in the form of a lead sheath that coats the insulation. However, this type of sheath cannot withstand the waves’ dynamic movements and bending stresses. An alternative barrier must be thick enough to provide adequate protection yet possess a good level of flexibility. To meet this need, Nexans has developed cables that feature metallic foil and polymer insulation layers, which are more suited for dynamic cables.

Fortunately, the offshore oil and gas industry has been successfully using cable and umbilical technologies in deepwater environments for many years now. Power-from-shore applications have been used offshore Europe for many years, and the use of these systems is expected to grow in the coming years. These types of systems can be used as a model for floating offshore wind facilities.

A recent project awarded by Chevron offshore Australia will provide a key example and case study for offshore wind. The project involves one of the largest gas fields in operation, and it will be especially challenging since it is extremely far from the coast, and in deep waters. A subsea compression technology will be used to maintain long-term natural gas supplies for domestic gas markets. As part of this, a power and communication transmission system will be installed that runs from the shore to the offshore compression facilities, which will reside at a water depth of 1,400 m. This 145kV deepwater dynamic cable will provide power from shore to an offshore floating facility that will subsequently power and control the subsea compression. This type of innovation in high voltage dynamic subsea cables will be pivotal in many offshore projects moving forward, both for floating offshore wind systems and the electrification of floating offshore oil and gas facilities.

Going forward, these offshore industries will need to adopt a holistic approach to engineering design that takes into account factors such as resistance, flexibility, flotation, and temperature regulation. It is also possible to incorporate fiber optics in the dynamic power cables at a minimal cost. This allows end-to-end communication, which provides an excellent cable condition monitoring system for operators.

Both offshore wind and offshore oil and gas have their challenges in terms of engineering design and construction. While they require similar infrastructure, each industry faces unique challenges. Going forward, these industries will need to rethink and scale up the design and installation of their offshore power generation and transmission infrastructure. But the good news for offshore wind is that many solutions already exist and can be found in the well-established oil and gas industry.

Maxime Toulotte, Head of Technical Marketing for the Subsea & Land Systems, Nexans