Global Marine Systems on the future of offshore wind cabling
Gabriel Ruhan, CEO of Global Marine Systems, talks to Wind Energy Update about how to cut the cost and increase the quality of subsea cabling.
WindEnergyUpdate: How is Global Marine tailoring its vessels / equipment to offshore wind farm cable laying?
Ruhan: Many of the requirements of offshore wind farm cable installation are similar to those of telecoms cabling, which is why we spotted an opportunity in the market nearly 10 years ago to turn our telecoms expertise to this burgeoning sector. As a result, we formed Seabed Power, a joint venture with Visser & Smit Marine Contracting, which delivers power-cabling solutions from the landfall to subsea for the power and offshore renewable energy markets. Both our companies’ experience in installation and maintenance of all types of subsea cables is in excess of two centuries.
We apply what we’ve learned from our telecoms experience to offshore wind farms, meaning we have been able to utilise our years of expertise in areas such as route planning, vessel scheduling and vessel selection. In many cases, we are also able to use our fleet of vessels, sea ploughs, and remotely operated vehicles (ROVs) for cable lay and post-installation inspection in the offshore wind sector.
However, there are key differences that we have learnt over our years of experience from our first Round 1 projects. Firstly, as power cables are much bigger than fibre-optic telecoms cables, the weight and coiling characteristics are therefore different, so we use deck-level turntables to deploy the cables without twisting them. Secondly, the Round 1 and Round 2 wind farms have typically been located in shallower waters, compared to the vast majority of telecoms cabling which takes place in deep-sea waters.
The Stemat Spirit, our new vessel that will be launched early next year, has been specifically designed to address some of the issues associated with offshore wind farm cable installation. It will be equipped with a 25m diameter, 4,000 ton turntable system capable of deploying a variety of products and cables, including power cable trunk lines, up to a weight of 150 kg/m. The Spirit will also be wider than a standard vessel and will be equipped with advanced dynamic positioning technology that will make it more agile than the barges used in the market today, and enable it to ‘hold station’ without the use of anchors.
WindEnergyUpdate: Are the traditional telecom cable laying methods, using a large crew and boat cost efficient in the offshore wind environment?
Ruhan: One of the engineering challenges of installing power cables is that a single length of cable is more conductive than a series of joined cables, so the sheer length of cable required to connect an offshore wind-farm to the power grid requires a large turntable. A vessel therefore must be able to carry that kind of weight and operate in shallow water yet it also must provide a stable platform in deeper, rougher seas.
Of course, it is important to get the installation right first-time around as this is what makes a project cost-efficient in the long-run. It may be a ‘false economy’ to use a smaller vessel, as ultimately it will not be properly equipped for the job – especially as we move to Round 3 installations that will be taking place further offshore and in deeper waters.
It’s also worth mentioning that, as well as learning from the equipment and techniques used in the telecommunications industry, a well thought-out subsea cable maintenance plan is a core element to the telecoms cable owner’s business model. Similarly, in Oil & Gas Life of Field (Riser Monitoring) is a major priority. In the same way, this needs to be the case with offshore wind farms. Cable and turbine maintenance will make the difference between reliable output and prolonged interruptions and downtime – the power cable is, after all, a key part in the jigsaw of any offshore wind farm that delivers the power to the grid. Without it, an offshore farm will never perform to its projected operational capacity.
WindEnergyUpdate: What’s the future of cable laying for offshore wind? Will we see it becoming cheaper and quicker? How?
Ruhan: While our business, the installation and maintenance of subsea cables, is a niche part of any windfarm project, we understand that all the suppliers and contractors in this business are interdependent. We are in the beginning stages of a new, world wide industry. As the industry continues to grow here in the UK and Europe, as well in North America and Asia, all parts of the industry, the tower, turbine and cable manufacturers, power companies, local and national governments, will continue to refine and scale our businesses. I have no doubt that throughout that process we will find any number of areas where we can improve overall efficiencies and control costs.
Take cable detection as a small but interesting example. Once installed, and prior to powering the system, a cable needs to be detected for burial verification, optical integrity testing and possible future maintenance. Once buried, the detection of a power cable is fraught with difficulty due to ‘ghosting’ of the signals – relative to the coil array, the cable usually appears deeper than expected. A simple solution to this problem is to use temporary power and Wi-Fi optical connections to effectively daisy-chain the turbines, with the cable vessels controlling the application of electrical and/or optical power. This would require a minor piece of inexpensive technology to be added to each turbine to allow for such future testing. The main barrier to implementation is the integration of this into the overall scheme of installation and operations. However, with a little planning and coordination, a simple idea like this, and others like it, could save time and money in the long run.