The way the world thinks about renewable energy has transformed. It is no longer just a concept but a reality, and interest in renewable energy is growing globally. With much of the world looking for fossil-free energy sources, wind power is becoming increasingly popular, and forward-looking companies are adapting their oil and gas solutions for use in the renewables sector.
As the industry continues to move further offshore, oil and gas companies can shorten the development time for new concepts by transferring oil and gas industry knowledge and expertise to renewable energy.
The offshore oil industry can bring four main lessons to the offshore wind industry: proven technologies and experience from offshore applications that can be tailored to offshore wind applications; maintenance of the high standard of safety and compliance levels for product design, manufacture and installation; innovation and pushing boundaries; and suppliers' and customers' engineers working shoulder-to-shoulder.
Using these four lessons, Trelleborg has found that its passion for innovative polymer engineering in the offshore oil and gas sector has helped accelerate performance for its customers in renewables. One example of this knowledge transfer is the development of a cable protection system using similar materials to those in oil and gas applications and rethinking the design for use on offshore wind farms.
The requirements for design integrity are subtly different for the different sectors, and renewable cable protection is generally for power cables, as opposed to risers and umbilicals, and most often with much smaller diameters and less dynamic loads than in the oil and gas sector.
Industry Knowledge Sharing
Trelleborg has historically been the supplier of choice in safety critical applications where failure of the key components is simply not an option. For example, many thousands of dynamic bend stiffeners have been supplied to projects across the globe with zero failures. The main driver for this is the rigorous design methodology, with key safety factors an inherent part of the process.
This same rigor is used in the design of renewable products, but the key difference is that materials, tolerances and conservatism can be reduced due to the nature of the power cables compared to risers and umbilicals.
With the world looking increasingly for more sustainable forms of energy, Trelleborg devised equally reliable solutions for wind farms. One of these solutions is NjordGuard, a cable protection system specifically designed for the renewables market, used to protect cables carrying electrical power generated by wind farms from the converter platform back to shore. The system also protects the interarray cables connecting each wind turbine subsea.
The entry and exit point for the power cables at each turbine will see significant loads due to a combination of wave height, water depth, storm conditions and tidal currents. These areas can see significant cable fatigue and damage, therefore, protection is required from each entry and exit point to the burial point. In some cases the burial point can be 20 to 30 m from the turbine base with a significant free span. Trelleborg’s experience in dynamic cable protection can overcome these issues using tried and tested design methodology gained from years of oil and gas design.
Reworking for Renewables
Adapting the cable protection system for wind farms involved rethinking a number of design features. One of the main challenges was to stop being so conservative in the design process. After analysis, it was decided that the cables did not need to be so large and the wall thickness of the polymer used could be reduced and still meet the requirements. Another modification was ensuring that the cable protection material could manage the increased amount of heat generated by power cables.
Working shoulder-to-shoulder with customers’ engineering teams, Trelleborg was able to address other issues that were important in reducing installation time and costs. By listening to customers’ needs, the product development team designed an innovative protection system so that cable protection could be installed, removed and reused without the use of an ROV or diver intervention. This specific design improves safety and reduces installation complexity. The cutting-edge solution also permits both monopile and J-tube installation for wind turbine generators and offshore substation platforms without procedural variation.
By rethinking the design to meet the requirements needed for wind farm power cables, Trelleborg was able to successfully overcome the design challenges, and the protection system is now ready for rollout on offshore wind projects.
Trelleborg successfully completed a series of wet tests in November and December 2016 to verify the capabilities and functionality of its NjordGuard cable protection system for installation and removal on J-tube and monopile interfaces for offshore wind farms.
The testing took place at the Offshore Renewable Energy (ORE) Catapult’s National Renewable Energy Centre, the U.K.’s flagship technology innovation and research center for offshore wind, wave and tidal energy.
Trelleborg was able to perform eight full-scale wet tests of NjordGuard using ORE Catapult’s controlled open-access shallow-water testing environment facility located in Blyth, England, covering a range of installation scenarios without having to go offshore. In addition to passing all the tests, the cable protection system was installed and removed from the test rig without use of an ROV.
The successful tests definitively prove NjordGuard is capable of installation into both monopile and J-tube openings and can be successfully removed without the need for ROVs. The test results provide a greater understanding of potential installation issues customers might face, such as pull-in and pull-out loads. We also gained valuable insights into the dynamics of the system to help further refine and optimize our designs to optimize performance for our customers' critical applications.
Currently available to the market for both array and export cables, further testing of NjordGuard will be an integral part of developing and enhancing the solution to meet our customer needs and further highlights our commitment to supporting renewable energy projects.
“It is essential for companies to be able to test their products in a controlled environment, allowing input into the design and installation procedures at an early stage," said Stephen Robertson, head of business development for ORE Catapult. "Our marine and subsea renewable testing facilities provide an excellent environment in which to carry out these kinds of tests.”
The offshore wind industry can gain insight from the offshore oil industry through transferrable, proven technologies and experience from offshore applications; a high standard of safety and compliance levels for product design, manufacture and installation; constant innovation; and working shoulder-to-shoulder with customers’ engineers to design the best solution.
Phillip Walsh will be speaking during the Industry Demands for Offshore Wind Engineering and Design session at the Offshore Wind Executive Summit in Houston, Texas, on August 9. To learn more or to register for the event, please click here.