Utilizing specialized equipment and advanced manufacturing ensures accurate dimensions and alignment when fabricating offshore wind structures. These processes eliminate structural deviations that can lead to significant installation challenges and negatively affect performance. Innovative material handling produces wind assemblies that resist saltwater corrosion, extreme weather and wave action.
EMILIO TATAY, Navacel Process Industries
The offshore wind turbine market has continued its extraordinary growth since the first turbine was installed offshore Denmark in 1991. BloombergNEF predicts that the global installed capacity of all offshore wind farms will increase from 60,000 MW (end of 2022) to approximately 270,000 MW by 2031. The floating deepwater platform market segment is experiencing remarkable growth, as fixed-bottom sites become scarce. Current estimates suggest up to 80% of global wind power potential exists in deepwater locations.
The offshore wind market will continue to expand, as new floating platform technologies are introduced, and new markets emerge in deepwater sites. Harnessing offshore wind with deepwater floating wind turbines is an essential source of untapped clean and renewable energy. However, harnessing the wind requires extensive experience with custom fabrication and precision machining of equipment and assemblies used in offshore environments.
Offshore wind turbine structures. The oil and gas industry’s experience with floating platforms has enabled the recent rapid increase in interest in floating wind turbines. Oil and gas companies have used floating offshore platforms for their production fields for many years. However, few steel fabricators have extensive experience producing equipment and assemblies that are subjected to harsh marine conditions, including saltwater corrosion, extreme weather and wave action. In addition, many modern-day offshore platform designs must consider the potential environmental impact on marine ecosystems, wildlife and habitats. Minimizing the platform’s footprint and employing measures to mitigate environmental impact are essential for sustainable offshore wind development.
Classification of offshore wind turbines. Offshore structures are designed in various forms and types to perform multiple services, such as offshore wind platforms and for drilling and producing hydrocarbons. Depending on the sea depth where deployed, these structures are generally categorized as fixed or floating, Fig. 1.
A monopile is a common type of bottom-fixed offshore foundation that supports wind turbines and other structures in shallow-to-moderate water depths. The jacket structure, also known as a lattice structure, is another type of bottom-fixed offshore foundation used for supporting wind turbines, particularly in deeper water depths. It consists of a steel framework resembling a jacket anchored to the seabed. Both monopile and jacket foundations have advantages (and disadvantages) and are used, depending on the specific offshore site’s characteristics, including water depth and seabed conditions.
The water depth at the offshore site is a significant limitation that impacts the platform design choice. Bottom-fixed platforms, like monopiles and jackets, are suitable for shallow-to-moderate water depths. As water depths increase, floating platforms like semisubmersibles, spars, and tensioned legs become more viable options. However, each floating platform has limitations regarding water depth and site-specific conditions considered during the design phase. Further, the size and weight of the wind turbines installed on the platform impact its design. Larger and more powerful turbines require more substantial platforms to support the increased vertical and horizontal forces to provide adequate stability.
Deepwater wind platforms have different designs, but the common characteristic is their ability to remain stable and anchored in deep water using mooring systems. Floating platforms deploy wind turbines in deep water areas where wind resources are typically better and more consistent. Unlike fixed platforms, floating platforms do not require jackup or dynamic positioning vessels to install fixed foundations on the seabed.
The design and performance of the mooring and anchoring systems for floating platforms are critical. Properly designed and installed mooring systems are essential to keep the platform in place and maintain tension in the mooring lines. Standard floating platform designs include semisubmersibles, spars, tension leg platforms and barge-like structures.
Semisubmersible platforms consist of columns or pontoons partially submerged to provide stability. The submerged portion acts as ballast, while the columns offer buoyancy. The spar platform is a cylindrical structure with a heavy counterweight at the bottom, designed to minimize platform motion in response to waves and wind. Tension leg platforms have buoyant platforms tethered to the seabed by vertical tensioned legs. The legs maintain the platform’s position and provide stability while allowing vertical motion in response to waves. Finally, dynamically ballasted barge-like platforms achieve the desired stability. It is a simple, cost-effective design, suitable for shallow-to-intermediate water depths.
Well-established oil and gas platform design technologies have been transferred to floating wind turbine plant design, although significant design differences remain. For example, the loads on oil and gas platforms are principally static loads. Floating wind turbine platforms experience primarily dynamic loads, based on wind speed and frequency.
Further, the typical oil and gas platform will concentrate on a single well, so that equipment redundancy and conservative design margins are desirable. A typical floating wind turbine platform must link with perhaps dozens of other platforms to a floating or ground-based electrical substation. Overall, electrical system reliability is based on the number of wind turbines connected to the substation.
Floating offshore wind projects promise to significantly increase renewable energy production in deepwater regions, with much higher wind potential than shore-based projects. Floating wind farms have the added performance advantage of higher and more constant wind speeds, with no obstacles in the wind path. Floating wind farms can be economically installed in water depths between 60 and 300 m.
However, studies are underway for projects in shallow waters down to 30 m and depths as great as 800 m, much less than the range of depths serviced by oil and gas semisubmersible production platforms. The technology of deepwater wind platforms is advancing continually. Research and development efforts are focused on improving efficiency, reducing costs, and expanding the range of suitable water depths. Materials, engineering and design advancements are driving progress in this field.
Extensive offshore structure expertise. Navacel is a leading provider of high-quality manufacturing of capital equipment and steel machining and fabrication for the global offshore oil and gas and offshore wind markets. Fabricating offshore wind turbine platforms presents several unique challenges, due to the harsh marine environment, the size and weight of the components and the need for precision and quality. Offshore wind turbine platforms and related facilities are massive structures, often requiring the fabrication of large and heavy components. Handling and maneuvering these components during fabrication can be challenging. Navacel has specialized facilities and equipment to handle and transport these oversized parts.
Navacel is a recognized industry expert in precision cutting, welding, machining and assembly of large-dimension parts, with tight tolerances required in offshore structures, Fig. 2. Specialized equipment and advanced manufacturing techniques are necessary to ensure accurate dimensions and alignment during fabrication. Any errors or deviations can lead to significant challenges during installation and affect the structure’s performance.
Ensuring the quality and reliability of the fabricated components is of utmost importance for the long-term performance of offshore wind platforms. Strict quality control measures, non-destructive testing, and inspection protocols are necessary to identify defects or weaknesses during fabrication. Given the critical nature of the components, welds and materials used in offshore wind platforms, stringent qualification procedures are required. Welding procedures and materials comply with industry standards and regulations to ensure reliability and durability.
Further, Navacel has extensive experience selecting and applying coatings suited to survive periods of approximately 25 years in very adverse conditions. Implementing effective anti-corrosion measures and developing maintenance strategies are essential to extend the platform’s lifespan and reduce operational costs. Navacel maintains robust quality control systems and procedures and adheres to relevant certification standards to ensure the reliability and safety of offshore wind structures. Regular inspections, testing and certification of components and materials are vital to a well-managed offshore manufacturing operation.
Navacel’s access to a robust supply chain is anchored by many long-time suppliers and sub-contractors. Navacel is also committed to maximizing local content through partnerships with local suppliers, manufacturers, and service providers whenever possible. This program involves sourcing materials, components, and services from local suppliers to support economic growth and reduce logistical complexities. Assessing and mitigating supply chain risks, such as potential disruptions, delays, or quality issues, is essential to maintain project timelines and reliability. Diversifying suppliers and having contingency plans helps manage these risks.
Floating wind turbine platforms are still an emerging technology. Cost is a critical consideration for any offshore wind project. Navacel is at the forefront of the industry in research and development of improved platform design, construction methods, and cost-effectiveness of offshore structures. Balancing the cost of fabrication, installation, and ongoing maintenance with performance and reliability is essential to ensuring the project’s economic viability and competitiveness with other renewable energy sources. Advancements in floating platform technology will play a significant role in expanding offshore wind development into deeper waters.
Extensive offshore structures experience. Navacel was founded in 1974 to address a precision steel fabrication and manufacturing market opportunity. Navacel’s first offshore work was an FPSO project, followed by its first subsea project in 2010. In 2016, Navacel provided the manufacturing and electrical installation of the five tower and bottom sections for Equinor’s 30-MW Hywind Scotland project, the world’s first floating wind farm. The five-turbine project entered commercial service in October 2017.
According to Hywind Scotland, since the project “started production, the floating wind farm has achieved the highest average capacity factor of all UK offshore wind farms, proving the potential of floating offshore wind farms.” The project operates at a 95-to-120 m water depth with a simple three-line mooring system, Fig. 3.
Navacel’s sustained experience in oil and gas markets, plus having supply chain sources for critical materials, has contributed to the success of several first-of-a-kind offshore wind farm projects. In addition to Equinor’s Hywind Scotland project noted above, Navacel fabricated and machined the transition piece for the offshore substation (OSS) with monopile for an offshore wind project, the first OSS with monopile configuration, Fig. 4. The 309-MW wind farm installed in the Belgian North Sea. The OSS collects and exports the power generated by 42 Siemens D7 wind turbines, each rated at 7.35 MW.
Navacel is also investing in protecting the undersea environment with its partnership with IQIP and the BLUE Piling Project to produce the next generation of monopiles for the next generation of offshore wind projects. The venture has two goals. First, the BLUE Piling technology can be used to install the largest monopiles in the world, and second, significantly reduce the noise produced during installation. A large water mass drives down the monopiles into the seabed. The typical BLUE Piling blow significantly reduces the underwater noise produced by more than 20 dB, compared to conventional hammers. Further, the design allows lower acceleration levels, simplifying the monopile’s design and reducing steel fatigue damage to the pile by up to 60% during installation, Fig. 5.
In addition to monopiles, offshore wind platforms may be held into place using suction anchors. Recently, three floating foundations were required for France’s first floating wind farm. The 25-MW floating wind farm uses three Siemens Gamesa wind turbines on tensioned line floats. For this project, Navacel manufactured the suction anchors for the mooring system for the floating platforms and the platform ballasting modules, Fig. 6.
Final thoughts. Navacel has demonstrated its experience with a supply chain specializing in fabricating and installing large offshore structures. There are many challenges when operating deep wells at great depths in the ocean. These harsh operating conditions required specialized fabrication and precision machining of large-dimension assemblies with very tight tolerances to ensure the final assemblies could operate for 25 years in adverse environmental conditions above and below the surface. The company has established experience and expertise in the large-scale, precision machining and fabrication of wind turbine structures and various production and R&D apparatus used in the rapidly growing offshore wind industry. WO
EMILIO TATAY is CEO of Navacel Process Industries SA, based in Bilbao, Spain. He has been with Navacel group since 2020 and brings more than 25 years of experience in business development, commercial and project operations leadership. He has held several senior positions, including V.P. of regional sales, E.V.P. for commercial and thermal operations, and most recently served as president and CEO of Amec Foster Wheeler Energía, Industrial Power. For more information contact info@navacel.com.