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Above: Launch of the foundation using semisubmersible barge
Left: Installation of the turbine using a conventional landbased onshore crane
directors of TetraSpar Demonstrator ApS, said that grid connection and full commissioning represented a huge milestone for the project. “First and foremost, we are happy to have completed all phases of the project without any significant safety incidents, even though we have deployed a very innovative project with a range of world first elements. The deep experience of our project partners has been invaluable in this regard. Next, we are obviously very pleased that the new technologies, a few years ago only ambitions and design proposals, have now come to fruition. All indications are that our key target, to accelerate the industrialisation of floating offshore wind, can actually be met, not only at prototype level but at large scale.” Thomas Brostrom, senior vice president renewables, Shell said: “Shell is committed to further develop the floating wind industry globally by providing technical and financial support to promising concepts such as TetraSpar. Ultimately, we hope to deploy floating wind technology globally and at large scale.”
Seiichi Fubasami, president of TEPCO RP, said: “In Japan we expect more floating offshore wind farms to be built from 2030 onwards as we aim for realisation of carbon neutrality in 2050.” The TetraSpar concept suits Japanese conditions, he noted, and lends itself to the establishment of regional supply chains.
“The spark of genius with the TetraSpar concept”, said Sven Utermöhlen, CEO offshore wind, RWE Renewables, “is its industrialised manufacturing and assembly methodology, which we think is crucial for long-term cost reduction. Our deep involvement in this project means we have now gathered first-hand evidence about how this approach can be scaled up to commercial projects. This project has taught us more crucial lessons than we could have ever expected, and it has been great to work so collaboratively with our project partners to safely deliver such an innovative technology. It has been particularly interesting to see how important it is to transfer RWE’s experience in seabed-fixed offshore wind into our floating projects.” The upcoming test phase will provide the
16 | January/February 2022|
www.modernpowersystems.com
Towing with keel fully deployed. The keel was lowered once the vessel reached sufficient water depth, north of Skagen
four partnering companies with important new knowledge and opportunities to further refine the TetraSpar technology.
The TetraSpar foundation components were manufactured at the facilities of the Danish wind turbine tower manufacturer Welcon, in Give, Denmark. Welcon is a leading supplier of offshore wind turbine towers, and its automated production lines are ideally suited for the manufacturing of the tubular braces and tanks deployed for the Tetra concept.
Tetra’s modular components resemble wind
turbine towers, “the world’s lowest cost-per-kg steel structure”, says Stiesdal. Manufacturing of the modules would typically take place at tower or monopile production facilities, as exemplified by Welcon, applying automated processes and benefiting from the existing offshore supply chain. All structural welds are implemented as longitudinal or circumferential butt welds suited for automated submerged arc welding. Surface protection is also carried out in a factory environment, and the result is high-quality, low- weight and low-cost foundation modules. Following manufacture by Welcon, the components were transported to the port of Grenaa over the summer of 2020. Assembly took place at Grenaa in October and November 2020. A flat area of quayside was reserved for the assembly at Grenaa, with no special facilities needed. The quayside assembly involved no welding or other special processes, and, in fact, key elements of the assembly process took less time than had been expected. The fact that all parts of the foundation were manufactured offsite with industrialised processes “makes TetraSpar the world’s first fully industrialised offshore wind foundation”, say its developers, reducing manufacturing hours by 85-90%.
The subsea cable connection to the Norwegian grid was carried out by Bourbon Subsea Services.
Source of all pictures: Stiesdal
Tow out from Grenaa, July 2021. The keel is in place under the foundation. Port basin water depth: 10.5 m
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