Offshore wind farms are a growing part of energy development, offering cost-effective renewable energy to customers. For Equinor, an offshore wind farm was key to powering its offshore operations while reducing CO2 emissions in the process. The energy company is constructing the world's largest floating offshore wind farm, but to do so it needed help in a big way and turned to Mammoet for assistance.
Equinor's Hywind Tampen is the largest floating wind farm to date, and together with the earlier Hywind Scotland pilot project will generate around half of the world's floating wind power.
A technology that is still growing, the floating wind turbines must be used on floating foundations, as the water depth and seabed geology in the area are challenging for fixed-bottom turbines. That meant that the entire 8.6 MW turbines - including tower sections, nacelles and blades - onto 107 metre spar buoys that are mostly underwater. That work was performed in port, where the system can be controlled and kept static, prior to towing to the installation point.
Assembly took place in the Gulen Industrial Harbour on Norway's rugged west coast, which had the draft needed to handle the floating foundations and a location convenient to the project site. Crane vessels were considered but it was determined they would increase the complexity of assembly, and jack-up vessels would be too short to reach the turbine sections. Plus, the foundation needed clearance from the seabed, requiring a spacer barge between the quay and spar and a reach from the shore of around 143 metres.
Mammoet, which was involved with deployment of the Hywind Scotland floating wind farm, was brought in for turbine assembly and associated port handling work.
"We recognized that we would need a crane with a huge outreach to make the required lifts. The majority of land-based cranes in any fleet would not be able to achieve a 143m distance at these weights, but we knew that if it could be done the project would benefit significantly. This would create a smooth production line from marshalling yard to turbine assembly to commissioning - all at the same location - optimizing the use of offshore assets," related Martin Tieman, Mammoet project manager.
Mammoet turned to its PTC 200-DS ring crane, once the port confirmed its quay would be able to handle the ground pressures of the project. To counteract weather conditions, especially challenges generated by the effects of wind on large turbine blades, the crane was modified to ensure precise control of components, with the goal of preventing potential work stoppages due to weather.
The modifications allowed the crane to work with third-party blade yoke and tugger winch systems, which orient the load under hook without the need for taglines operated by hand and prevent damage while improving safety.
In addition to assembly work, Mammoet managed port handling capabilities for receiving tower pieces, nacelles and blades from vessels and storing for easy retrieval and use. The project also involved uses of 24 axle lines of Mammoet's SPMTs (self-propelled modular transporter) and an LR1750 crane that assisted the PTC on lifts requiring rotation of components.
As a result, the project was completed efficiently, and Hywind Tampen was scheduled to begin producing power in the third quarter of 2022.
"Having worked on numerous large-scale offshore wind projects, we understand how important the logistics between port delivery and installation are to maintaining schedule. Our specialist team has successfully executed this scope for some of the biggest offshore wind projects in the world, giving us the experience to maximize utilization of key assets and so deliver the highest levels of project cost-efficiency," Tieman concluded.
