This is what the foundation of the world's deepest offshore wind park looks like. The technology is Norwegian
Huge buckets are heavy feet that hold wind turbines in place on the seabed. The deepest bucket foundation was installed at a water depth of 58.6 meters, setting a new world record.
During Easter, the final foundation for the world's deepest bottom-fixed wind turbine park was installed for Scotland's largest wind farm, Seagreen.
The foundations, called bucket foundations, consist of a steel substructure with three legs and are anchored in the seabed. The bucket foundations are installed by suctioning the upside-down buckets into the seabed.
The foundations were further developed and industrialized by Norwegian experts from Equinor (formerly Statoil) and the Norwegian Geotechnical Institute (NGI) in the 1990s.
Technology developed for oil and gas is used in environmentally friendly installations.
Technical expert at NGI, Per Sparrevik, explains that this demonstrates how technology developed for oil and gas can be utilized in environmentally friendly installations that provide renewable energy to the world and contribute to the green transition:
"The bucket foundations, or suction anchors as they are often called, were developed in connection with anchoring floating and bottom-fixed oil and gas platforms in the 1990s," says Sparrevik.
The technology is widely used worldwide today, but it is no longer solely used for oil platform foundations.
"This Norwegian niche technology remains an attractive foundation solution for installations in offshore areas around the world, now also for offshore wind turbines," adds Sparrevik.
Power for 1.6 million households
Seagreen is a wind farm located 27 kilometers east of Scotland. It has 114 wind turbines installed and is now Scotland's largest wind farm.
Once operational, the wind farm will generate 5,000 gigawatt-hours of green energy annually.
That's enough to supply power to over 1.6 million households in England and Scotland.
The bucket foundations withstand extreme loads
The foundation system was developed as an alternative to long piles. In deep water and when the soil conditions make pile installation challenging, there was a need for a solution that could be efficiently installed on the seabed without noise. It also had to withstand significant loads from waves and wind.
The weight of the water keeps the foundations in place.
When the bucket foundations reach the seabed, they initially penetrate the soil due to their own weight. The water is then pumped out from the inside of the buckets.
Translate this into English: The bucket foundations are then further pressed into the seabed using suction force, similar to enormous hydraulic jacks.
Once the installation is complete and the pumping units are removed from the top of the buckets, they are sealed.
"If you try to pull up the foundations, there is suction on the inside while the pressure on the outside remains the same. This stability can be demonstrated by using an open tin can on the beach this summer," explains Sparrevik.
Complex soil conditions
The soil conditions at Seagreen are complex. The installation of the 114 steel substructures, each with three suction buckets, has contributed to increased knowledge.
"Through our work, we have expanded our understanding of calculating the forces required for seabed penetration and how to best handle challenging installation conditions. These experiences will provide valuable lessons for the future development of offshore wind power in Norway," says Per Sparrevik.
Additionally, the installations at Seagreen demonstrate the robustness of the concept. The expert believes that these foundations can be used in many offshore areas with varying soil conditions.