This article introduction comes from the media center of Offshore Foundations, here: https://goo.gl/E1NPQl . The suction bucket foundation, quite a clever design, will be used in the IceBreaker project slated for Lake Erie.
According to the Carbon Trust’s Offshore Wind Accelerator (OWA) program, the design, fabrication and installation of turbine foundations in an offshore wind farm makes up about 30% of its total capital cost. At a time when the focus in the industry is firmly on cost reduction, foundations are considered one of the key areas where cost savings can be implemented.
More than costs
While it may be the driving force, cost is not the only issue concerning foundations. With the progression of the UK’s Round 3 of development and with the move to deeper water across the industry in general, the traditional monopile foundation will become less practical. Larger turbines (up to 10 MW or more) are crucial to the future of the industry in terms of improving the cost of energy, and these turbines will need suitable and cost-effective foundations.
There are several new types of foundation in development and testing, and suction buckets are one of the most promising options, with various prototypes already installed. The technology is far from new, having been used in the oil and gas industries for several decades, so it makes sense that as wind farms move further from shore, they move away from the traditional monopile foundation and progress to a more suitable foundation for the prevailing conditions.
Suction buckets in the oil and gas industries
The oil and gas industries are many years ahead of the wind industry in terms of expertise and experience at sea. The established technology at use in those industries can be adapted and developed for wind farms. When oil recovery began in the 1970’s the early foundations were steel-framed jackets, which were fixed to the seafloor using open-end steel pipe piles that were driven through the jacket legs and then welded to the jacket. When oil was discovered in the North Sea, the subsoil was found to be stiff enough that shallow foundations could be used, and gravity platforms became the common design. To minimize potential problems with scour, the sides of the foundations were built with side walls called skirts which extended down into the subsoil. As the platforms were sunk, the skirts would penetrate until equilibrium was established and then any remaining water trapped between the platform and the seafloor was pumped out to create a pressure differential and force the platform down. The concept of using skirts with smaller steel tubes and installing them with suction was first introduced in Norway in the mid 1990’s with the Norwegian Geotechnical Institute (NGI) playing a major role in their development. It was then that the term ‘Suction Bucket’ was first coined.
Trials with wind energy
The wind industry faces the same challenges of moving to deeper water and developing more cost– effective foundations. Suction buckets are a viable option.
For the full six-page, suction-bucket report: https://goo.gl/FlKEqh