Finnish engineering and consulting company Elomatic has unveiled a new type of foundation for offshore wind turbines that eliminates the need for heavy-lift vessels
The company believes its invention, the Float Foundation – a version of the well-known gravity-base structure (GBS) – could be significantly less expensive than a conventional foundation.
Compared with conventional installation techniques, Elomatic believes the new foundation could provide cost savings of as much as €70M (US$76M) for every 1 GW of windfarm capacity.
There are a number of gravity-base foundations. Elomatic’s is a ‘float-out-and-sink’ concept based on a structure assembled on land that tugs tow to an offshore site using pontoons. Once at the site, an injection of water ballasts the structure to the seabed.
Additional ballast can used, in the form of sand or aggregate, if required by the location or environmental loads, but the Float Foundation is designed in such a way that, normally, additional ballast is not needed.
The structure consist of voids or ‘tanks’ into which seawater is pumped. If the skirts of the foundation do not achieve full penetration, pumps inside the modules from which it is built can be used to remove material underneath them to achieve full penetration.
As Elomatic vice president offshore technology Ted Bergman told OWJ, the company, which has a lengthy background in the offshore oil and gas industry, has adapted a concept it originally developed to fabricate artificial islands in the oil and gas industry in the Caspian.
“The Float Foundation enables the foundation and turbine to be integrated onshore, and then towed to the offshore site and lowered to the seabed without the use of heavy-lift vessels, “ Mr Bergman explained. “That saves a lot of money, and eliminates a potential bottleneck caused by a dearth of installation vessels.
“Apart from that, the concept has several other advantages. We developed it to produce artificial islands around 90 m in diameter, which are also towed into place and then sunk to the seabed. Like the man-made islands, the structure of the foundation is constructed from steel blocks and modules, which creates local manufacturing content wherever manufacturing takes place.
“Another advantage of the Float Foundation is that it makes possible the construction of offshore windfarms in water depths of less than 10 m, for which conventional installation technology is unsuited, in addition to constructing windfarms in deep water.”
Elomatic said Float Foundation is suitable for use in water depths of up to 45 m and the company has developed it with 15-GW offshore wind turbines in mind. Larger turbines, of up to 20 MW could be accommodated by increasing the diameter of the foundation.
Mr Bergman said the patent-pending solution is also environmentally friendly, because it does not require the use of piling, as is the case with the most widely used foundation in the offshore wind industry, monopiles. “The Float Foundation is safe and cost-effective to build, install and operate. It is suitable for use in ice-prone areas,” Mr Bergman concluded.
Elomatic has presented the Float Foundation to developers and construction companies and said it has been well-received. It has conducted a number of case studies to compare the cost of using it with conventional technology and has begun proposing it for upcoming projects.
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