foundations
faster. These are just a few of the key benefits of our value proposition.” As highlighted previously in OWJ, the suction bucket foundation has a number of other advantages, not least that the installation process does not require the use of jack-up vessels, there is no requirement for seabed preparation or the use of divers and there is no need for a separate transition piece, eliminating the need for a grouted connection. The suction bucket also needs less scour protection (or no protection at all, depending on location and seabed conditions), and the suction operation can be reversed, allowing complete removal of the foundation and its reuse.
The suction bucket foundations are
far from being the only type of new foundations that are being designed, built and tested, however.
As highlighted in the second-quarter 2014 issue of OWJ, later this year, the first example of another innovative foundation design is expected to be installed, the first ‘base plate’ for Seatower’s crane-free foundation having recently been cast in France.
The foundation is due to be installed
approximately 17km offshore from Fécamp in France in a water depth of 27m. Seatower is working with MT Højgaard in Denmark and Eiffage TP in France on the project on the Parc éolien en mer de Fécamp on behalf of French energy company EDF Energies Nouvelles, Dong Energy and wpd Offshore in Germany. The base plate for the prototype foundation is slightly in excess of 23m in diameter and approximately 1m high. Once ballasted and fitted with the met mast it will carry, it will weigh 1,760 tonnes. The foundation will be lowered to the seabed having first been ballasted with seawater, the seabed having been prepared in advance, so that the foundation will be self-levelling. The new type of concrete gravity foundation was primarily designed for locations where the seabed conditions make driving a monopile impossible, but it is also suitable for use in deep water. It is also designed to be inexpensive and easy to install, being towed into location using tugs, without the need for large installation vessels. This means that several foundations can be installed in parallel in a relatively short weather window. Like the suction bucket foundations described above, the crane-free foundation is also more
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environmentally friendly because it does not require the use of piling. The structure is a hybrid one, made from concrete and steel, and can be mass produced efficiently. Usually, foundations and towers for
offshore wind turbines mounted on monopiles are connected by means of a transition piece, but a new approach is being pioneered on the Luchterduinen offshore windfarm in The Netherlands. Luchterduinen will be one of the first windfarms without separate transition pieces and instead will make use of foundations into which the transition piece is already integrated. This will reduce material costs and reduce the time it takes to install the turbine. The key element of the design, conceived by the main contractor for Eneco’s Luchterduinen windfarm, Van Oord, is the greater height of the
foundation piles, which will extend 17m above sea level rather than approximately 4m, as has been the case previously. The main innovation in the design is the fact that the flange connection between the turbine and the foundation pile can sustain the impact of the pile driver. Components such as the ladders and the platform will be connected to the pile offshore, after completion of the pile-driving process. This eliminates the need to design mounting structures for components such as these that could withstand the substantial forces imparted by a pile driver. The foundations are being built
by Sif Group in Roermond. Smulders Projects in Antwerp will then weld the mounting structures onto the piles. Van Oord was due to begin installing the foundations in July. OWJ
TAG foundations bound for Humber Gateway
TAG Energy Solutions achieved a significant landmark in its project to produce foundations for the Humber Gateway offshore windfarm recently when the company undertook the load out and sailaway of four 60m long, 650 tonne monopile foundations and four transition pieces destined for the windfarm, which is 8km off the Yorkshire coast close to the mouth of the Humber Estuary. The foundations are part of a project to deliver 16 monopiles and transition pieces for the Humber Gateway development. The remaining 12 foundations were due to sail away from TAG Energy
The first base plate for Seatower’s crane- free foundation was recently completed
Solutions’ site on the River Tees by the end of August. The first set of monopiles was loaded onto a barge by a self- propelled modular transporter (SPMT) with the transition pieces lifted by crane onto the barge at TAG Energy Solutions’ wet dock facility. The barge was then taken down the River Tees where the turbines were loaded onto the turbine installation vessel MPI Discovery. The contract to build the foundations made TAG Energy Solutions the first UK manufacturer to secure a substantial monopile and transition piece project for a windfarm in British waters.
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