Most offshore wind projects are installed in several steps: a monopile is driven into the seabed, a transition piece is put on top if this, followed by the tower, and nacelle and rotor blades. Each step takes time, is sensitive to weather conditions, and makes installation an important component in overall project costs. By reducing both the number of steps, the installation time and/or weather sensitivity of each step, significant cost savings could be achieved.
The Slip Joint is a new type of connection between the wind turbine and the monopile developed by the company Delft Offshore Turbine (DOT). The tower section of the wind turbine has a conical shape which is matched by the conical shape of the foundation monopile. Installation is done by simply sliding the wind turbine over the monopile thus creating a friction-based connection without the use for grout or bolts. This simple mechanism allows for cost reduction through both savings on required material/equipment/personnel as well as a shorter installation time.
Within the Slip Joint Offshore Research (SJOR) project the principle of this innovation will be tested under offshore conditions in the North Sea. The project is a collaboration of the GROW partners DOT, TU Delft, TNO, Van Oord and Sif Group, and the offshore test is enabled by GROW partner Eneco, the owner of the Princess Amalia offshore wind farm where the monopile and turbine will be installed. Project partner Heerema Marine Contractors provide the tools and expertise to successfully install monopile and turbine.
In September 2018 a full wind turbine has been successfully installed in the North Sea (Prinses Amalia offshore wind farm) and will stay offshore for a year to test and collect data regarding this innovative connection. The next step will be the commercialisation of this technology. The successful demonstration of slip joint technology is one of the first tangible achievements under the GROW program. DOT develops various new concepts that should contribute to a further cost reduction of offshore wind energy. Next to the slip joint technology, the monopile has been vibrated into the soil using a Vibro Lifting Tool, and the turbine itself is an example of an hydraulic turbine.
Slip Joint Offshore Research project (SJOR) (presentation at GROW side-event 2019)
Dutch Innovations Promise Lower Maintenance Costs For Offshore Wind (article in Clean Technica 2018)
First offshore wind turbine using the Slip Joint connection successfully installed (Press release installation 2018)
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