Growth through Research, development & demonstration in Offshore Wind

First offshore wind turbine using the Slip Joint connection successfully installed

SJOR project tests innovative connection offshore: ready-to-use installation within an hour.

The DOT wind turbine was successfully installed on its previously installed monopile using a Slip Joint connection. The Slip Joint is an alternative connection between an offshore wind turbine and its foundation. It works and looks like two paper cups upside down stacked on top of each other. The connection is based on friction, where the weight ensures a firm and stable connection. Installation is done by simply sliding the wind turbine over the monopile without the use of grout or bolts. This simple mechanism allows for cost reduction in material, equipment & personnel as well as allowing for a shorter installation time. It is the first time a slip-joint connection is deployed offshore.

The DOT wind turbine is located in Eneco’s Princes Amalia Wind Park off the coast of IJmuiden, the Netherlands. The complete wind turbine was picked up in a single lift by Heerema’s DCV Aegir from the quay of Sif Rotterdam and transported towards its designated location. The installation of the wind turbine took within an hour in total, which is noticeably faster than usual installation. Jan van der Tempel, Director of DOT BV: “This offshore installation is a major milestone in the commercialisation of the Slip Joint.” The wind turbine will stay offshore for a year to test and collect data regarding this innovative connection after which the gathered data will be processed and used for validating lab tests by both TU Delft and TNO.

The Slip Joint connection is a logical next step in the evolution of the monopile-turbine interface. Initially, the connection was created using concrete (grout) to fill in the gap between a transition piece and the monopile. The industry then moved to bolted connections. These kind of connections between a monopile and the tower of the wind turbine are less interesting since the constructions of future turbines will be larger and heavier. Sometimes innovations need time to develop.

The SJOR project is part of the GROW program. David de Jager, Managing Director Stichting GROW adds: “This step in the SJOR project marks a significant moment for the GROW consortium. Through intense cooperation and knowledge exchange between industry and research institutes we now see the Dutch offshore wind sector introduce new technologies faster. This will help to ensure the leading position of this sector, both in Europe and around the world”.

Within DOT; a spin-off of Delft University of Technology, innovations like the Slip Joint are subjected to the final proof of the pudding: putting the steel in the water. As partner in the GROW consortium, DOT found the funding and appetite with the larger industry partners. De Jager: “The open Dutch culture helps to collaborate on issues that are relevant for the sector as a whole and accelerates the market introduction of innovations as the Slip Joint. With a projected cost reduction of around 10-20 million euro per offshore wind farm, the Slip Joint certainly adds to further cost reductions in offshore wind.”

Installation Slip Joint Connection, source DOT

            Installation Slip Joint Connection, source DOT
Installation Slip Joint Connection, source DOT