‘Breakthrough TLP technology’ to be tested in Mediterranean

Several floating wind platforms are currently being tested in projects in Euope, among them a novel inclined tension leg platform originally developed by SBM Offshore and IFP Energies Nouvelles that is being used in an upcoming French project.

One of a quartet of floating wind demonstration projects awarded contracts following a call for projects issued by ADEME (France’s Agency for Environment and Energy Management), Provence Grand Large (PGL) in the Mediterranean combines industrial challenges with significant research and development content, as EDF Energies Nouvelles EPCI director Sébastien Tessier told the US Offshore Wind Virtual conference.

Led by EDF and Enbridge, who each have a 50% stake in PGL, the pilot project has led to the award of three contracts for the construction phase and an interface contract with incentives for the contractors. The construction contracts were awarded to Siemens Gamesa Renewable Energy, who will supply the 8.4-MW turbines for the project, SBM Offshore, which is responsible for the floater and for turbine installation, and Prysmian, for the inter array and export cables. RTE is responsible for the grid connection. A separate contract will also be awarded for the maintenance of the balance of plant over the lifetime of the project.

The SWP-8.0-154 turbines will be installed on SBM Offshore’s inclined tension leg platform at a site approximately 40 km west of Marseille, which will act as the marshalling harbour for the project, in a water depth of approximately 100 m with a mean wind speed of circa 10 m/second.

Describing the inclined TLP as a ‘breakthrough technology,’ Mr Tessier said it had several potential advantages in the floating wind sector. Consisting of three side buoys with a central buoy and bracing structure, the inclined TLP has two mooring lines per buoy. The structure is essentially ‘transparent’ to wave action and has been designed for high performance throughout its lifecycle, including in-place dynamics, as well as for wet tow with the turbine installed and during the mooring and hook-up phase.

The specially designed mooring configuration adopted by SBM Offshore ensures it is well-adapted to loads imparted by the turbine. Tower base movements are reduced by the concept, ensuring the plane of the rotor is always realigned to vertical. Using three bundles of two lines, it uses conventional, proven mooring components – including the chains and wire ropes – thanks to the low level of tension in the design. It also uses field-proven accessories to limit out of plane bend fatigue in the mooring chains.

Another important advantage of the TLP concept is that it has been designed to scale well as the size of the wind turbine installed on it grows and – apart from important considerations such as low cost industrialisation – its use ensures the nacelle will have what Mr Tessier described as ‘excellent dynamics.’ Yet another important advantage is that the TLP does not require active ballasting or stabilisation systems to operate and maintain it.

An experimental campaign in a basin using a 1/33 scale that simulated the combined effect of wind and wave swell demonstrated very positive results, as did an assessment of the combined effects on the turbine of aerodynamic and hydrodynamic forces. “Overall, the TLP gives very good in-place dynamics,” Mr Tessier noted.

“When the TLP structure is being towed, its waterplane area is limited,” he explained, “so it behaves well in waves. Its compact layout minimises its environmental footprint, and unlike catenary mooring systems used some floaters, there is little risk of chain dragging or of any impact on fisheries in the areas in which it is installed.”

Development started in 2016 and a final investment decision is expected in Q3 2020. If all goes according to plan, the floating windfarm should be in production by mid-to-late 2022.