• Energy transition,

SEM-REV - our offshore test site ready to supply its first kWhs to the French electrical grid

Our team has worked 24/7 with Mojo Maritime France for the last week on the SEM-REV offshore test site off the coast from Le Croisic. The goal was to replace a defective connection box which was preventing electrical connection to marine energy (wind and wave) converters.


on June 28, 2018

SEM REV Floatgen
SEM REV Floatgen
The Floatgen floating wind turbine, the first French offshore wind turbine, is one of the few floating wind turbine prototypes installed in the world today. The turbine had been waiting for this moment since the day it arrived on site last May. The operation, carefully managed by Mojo Maritime France, was a total success and the 8MW electrical connection is now operational and will start supplying energy this summer.

For the record, it was two years ago that Centrale Nantes researchers and engineers installed the subsea connection hub, to which three demonstrators can connect simultaneously on the SEM-REV site. Since then, projects have been queueing up to access one of the few multi-technology test sites in the world. The first of these was the iconic Floatgen floating wind turbine, developed in a consortium with Ideol and Bouygues Travaux Publics.

However, the final validation checks on the connection revealed an insulation defect on one of the phases of the 25km-long underwater cable. It was then a race against the clock to not jeopardize the future of the site and its projects: the connection had to be repaired by 2018.

But where exactly was the defect? The answer is far from obvious when you consider that the export cable, intersected by fifteen connection boxes, is buried 20m deep under the rock of the Croisic coastline from where it extends for a further 23km towards the offshore site, under more than two metres of sand and at sea depths of up to 40m. It took eighteen months of intensive research at Centrale Nantes to pinpoint the exact location, thanks to advanced technologies based on electrical echometry and acoustics, implemented by the ENEDIS and EDF teams. The defect was gradually tracked down to a faulty connection box which fortunately lay on the seabed, accessible and interchangeable.

The decision was made quickly: change the box and restore the integrity of the electrical connection while maintaining the quality of the optical fibres that run through it, all at a depth of 40m. Centrale Nantes thus drew on the expertise of Mojo Maritime France, the Nantes-based local subsidiary of James Fisher Marine Services whose offshore project management experience is well established in the marine renewables sector. An imposing offshore construction vessel, the Ariadne, was chartered for the occasion; in favourable weather, five days was ample enough time to complete the operation and allow the site to supply its first kilowatt hours.

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Published on June 28, 2018 Updated on March 19, 2021