A "technical problem" affecting the export cable from the SEM-REV test site, where the Floatgen floating platform was recently installed to much fanfare, was identified about two years ago, site owner Ecole Centrale de Nantes (ECN) has admitted.
Although the fault was first discovered in 2016, it took a long time to identify exactly where the problem was, a source close to the test site explained.
It eventually turned out to be a fault in the junction box between the 20km-long export cable, installed in 2012, and a 400m-long extension added in 2015 when the hub – to which up to three demonstrators can be connected – was also installed, the source added.
When the Floatgen demonstrator was installed at the site in May, Ideol announced that "the connection to the export cable and to the power grid will be scheduled in the very near future after a last series of tests."
According to ECN, however, the plan was always for the final connection to take place in the summer.
Once connected, Floatgen will undergo a series of tests at the SEM-REV site for a period of at least two years.
UPDATE - ECN has now explained the nature of the fault:
"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 jeopardise the future of the site and its projects: the connection had to be repaired by 2018," ECN said in a statement.
It was difficult to find the fault "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 to 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."
ECN engaged Nantes-based Mojo Maritime France, a subsidiary of James Fisher Marine Services, to carry out the work and the 8MW electrical connection is now operational.
Floatgen "will be connected this summer and start supplying its first kilowatt hours (kWh)", ECN stated.
