David Foxwell reflects on the high cost of manufacturing, installing and repairing subsea cables for offshore windfarms, and on a potential solution
Installing inter-array and export cables for an offshore wind project is an expensive undertaking. It is expensive because the cable has to be armoured, protected, and installed by specialist vessels.
The cost is also higher than it could otherwise be because the number of manufacturers of subsea cables can be counted on one hand and because the number of contractors that can install cables is limited.
Once cables have been installed on the seabed, if they need to be repaired, that can be an extremely expensive undertaking in its own right. Cables can be damaged during the cable-lay process and once they have been installed on the seabed. Sometimes manufacturing faults in cables only come to light after they have been installed.
Cable faults continue to account for a significant proportion of insurance claims in the offshore wind industry. Taken together, inter-array and export cabling claims account for almost half of all losses, it is said, primarily as a result of mishandling during installation and in-situ damage.
But cables for offshore windfarms and cable-laying could become significantly less expensive if a research project being carried out by a network of leading companies bears fruit.
That project, i4Offshore, is the subject of an upcoming feature by OWJ, but a glimpse of how important it might be was provided at the Wind Europe exhibition and conference in Bilbao in April.
One of the aims of this ambitious project is to demonstrate a ‘very low-cost’ cable-in-pipe solution for cables for offshore windfarms.
One reason cable-in-pipe is likely to be less expensive is because it would allow cables much more like those used on land to be used offshore. There are a lot more manufacturers of this kind of cable. Another is that it does not require a large, expensive and very specialised cable-lay vessel.
The concept has already been tested on the Nissum Bredning offshore windfarm and is being taken forward in the i4Offshore project. That project used what was, essentially, an off-the-shelf onshore cable housed in standard high-density polyethylene, with post-lay burial of HDPE bundle/cables using a standard jetting technique.
I am told that cable-in-pipe laid on offshore windfarms could be more than 30% less expensive than conventional offshore cabling. Watch this space.