New Year’s Eve 2011, 19.00 hours: the rest of Denmark is gathered for their celebrations. The installation vessel ‘Svanen’ is hammering a foundation pile into the seabed approximately 20 kilometres north east of Grenaa. The pile marks the beginning of construction of DONG Energy’s new facility, Anholt Offshore Wind Farm.
In June 2012, the cable-laying vessels commence work laying the array cables on the seabed between the substation and the 111 foundations. By 12 September – three weeks ahead of schedule – all cables are in place.
“An offshore wind project of this size can be understood as the serial production of 111 small power plants connected by cable to a large central power station. To ensure that all deliveries are ready in the correct sequence requires thorough preparation and detailed coordination with all providers from the outset,” says Claus Bøjle Møller, Project Manager, DONG Energy.
“We focused on a strict schedule and in doing so applied our principles for avoiding waste in the form of vessels waiting, for instance, and less-than-optimal installation sequences”.
New design
The fact that cable laying was so fast is not least due to a newly designed on-board layout: a magazine holding nine cable drums on the vessel deck can have the next drum with its 20 to 30 tonnes of cable at the ready whilst the previous drum is still being fed to the seabed. At best, we were able to unreel three cables.
As soon as the cables are laid, technicians work on connecting the Anholt Offshore Wind Farm array cables with Energinet.dk’s substation. On 5 December, technicians can report that all cables are ready and shortly afterwards, on 13 December 2012, all 111 installations are energised and connected to the Danish electricity grid.
“This means cables were laid and connected faster than on previous projects: everything was ready before installation of the wind turbines”.
In many wind farm projects, complete energising of cables isn’t possible ahead of installing wind turbines. “But it’s a considerable advantage if this can be done because it means that we don’t have to ship diesel generators out to each turbine to supply power in the initial period. It also allows swift start-up of electricity generation as soon as the wind turbine has been installed. And this is important when it comes to project finance”, says Claus Bøjle Møller.
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Press release, January 29, 2013; Image: dongenergy