Offshore wind farms rely on subsea power cables to carry electricity between wind turbines, offshore substations, and the onshore grid. A single cable section can stretch for tens of kilometers and weigh thousands of tonnes.
So, where does all that cable go before it is laid on the seabed?
One answer is the Cable Carousel- a massive circular cable storage system commonly found on cable-laying vessels.

Note: Cable storage systems vary between vessels, so not all subsea cables are stored in a carousel. Terms such as Carousel, Turntable, and Cable Tank can all be found across the industry. This article focuses specifically on the Cable Carousel, one common type of large-scale cable storage system.

A Giant Reel for Subsea Cables?
At first glance, a Cable Carousel may look like an enormous version of a household extension-cord reel. The basic idea is somewhat similar, but its scale and engineering requirements are completely different.
A Cable Carousel is a large circular structure in which subsea cable is stored in carefully arranged layers. As the carousel rotates, cable can be gradually paid out according to the vessel’s installation speed.
Modern cable-laying vessels can carry thousands of tonnes of cable.

Why Not Simply Wind the Cable onto a Small Drum?
A subsea power cable is not a rope that can be bent freely.
It contains multiple layers, including conductors, insulation, protective materials, and sometimes armouring. Excessive bending can place unwanted mechanical stress on these components. Cable handling must therefore respect the cable’s specified minimum bending radius.
The large diameter of a Cable Carousel allows long lengths of cable to be stored while maintaining an appropriate bending radius. Since the cable itself can weigh thousands of tonnes, the carousel and supporting vessel structure must also withstand enormous loads.

How Does the Cable Get onto the Vessel?
Before offshore installation begins, the completed cable must first be transferred from the manufacturing or storage facility onto the vessel - a process known as cable load-out.
During load-out, the cable is gradually fed aboard while the carousel rotates and stores it in a controlled arrangement. Once loading is complete, the cable-laying vessel sails to the installation site.
Offshore, the process is reversed. The carousel gradually pays out the cable, while other onboard equipment controls its tension and guides it safely toward the sea.
A Cable Carousel, therefore, is much more than a giant storage wheel. It is an important link between cable manufacturing, marine transportation, and offshore installation.

The next time you see a huge circular structure aboard a cable-laying vessel, remember: coiled inside may be tens of kilometers - and thousands of tonnes-of the electrical lifeline that connects an offshore wind farm to the grid.


References
 • Guide to an offshore wind farm | An informative resource for offshore wind (Image source)
 • Pure player in sustainable electrification - Nexans
 • Prysmian | Cables, Energy & Telecom Solutions | Prysmian