Fibre in the Array Cables

Every subsea array cable in a modern offshore wind farm has a fibre optic element built into the cable filler during manufacture. The fibre is not an afterthought, it is specified at the same time as the power conductors and routed through the same cable, splice joint, and termination sequence. A typical array cable fibre is a 48 or 96-core single-mode cable, far more capacity than any single turbine needs, with spare cores held in reserve.

This approach has two large advantages. First, the fibre follows the same physical route as the power, so a cable survey, install, or repair handles both at once. Second, there is no separate subsea fibre network to consent, install, or insure. The trade-off is that an array cable failure usually takes the fibre down with it, which is why the design includes redundant paths at the ring level or dedicated backup links from each turbine.

The Offshore Ethernet Network

At each turbine and at the offshore substation, the fibre is terminated in an industrial Ethernet switch. Together, these switches form a managed Layer 2 or Layer 3 network spanning the whole farm. The topology is usually ring-based, each array string forms a ring with two paths back to the substation, so a break at any single point reroutes traffic the other way round the ring. This gives sub-second failover for control traffic and is functionally equivalent to the protection schemes used on industrial process networks elsewhere.

Switches are industrial-grade, hardened for offshore operating temperatures, vibration, and limited access for maintenance. Major vendors include Hirschmann, Moxa, Siemens RUGGEDCOM, and Cisco Industrial. VLAN segmentation separates turbine SCADA, substation protection traffic, CCTV, access control, and administrative traffic on shared physical infrastructure, an important cybersecurity control that is often implemented inconsistently in practice.

The Shore Link

Between the offshore substation and the onshore control room, the data network runs on fibre embedded in the export cable. The fibre is spliced into the export cable during manufacture and follows the cable all the way through landfall, transition joint, and onshore burial. At the onshore substation, the fibre is terminated in a communications room alongside the export cable electrical termination.

The shore link is the most critical single point in the communications infrastructure, and it is almost always redundant. Common configurations include:

• Fibre in both export cables (where there are two parallel export circuits).
• A dedicated backup fibre, either a standalone subsea fibre or fibre in an adjacent cable.
• A microwave radio link from the offshore substation to a shoreline receiver, used as emergency backup if both fibre paths fail.
• A satellite uplink on the offshore substation, providing a third independent route.

The choice of redundancy configuration depends on site geography, regulatory requirements, and the developer's risk appetite. Grid codes in some jurisdictions mandate specific levels of communications redundancy for generators of a certain size.

Radio and Satellite Links

Point-to-point microwave radio is used as a backup to the fibre shore link and as a primary link on some smaller near-shore farms where running fibre in the export cable is not justified. A typical microwave link uses licensed frequencies in the 6 to 18 GHz bands, delivers 100 Mbps to 1 Gbps, and reaches distances of 30 to 60 km line-of-sight. Links require a clear radio path and high masts at both ends, and are sensitive to heavy rain and marine atmospheric effects.

Satellite communications, historically VSAT over geostationary satellites, and increasingly low-earth-orbit (LEO) services such as Starlink and OneWeb, provide a third-path backup and primary connectivity for vessels. LEO satellite service has materially changed offshore communications economics in the last two to three years. A service that used to cost tens of thousands a month per vessel with unacceptable latency is now available at a fraction of that cost with sub-100 millisecond latency. The trade-off is that LEO services are currently ungoverned by the regulated frameworks that apply to licensed fixed radio and maritime communications.

Operational Communications

Beyond the control and data network, every operating farm has a layer of operational communications used by people and vessels:

• Marine VHF radio for crew transfer vessels (CTVs), service operation vessels (SOVs), and helicopter-ship communications, operating on regulated maritime channels.
• UHF/VHF radio networks for on-site work parties, confined space entry, and emergency response, with repeaters on the substations.
• Aviation communications for helicopter operations, typically on aeronautical VHF with ground stations at the shore base.
• Public Address and General Alarm systems on the offshore substations for emergency broadcast.
• Emergency beacons and man-overboard systems integrated with the farm's HSE response plan.

Operational communications are covered by maritime, aviation, and HSE regulations rather than the grid code, and they have to integrate with the UK MCA, coastguard, and search and rescue frameworks. The communications architecture on the offshore substation therefore has a maritime side and an industrial side that are usually kept separate at the physical layer even when they share some infrastructure.

Cellular Offshore

Dedicated cellular coverage offshore has grown significantly over the last few years. Several projects now include a private LTE or 5G network deployed on the substations with small cell sites on selected turbines, providing coverage to crew devices, handheld inspection tools, and vessel-mounted equipment. The operational benefits are large, crews can use standard smartphones, bring-your-own-device inspection tools, and commercial apps in the field instead of purpose-built hardware.

Private cellular is expensive to deploy but avoids the reliability and capacity problems of trying to extend terrestrial mobile coverage offshore. Public mobile coverage offshore, where it exists, is incidental to the coastal network and is not designed for offshore wind operations. For most practical purposes, offshore cellular is either private infrastructure or LEO satellite.

Redundancy and Resilience

Communications redundancy on an offshore wind farm has to address three failure modes: a single cable fault, a total substation loss, and a shore-side infrastructure failure. A well-designed communications architecture has diverse paths for each, typically fibre-ring topology inside the farm, dual-fibre paths to shore, radio or satellite backup, and physically separated shore termination points. Getting this right is as much an O&M process question as an engineering one, the redundant links have to be tested regularly to confirm they still work, and planned maintenance on primary paths has to be scheduled against confirmed backup availability.