Port requirements to construct a floating offshore wind farm
At a glance
Without ports, there is no offshore wind.
Ports play a strategic role in the growth of the offshore wind sector, and in turn, offshore wind creates opportunities for ports. Ports can use offshore wind to expand and diversify their activity portfolio.
Their capacity to host manufacturing facilities, assemble large-scale structures and facilitate marine logistics such as offloads and load-outs is key to the success of any offshore wind farm (OWF). However, in their current form, many ports deemed suitable from a geographical perspective are not set up to adequately accommodate what is required to support an OWF, particularly true when it comes to floating offshore wind (FLOW).
FLOW is now a proven technology with demonstrators and projects in both Europe and Asia. There is currently an estimated 277 MW of global installed FLOW capacity. However, the global pipeline for new floating projects stood at around 244 GW as of 2023.
Geographical advantage
There is a vast number of geographical locations with depths or soil conditions that are unsuitable for fixed-bottom offshore wind. FLOW technology enables projects to be built further from the coast, where competition for space is lower. In addition, environmental impacts, especially during construction, are reduced because of the absence of a fixed foundation piled or sunk into the seabed.
Assessing port facilities for FLOW
As the FLOW industry continues to develop and grow, the capabilities of established port facilities need to be assessed in terms of their ability to support the increased level of construction, storage and installation required by these technologies.
Unlike bottom-fixed foundations that rely on large jack-up vessels to assemble the turbine components (tower sections, nacelle and blades) at sea, floating offshore wind turbines (FOWTs) are most likely to be assembled in a port. This requires adequate infrastructure such as heavy-duty cranes, assembly areas, deep-draught berths, dry docks or large gantry cranes. These requirements will vary depending on the floating foundation type.
The function of ports for the manufacture, assembly, installation and maintenance of FLOW is varied and can include the following:
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Support base for the pre-construction geophysical, geotechnical, metocean and environmental surveys of the offshore site.
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A manufacturing site for the floating foundation, with launch and wet storage facilities — floaters can be built using steel, concrete or even a hybrid configuration. The choice will affect the assembly process. Manufacture/assembly may be carried out in a drydock or an assembly area adjacent to a load-out quay.
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Manufacturing sites for the tower, nacelle and blades (turbine components) with adjacent load-out quay — these components will be loaded by crane or, increasingly, by roll-on/roll-off (RO-RO) vessels, which can reduce both time and cost. Components do not necessarily need to be produced in port, but logistical costs will be reduced if the manufacturing facility is adjacent to a port with a suitable load-out quay for marine transportation. The rapidly increasing size of turbines makes road transportation less viable for nacelles and blades.
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A manufacturing site for the FOWT mooring components with adjacent port load-out quay — the mooring system needs to be installed prior to the offshore arrival of the completed FOWT. The mooring lines and anchors will be delivered from their respective manufacturing ports to a mobilisation storage port with a large laydown area. Mooring and anchor systems can be stored at a separate port and do not require a high lifting capability. There is potential to use drums to store synthetic rope, which would require less space.
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Manufacturing site for the dynamic array cables, with adjacent port load-out quay — the cables are usually installed or wet-stored on the seabed prior to the offshore arrival of the completed FOWT. Subsea array cables are usually loaded out (or drum-spooled) onto a large cable-lay vessel at the manufacturing facility and then transported directly to the offshore site and installed.
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Mobilisation laydown (and pre-assembly) areas for towers, blades, and nacelles, with adjacent port facilities and offload/load-out quay.
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Deep-water fit-out quay (or dock) for installing and hooking turbine components onto the floating foundation — in general, draught and crane capacity remain significant constraints, particularly as turbines increase in size and weight.
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Wet storage area for floating foundations prior to the installation of turbine components, as well as completed FOWTs awaiting towage to the site using tugs — this will require the laying of temporary moorings.
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Hook-up and commissioning support during the offshore-construction phase — for this function, the port will need to accommodate SOVs and other construction support vessels.
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Operations and maintenance (O&M) base.
Construction port requirements for a 450 MW example project:
1. Land and storage
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Large land areas (15 to 20 hectares) for the laydown and pre-assembly of turbine components
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Wet storage areas (10 to 12 hectares) for floating foundations and assembled FOWTs awaiting towage to site
2. Quayside specifications
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Total length of around 500 metres with a load-bearing capacity of 30 to 50 tonnes per square metre
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Water depth of 10 to 15 metres to accommodate floating foundations and heavy transportation vessels
3. Water access
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Sufficient water depths and access channel width
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Ability to handle construction support vessels up to 160 metres in length, 45 metres in beam and 6 metres in draft
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Floating substructures will likely be wider than most construction support vessels and require deeper channels. The channel width may need to be 100 and 150 metres, depending on specific geometry and technology.
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No air draft restrictions to allow the tow-out of FOWTs with tip heights of up to 300 metres.
4. Proximity to the installation site
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Ports should ideally be close to the wind farm to minimise transportation times, which helps reduce the weather window required to undertake offshore construction operations.
5. Quayside cranes
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Crane capacities will vary depending on the activities carried out at the quay. Installing turbine components onto the floating foundation will require a lift capacity of between 600 and 1,200 tonnes for a 10 to 15 MW turbine. Depending on the geometry and location of the turbine, cranes will also require sufficient reach to accommodate hub heights of approximately 160 metres.
Operations and maintenance
Maintenance of the wind farm is usually undertaken at a nearby port using service operation vessels (SOVs). These ports accomodate the maintenance crew and vessels needed to respond to FOWT faults, along with storage and repair facilities. O&M activities can be classified into preventative and minor corrective maintenance, as well as heavy maintenance (e.g. large component replacement). This will impact the infrastructure requirements needed to perform these activities.
Most FOWTs allow for large-scale repairs or component replacement to be undertaken at a suitable port, with the FOWT towed back into a drydock or positioned alongside a quay.
In the case of a semi-submersible or barge floaters, it may be more cost-effective to disconnect the mooring lines and array cables and tow the FOWT back to port. In the case of spars and TLPs, both shoreside and offshore repairs are possible, but this largely depends on the mooring system’s design and the ability to stabilise the motion of both the FOWT and crane vessel during repairs or component replacement.