Floating Substructures

This section covers a range of floating substructures either already deployed in Scotland or actively being assessed by ScotWind and INTOG developers

Scotland's journey to become one of the world's floating offshore wind pioneers started with the visit of our then Deputy First Minister, Nicol Stephen (now Lord Stephen), to Norway in July, 2006. In a meeting with Statoil (now Equinor) their plans to build Hywind, a 2.3MW floating wind turbine on a spar type substructure, was discussed. They had investigated manufacturing it in concrete but had decided that steel was the simplest option. The plan was to deploy it off Utsira in 2008, the DFM opened a dialogue with Statoil about the potential for the next iteration of Hywind to be deployed in Scotland.

Statoil then installed their Hywind demonstrator in 2009. Further negotiations between the Scottish Government and Statoil then resulted in the first floating wind farm in the world, Hywind Scotland, with five 6MW turbines being installed 25km off Peterhead in Scotland in 2017.
This was followed in 2022 by the Kincardine project with five 9.5MW turbines on a steel semi-sub design substructure from Principle Power.
With these project's 78MW of installed capacity Scotland still leads the world in grid connected floating wind capacity (Hywind Tampen is not grid connected).
With the Culzean INTOG project to be delivered this year (2026) and the Pentland and Green Volt projects before 2030, Scotland's floating wind projects will reach a world beating 733MW by the end of this decade.

This section of our Innovation Spotlight feature is dedicated to floating substructures which have already been deployed, are soon to be deployed or are the main candidates for deployment in Scotland. All three main types of floating substructure technologies are represented in these examples i.e. semi-submersible, floating spar and barge type.

Hywind substructure - Equinor

Equinor have now deployed their Hywind technology at three separate sites in Norway and Scotland. The first was a 2.3MW single turbine on a Hywind spar steel type substructure. This was followed by a 5 turbine project in 2017 at the 30MW Hywind Scotland project off Aberdenshire which was the first floating wind farm in the world. These substructures were also fabricated in steel.
The most recent deployment was for the Hywind Tampen, which saw 11 turbines on concrete spar substructures which was commissioned in in May 2023. With 17 substructures deployed this is the most numerous of any floating substructure design to date.
The drawback for this substructure type is the water depth required to install the turbine on the foundation. Deep Norwegian fjords were ideal for this approach but such bathymetry features are rare making for a difficult export market.

Image: Equinor

Equinor - Hywind Scotland

WindFloat TC - Principle Power

US company, Principle Power Inc (PPI) have seen their semi-sub steel substructure deployed off Portugal and Scotland. PPI currently have two designs, the WindFloat TC (tubular) and the WindFloat FC (flat panel) both with a centre mounted turbine.
In 2011 their first pilot project was a 2MW turbine on their WindFloat semi-sub substructure. Some years later in 2018 this Windfloat 1 system was sold to Cobra Offshore Wind and redeployed to the Kincardine Wind Farm site in Scotland.
Meanwhile, the company also delivered the three substructures for the 25MW WindFloat Atlantic project in Portugal in 2020.
The Windfloat 1 system on the Kincardine site in Scotland was replaced in 2022 by the five larger Windfloat systems with 9.5MW turbines. This became the largest (at the time) floating wind project in the world.

Image: Principle Power

Principle Power

OCG Wind - Ocergy/Archer Wind

Neo Next+ Energy are now ready to deploy their Culzean 3MW floating substructure and turbine to their Culzean platfrom site in the Scottish North Sea. This demonstration project is part of the INTOG leasing round and will be connected to the Culzean oil and gas platform as a way of reducing the carbon footprint of the platforms production energy.
The substructure is the first example of California based company, Ocergy's OCG Wind design, to be deployed and the construction and installation is being handled by their fabrication and construction partner, Norwegian EPC company, Archer Wind.

Image: Archer Wind

Ocergy

Dampening Pool Barge - BW Ideol

One of the few floating wind substructure technologies to have been deployed at more than one site. BW Ideol's barge type substructure has been deployed at the Floatgen project at the 2MW SEM-REV in France since 2018. The 3MW Hibiki project in Japan, also in 2018, and the most recent, in May 2026, is their first multiple substructure project (3 machines) at the 30MW EOLMED project in the South of France.
The company are now involved in looking at setting up serial production facilities at Ardersier in Scotland for the 960MW Buchan floating wind project, part of the ScotWind leasing round, and at Fos-sur-Mer in France.

Image: BW Ideol

BW Ideol

Tetrasub Mark II - Stiesdal Offshore

One of the next floating wind demonstrator project to be deployed in Scotland is the Pentland Floating Offshore Wind project. Developer COP have selected the Tetrasub Mark II substructure from Danish company Stiesdal Offshore.
This light weight semi-sub type steel substructure features a unique pinned construction approach which the company says will considerably reduce the need for welding during the assembly process.
The Pentland project will see 6 such substructures deployed to their site in the Pentland Firth between Caithness and Orkney.

Image: Stiesdal Offshore

Stiesdal Offshore

Deepsea Star - Odfjell Oceanwind

Norwegian company, Odfjell Oceanwind, have a semi-sub design for a floating steel substructure called Deepsea Star. It consists of three large tubular components with smaller tubular bracing elements and is designed for 15MW plus turbines.
The company have bought over Orsted's share of the Salamnader floating wind project, one of the projects in the INTOG leasing round in Scotland. It is expected that this will secure a 100MW demonstration project for their Deepsea Star substructure design.

Image: Odfjell Oceanwind

Odfjell Oceanwind

Gusto_MSC_Tri-Floater_floating_foundationtri2_windfarm_18_3_Main.jpg

Tri-Floater - NOV

The Tri-Floater substructure was designed by NOV subsidiary, GustoMSC, and is a steel semi-sub structure with three hexagonal main floater components with smaller tubular cross members. This lends itself to a construction method similar to the flat steel plate approach used in shipbuilding.
INTOG leasing round developer, Cerulean Winds, have chosen the Tri-Floater as their substructure choice for the first of their three 1GW projects in this round. The Aspen floating offshore wind farm would see 72 such substructures deployed 84km off Peterhead on the East Coast of Scotland.
UEA based company, Lamprell, was announced as NOV's collaboration partner for Aspen in Nov 2022 for the fabrication, assembly and outfitting of the floating substructures.

Image: NOV/Gusto MSC

NOV - GustoMSC

CONFloat™ 7C - Aker Solutions

The CONFloat™ 7C substructure design from Aker Solutions is based on the company's CONDEEP design from Oil and Gas projects. The substructure is made up of seven identical circular concrete compartments with, six surrounding a central one for the turbine position.
This simple design, say the company, lends the substructure to mass production as there is basically only one component to manufacture and assemble.
The company have experience of concrete substructure production from not only the oil and gas sector but also in offshore wind with Equinor's Hywind Tampen project and the concrete slip-forming process for the spar substructures.

Image: Aker Solutions

Aker Solutions

Crown FW® - Brezo Energy

Concrete semi-sub design from Spannish company, Brezo Energy. Made up of four tubular, modular components with the transition piece in the centre of a square arrangement of these components.
The modular system allows for the components to be manufcatured using a tried and tested concrete slipforming process. This process is key to the industrialisation of their substructures which the company believe can assist in the cost reduction pathway for flaoting wind. Concrete construction also lends itself to a high percentage of local supply chain particiaption as most countries have an established civil engineering and constructuion supply chain.

Image: Brezo Energy

Brezo Energy

OO-Star - Bouygues

The OO-Star substructure concept was originally the work of Norwegian company, DR.techn Olav Olsen, which was acquired in 2022 by Bouygues Travaux Publics, a subsidiary of Bouygues Construction.
This is semi-sub concrete platform with three arms and a centrally mounted turbine configuration. The design was awarded Approval in Principle (AiP) by the American Bureau of Shipping in Sept 2024 and paves the way for a full scale demonstrator of the technology.
The substructure is suitable for up to 20MW + turbines and the concrete design lends itself to serial construction and industrialisation.
Bouygues Travaux Publics point to their recent experience of mass production of the 71 concrete gravity base foundations for the Fecamp wind farm in France as an example of how a lean and efficient production line aimed at manufacturing OO-STAR floaters, at an industrial scale, is well within their capability.

Image:- Bouygues

Bouygues Construction

Star1 - Saipem

Steel semi-sub design from Saipem that features a 4 column star shape with the turbine in the centre column. The company point to their track record in offshore wind EPCI contracts which stands them in good stead to deliver a robust plan for Star1 optimised pre-fabrication and final assembly. They plan to produce 1 unit per week.
They have a low draft requirement, less than 5m, for turbine integration which more than matches infrastructure requirements at many port sites.
Saipem partnered with Bouygues on the delivery of the 71 gravity base substructures for the Fecamp project and that has given them experience of offshore wind substructure mass production. Their Star1 semi-sub has already been selected for deployment at two floating wind projects in the Italy.

Image: Saipem

Saipem

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