Why Depth Changes Everything
Fixed-bottom offshore wind turbines are installed on monopile, jacket, or gravity-base foundations that are driven or placed on the seabed, limiting their commercial deployment to water depths of approximately sixty metres or less. This depth constraint, which reflects the engineering and cost limits of fixed foundation structures in deeper water where foundation mass, material costs, and installation complexity grow rapidly with water depth, restricts fixed-bottom offshore wind to the relatively shallow coastal seas around Northern Europe, the US Eastern Seaboard, the Gulf of Mexico shelf, and portions of Asian coastlines where appropriate water depths and seabed conditions coincide with good wind resources. The deep-water offshore wind resource, accessible in water depths from sixty to one thousand metres or more, represents a larger total resource than the shallow-water resource that the fixed-bottom industry has been developing, and it is located in proximity to coastlines in Japan, Norway, the US West Coast, Portugal, and many other markets where water depths preclude fixed-bottom development. Floating offshore wind foundations whose mooring systems allow turbines to be deployed in deep water without a fixed seabed connection are the technology that makes this resource commercially accessible.
The commercial development of floating offshore wind is at a stage analogous to fixed-bottom offshore wind in the early 2010s: technically proven at demonstration and pre-commercial scale, with first commercial projects in development, but with capital costs that substantially exceed those of the fixed-bottom technology it needs to eventually match to compete for the same electricity market. The cost reduction pathway for floating offshore wind involves the same drivers that reduced fixed-bottom costs: series production of standardised substructures, installation vessel and procedure optimisation, supply chain development, and the learning that accumulates as more projects are built and operated. The rate at which floating offshore wind costs can follow the fixed-bottom trajectory depends on how quickly the industry can move from the one-off engineering that characterises current floating foundation design to the standardised production that enables manufacturing learning curves.
Foundation Types and the Commercial Race
Three floating foundation concepts have progressed to demonstration or pre-commercial scale and are competing for dominance in the commercial floating offshore wind market. The spar buoy concept, used in Equinor's Hywind installations, suspends the turbine from a deep cylindrical hull that extends below the surface to a depth where wave motion is attenuated, providing the inherent stability that the spar's low centre of buoyancy creates without active ballast control. The spar's depth requires installation in water deep enough to accommodate the hull, limiting its deployment to sites with minimum water depths of typically one hundred metres or more, and its large steel mass creates material and fabrication cost that the other concepts seek to reduce. The semi-submersible concept, used by BW Ideol, Principle Power, and several other developers, uses a network of buoyant columns connected by horizontal bracing whose combined buoyancy supports the platform and whose geometry provides the stability that the spar achieves through depth. The semi-submersible can be constructed in shallow-water fabrication yards and towed to site rather than requiring the deep-water installation procedures that the spar demands. The tension leg platform concept mooring the floating structure with vertical tendons to seabed anchors provides the smallest platform motion of the three concepts and potentially the lowest steel mass, but requires the precise seabed anchor installation that its vertical mooring geometry demands.
The commercial choice among these foundation concepts for the first commercial floating offshore wind projects reflects the site conditions, supply chain availability, and technology maturity that each project's developer is working with. Equinor's Hywind Tampen project in the Norwegian North Sea, the world's first commercial floating offshore wind farm with eleven spar turbines serving the power needs of five oil and gas platforms, is the largest floating offshore wind project operating and is the commercial evidence base that the industry uses to model floating offshore wind production costs and O&M requirements at the small commercial scale that first projects represent.
The Supply Chain That Needs to Be Built
The commercial development of floating offshore wind at scale requires a supply chain that does not fully exist yet. The steel fabrication capacity for floating substructures, whose mass per unit is larger than fixed-bottom foundations and whose geometry is more complex, needs to be established at the port locations that can accommodate the size and weight of floating platform fabrication and from which tow-out to site is logistically practical. The mooring and dynamic cable systems that connect floating turbines to the seabed and to the offshore electrical collector are specialist marine products whose supply is concentrated in the subsea oil and gas industry and whose adaptation and scaling for offshore wind application requires development investment that the offshore wind industry is beginning to fund as commercial floating project pipelines become visible to supply chain investors. The installation vessels and procedures that can safely tow and moor floating turbines in the open ocean conditions of deep-water sites are different from the jack-up vessels that fixed-bottom installation uses, requiring the heavy lift and semi-submersible vessels whose scheduling conflicts with other offshore energy projects create the installation capacity constraint that floating offshore wind shares with other specialised offshore operations.
Top 10 Companies in Floating Offshore Wind Foundations Globally
- Equinor (Hywind): Developer of the world's first commercial floating wind farm with Hywind Scotland and Hywind Tampen; its spar buoy technology has the longest operational track record of any floating wind concept and its pipeline of commercial floating projects positions it as the commercial leader in a market whose development it has been defining since Hywind Demo in 2009.
- BW Ideol: Developer of the damping pool semi-submersible floating foundation whose Floatgen demonstration project off the French coast is the first grid-connected floating wind turbine in France; its foundation technology licensing model and its project development pipeline in France, Japan, and the US create the international commercial presence that proprietary foundation technology can generate when it is commercialised through licensing rather than self-development.
- Principle Power: Developer of the WindFloat semi-submersible foundation whose WindFloat Atlantic project off Portugal is the largest operating floating wind project after Hywind Tampen; its WindFloat foundation technology and its joint development agreements with energy companies in Portugal, France, and the US create the commercial pipeline that demonstrates its technology's adaptability to diverse site conditions.
- RWE Renewables: Offshore wind developer with floating wind project development activities in the UK, Germany, and international markets; its fixed-bottom offshore wind operational experience and its financial resources create the commercial credibility that floating wind project finance requires from a project developer whose track record spans the technology transition from shallow to deep water.
- TotalEnergies: French energy major with floating wind project development in France, Scotland, and internationally through its Flagship and other project vehicles; its balance sheet and its engineering expertise from offshore oil and gas operations in deep water create the financial and technical capability for floating wind development at commercial scale.
- Saipem: Italian offshore engineering and construction company developing the Hexafloat semi-submersible floating foundation; its offshore engineering heritage from oil and gas platform design and installation and its fabrication facilities create the integrated engineering and construction capability for floating foundation delivery that pure-play technology companies lack.
- Aker Offshore Wind: Norwegian floating wind developer pursuing projects in Norway, the US, and Asia using spar and semi-submersible concepts; its Aker group heritage in Norwegian offshore oil and gas engineering and its access to Norwegian fabrication infrastructure create the development capability for floating wind in the Norwegian market where regulatory support for deep-water wind development is most advanced.
- Naval Energies: French marine technology company with floating foundation concepts for the French floating wind tender programmes; its naval architecture and marine engineering expertise creates the technical foundation for floating wind substructure design in the French market whose regulatory programme is the most commercially structured floating wind development framework in continental Europe.
- ENGIE: French energy utility with floating wind project development activities including the EolMed project off Languedoc and international development partnerships; its utility-scale renewable energy development experience and its European offshore wind track record create the commercial foundation for floating wind project development at the scale that utility procurement processes require.
- Technip Energies: Engineering company with floating wind substructure engineering and project management capabilities; its EPCI experience from floating production platforms in offshore oil and gas creates the engineering and project execution expertise that floating wind substructure projects share with the more demanding floating oil and gas production installations that Technip has managed for decades.