Floating offshore wind involves one or more offshore wind turbines mounted on a floating structure that allows the turbine to generate electricity in water depths where fixed-foundation turbines are not technically/economically feasible. Floating wind farms have the potential to significantly increase the sea area available for offshore wind farms, especially in countries with limited shallow waters, such as Spain, Portugal, Japan, France and the United States' West Coast, and countries with few remaining viable shallow-water sites (like the United Kingdom). Locating wind farms further offshore can also reduce visual pollution, provide better accommodation for fishing and shipping lanes, and reach stronger and more consistent winds.
Commercial floating wind turbines are mostly at the early phase of development, with several single turbine prototypes having been installed since 2007, and the first farms since 2017. , there are 245 MW of operational floating wind turbines, with a future pipeline of 266 GW around the world.
The Hywind Tampen floating offshore wind farm, recognized as the world's largest, began operating in August 2023. Located approximately 140 kilometers off the coast of Norway, it consists of 11 turbines and is expected to supply about 35% of the electricity needs for five nearby oil and gas platforms. When it was consented in April 2024, the proposed Green Volt offshore wind farm off the north-east coast of Scotland was the world's largest consented floating offshore wind farm at 560 MW from 35 turbines each rated at 16 MW. If built, it will mostly supply electricity to decarbonise offshore oil production, but will also provide power to the UK national grid. However the nearest oil platform has refused to be connected and doubts have been expressed about relying on renewable energy on oil platforms, potentially causing problems with the viability of the project.
There is a very wide variety of technology concepts for floating offshore wind farms, which typically involve steel or concrete substructures (effectively a hull) connected to the seabed (moored) using steel chains or synthetic ropes. A 2026 study of available concepts counted over 100 such concepts.
History
The concept for large-scale offshore floating wind turbines was introduced by William E. Heronemus at the University of Massachusetts Amherst in 1972. It was not until the mid 1990s, after the commercial wind industry was well established, that the topic was taken up again by the mainstream research community. A summary of projects and developments is given below.
Individual turbines In December 2007, Blue H Technologies of the Netherlands deployed the world's first floating wind turbine, off the coast of Apulia, Italy. The 80 kW prototype was installed in waters deep in order to gather test data on wind and sea conditions, and was decommissioned at the end of 2008. The turbine utilized a tension-leg platform design and a two-bladed turbine.
In December 2009, the first large-capacity, 2.3 MW floating wind turbine named Hywind became operation in the North Sea near Norway. The turbine was constructed by Siemens Wind Power and mounted on a floating tower with a 100 m deep draft, with a float tower constructed by Technip. After assembly in the calmer waters of Åmøy Fjord near Stavanger, Norway, the 120 m tall tower was towed 10 km offshore into 220 m deep water, 10 km southwest of Karmøy, on 6 June 2009 for a two-year test deployment. Hywind, owned by Statoil, cost 400 million kroner (around US$62 million) to build and deploy. The long submarine power transmission cable was installed in July 2009 and system test including rotor blades and initial power transmission was conducted shortly thereafter. The installation was expected to generate about 9 gigawatt-hour of electricity annually. In 2010 it survived 11 meter waves with seemingly no wear.Nilsen, Jannicke. Statoil wants Hywind in Japan Teknisk Ukeblad, 4 April 2011. Accessed: 4 April 2011 By 2016, the turbine had produced 50 GWh; an overall capacity factor of 41%. The turbine survived 40 m/s wind speed and 19 m waves and was sold in 2019, expecting 10 more years of production and tests. At the same site, the 3.6 MW TetraSpar was commissioned in December 2021.
In September 2011, Principle Power, backed by EDP, Repsol, ASM and Portugal ventures installed in Portugal the second grid-connected full-scale prototype. WindFloat WF1 was fitted with a Vestas 2 MW turbine and went on to produce over 17 GWh of electricity over the next 5 years. The unit was decommissioned in 2016 and was later repurposed.
In June 2013, the University of Maine deployed the 20 kW VolturnUS 1:8, a tall floating turbine prototype that is 1:8th the scale of a 6-MW, rotor diameter design. VolturnUS 1:8 was the first grid-connected offshore wind turbine deployed in the Americas. The VolturnUS design utilizes a concrete semi-submersible floating hull and a composite materials tower designed to reduce both capital and Operation & Maintenance costs, and to allow local manufacturing. The technology was the result of collaborative research and development conducted by the University of Maine-led DeepCwind Consortium.
The first 2 MW Hitachi turbine became operational in November 2013,Elaine Kurtenbach. "Japan starts up offshore wind farm near Fukushima" The Sydney Morning Herald, 12 November 2013. Accessed: 11 November 2013"Japan: Experimental Offshore Floating Wind Farm Project" OffshoreWind, 11 October 2013. Accessed: 12 October 2013 and had a 32% capacity factor and a floating transformer (see also List of offshore wind farms in Japan). Two larger turbines of 5 and 7 MW have been unsuccessful. The first floating turbine in Japan was floated near Fukue Island in 2016, after a 5-year demonstration period near shore.Japanese floater gets relocated 4C, 21 April 2016
In late 2021, China started its first floating wind turbine, a 5.5 MW MingYang at the 400 MW fixed-bottom Yangxi Shapa III wind farm.
PivotBuoy received €4m EU funding in 2019, and installed a 225 kW Vestas downwind turbine in 50-metre water depth at the Oceanic Platform of the Canary Islands in 2022.
In 2023, the first floating wind platform in Spain became operational after being connected to the grid. The 2 MW DemoSATH project is a joint effort by Saitec Offshore Technologies, RWE, and the Kansai Electric Power Company.
Turbine arrays Commissioned in October 2017, Hywind Scotland was the world's first commercial wind farm to use floating wind turbines. The farm has five 6 MW Siemens direct-drive turbines mounted on spar platforms, with a total capacity of 30 MW. Since this, several other wind farms have been installed including WindFloat Atlantic in 2020, Kincardine in 2021, and Hywind Tampen in 2023.
Mooring systems
The mooring system provides the station keeping capability and ensures stability of the substructure and turbine. There are three mooring systems for floating offshore wind: catenary, taut, and tension-leg. These differ in the magnitude and inclination of the load transferred to the anchor.
As of 2023, the most common type is the catenary, which uses free hanging chain mooring lines, with the station-keeping force provided by the self-weight of the chain. A catenary mooring touches down on the seabed in advance of the seabed, meaning the anchor is loaded almost horizontally. The radius from the turbine to the anchor is approximately six to eight times the water depth. A catenary mooring system is used for the Hywind Tampen 88 MW floating offshore wind farm off the coast of Norway. Notably, this project also utilizes a novel concept of shared anchoring, where multiple mooring lines from adjacent turbines are connected to a single anchor, reducing the total number of anchors.
Taut mooring systems use synthetic rope to provide restoring force through the stiffness of the line, typically at an inclination to the seabed of 30 – 45 degrees.
Tension leg platforms use pre-tensioned vertical tethers to secure the turbine in place, providing large restoring moments in pitch and roll.
The IEC 61400–3 design standard requires that a loads analysis be based on site-specific external conditions such as wind, wave and currents. The IEC 61400–3-2 standard applies specifically to floating wind turbines.
Economics Introduction The technical feasibility of deepwater floating wind turbines is not questioned, as the long-term survivability of floating structures has been successfully demonstrated by the marine and offshore oil industries over many decades. However, the economics that allowed the deployment of thousands of offshore oil rigs have yet to be demonstrated for floating wind turbine platforms. For deepwater wind turbines, a floating structure will replace pile-driven monopoles or conventional concrete bases that are commonly used as foundations for shallow water and land-based turbines. The floating structure must provide enough buoyancy to support the weight of the turbine and to restrain pitch, roll and heave motions within acceptable limits. The capital costs for the wind turbine itself will not be significantly higher than current marine-proofed turbine costs in shallow water. Therefore, the economics of deepwater wind turbines will be determined primarily by the additional costs of the floating structure and electric power distribution system, which are offset by higher offshore winds and close proximity to large load centres (e.g. shorter transmission runs).
With empirical data obtained from fixed-bottom installations off many countries since the late 1990s, representative costs and the economic feasibility of shallow-water offshore wind power are well understood. In 2009, shallow-water turbines cost US$2.4-3 million per megawatt to install, according to the World Energy Council, while the practical feasibility and per-unit economics of deep-water, floating-turbine offshore wind was yet to be established. In 2021, a French auction closed below €120/MWh (US$141/MWh) of electricity for a 250 MW project, and the high cost, small project size and lack of experience keep project developers and financial institutions from the risk of committing to the technology. In 2024, the 250 MW Pennavel project won an auction at €86/MWh.
Cost data from operational windfarms Initial deployment of single full-capacity turbines in deep-water locations began only in 2009. The world's first commercial floating offshore windfarm, Hywind Scotland was commissioned in 2017. Its capital cost was £264 million, or £8.8m/MW, which is approximately three times the capital cost of fixed offshore windfarms and ten times the capital cost of gas-fired power stations. Its operating costs, at approximately £150,000/MW were also higher than for fixed offshore windfarms. A second UK project, the Kincardine Floating Offshore Windfarm, has been reported as costing £500 million to build, or £10m/MW. In 2023, costs for the 88 MW Hywind Tampen was calculated at NOK 8 billion.
Cost reduction strategies , feasibility studies supported that floating turbines are becoming both technically and economically viable in the UK and global energy markets. "The higher up-front costs associated with developing floating wind turbines would be offset by the fact that they would be able to access areas of deep water off the coastline of the UK where winds are stronger and reliable." The Offshore Valuation study conducted in the UK has confirmed that using just one third of the UK's wind, wave and tidal resource could generate energy equivalent to 1 billion barrels of oil per year; the same as North Sea oil and gas production. A significant challenge when using this approach is the coordination needed to develop transmission lines.
A 2015 report by Carbon Trust recommends 11 ways to reduce cost.Floating Offshore Wind Market Technology Review Carbon Trust Also in 2015, researchers at University of Stuttgart estimated cost at €230/MWh.