Floating Offshore Wind Energy: Reaching Beyond the Reachable by Fixed-Bottom Offshore Wind Energy

The future net-zero society relies heavily on wind power as one of the main sources of renewable energy. To exploit that natural source of energy, huge wind turbines have been installed all over the globe, high on the mountains, in large open plains, on the edge of bodies of water and in the heart of our seas. Offshore wind farms are considered more efficient than onshore wind farms mainly due to their access to stronger and more consistent wind speeds over the seas and their almost complete lack of interfering physical objects.

Since the installation of the first offshore wind turbine in 1990 in Denmark, the size of the turbines, their distance from coasts and the water depth in which the foundations are installed have been continuously substantially increased. Figure 1 displays the average water depth of offshore wind projects and related forecast globally (excluding China). According to BloombergNEF, the average water depth has risen more than six times between 2000 and 2022, and the forecasted average trendline indicates that the upward trend will continue to about 44-meter water depth by 2035.

Fixed-bottom wind turbines have been dominant in the offshore wind power harvesting process, and fixed-bottom wind farms will continue to grow at a steady pace for many years. However, the development of such farms will eventually slow down as the installation of fixed-bottom foundations are limited to water depth of less than 60 meters – at least with the technology and technical solutions available today. To unlock the wind power potential of waters deeper than 60 meters, floating wind turbines are technically-viable options. Therefore, floating wind turbines will be crucial for the future expansion of offshore wind energy when the low hanging fruits of shallow water sites are filled up with fixed-bottom wind turbines. For countries with limited shallow waters, such as Japan, France, Italy and the US, particularly on the West coast, floating wind turbines could be a key technology to harness great wind resources. It must be noted that 80% of Europe’s offshore wind resource potential is in waters deeper than 60 metres with a total estimated potential of 4,000GW floating wind capacity. The numbers for the US and Japan are 60% and 80%, with 2,450GW and 500GW potential from floating wind capacity, respectively. Thanks to stronger and more frequent wind speeds further offshore, floating wind turbines could have a higher capacity factor than wind turbines located closer to shore, thus generating more energy throughout the year. Moreover, floating wind turbines create less visual pollution, leading to less NIMBY effects than near-shore fixed-bottoms, as most floating wind turbines will be located far from the coast.

The first concept for large-scale offshore floating wind turbines was introduced by William E. Heronemus, professor emeritus of University of Massachusetts, back in 1972. 35 years later, in 2007, the world's first floating wind turbine prototype with 80KWcapacity was deployed by Blue H Technologies, 21 kilometres off the coast of Apulia in Italy. It was installed in 113m water depth and was decommissioned after one year. One year later in 2009, Hywind, the world's first commercial-scale floating wind turbine with 2.3MW capacity was launched in the North Sea near the Norwegian coastline. It was owned by then Statoil (now called Equinor) and cost around EUR 57m to build and install. In 2019, Hywind was sold to Unitech Offshore and its name changed to UNITECH Zefyros. The turbine is still operational and is expected to keep generating electricity at least until 2029. A second Hywind project with 30MW capacity was installed off Scotland in 2017, and, two years later, the Windfloat Atlantic project with 25.5MW capacity went operational in deep waters off Portugal. After that, the Kincardine wind park was installed in 2020, near the shores of Scotland, with 48MW capacity. In this project, each turbine capacity is 9.5MW. This shows that floating wind turbines can be as big as the fixed-bottom turbines. The Hywind Tampen project in Norway, the latest large-scale operational floating wind project went operational in August 2023 with a total of 94.6MW capacity. Electricity generated by this project is used to power an oil and gas platform. Figure 2 shows the main floating wind projects that are currently operational.

Most of the components of floating wind turbines are the same as those for fixed-bottom wind turbines, including the nacelle, most of the electrical system, the blade and tower. The foundation’s components are different. Generally, a floating foundation of offshore wind turbines consists of two main parts: a floating structure and the mooring system that keeps the floater in position. There are about 120 different floating design concepts on which many pilot projects have been built around the world. Three platforms are currently the most popular in the market (see Figure 3):

So far, semi-submersible platforms have been the preferred foundation type in the market.

To keep the floaters in place, pre-installed mooring and anchoring systems are used. Designing the mooring and anchoring systems is quite a complex process, but overall, the technology is mature given the many years of experience and knowledge acquired by adjacent sectors such as offshore oil and gas. Knowledge from these sectors is transferrable to the floating wind market. Mooring system differs for different floaters, for example semi-submersibles and spar floaters, use longer but simpler mooring system, while TLPs are secured with more complex anchoring systems and vertically-loaded mooring lines.

Globally, a total of 232MW capacity of floating wind energy is currently operational. According to the forecast by 4C Offshore (released in June 2023 and updated in September 2023), 12.3GW floating wind energy is expected to enter construction globally by 2030. New project capacity is expected to more than double to 38.7GW between 2030 and 2035. Of the forecasted 12.3GW by 2030, 6 to 7GW is projected to be operational, while the remainder is expected to be under construction. As displayed in Figure 4, about 70% of the pipeline of floating wind energy would be realized after 2030.

Taking a regional perspective, Europe is currently leading the global floating wind energy market with 208MW of operational capacity. Norway, with 101MW capacity installed, accounts for 44% of global operational capacity. Based on the 4C Offshore forecasts, Europe (17.9GW) is expected to have the biggest share of the total capacity of almost 40GW that is planned to enter construction by 2035. This is close to 50% of the total forecasted capacity entering construction in that period globally. Based on their forecasts, Europe is followed by APAC (ex. China) with about 12.6GW, the Americas with 5.1GW and lastly China with 3.1GW capacity (see Figure 5).

If we look at the top ten countries with the largest forecasted capacity of floating wind energy entering the construction phase by 2035, South Korea has the largest share with 8.6GW, which is more than the cumulative forecasted capacity for France, Portugal, Spain and Japan. The US has the second place in this forecast, with 5GW capacity by 2035.

As mentioned earlier, the main difference between the structures of fixed-bottom and floating wind turbines is the foundation. As the technology differs, the supply chain of the foundations diverges, so do the foundation manufacturers. Thus, the main fixed-bottom foundation manufacturers such as SIF, Bladt, and EEW are not yet playing a role in the supply chain of floating wind foundations. The top-five commercial scale designers and manufacturers of floating foundations today are Hexicon, GustoMSC, AWC technology, Bouygues construction and Principle Power. As for the platform with the largest pipeline, currently Hexicon’s TwinWind design has 7.1GW in development. It is a semi-submersible type of platform that utilizes two turbines on one foundation, enabling more power generation per sea area, and is expected to lower LCOE compared to a single turbine system.

Floating wind energy is currently more expensive than energy generated from fixed-bottom wind turbines. According to DNV 2022 Energy Transition Outlook forecasts, the levelized cost of energy (LCOE) of floating wind energy in 2022 was almost four times higher than for fixed-bottom wind energy. However, DNV forecasts a drop in LCOE for floating wind turbines by 74% by 2035 and 82% by 2050. Based on this forecast, the LCOE of floating wind could reach to EUR 78/MWh by 2030, EUR 61/MWh by 2035, EUR 56/MWh by 2040 and EUR 43/MWh by 2050. 4C Offshore's estimation for LCOE drop is EUR 85-100/MWh by 2030, EUR 70/MWh by 2035 and EUR 50/MWh in 2040. In the same period of time, average LCOE costs of fixed-bottom offshore wind turbines are expected to decline gradually yet slowly. The net result is that the LCOE difference between the two offshore wind turbine solutions will narrow, but fixed-bottom offshore wind turbines will remain more cost competitive. Figure 7 depicts DNV’s forecasted LCOE of offshore floating and fixed bottom wind turbines between 2020 and 2050.

The LCOE reduction will depend on several factors, such as technological advances, cost and technical optimizations, wind farm and turbine size increase, economies of scale and standardization.

Currently, more than 120 floating wind concepts have been put forward while not many optimizations and scale-up projects are happening. Standardization could help to reduce the number of concepts and let the industry focus on optimizing the most optimal platforms and not get stuck in the innovation game. This would reduce uncertainties about the technology, building trust in the market and getting required volume flowing into the sector.

Optimization and scale-up require high investments which are difficult to provide without having a reliable and visible pipeline of projects. Companies need to have a predictable volume flowing into the sector to make sure their high capital investments will have returns. Without steady demand, investments in floating wind projects could remain risky. So, a steady pipeline is key to scale-up supply and reduce costs.

Governments can play a key role in increasing visibility in the market by acknowledging the potential of floating wind technology and by planning the integration of this technology in their renewable energy production. This requires governments to give more attention to all the social, economic and environmental values that floating wind can offer society, such as the creation of local supply chains, system integration, ecological considerations, and emissions reduction. Unleashing the huge potential of floating wind energy seems very far off if the focus is merely on LCOE as it has been so far in the market.

On a positive note, the shift away from a focus purely on LCOE is being acknowledged in Europe, as more and more EU governments have been experimenting with non-price criteria in their auction design, notably in fixed-bottom offshore wind. Also, very importantly, inclusion of the non-price criteria in the EU renewables auctions is clearly stated in the Net Zero Industrial Act (NZIA) that is now being amended by the European Parliament and EU Member States in the Council. This could have a positive impact on floating wind project development, facilitating the technology’s scale up faster.

Supply chain bottlenecks have been flagged by the wind industry as a looming problem, especially for offshore projects. The short supply of vessels, skilled personnel and port facilities are among the main bottlenecks that floating wind could struggle with.

In general, offshore renewable energy targets are increasing, but the number of technically skilled individuals capable of doing the work is not growing with the same pace. The declining base of highly skilled trade workers relative to demand has been flagged by the Global Wind Energy Council. WindEurope has estimated that the offshore wind workforce (both fixed-bottom and floating) in Europe needs to grow from currently 80,000 to 250,000 people by 2030. This calls for an urgent need to train new talent and reskill experienced workforces from adjacent sectors. One of the reasons for a talent shortage in this sector is the lack of long-term job security, partly due to uncertain project pipeline, lack of investment in lifelong skills training, failure to attract international workforce to work in remote coastal areas, and strong competition from talent-competing sectors.

Overcoming the talent gap requires collaboration between governments, industry and educational institutes. The European Commission has acknowledged the skill shortage in its Green Deal Industrial Plan and dedicated a pillar in its plan to developing the skills needed to make the transition happen. Whether this can be done in the necessary time frame remains to be seen.

Vessels that are used to transport and install floating wind turbines are different from vessels used for fixed-bottom turbines. Currently, towing, performed by tugboats, is the main method to transport the floaters or the whole assembled turbines (see Figure 8 for an example).

Installation of floating wind turbines doesn’t necessarily require a vessel as advanced as the jack-up vessel used for fixed-bottom wind turbines. However, the capabilities and availability of vessels needed to efficiently install anchors and mooring systems, implement towing and assembly of the floating structure, and install dynamic cables are uncertain. As a result, the sector can face a vessel shortage bottleneck in the future when the floating wind sector has a full pipeline of projects.

Ports play a key role in the expansion of wind energy in general, but the development of floating wind projects are more dependent on the availability of suitable ports. This is because many operational processes such as fabrication, storage, transportation, installation, operation and maintenance, and decommissioning of floating wind turbines involve port infrastructure. Existing ports already have difficulties keeping up with the fast-paced development of the offshore wind industry. To reach ambitious offshore wind targets, newly-equipped ports most likely need to be built and existing ones should be upgraded and increase capacity. However, capacity increase is not always possible, because many ports are surrounded by urban built environment or industrial complexes that do not leave enough free space for port expansion.

Port upgrades should provide a smooth manoeuvre of floating wind turbine structures around the port. The port capacity extension also should provide enough space for the possible dry and wet storage of multiple floaters. Because wind turbines can be up to 3 times the size of a normal ship, the dredged tunnels’ depth and width need to increase. The depth of water alongside the quay determines the type of floating wind turbine. Just to put this into perspective, semi-submersible wind turbines require 12-14 meters water depth, whereas spar models require 90 meters. A port that can handle large platforms would be highly in demand, obviously considering the distance between the port and wind farm locations. The location of the ports relative to the wind farm influences transit time, installation costs and dependency on weather windows.

In general, the expansion of offshore wind projects (both fixed-bottom and floating) requires significant investments in port infrastructure. As an example of such investments, WindEurope has estimated that between 2023 and 2030, Europe needs to invest EUR 9bn in its port infrastructures to make it ready to achieve its offshore wind ambitions. It should be noted that even if the finance is available, port development is not a quick project and it can take up to a decade, making timing a crucial factor here.

Currently, fixed-bottom offshore wind turbines completely dominate the offshore wind market. However, floating wind technology holds a lot of promise and is becoming increasingly popular in the market. Around 80% of the world’s offshore wind resource potential is in waters deeper than 60 metres, where fixed-bottom wind turbines are not a viable option. Thus, floating wind turbines could shape the future of wind energy. Europe is currently leading the floating wind energy market and is forecast to hold about 50% of the market by 2035. In that same year, the top three nations with the largest installed capacity would be South Korea, the US and the UK. The build-out of floating wind farms could be expected to scale significantly until after 2030, to reach an installed capacity of 38.7MW by 2035 if all announced projects would be built according to plan.

The supply chain of floating wind turbines is different from that of fixed-bottom turbines, in particular the foundation parts, the availability of suitable vessels, and port requirements. Thus, it is essential that a viable supply chain for floating wind is established and that existing infrastructure is upgraded and strengthened. The future of the floating wind sector largely also hinges on investments into port infrastructure, the availability of transport and installation vessels and other specialised vessels, and on training new talents and reskilling the experienced workforce.

Furthermore, the lack of predictable volume flowing into the sector, insufficient focus on optimizing and limiting the types of concept platforms, and the higher LCOE compared to fixed-bottoms are among the main challenges that are preventing or delaying the scale-up of floating wind energy. Standardization, optimization and commercialization are keys to make floating wind energy cost competitive.

Governments can also play a catalyst role in kickstarting floating offshore wind deployment by acknowledging the potential of floating wind technology and by planning the integration of floating wind energy in their renewable energy production. This requires more attention to the long-term social, environmental and economic advantages that floating wind energy can provide to society rather than merely focusing on LCOE.