Overcoming Floating Wind Challenges Is Key to Global Energy Transition – Houlder

The following article is a guest post by Mark Goalen, Director – Offshore Engineering, Houlder.

The scaling up of renewable energy capacity will be essential for the success of the global energy transition. Increasing offshore wind capacity is, in turn, key to scaling up renewable energy production but is reliant on developers installing high-capacity farms in deeper offshore sites. To achieve this, floating offshore wind technology needs to reach full commercialisation.

Exciting developments are underway for the floating offshore wind industry. Last November, first power was generated by the world’s largest floating offshore wind farm, the 88MW Hywind Tampen wind farm located in the Norwegian North Sea. Ambitious targets are on the table throughout the UK, perhaps most notably 14 projects in Scotland’s ScotWind leasing round anticipated to supply over 17GW of power. ScotWind will start to generate power at the end of the decade and into the 2030s, but there is plenty of industry activity to look forward to in the meantime. Copenhagen Offshore Partners’ Pentland development is due online in 2026, the INTOG (Innovation and Targeted Oil & Gas) leasing round application window is now closed with applications under review, and there is a Celtic Sea leasing round anticipated to open this year.

In Europe recent developments in the Mediterranean include Renexia’s proposed 9-billion-euro Med Wind project in the Strait of Sicily, expected to be operational in 2025. The project will have 190 floating foundations for the wind turbines and installed power capacity of 2.8 GW, enough to power more than three million Italian households. Globally, offshore floating wind is forecast to be big from Asia to the USA.

Despite this massive growth forecast, and while the global offshore wind market enjoyed its best year ever in 2021, with 21.1GW of capacity commissioned, only 57MW of that was floating wind – as reported by the Global Wind Energy Council (GWEC). Why? Because significant barriers to full commercialisation still exist. There are challenges that must be overcome before floating offshore wind will realise its full potential.

One of the key technical barriers to floating wind commercialisation faced by developers is selecting the most suitable floating foundation type for a given location. Every development is unique; water depth, seabed type, environmental conditions are just some of the factors that must be accounted for. There are many floating foundations to choose from, but they can essentially be categorised into four main structure types: spar buoy, tension leg platform, semi-submersible platform, and barge.

They all have fundamental differences in their characteristics that affect how the turbine responds to the environmental conditions, so a fundamental factor that should heavily influence foundation selection is the foundation’s motion response to environmental conditions. Understanding the effect of motion characteristics on the whole system is essential. It directly impacts all components from nacelle, tower, to the dynamic cable, and the mooring system.

Most floating wind farms that have been developed to date can be seen as demonstrators, which have been driven by the floating structure designers themselves to prove their technology, rather than to provide developers with an objective demonstration of each technology for a given site and environmental conditions. As such, there is still a fundamental need to identify the best technical solutions for each planned floating site that will minimise costs and risk and maximise efficiency for developers.

These demonstrator projects have also used conventional wind turbine generators which were originally designed for fixed or onshore wind turbines. There are several known challenges associated with operating and maintaining these conventional turbines in a dynamic environment. Therefore, it is expected that disruptive technology such as X1 Wind’s weathervaning downwind concept, SEATWIRL’s vertical axis turbine and SENSEWind’s self-erecting nacelle system amongst other technology innovations will gain traction over time. Understanding and leveraging the latest relevant innovations is key to floating winds evolution and, ultimately, its full commercialisation.

No single, definitive structure type or floating foundation will be optimal for every site. There are many variables that will impact the decision, including a technologies’ operability, reliability, practicality, readiness, CAPEX, OPEX and potential longevity to name a few. A developer must choose a foundation that is most suitable for the wind farm they are developing and, given that many developers’ portfolios are global, that will vary from site to site.

Effectively selecting a floating foundation involves collaborating with the right partners to analyse a combination of technical and operational factors. Importantly, it should be recognised that operational factors may have a bigger impact than technical ones over the asset’s lifecycle.

One vital operational factor that will determine floating foundation choice is the project’s supply chain. Indeed, constructing the required infrastructure and putting in place the appropriate supply chain is one of the largest barriers to quick and effective floating offshore wind commercialisation.

Turbines, foundations, mooring system components, cables, port infrastructure, are all critical elements of the supply chain that must be considered. Transport routes, logistics, infrastructure as well as installation and O&M (operations and maintenance) vessels make matters complex. To attain a clear understanding of all supply chain requirements and optimise their floating wind projects, it is key that developers and other stakeholders have a holistic understanding of the development and how it varies from fixed wind which many are more accustomed to.

The supply chain has recently proven to be a barrier for Shell and Equinor. In November, Shell had to cancel the construction of a demonstrator floating wind farm in French waters. It cited supply chain issues among the key reasons for abandoning the project. Just a few months before, Equinor announced delays to the Hywind Tampen project, also citing supply chain issues.

The 14 floating ScotWind projects are also expected to face supply chain constraints. ScotWind is boldly assuming that 18-20MW turbines will be used even though they are not yet available. Given a 10-year period (2029 – 2039) for manufacturing and installation, achieving ScotWind’s ambitious goals would require approximately 125 units to be made per year.

Most Scottish ports do not have the required area to deliver commercial scale floating offshore wind components without significant investment and infrastructure development. Most decisions on floating foundation type are yet to be made, so this creates a Catch-22 dilemma. Until the foundation type is known, the supply chain cannot form, and investment cannot be made in port infrastructure.

Infrastructure, location, water depth, available space for fabrication, and storage are all important for ports that will support new floating wind development. Taking ScotWind as an example, current port options are limited. Individual ports do have plans to invest, but none will be sufficient to cover all the requirements, so there is a chance that significant parts of the manufacturing required could go to Europe or Asia, or face schedule delays.

Up to now, the lack of port infrastructure has made concrete look to be an attractive option over steel as the core foundation material. It would appear easier to manufacture concrete structures because it requires a less skilled workforce. These structures only require the moulds and raw materials, not the specialised welding equipment or qualified welders. Steel can be prefabricated elsewhere and assembled, but that builds in additional fabrication risk and requires additional transport of large components, potentially increasing costs and carbon footprint.

There is one possible solution being used by Copenhagen Offshore Partners on the Pentland development that specifically addresses these concerns. The company has selected the Stiesdal TetraSub for the site. The philosophy of the Tetra concept is that the parts can be fabricated at any number of existing fabrication facilities. The completed parts are then delivered to site for assembly. They do not need welding to assemble, and it is expected that two full units per site per week can be completed. This kind of system looks very attractive from the supply chain perspective as it overcomes a lot of the existing barriers. All focus is expected to be on the performance of the units in Pentland ahead of developers selecting floating foundations for ScotWind.

Cost and resource efficient O&M is another key element that developers must consider from the outset of a project. If not properly considered, O&M can become a major barrier to the commerciality and day-to-day running of a floating wind farm.

Floating foundations are currently towed back to port for maintenance and repairs. However, this will not remain feasible or economical as wind turbines are located further offshore and the distance to O&M ports increases. The ability to conduct O&M on-location must be developed, because the risk and costs associated with connection and disconnection and transportation of the wind turbines will prove too high over time. A combination of modifying the turbine, as well as developing the tools and offshore support vessels required to support this O&M phase, will be crucial to the success of floating wind projects.

To summarise, floating offshore wind is a truly exciting global opportunity that will play a key role in the energy transition. However, there are barriers to full commercialisation that must be addressed and overcome. Choosing the right structure type and floating foundation for each site is a key step in the right direction. This is not an easy decision to make. Technical challenges, such as a floating foundation’s motion response to environmental conditions, must be considered. Plus, there are several operational factors to analyse, including supply chains, port infrastructure, and O&M.

The bottom line is that, to effectively commercialise floating wind, developers can benefit from independent consultancy. Involving marine and offshore design and engineering specialists from the start of a project can ensure that costs and risks are minimised, timeframes are realistic, and efficiency is maximised. With the right collaboration, and investment supported by technical analysis, the barriers to floating wind can and will be overcome. Ultimately, this will allow floating offshore wind to fulfil its potential in supporting the global energy transition.

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