As the technology has matured, enabling small-scale prototype projects and the world’s first pre-commercial array, it has become clear that floating wind farms are the key to opening up enormous new wind resources in expanses of water too deep for conventional, bottom-fixed farms.
This makes it an important area of research for the industry. But as with many new technologies, one of the biggest obstacles standing in the way of full-scale floating wind commercialisation is cost.
Trial projects like the WindFloat project in Portugal, the FORWARD project in Japan, and Hywind in Scotland have yielded progress. But floating wind still lags far behind bottom-fixed wind in terms of commercial readiness, and government support will be required in the medium term if, as predicted, it is to achieve or outstrip the cost reduction that has been witnessed in bottom-fixed offshore wind in recent years.
There are three common types of floating wind substructure: semi-submersible, spar, and tension leg platform (TLP). By analysing the costs associated with building a floating wind farm using each typology, and comparing them to that of a bottom-fixed monopile offshore wind farm, it’s possible to gauge how far away floating wind is from reaching financial parity.
The cost of developing and consenting a floating wind farm is expected to be slightly less expensive than a bottom-fixed. Shallower bore samples – with a possible exception in the case of TLP technology – when conducting geotechnical surveys could potentially contribute to these savings. However, with multiple anchors, more samples would be required.
The turbines used in bottom-fixed and floating situations are nearly identical. Both use adapted onshore machines, and modifications are made to the blade pitch control algorithms for floating turbines. This makes floating turbines cost-equivalent when compared to bottom-fixed.
Compared to monopiles, substructures for floating wind turbines are, for now, considerably more expensive to manufacture and assemble. Steel substructures are many times heavier and more labour-intensive to put together, whereas concrete substructures are cheaper per tonne of material but considerably heavier. In addition, all floating wind turbines require mooring lines and anchors.
Attaching the turbines to their substructures is one of the areas where floating wind has a clear cost advantage over bottom-fixed: turbines can be installed in a much more controlled environment, and without the use of expensive jack-up vessels. However, spar technologies require deep, sheltered waters and offshore cranes, resulting in a mating process that is more costly than semi-submersibles and TLPs.
Array cables for floating wind are currently more expensive, as they require dynamic cables (umbilicals) and bespoke electrical connectors, of which there is a limited availability. However, they can be installed before turbine installation, allowing multiple processes to be performed in parallel.
While more vessels are required for floating wind installation compared to monopiles, these are considerably cheaper to charter than a jack-up vessel. An exception would be in the case of TLPs that, if not self-stable in towing, require bespoke installation barges, which would incur significant expenditure.
Higher transmission costs for floating wind come from the necessity of putting an electrical substation in deep waters. While this could take the form of a fixed or floating platform, a floating solution would require the development and qualification of very high-power dynamic cables, which are currently not available on the market.
Costs for O&M and minor repairs are expected to be very similar to current bottom-fixed costs. Tests have demonstrated the applicability of crew transfer vessels (CTVs) used in bottom-fixed offshore wind to floating turbines and in the case of concrete substructures, inspection frequency could be reduced. Costs for major repairs will vary by typology and the process is, in essence, a reversal of the installation procedure: semi-submersible structures can be decoupled and towed back to port for repairs, making them cheaper than offshore repair work for bottom-fixed. Bespoke equipment for TLPs and spars erode the cost advantages compared to bottom-fixed.
Decommissioning costs for floating wind turbines are expected to be lower than for bottom-fixed. This is particularly true for semi-submersibles that do not require bespoke equipment or heavy lift operations offshore.
In general, costs are reduced compared to bottom-fixed in areas where operations can be performed onshore rather than offshore. Even for the offshore operations, less-complex, more readily-available vessels are required during mating, O&M and decommissioning.
Ultimately, cost will determine whether floating wind sinks or swims. Reductions will be driven by the development of specific components and enabling systems, techniques and infrastructure, such as electrical connections and bespoke vessels and port facilities. But with continued innovation as the technology matures, there are no areas where floating turbines will be materially more expensive than bottom-fixed. Floating wind has a buoyant future ahead.