Wind Catcher: The next step in the evolution of offshore wind power
By John Mathews and Michael Peck
Far offshore wind power is the next frontier in renewables. While onshore wind power has grown over the past two decades to become the largest segment of the renewable sources in power generation, it is limited by the availability of land and community resistance. Offshore wind turbines take advantage of the higher wind speeds found offshore compared to land, and projects are generally free from NIMBY opposition. Typically, such turbines are sited on fixed foundations in relatively shallow coastal waters or lakes less than 60m deep. Wind turbines on floating platforms that can be located far offshore have only recently been developed and deployed in recent years and make the potential for offshore wind power (OWP) virtually limitless.
As OWP has matured, so the single wind turbines involved have expanded to become veritable monsters of power generation. The latest such turbine is the Vestas 15 MW turbine, now taken up commercially for the first time by EnBW (EnBW First to Select Vestas 15 MW Offshore Wind Turbine | Offshore Wind) The larger the turbine, the greater the concentration of power and size - and the greater the penalties of stoppage if things go wrong.
Enter the newest player in OWP – the Wind Catcher modular system consisting of a vertical rectangular array or “sail” of small turbines mounted on a floating platform. This next step in the technological evolution of OWP consists of 126 small 1-MW turbines arrayed in 14 columns of 9 turbines each. This new modular unit has been given the name “wind catcher” by the company that has brought it into being, Wind Catching Systems of Norway (Windcatching). Whereas the technology of wind power was dominated in the 17th and 18th centuries by windmills, and the technology evolved in the 20th century to wind turbines (growing ever larger with the extension of wind power to offshore locations) it is wind catchers that promise to dominate in the 21st century.
Fig 1 illustrates the possible clustering of wind catcher modules in a group of five floating platforms (decks) to provide 630 MW (0.63 GW) of power generation. Only two such clusters operating at full capacity would generate about 20% more power than the typical 1 GW output of a large nuclear power plant. The big difference from a nuclear power station is that the wind catcher modules would be fabricated at an onshore manufacturing facility, and benefit from scale economies as their deployments expand. They would be towed to their operating position where they would be moored by cables anchored to the seabed. Their operation would draw on competences already well-established in oil and gas offshore platform rigs. Wind catcher operation would also be safe, clean, low cost and reliable (based on redundancy) – unlike the case of nuclear power.
Fig. 1 Artist’s rendition of a cluster of five wind catcher floating modules
Source: Wind Catching Systems
Since there are no practical obstacles in the way of expanding the scale of these wind catcher platforms, it would be feasible to think of even 100 such 5-unit clusters in the open sea, rated at 63 GW, generating power to feed into major grids like that of China, the EU or South Asia. Such a wind farm would be by far the largest electricity generating entity in the world, and one that is 100% clean, reliable, low-cost and with falling costs. The manufacture of such wind catcher arrays would be limited only by the supply of raw materials – and it is relevant that WCS are actively investigating making the turbines within the wind catcher array fully recyclable.
Each wind catcher module is rated at 126 MW – more than 5 times larger than the largest extant 15 MW offshore wind turbine. It is designed to be based on redundancy to ensure continuous operation. Each small constituent 1MW turbine is amenable to quick repair or replacement without requiring the whole wind catcher module to be stopped or dismantled. This is a huge advantage as conventional offshore wind turbines grow ever larger and more cumbersome. The WCS design includes an elevator located within the array itself to facilitate quick and easy substitution of turbines, thus ensuring uninterrupted operation.
The scale of the projected 126-turbine wind catcher array is best given by visual comparison with comparable structures like the Eiffel Tower or major cruise ships – as in Fig. 2.
Fig. 2 Relative sizes of wind catcher modular array and comparable structures
Source: Wind Catching Systems
The wind catcher is thus best described as a radical innovation promising virtually unlimited expansion of offshore wind power. Floating platforms can be positioned far from the shore, beyond sight and out of harm’s way for seabirds. The wind catcher modules can be grouped in small clusters equipped with electronic signalling that will warn ships and seabirds alike of their presence.
The major capital investment aspects of the project, apart from the wind turbine arrays themselves, would be the connection to mainland power grids. This would involve a power collection point within a cluster of wind catcher arrays, and subsea cables connecting to the mainland grid. An alternative approach that WCS has not yet (apparently) investigated is to use the power generated to feed an electrolysis unit to split water to produce green hydrogen, which could then be shipped to major industrial destinations as substitute for fossil fuels, and with oxygen as a valuable by-product.
Wind Catching Systems (WCS) is a small Norwegian start-up that has been launched specifically to bring the wind catcher technology to market, initially in the North Sea where floating wind platforms have already been erected using conventional large-scale wind turbines. The company has plans to push the button on its first wind catcher module in the second half of next year, 2022.
The man behind the idea of the wind catcher is Asbjorn Nes, a veteran of Norway’s maritime sector. The initial design and testing work was conducted by Nes and colleagues, and then extended via partnership with the marine services company Aibel (Aibel) as well as the Norwegian Institute for Energy Technology (IFE) (IFE, Institute for Energy Technology. Research for a better future - IFE). Principal owners of the company are Ferd (English | Ferd) and North Energy (North Energy). Modelling of the structure of the wind catcher modules, and the initial assessments of the behaviour of the turbines in the sail, was modelled by the technical partners Aibel and IFE. WCS have also conducted tests in a wind tunnel at Milan Polytechnic over the summer of 2021.
It is WCS that is promoting the name “wind catcher” for their 126-MW module, to distinguish it from the giant single turbines that have hitherto been the only option for extending the reach of offshore wind power. This is a name that we endorse and see as catching on rapidly to demarcate this radical technological breakthrough from the single turbine alternative.
Capacity factor and energy production
WCS have modelled the Annual Energy Production (AEP) for the systems for different relevant locations using high resolution weather data. For the Norwegian Utsira area which is scheduled to host the first Norwegian commercial deployments of floating offshore wind, WCS are looking at annual production figures in the range of 330 GWh. For the high wind sites off California, WCS are looking at annual production figures in the range of 410 GWh.
One of the issues that interests the company now is the multirotor effect generated by synchronised turbulence from the array of turbines mounted together in the sail. WCS have been able to confirm the hypothesis that the multirotor effect is indeed relevant but given the constraints of a wind tunnel test they have not yet been able to establish the exact magnitude of the effect in a structure of 126 individual turbines.
WCS see redundancy as a major advantage of their system. A single turbine failure only reduces output by less than 1%, compared with 100% for a single turbine system. With a large semi-submersible structure like this, the movement of the sail is limited, but it will of course be noticeable 300m or more up in the sail and provide a challenge for maintenance and repair crews. However, one of the key benefits of the system’s redundancy is that the operating company would be able to plan maintenance for beneficial weather windows without significant negative effects on production. Moreover, the design’s built-in elevator system allows individual faulty units to be removed and lowered down to the main deck for refurbishment or replacement.
WCS plan to exploit the inherent redundancy of the 126-turbine array in two significant ways. Firstly, they propose to use simple turbines with fewer fail-points. These would be easily transported to and from shore as individual units. Secondly, the structure itself is designed to outlast its individual turbine components. This makes sense for the wind catcher, due to its modular concept. These are important advantages favouring the wind catcher over an offshore single turbine system.
As for cost, WCS are certainly benefiting from the learning curve from offshore wind deployments in the North Sea and elsewhere in recent years. There can be no definitive idea of costs until a pilot plant has been built and becomes operational as anticipated in 2022. An important feature of the design of the wind catcher system is that the complexity of the power producing units is considerably reduced compared to conventional offshore turbines, which can translate into lower capital investment costs. Knowhow concerning complex structures for offshore oil and gas deployments has been an important starting point here for WCS, and for the wind catcher the learning curve is arguably as relevant for the overall cost picture as for other manufactured renewable technologies.
"Wind Catching will make floating offshore wind competitive as soon as in 2022-2023, which is at least ten years earlier than conventional floating offshore wind farms," says Wind Catching Systems CEO Ole Heggeheim. "Our goal is to enable offshore wind operators and developers to produce electricity at a cost that competes with other energy sources, without subsidies.”
WCS is on record as stating that they want to push the button on a pilot/demonstrator unit in the second half of next year (2022). This type of development takes time, obviously, but WCS anticipates being helped by the fact that the system uses known components and relies on low complexity of individual parts, even if the combination of these is new.
An important feature of the WCS design is that the turbine blades could be made from aluminium, which is 100% recyclable, rather than the fibreglass that is used for most large stand-along wind turbines. The fibreglass is difficult to recycle, and much of the material used for large turbines in wind farms ends up in landfill. It is the smaller scale of the blades used in the windcatcher that allows them to be considered as candidates for aluminium construction. To make components in renewable systems completely renewable (recyclable) is clearly an important feature to guide their design.
In sum, the wind catcher array is an instance of radical innovation that promises to make offshore wind power an unstoppable force for generating power that is safe, reliable, cheap and clean and recyclable. It represents another important chapter in the inevitable passage from fossil fuels to clean energy.
 Currently efficient water splitting depends on catalytic electrodes requiring pure water, however we note that a high-performance novel catalyst has been developed by Swinburne University’s Centre for Translational Atomaterials and Shaanxi Normal University which produces solar-triggered hydrogen from seawater. Another discovery having great potential for renewable energy systems (Novel catalyst produces green hydrogen from seawater).  See “Giant wall of turbines could reduce the cost of floating offshore wind”, The Maritime Executive, Aug 25 2021, at: Giant Wall of Turbines Could Reduce the Cost of Floating Offshore Wind (maritime-executive.com)
John Mathews , Emeritus Professor, Macquarie Business School, Macquarie University, Sydney; firstname.lastname@example.org Michael Peck, PhD graduate, University of Sydney Business School; email@example.com