Windstory #29 - WHEEL: the revolutionary floating, concrete-hulled, two-bladed 6 MW wind turbine to be tested in Spain
After more than a decade developing the WHEEL floating platform, Esteyco is preparing to install an interesting 6 MW prototype in the waters off Gran Canaria.
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🌊 WHEEL: the floating, concrete-hulled, two-bladed 6 MW wind turbine to be tested in the Canary Islands
Floating wind is the great promise for unlocking thousands of megawatts of offshore resource that conventional fixed-bottom technology cannot reach. But it has a technological and industrial maturity problem that is far from resolved.
More than twenty floating platform designs are currently competing in the market: semi-submersibles, SPARs, TLPs, barges and hybrid variants of all of them. And while some consolidation is beginning to emerge, nobody yet knows with certainty which designs will survive the commercial filter.
For southern Europe in general and Spain in particular, this is an especially pressing issue. Along most of our coastline, the seabed drops rapidly to depths where monopiles and jackets are technically and economically unviable. None of the areas identified in the Maritime Spatial Plans is compatible with fixed-bottom offshore wind. If Spain wants to tap its offshore wind resource, floating technology is the only realistic option.
Perhaps that is why R&D and prototype activity in our country is so intense. Spain already has three marine test facilities: BIMEP in Armintza (Bizkaia), PLOCAN off the coast of Gran Canaria, and PLEMCAT in the Bay of Roses (Girona), the last of these with the objective of being operational in 2026.
They have already hosted floating technology prototypes including Saitec’s DemoSATH (at BIMEP), X1 Wind’s scaled prototype (at PLOCAN), and EnerOcean’s W2Power prototype, also in the Canaries. The next full-scale prototype to be installed in Canarian waters is Esteyco’s WHEEL, also at PLOCAN. Esteyco, incidentally, already has offshore experience with its Elican fixed-bottom prototype, also installed in the Canaries, and one that would deserve a separate article for the peculiarity of its design.
The Canary Islands are precisely the region expected to host Spain’s first floating offshore wind farm. The logic is straightforward: generating electricity on the islands costs more than on the mainland, so offshore wind has a relative economic advantage there that it lacks elsewhere. It is taking longer than expected, but in February 2026 the government launched at least a first public consultation on the basis of the competitive process, identifying the Canaries as one of the priority zones alongside Galicia and Catalonia. As I noted in Windletter #87, all signs point to a first auction in the Canaries of not much more than 200 MW. Something is something.
The WHEEL prototype arrives at a moment when one of the sector’s great debates remains unresolved: steel versus concrete. The vast majority of floating platform designs competing today are steel. But concrete has its advantages and some platform developers continue to bet on it. Esteyco is one of them, as could hardly be otherwise. Concrete is part of their DNA.
Yet concrete does carry an industrialisation challenge that should not be ignored. Concrete construction requires large port areas and a serial manufacturing chain that only makes economic sense when dozens of units are to be produced. Otherwise, building a single floater becomes an almost artisanal task that makes cost reduction impossible.
Steel, by contrast, lends itself more readily to industrialisation from the outset: shipyards, tower factories or monopile manufacturers can adapt with relatively modest investment.
🎡 What is the WHEEL project
WHEEL stands for Wind Hybrid Esteyco Evolution for Low-Carbon solutions. It is a technology patented by Esteyco since 2014, although the company has deliberately chosen to grant licences to other developers: “far from wanting to slow down the development of floating wind, we have always wanted to promote it,” the company says.
Among others, Esteyco has granted a non-exclusive licence to Stiesdal Offshore Technologies (SOT) for the use of this patented solution, limited to steel-based platforms. Stiesdal has used it to develop the TetraSpar Demonstrator, a 3.6 MW prototype with a Siemens Gamesa Direct Drive turbine installed at the METCentre test facility in Norway, which will be decommissioned after five years of operation with outstanding results: an aggregate capacity factor of 51.4% and availability of 98%.
The original idea emerged more than twelve years ago, and the design has evolved considerably since then. Six years ago, the team considered that it had the maturity needed to make the leap to a full-scale prototype. After winning European funding at the end of 2022, the project formally began in early 2023.
It is a 6 MW prototype funded by the European Commission through Horizon Europe (Grant Agreement No. 101084409), with a total budget of €25.3 million and a European contribution of €16.7 million. The consortium comprises eleven partners: Esteyco as coordinator, 2-B Energy, Rover Grupo, PLOCAN, IHCantabria, EnBW, Bridon-Bekaert, Boskalis, Vicinay Sestao, REPNAVAL and Cemex.
It is the first full-scale floating wind turbine to be installed at the PLOCAN test site, just 3 kilometres off the coast of Jinámar, with the seabed at 90 metres depth.
🔧 The platform: a SPAR that solves the problem others have not been able to solve
WHEEL’s design belongs to the SPAR family, but Esteyco defines it as an “evolved SPAR.”
A conventional SPAR gains stability by sinking an enormous weight to great depth, displacing the centre of gravity below the centre of buoyancy. The principle is robust and proven, in both oil and gas and in the first SPAR wind turbines such as Hywind.
One of the main challenges of SPAR designs is their own geometry. A conventional SPAR is an extremely long and deep structure, which introduces significant complexity both in its launch and in the subsequent installation of the turbine.
This type of platform is typically launched horizontally and then uprighted through ballasting operations to reach its vertical operating position.
Once vertical, the SPAR’s deep draft prevents the turbine from being assembled in the conventional way directly onto the platform at most conventional ports. Without sufficient depth alongside the quay, the assembly must be moved offshore or to areas with adequate draft, with the corresponding increase in complexity and cost.
A striking example is Hywind Scotland, where the fully assembled turbine is installed onto the SPAR floating offshore, at a location with sufficient depth to complete the spectacular operation (the video links directly to that manoeuvre).
WHEEL resolves this by separating the two functions of a SPAR platform into two elements that can travel together. The design consists of two concrete tanks: an upper one providing buoyancy and a lower one acting as ballast. Both have a ring geometry that allows them to be built and transported one inside the other.
In port, and before "lowering" the inner ring, the WHEEL platform acts as a shallow-draft barge with which the complete turbine can be assembled using a quayside crane, just as with a semi-submersible, but with much less width and draft, and without specialised port infrastructure.
Once in sufficiently deep water, the lower tank, ballasted with sand, is deployed downward in a controlled manner. The tendons connecting it to the upper tank work in pre-tension under the lower tank’s own weight, which acts like a pendulum. These tendons behave as rigid bars, making both elements move in unison. The system thus transitions from barge configuration to SPAR operating configuration.
The result is a platform that integrates SPAR stability in operation with the handleability of a semi-submersible in port. For a 15 MW version, Esteyco states the transport barge would have a 5.3-metre draft, roughly half that of an equivalent semi-submersible, which opens up a very wide range of ports suitable for manufacturing.
A 17-metre steel tripod sits atop the upper tank, connecting the floating structure to the tower, which is 72 metres tall in the 6 MW prototype. The tripod consists of seven tubular tower-like elements, six of which are road-transportable and can be manufactured by conventional onshore tower suppliers.
According to Esteyco, the dynamic behaviour of the system allows savings of up to 40% in tower steel compared to equivalent semi-submersible designs.
The mooring system consists of three mooring lines separated 120° apart, with a total length of approximately 1,050 metres. The 20 kV export cable is 3 km long: the first 500 metres are dynamic cable designed to absorb the platform’s continuous movements, and the remainder is static cable on the seabed. A curiosity: this prototype will connect first to the Elican prototype, forming a circuit before connecting to the Jinámar substation.
🌀 The two-bladed turbine: a different choice
The turbine to be installed on the platform is a 2B6 from 2-B Energy: 6 MW, two-bladed rotor of 140.60 metres diameter, operating downwind.
The choice of a two-bladed downwind turbine was not, according to Esteyco, a technical decision. “The WHEEL technology is not limited to two-bladed or downwind turbines; it is compatible with any turbine,” the company says. The reason was more practical: for a 6 MW prototype, “small” in inverted commas as the team itself qualifies it, finding one of the major OEMs willing to collaborate is not easy.
2-B Energy, a more modest manufacturer but with greater willingness to engage in projects of this kind, had a two-bladed downwind machine available. “For us it was not a problem,” Esteyco says, adding that the downwind turbine “is having virtually no effect on the design, neither in the temporary phases nor in operation.”
That said, the advantages of the downwind configuration on a floating platform are real, and some existing designs exploit them. A downwind turbine has the ability to self-orient into the wind, reducing the complexity of the yaw system.
It should be noted, however, that this advantage is only fully realised when the platform incorporates a single point mooring system, which allows the entire assembly, floater and turbine, to rotate freely following the wind direction. This is the case, for example, with X1 Wind’s PivotBuoy. WHEEL uses a conventional three-point mooring system, so it retains the yaw system, albeit perhaps simplified compared to a conventional upwind turbine.
As for the two-bladed configuration, the advantage is that the weight of the nacelle-rotor assembly is reduced significantly, a critical factor for the cost and size of the entire platform.
Moreover, interest in two-bladed rotors is not marginal in the sector. In Windletter #118 we reported that Envision had successfully tested a two-bladed prototype for more than 500 days. Despite not yet achieving commercial success, it is a design that refuses to die.
📋 Project status: the launch, after the summer
In July 2025, the BOE published the environmental clearance: the prototype does not require a full environmental impact assessment. The most complex administrative hurdle had been cleared.
A lesson learnt from Elican, as Esteyco’s own team acknowledges: “it is easy to underestimate the time that all administrative procedures really take. The first prototype has given us the lessons learnt to properly estimate this aspect in our schedule.”
At the port of Las Palmas, the AIRBARGE, the assembly platform that allows heavy structures to be manufactured without specialised port infrastructure, was completed in August 2025 and passed its commissioning tests.
Currently, Rover Grupo is fabricating the lower section of the concrete slab of the upper tank on it. The launch of the WHEEL tanks is planned for after the summer of 2026. They will then move to a safe area of the port where the floater will be completed and the tower and turbine integrated. Installation at PLOCAN and energisation are expected in the winter of 2026-2027.
Esteyco’s team acknowledges that building a single unit rather than a series generates pressure on the project budget. “The design is advancing towards maturity at the same time as manufacturing progresses,” they say. “We are trying to speed up the adaptation in design of improvements identified during the process so that the platform that is tested is the most representative of the WHEEL technology for the future,” they add.
🔭 Beyond the prototype
If the prototype proves what it needs to prove, WHEEL will have simultaneously solved the three problems that have historically held back the SPAR family: constructive viability in conventional ports, competitive cost thanks to concrete, and dynamic behaviour favourable for large turbines.
The next step would be to consolidate the design for 15+ MW turbines and develop a pre-commercial execution plan. “Ideally, developing a prototype for a 15+ MW turbine would reaffirm the design at commercial scale and provide a great deal of information for the future development of a larger-scale offshore wind farm,” Esteyco says.
“Conceiving a floater that works properly once installed is only part of the problem. Conceiving a floater that is easily industrialisable anywhere in the world adds many variables to an already complex equation.”
Interest is already there. “For some time now we have been perceiving an increase in interest from potential developers in our design, looking to better understand the technology and its compatibility with the areas they have under development.” The main target markets range from Spain and Europe, including the UK, Norway, France and the Mediterranean, to Asia, where they have received “great reception” for both WHEEL and the AIRBARGE.
We at Windletter will continue to report on the progress of this prototype. If you don’t want to miss it, subscribe for free.
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Disclaimer: The opinions presented in Windletter are mine and do not necessarily reflect the views of my employer.