Windstory #26 - OptiGen: the startup that wants to revolutionise the drivetrain of direct-drive wind turbines (I)
The Spanish startup OptiGen has presented an innovative drivetrain design for direct-drive wind turbines. We have spoken with them to bring you all the details.
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Last July, the Spanish startup Optimized Generators (OptiGen) presented its patented drivetrain solution for direct-drive wind turbines to the market. It did so exclusively through Windpower Monthly, and its technological proposal has attracted considerable attention within the sector.
I was left wanting to know more about the company and to better understand its technology, so I decided to prepare an in-depth feature to analyse it in detail.
In addition, the OptiGen team has kindly agreed to answer our questions, which allows us to offer exclusive content to Windletter.
Given that I am not a specialist in wind turbine drivetrains, and although I have researched and studied the topic as much as I could, for the review of this article I have relied on the kind collaboration of Windtechs, a consultancy and Market Intelligence firm specialised in wind turbine technology.
Windletter is a publication supported by its community of readers. If you enjoy the content, you can subscribe for free or become a paid subscriber to support the publication.
OptiGen: revolutionising the drivetrain of direct-drive wind turbines
OptiGen was founded in Barcelona in 2023 and has a founding team that is, without a doubt, its best calling card and one of its greatest assets, thanks to their extensive experience in the sector.
Blai Pié i Valls – CEO and CFO, with a background in renewable energy investment.
Stefan Keller – co-CEO, with experience at Alstom and GE, and currently at the engineering consultancy CREADIS.
Santiago Canedo – CTO, with an extensive career in the wind sector, from the days of Ecotècnia, through GE, to X1 Wind.
Between the three of them, they add up to more than 40 years of experience in the wind sector, including the development of offshore turbines from 6 to 15 MW, covering everything from feasibility studies to commercial operation.
The origin of the project
According to Santiago, the seed of the idea emerged at PortAventura, shortly after COVID: “As I was leaving the park, I stopped to look at Red Force at Ferrari Land, a roller coaster with a semicircular shape, and I started thinking about how to maintain the air gap of a direct-drive generator using a wheel–rail system.”
When he got home, he drew the idea on the whiteboard in his kitchen and could not get it out of his head. After reviewing several existing patents, he found his own approach, the details of which we will explain later.
He discussed the idea with Stefan, a former GE engineer with extensive knowledge of direct-drive generators and responsible for the early development phases of the 12 MW Haliade-X. “At first he had doubts, but he eventually became convinced and wanted to take part in the project,” Santiago tells us.
The third partner, Blai, appeared almost by chance. They met at a dinner and, after an informal conversation about the idea, they reconnected a year later.
“We met the three of us,” Santiago recalls, “and decided to get the company started.”
What is OptiGen?
OptiGen aims to revolutionise the drivetrain of direct-drive wind turbines, that is, those using permanent magnet generators without a gearbox. Its proposal seeks to replace and optimise the current design of the generator assembly, main shaft and bearings, and hub, with the objective of reducing both the cost and the weight of the turbine and the tower (or the platform in the case of floating wind). In addition, if the results are confirmed, it could allow a significant reduction in the use of rare earths.
The company has presented to the market an initial design for a 15 MW wind turbine based on an innovative drivetrain technology, whose patent has already been granted in both Europe and the USA.
They did not want to disclose the idea until having a solid foundation. “We preferred to wait until defining the most suitable architecture and completing an initial theoretical feasibility before speaking publicly about the project,” explains Santiago. That step came thanks to collaboration within the LightWind project, funded by the Horizon Europe programme.
Since then, the calls have not stopped. “We have been contacted by bearing manufacturers, developers, and several OEMs,” he says. “You can tell that the sector is concerned about the reliability of rotor bearings and the high cost of direct-drive turbines.”
In practical terms, this design could be integrated into offshore wind turbines from manufacturers such as Siemens Gamesa, GE Vernova, or Dongfang. By contrast, for Vestas, which currently uses Medium Speed PMSG technology, a complete change in its drivetrain approach would be required. Although the company is already studying the possibility of integrating its wheel–rail system into that type of turbine.
In any case, integrating this solution into any of the current models would require a significant redesign.
👉 For those of you who want to delve deeper into the different types of wind turbine drivetrains, I recommend this article that we published in Windletter before the summer.
In fact, if you look closely at the previous image, you will notice that the morphology of the nacelle + hub assembly is somewhat different. Indeed, one of the first details that caught my attention when seeing the render shared by OptiGen was how small the blade root appears relative to the size of the hub.
However, this is an optical effect caused by the absence of a “nose” or cone, combined with a generator/hub diameter of over 10 metres. This is explained by one of its co-founders, Stefan Keller, in this LinkedIn comment.
We will go into the technical details later, but, in short, we can say that OptiGen’s proposal aims to revolutionise the design of the generator, main shaft and bearings, and hub of current direct-drive solutions, promising a reduction in both turbine weight and cost. In addition, according to the startup, its design reduces maintenance costs by facilitating the inspection, repair, and replacement of components in situ.
Although the solution is oriented towards the offshore market, where large dimensions maximise its competitive advantage, there is no technological impediment to also adapting it to onshore wind turbines.
In any case, it is important to stress that in onshore wind, with the exception of Enercon, Goldwind (whose portfolio currently includes both direct-drive and MS-PMSG turbines), and Siemens Gamesa with its DD (which is a niche product), there are no OEMs left with direct-drive technology in their portfolios, mainly due to its higher CAPEX compared to other configurations. OptiGen would arrive precisely to overcome that challenge.
Technical details
On OptiGen’s website, technical information can be found, including infographics, 3D renders, and even animations. Below, we try to explain the technology in an accessible way, highlighting the main differences compared to conventional direct-drive designs.
Without main rotor bearings
In a conventional direct-drive wind turbine, the rotor with the three blades and the generator magnets rotates supported by large main bearings that allow blade rotation while also ensuring the air-gap distance.
These bearings are extremely costly to manufacture and are subject to considerable wear due to the enormous weight of the rotor and the aerodynamic loads generated by the wind during turbine operation. As turbines increase in size, the design and reliability of these bearings become an ever-greater challenge, as do the structures required to keep the air gap stable.
In the event of critical failures, these bearings can only be replaced by dismantling the entire rotor and generator, an operation that requires completely dismantling the turbine and transporting the nacelle to shore. This involves large and sophisticated vessels equipped with very high-tonnage cranes, which are extremely expensive and also require long periods of downtime.
OptiGen’s proposal completely eliminates these bearings, reducing maintenance costs thanks to its modularity, which allows component replacement and “in situ” inspection and repair in the event of failures.
It is worth noting that OptiGen’s design is an outer-rotor configuration, meaning that the permanent magnets are located on an outer ring that rotates around the stator. This is the typical offshore solution used by both SGRE and GE.
👉 For those who want to learn more about main bearings, I liked this article from the European Academy of Wind Energy.
Integrated rotor
Unlike other wind turbines, in this case the hub, in addition to supporting the blades, houses the generator magnets longitudinally inside it and, on both sides, two rails that allow the rotation of the assembly.
Modular stator
The stator (the fixed part of the generator) is made up of bogies similar to those used in the railway sector, which contain the generator coils and a set of wheels, and which are installed on pre-compressed elastic supports.
This not only guarantees permanent contact between the wheels and the rails, but also ensures that the air-gap distance does not change, regardless of wind conditions. It even allows the distance between the magnets and the coils to be reduced, which enables significant savings in the use of magnets, and therefore of the highly sought-after rare earths.
Following the railway analogy, these wheel assemblies would be the train axles and the rails the tracks along which they move around the stator.
Thanks to this design, each module can be replaced individually from inside the nacelle, without the need to dismantle the entire assembly, which simplifies repairs and significantly reduces turbine downtime.
Assembly
Regarding assembly, OptiGen has shared the following infographic.
In this way, the rotor is integrated into the structure of the hub itself, while the stator is fixed to the nacelle structure. As you can see, the design combines the generator, the main bearing (although in this case it is not a bearing), and the hub into a single assembly. This concept had already been used by the Argentine company IMPSA in turbines of up to 2 MW (the “Unipower” concept), but using conventional bearings.
One notable aspect is that, in the design shown in the images, the hub is made up of three pieces bolted together. According to Stefan, at OptiGen they believe that these three pieces can be machined separately (that is, without pre-assembly), which broadens the range of potential suppliers. Any misalignments (or lack of perfect circularity) that may arise from being bolted parts rather than a single block could later be absorbed by the elastic supports.
In Thursday’s edition we will talk about:
The principle of operation
The LightWind project
The impact on the offshore sector, especially floating wind
Testing and prototypes
Next steps
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Disclaimer: The opinions presented in Windletter are mine and do not necessarily reflect the views of my employer.