The invention relates to a wind turbine having a vertical rotor axis, also referred to as VAWT.

Background of the invention

These types of wind turbines are usually referred to as a "vertical axis" wind turbine, or a "counter-rotating, vertical" wind turbine or VAWT. These types of wind turbines are also identified as having "rotational axis substantially at right angles (or "substantially perpendicular") to a wind direction". These wind turbines usually have one rotor, but in some art, a wind turbine can comprise two rotors.

For instance, US20120148403 in its abstract describes: "a vertically-oriented, counter-rotating wind turbine assembly is disclosed. The assembly can include two or more wind turbines, and each adjacent pair of wind turbines is configured to rotate oppositely. The wind turbines are separated by supporting plates, and include a rotor and a stator, respectively. The relative rotation of the rotor and stator generates electricity. The wind turbines are supported above and below levitation and compression bearings, respectively. A motor can initiate rotation of the wind turbines when the ambient wind is below a break-in speed and above a steady state speed." The wind turbine is centrically aligned and supported above and below by a (solid) central stationary shaft and levitation and compression bearings, respectively.

US201001941 12 in its abstract describes "This invention relates to vertical axis turbines particularly ones which are suitable for use in swirling conditions. The vertical turbine (10) may have first and second rotors (13, 14) mounted about the axis for contra rotation and a generator (14) located between the rotors for generating electricity in response to rotation of the rotors characterised in that one rotor is a substantial mirror image of the other." Documents WO03089787A1, WO03016714A1, US2011042962A1, JPS63154865A, and JP2008063960A, all disclose various types of vertical-axis wind turbines.

The sketched designs are unsuited for a full-scale wind turbine.

Summary of the invention

Hence, it is an aspect of the invention to provide an alternative vertical axis wind turbine, which preferably further at least partly obviates one or more of above-described drawbacks.

There is provided a wind turbine, comprising:

- a turbine rotor set comprising a first turbine rotor and a second turbine rotor having coinciding rotor rotational axes, said first and second turbine rotor having rotor blades mounted for in operation rotating said first and second turbine rotor in opposite directions;

- an electrical generator for converting mechanical energy of said turbine rotor set into electrical energy, comprising a generator rotor driviiigly coupled to the first and second turbine rotor for converting rotational motion of said turbine rotors into electrical energy;

- a rotation transfer system, coupling said first and second turbine rotor to said generator rotor;

- a buoyant structure, and

- an upper staicture comprising said turbine rotor set and said generator, and adapted for mounting on said buoyant staicture, in particular a vertical axis wind turbine (VAWT), comprising:

- a turbine rotor set comprising a first turbine rotor and a second turbine rotor having coinciding rotor rotational axes, said first and second turbine rotor having rotor blades mounted for in operation rotating said first and second turbine rotor in opposite directions, said first turbine rotor and said second positioned one above the other for providing an upper and lower turbine rotor and driving respective vertical, concentric shafts;

- an electrical generator for converting mechanical energy of said turbine rotor set into electrical energy, comprising a generator rotor drivingly coupled to the first and second turbine rotor for converting rotational motion of said turbine rotors into electrical energy, and coupled via said vertical, concentric shafts;

- a rotation transfer system, coupling said first and second turbine rotor to said generator rotor, said rotation transfer system comprising a gearbox comprising a planetary transmission comprising a ring gear drivingly coupled to one of said vertical, concentric shafts and a planet gear system drivingly coupled to the other of said vertical, concentric shafts;

- a buoyant stmcture, and

- an upper structure comprising said turbine rotor set and said generator, and adapted for mounting on said buoyant structure, said upper structure comprising a tower having tower segments which are mutually rotatably coupled, comprising an upper tower segment coupled to the first turbine rotor and a lower tower segment coupled to the second turbine rotor, said tower segments each comprise a flange, coupling each of said upper and lower tower segments to one of said vertical, concentric shafts.

There is further provided a wind turbine, comprising a turbine rotor set comprising a first turbine rotor and a second turbine rotor having coinciding rotor rotational axes, said first and second turbine rotor having rotor blades mounted for in operation rotating said first and second turbine rotor in opposite directions, an electrical generator for converting mechanical energy of said turbine rotor set into electrical energy, comprising a first generator rotor drivingly coupled to the first turbine rotor, a second generator rotor drivingly coupled to the second turbine rotor, a gap between the first and second generator rotor and mounted rotatable with respect one another for converting rotational motion of said turbine rotors into electrical energy a buoyant structure, and an upper stmcture comprising said turbine rotor set and said generator, and adapted for mounting on said buoyant stmcture. In this wind turbine, the generator thus has two generator rotors, each generator rotor coupled to a turbine rotor.

Some of the details and embodiments described can be applied to both wind turbines, and others specifically refer to the two-generator rotor wind turbine.

As already explained in the previous part, the current wind turbine relates to a type that is generally referred to as "vertical axis" wind turbine. In fact, the axis of rotation of the rotors of these wind turbines is usually "substantially at right angles" or "functionally perpendicular" to the direction of the wind. In use, often these wind turbines are installed with the axis or rotation of the rotor in vertical direction. It may, however, in certain embodiments, also be considered to place these wind turbines with the rotor axis in horizontal direction. But also in such a setup, the rotor rotational axis (or axes) is functionally perpendicular to the direction of the wind. Currently, in particular in larger wind turbines of 2-10 MW, the rotational axis of the rotor is functionally vertical even when the turbine is mounted at a floating platform. In an embodiment, the current wind turbine relates to a type that is generally referred to as Darrieus or H-type Darrieus wind turbine which operates according the aerodynamic lift principle. It is also referred to as VAWT, Vertical Axis Wind Turbine.

The rotors of the vertical axis wind turbine have rotor blades that extend parallel or substantially parallel to the rotor rotational axes. Thus, the blades in fact substantially extend in axial direction from the turbine shaft. In specific designs, the turbine blades may extend in a curved or spiralling manner. Alternatively, the rotor blades may have a shape of part of a helical curve. This in contrast to wind turbines that have a substantially horizontal shaft and rotor blades that extend radially.

These vertical axis wind turbines, in particular with counter rotating rotors, when carefully designed were found to enable off-shore use, more in particular for instance as floating wind turbines. Such wind turbines are for instance of a "semi-submersed", "SPAR" or "Tension leg" (TLP) type.

In an embodiment, tha vertical, concentric shafts are each coupled to said respective tower segments via a flexible or elastic coupling.

In an embodiment, the vertical, concentric shafts are each coupled to said planetary transmission via one selected from a toothed gear coupling, a spline-type coupling, a curved spline teeth coupling for allowing freedom of motion perpendicular to the longitudinal axis of the vertical, concentric shafts.

In an embodiment, the tower is a self-supporting tower, in particular having said rotors attached to an outer wall of said tower. This allows a constaiction that is stable in offshore, floating conditions and yet allows larger wind turbines, for instance of 1 MW or more.

In an embodiment of the wind turbine with one generator rotor, it further comprises at least one gearbox coupling one of said rotors to its generator rotor, said gearbox in particular comprises a planetary transmission, more in particular comprising a ring gear drivingly coupled to said first or second turbine rotor, and a sun gear drivingly coupled to said generator rotor.

In an embodiment of the wind turbine with one generator rotor, planetary transmission comprises a planet gear system having a first and second planetary gear on a common shaft, with first planetary gear drivingly coupled with said ring gear and said second planetary gear drivingly coupled with said sun gear, in particular said planet gear system comprises at least two first and second planetary gears on a planet gear carrier.

In an embodiment of the wind turbine with one generator rotor, the gearbox provides a gear ratio of between 1 :2 and 1 :44.

In an embodiment of the wind turbine with one generator rotor, at least one of said turbine rotors is coupled to said generator rotor via a gear coupling, in particular a planetary gear coupling, more in particular having a transmission rate of between 1 :5 and 1 :44.

In an embodiment of the wind turbine with one generator rotor, the rotation transfer system comprises an at least one stage planetary transmission.

In an embodiment of the wind turbine with one generator rotor, the rotation transfer system comprises a 1.5 stage planetary transmission comprising a ring gear, at least two planet gear systems and a sun gear, wherein said ring gear is coupled to one of said first and second turbine rotor, said planet gear systems are coupled via a planet gear carrier to the other of said first and second turbine rotor, and said sun gear is coupled to said generator rotor.

In an embodiment of the wind turbine with one generator rotor, the rotor rotational axes are functionally coinciding, in particular functionally coaxially.

In an embodiment to the wind turbine with one generator rotor, the turbine rotors are coupled to said generator rotor via a hollow outer shaft, and an inner shaft, wherein said shafts are concentric.

In an embodiment, the buoyant structure comprises a floating frame for floating in water, and said upper stnicture is mounted on said floating frame. The counter- rotating rotors provide a stable wind turbine.

In an embodiment, the turbine rotors are coupled to said generator rotors via hollow shafts, wherein said hollow shafts are concentric. In an embodiment, the said first and second turbine rotor each comprise 2 or 3 blades. This type provides an efficient wind turbine.

In an embodiment, the first and second turbine rotor each are Darrieus rotors.

In an embodiment, the first and second turbine rotor have different sizes, in particular wherein said turbine rotor set comprises in operation an upper and lower turbine rotor, and wherein said lower turbine rotor is larger than said upper turbine rotor, in particular said upper and lower turbine rotor differ between 1 and 10% in rated power. In this way, the loads on the turbine rotors will be comparable.

In an embodiment, the first and second rotor each comprise rotor blades, wherein said rotor blades have a controllable pitch.

In an embodiment, the generator comprises a dual mode generator having a setting motor for allowing actuation of the rotors in rotation. This, the generator will also set the wind turbine in motion to start it up.

In an embodiment, at least one of said turbine rotors is coupled to said generator rotor via a gear coupling, in particular a planetary gear coupling, more in particular having a transmission rate of between 1 :5 and 1 :41. This will allow a reduction in generator diameter.

In an embodiment, the upper structure comprises a tower having tower segments which are mutually rotatably coupled, in particular using a circumferential bearing near the tower circumference, wherein an upper tower segment is coupled to the first turbine rotor, and a lower tower segment is coupled to the second turbine rotor. The tower segments allow a stable construction for large structures of more than 1 MW, in particular up to 10 MW and even larger.

In an embodiment, the tower segments comprise a flange, in particular an internal flange, coupling said tower segments to mutually concentric hollow shafts coupling to said respective generator rotors. The tower segments provide a stable structure also in off shore conditions and for floating wind turbines.

In an embodiment, the upper structure comprises a tower comprising air ducts running from bottom to top through said tower. Thus, cooling or perhaps heating under polar conditions may be simplified.

In an embodiment, the upper structure comprises a tower comprising tower segments rotatably coupled to one another, comprising an upper tower segment comprising said first rotor as an upper rotor, and a lower tower segment comprising said second rotor as a lower rotor.

In an embodiment, in operation said first rotor is an upper rotor, and said second rotor is a lower rotor.

In an embodiment, the wind turbine comprising a stationary frame part, in particular a stationary tower part. Thus, a three- segment tower tower is possible.

In an embodiment, the generator comprises a generator housing coupled to a or said stationary frame part.

In an embodiment of the wind turbine where the generator has two generator rotors with each generator rotor coupled to a turbine rotor, the first generator rotor is an inner generator rotor and said second generator rotor is an outer generator rotor, with said outer generator rotor mounted concentrically about the inner generator rotor.

In an embodiment of this, the inner drive shaft is drivingly coupled to said inner generator rotor and said outer drive shaft is drivingly coupled to said outer generator rotor.

In an embodiment, the wind turbine further comprising at least one gearbox coupling one of said rotors to its generator rotor, said gearbox in particular comprises a planetary transmission, more in particular comprising a ring gear drivingly coupled to said turbine rotor, and a sun gear drivingly coupled to said generator rotor.

In an embodiment, the planetary transmission comprises a planet gear system having a first and second planetary gear on a common shaft, with first planetary gear drivingly coupled with said ring gear and said second planetary gear drivingly coupled with said sun gear. In an embodiment, the gearbox provides a gear ratio of between 1 :2 and 1 :41.

In an embodiment, the transmission system comprises a transmission housing and said generator comprises a generator housing, and in particular wherein said generator housing is attached to said transmission housing.

In an embodiment, the generator comprises a housing and a cooling system. In an embodiment, the cooling system comprises a liquid cooling system, wherein said housing comprises at least one cooling channel for a cooling liquid, in particular said housing comprises a doubled walled housing part with a space for containing said cooling liquid. In an embodiment, the cooling system comprises a gas cooling system, said gas cooling system comprising a gas cooling inlet in said generator housing for entering a flow of cooling gas into said generator, and a gas cooling outlet for allowing gas to exit said generator housing.

In an embodiment of the wind turbine where the generator has two generator rotors, the outer rotor is provided with one or more fanes for setting said cooling gas inside said housing in motion, in particular designed for in operation inducing a flow of cooling gas from said cooling gas inlet to said cooling gas outlet.

In an embodiment of this, the inner rotor is provided with one or more provisions, in particular passages, for setting said cooling gas inside said housing in motion, in particular designed for in operation inducing a flow of cooling gas from said cooling gas inlet to said cooling gas outlet.

In an embodiment, the gas cooling system comprises a heat exchanger for exchanging heat with a liquid flow.

The double cooling system can be more efficient and fail-safe.

The current upper structure may also be used on a solid foundation, for instance in land of off shore, when vibrations are to be avoided, foundations are limited or space is limited.

The invention further pertains to a wind turbine, comprising:

- a turbine rotor set comprising a first turbine rotor and a second turbine rotor having coinciding rotor rotational axes, said first and second turbine rotor having rotor blades mounted for in operation rotating said first and second turbine rotor in opposite directions;

- an electrical generator for converting mechanical energy of said turbine rotor set into electrical energy, comprising a generator rotor drivingly coupled to the first and second turbine rotor for converting rotational motion of said turbine rotors into electrical energy;

- a rotation transfer system, coupling said first and second turbine rotor to said generator rotor.

The invention further relates to a wind turbine, comprising:

- a turbine rotor set comprising a first turbine rotor and a second turbine rotor having coinciding rotor rotational axes, said first and second turbine rotor having rotor blades mounted for in operation rotating said first and second turbine rotor in opposite directions;

- an electrical generator for converting mechanical energy of said turbine rotor set into electrical energy, comprising a first generator rotor drivingly coupled to the first turbine rotor, a second generator rotor drivingly coupled to the second turbine rotor, a gap between the first and second generator rotor and mounted rotatable with respect one another for converting rotational motion of said turbine rotors into electrical energy.

In particular, these wind turbines further comprise

- a buoyant structure, and

- an upper staicture comprising said turbine rotor set and said generator, and adapted for mounting on said buoyant structure.

Embodiments described above and in the description of embodiments below can be combined with the further wind turbines.

The term " ^• substantially" herein, such as in "substantially all emission" or in "substantially consists", will be understood by the person skilled in the art. The term

"substantially" may also include embodiments with "entirely", "completely", "all", etc.

Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term "substantially" may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term "comprise" includes also embodiments wherein the term "comprises" means "consists of .

The term "functionally" will be understood by, and be clear to, a person skilled in the art. The term "substantially" as well as "functionally" may also include embodiments with "entirely", "completely", "all", etc. Hence, in embodiments the adjective functionally may also be removed. When used, for instance in "functionally parallel", a skilled person will understand that the adjective "functionally" includes the term substantially as explained above. Functionally in particular is to be understood to include a configuration of features that allows these features to function as if the adjective "functionally" was not present. The term "functionally" is intended to cover variations in the feature to which it refers, and which variations are such that in the functional use of the feature, possibly in combination with other features it relates to in the invention, that combination of features is able to operate or function. For instance, if an antenna is functionally coupled or functionally connected to a communication device, received electromagnetic signals that are receives by the antenna can be used by the communication device. The word "functionally" as for instance used in "functionally parallel" is used to cover exactly parallel, but also the embodiments that are covered by the word "substantially" explained above. For instance, "functionally parallel" relates to embodiments that in operation function as if the parts are for instance parallel. This covers embodiments for which it is clear to a skilled person that it operates within its intended field of use as if it were parallel.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices or apparatus herein are amongst others described during operation.

As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be constaied as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device or apparatus claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention further applies to an apparatus or device comprising one or more of the characterising features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterising features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Furthermore, some of the features can form the basis for one or more divisional applications.

Brief description of the drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figure 1 schematically depicts an embodiment of a floating wind turbine with vertical rotor axes;

Figure 2 a detail of figure 1, showing in cross section schematically an upper part of the wind turbine with a generator below the rotors, and

Figure 3 a detail of figure 1, showing a cross section similar to figure 2, but with an example of an embodiment coupling two turbine shafts, in particular counter-rotating shafts, a one generator rotor.

The drawings are not necessarily on scale

Description of preferred embodiments

Figure 1 schematically depicts an embodiment of a floating wind turbine 1 with vertical rotor axes. The wind turbine 1 has an upper structure 2, usually in the form of a tower. The upper structure 2 comprises two counter-rotating rotors 3, 4, here an upper turbine rotor 3 and a lower turbine rotor 4. These will also be referred to as upper rotor 3 and lower rotor 4 for brevity.

The wind turbine 1, this embodiment depicted in figure 1 is placed on or comprises a called "semi-submersed" or semi-sub type sub structure, where buoyant bodies are linked to a seafloor. The upper structure 2 is coupled to a lower structure 7 which couples the upper stnicture 2 to one or more floatation bodies 8. Cables 9 here couple the buoyant bodies 8 to a seafloor. Here, three buoyant bodies 8 in a triangular configuration are depicted. Other possible, suitable types of floating wind turbines are "tension leg" or TLP wind turbines, or SPAR type wind turbines. The embodiment with two counter- rotating rotors 3, 4 are very suitable for these floating wind turbines 1. One specific benefit is that the counter-rotating rotors (nearly) eliminate rotational moments on the sub-structure during operation.

The rotors 3, 4 have blades 5 which substantially or functional extend in vertical direction in operation, and which are in operation substantially or functionally perpendicular or at right angles with respect to the wind or a flow of air. In the current embodiment, the blades 5 are coupled via rotor stmts 6. In the embodiment of figures 1 and 2, the rotors have 2 or 3 blades. In particular, the rotors 3, 4 are Darrieus rotors. As such, this type of rotors are known to a skilled person.

In figures 2 and 3, two different embodiments of such a wind turbine of figure 1 are elucidated. In figure 2, the wind turbine has a generator with two generator rotors, and each wind turbine rotor 3, 4 is coupled to one generator rotor. This coupling may be a direct coupling, but the wind turbine rotors can also be coupled via a transmission or gearbox. In figure 2, coupling via a 1.5 stage planetary coupling is illustrated, but other couplings are also possible. For instance, a planetary coupling may be provided for each generator rotor, for instance at both sides of the generator, each thus coupling to one generator rotor. One turbine rotor is thus coupled via one planetary transmission to one of the generator rotors. One shaft may run through the generator.

In figure 3, an embodiment of wind turbine with two wind turbine rotors coupled to one generator rotor is illustrated.

Figure 2 shows an embodiment of the upper part or the upper structure 2 of wind turbine 1. In this embodiment, there is an upper rotor 3 and a lower rotor 4. They are provided with blades 5 that are mounted to make these rotors counter rotating, i.e., rotate in opposite direction, about rotor rotational axis R under the influence of wind.

The upper staicture 2 further comprises a generator 10 for converting rotational motion of the turbine rotors 3, 4 into electrical power. The generator 10 has two generator rotors, one coupled to the upper (turbine) rotor 3 and one coupled to the lower (turbine) rotor 4. In the embodiment of figure 2, the generator 10 has two concentric generator rotors 11, 12 that have a generator rotational axis Rg that is aligned, in line, with the rotor rotational axis R. In the embodiment of figure 2, the generator has an inner generator rotor 11 and a concentric outer generator rotor 12, concentrically about the inner generator rotor 11. As explained above, the generator 10 can also be of another topology or type, like an axial flux generator. The embodiment of the generator 10 as illustrated in figure 2 is a general type that is easy to integrate in the counter-rotating turbine rotor concept depicted here.

In the embodiment of figure 2, the generator 10 is mounted below the turbine rotors 3, 4. An advantage of this design is that the upper structure 2 can be designed as three modular parts comprising an upper module comprising the upper rotor 3, a middle module comprising the lower rotor 4, and a lower module comprising the generator 10. Furthermore, a large part of the weight is positioned as low as possible, which is an advantaged for a floating construction.

The upper rotor 3 is coupled to a first shaft 13 which in turn in this embodiment is coupled to the inner generator rotor 1 1. In the current embodiment, the first shaft 13 is a hollow shaft which is coupled to the inner generator rotor 1 1 via a first gear coupling 18 (in German "Bogenzahn-kupplung", eg from Renk AG). The coupling can also be of a functionally comparable spline-type coupling, for instance having curved spline teeth at the gear with outward facing teeth which allows some freedom of motion perpendicular to the longitudinal axis of the shaft 13.

Further, in the current embodiment the first shaft 13 is coupled to the upper rotor 3 via an upper flexible coupling 14. In wind turbines, various flexible couplings are known. An example of a suitable flexible coupling 14 is described for instance by the firm Geislinger GmbH, and referred to in the art as a "Geislinger Compowind coupling". In general, such a coupling combines high torsional stiffness with built-in flexibility in response to bending loads, thus providing a torsionally resilient shaft coupling for optimally protecting the critical drivetrain components generator (and gearbox) against non-torque loads.

One or more rotors 3, 4 may be coupled to the generator 10 via a transmission which increase the rotational speed. In the current example, the lower rotor 4 is coupled via such a transmission 30. In the current embodiment, the transmission 30 is of a planetary or epicyclic type. Such a transmission or gearing can be a 1.5 stage transmission, or even a full 2-stage planetary transmission which has an increase complexity. Such a 2-stage transmission increases the rotational speed with up to 41 times, or perhaps even more when for instance a differential type transmission (for instance from ZF Wind Power) is used. In the current embodiment, a shaft coupled to the lower rotor 4 drives a ring gear 31, and a sun gear 32 drives the outer generator rotor 12. The ring gear 31 is coupled to the sun gear 32 via planet gears 33. These planet gears 33 have two parts (also referred to as "stepped planet"), providing an additional speed increase. Lower planet gear 52 has a larger number of teeth than the upper gear 33, thus resulting in an additional speed increase. This is referred to as a 1.5 stage planetary transmission 30. Such a 1.5 stage planetary gear as such is for instance produced by Renk AG. In a particular embodiment (not depicted), the transmission 30 comprises at least three planet gears. In an embodiment, the transmission comprises set of two planet gears opposite one another with respect to the rotational axis R. Thus, usually in such an embodiment four planet gears are provided. In an embodiment, these planet gears are of the already-discussed "stepped planet" type. In a specific embodiment, the lower planet gears 52 are in offset planes, i.e., have different heights but still drive the same sun wheel 32. In an embodiment, this allows a circumference of the lower planet gears 52 to overlap. In other word, the projections of the circumferences of the lower planet gears 52 onto a (mathematical) plane having rotational axis R as a normal intersect. This allows lower planet gears 52 that are larger, thus increasing transmission ratio's. In particular, when having two sets of two opposite planet gears, the lower gears of one set of opposite planet gears and the lower gears of the other set of opposite planet gears are at different heights.

In alternative embodiments, a turbine rotor for instance drives the planet carrier and the ring gear is in this embodiment stationary. In this embodiment, the upper rotor 3 is coupled to a shaft 13 which runs concentrically through the lower rotor 4 and the parts coupling the lower rotor 4 to the outer generator rotor 12. It may be clear that a general 1 stage planetary gear might also be sufficient, but the 1.5 stage planetary gear 30 results in an additional speed increase. In yet another alternative arrangement, a design could comprise a gearbox with one 1.5 stage planetary gear and multiple planetary gear systems and/or different gear combinations of planetary gears, 1.5 stage planetary gears, and/or final parallel gears. The latter arrangement could allow asymmetric generator placement, adding to design freedom. In again an alternative arrangement with the counter-rotating generator (i.e., two generator rotors), each individual generator rotor is connected to a single-stage, or 1.5 stage planetary gearbox, or multiple combinations (2.5 stage, 3 stage etc.)

The generator 10 comprises a generator housing 15. The generator housing 15 is mounted on a stationary frame 16. In the embodiment of figure 2, the stationary frame 16 is mounted to a tower segment 17. A tower segment is in particular a circle or circular cylinder segment or more precise a right circular cylinder segment or end. In another or alternative embodiment, the generator housing comprises a fitting flange 26 for connecting the generator housing 15 directly to a corresponding flange on tower segment 17. In such an embodiment, the flange can be disconnected and the generator can be removed from the upper structure by lowering it out of the tower segment 17. In an alternative embodiment the flange is mounted atop the stationary frame, and it can now be removed by hoisting but would require rotor dismounting. In particular, if the upper and lower rotors 3, 4 are both coupled via a gear coupling, this provides a simple construction and maintenance facility.

In the embodiment of figure 2, the transmission 30 comprises a transmission housing 34. In the current embodiment, the transmission housing 34 is at least partly integrated with the generator housing 15.

In the current embodiment of figure 2, the lower rotor 4 is coupled to the outer generator rotor 12. In this embodiment, the lower rotor 4 is coupled via a second gear coupling 19 which is of the same type as the coupling 18 that couples the first shaft 13 to the inner rotor 1 1. Furthennore, the lower rotor 4 is coupled via a second flexible or elastic coupling 20. This flexible or elastic coupling 20 is of the same type as the first flexible coupling 14. The first shaft 13 runs through the lower rotor 4 and through the coupling of the lower rotor 4. The lower rotor 4 is coupled to a lower shaft 37 which again is coupled via a gear coupling if the same type as coupling 18 to a further (hollow) shaft 38 which is coupled to the transmission which is coupled to the outer generator rotor 12.

In the current embodiment of figure 2, the upper rotor 3 is coupled to an upper tower segment and the lower rotor 4 is coupled to a lower tower segment 22. The lower tower segment 22 is rotationally coupled to the tower segment 17 via a bearing 23. Thus, in an embodiment the tower segments 21, 22 comprise a bearing 23, 24 at or near their circumference.

In order to provide the circumferential bearing 23, 24 of tower segments 21, 22, a tapered double-roller bearing was found to be applicable. In an embodiment, that bearing comprises a double row bearing using tapered rollers. In an embodiment, a so called Nautilus bearing, from SKF (trade name), or functionally comparable competitor solutions were found to be applicable. The upper tower segment 21 is rotationally coupled to the lower tower segment 22 in the same way as the lower tower segment is couples to tower segment 17. The tower segments 21, 22, 17 here are right circle cylinder parts the provide a ridged and defined basis for the mutually rotatable parts. The tower segments 21, 22 are respectively provided with flanges 29, 36. Coupled to these flanges are in the current embodiment the shaft 13 coupled to the upper rotor 3 and concentric shaft parts 37, 38 that are coupled to the lower rotor 4.

In an alternative embodiment, instead of the bearings 23 which each comprise a double row bearing of tapered rollers, in an embodiment both tower segments 21 and 22 comprise a bearing system referred to as a main bearing unit or MBU. In such an embodiment, an end of a tower segment is tapered and comprises two ring taper-roller bearings or other bearing types at a longitudinal distance from one another about the tapered tower segment. The two ring bearings are biased towards one another. In this way, the tower segments can have a reduced circumference in comparison to the earlier double row bearing. In such an embodiment, a tapered lower end of the upper tower segment 21 can be nested into the upper end of the next tower segment 22, and the lower end of this next tower segment is again tapered and that tapered end can in turn be nested into the lowest tower segment 17. Thus, in fact, two main bearing units or MBU's are provided. In fact, the double row bearing like the "Nautilus" bearing mentioned above is split into two ring bearings, with the two rings at a longitudinal distance from one another and under pressure preloaded towards one another, and with the end of the tower segment tapered. Such a bearing is for instance as such described by Eolotec GmbH in a horizontal axis wind turbine. The bearings can be pre-loaded in a control system that measures and controls a preload pressing the ring bearings together. As such, such a bearing system is described in EP2710271 for a common horizontal axis wind turbine. The preload system is for instance described in US9284949. In the current embodiment the generator 10 comprises the generator housing 15. The generator 10 further comprises a cooling system. In the current embodiment, the cooling system comprises a liquid cooling system 35. The cooling system in addition comprises a gas cooling system 36. In the embodiment, the liquid cooling system is integrated in the housing of the generator and in the housing of the transmission 30 via a double of hollow wall. A liquid is guided though the hollow walls and for instance through a liquid-air radiator.

The gas cooling system comprises a gas inlet reaching into the generator housing 15 and a gas outlet for taking gas out of the generator housing 15. The gas inlet and gas outlet are can be in line. They can also be as remote from one another as possible.

The gas cooling system, usually based upon air that circulates inside the generator

10, in an embodiment comprises air displacement means on one or both generator rotors

1 1, 12. In an embodiment, the outer generator rotor 12 can be provided with vanes or fins to set air inside the generator 10 in motion. In an embodiment, the air displacement means on the outer rotor provide a pump function, displacing air from the gas inlet to the gas outlet. The gas cooling system may comprise a pump device for circulating air through the generator housing 15. The gas cooling system in the current embodiment may include a heat exchanger that gas-couples the gas inlet and the gas outlet. In the current embodiment, the heat exchanger is of the gas-liquid heat exchanger type. It allows the gas of the gas cooling system to exchange heat with liquid of the liquid cooling system which will be discussed further. In the current embodiment, in the gas cooling system, the inner generator rotor 1 1 is further provided with gas displacement means. Currently, gas channels are provided in the inner generator rotor 1 1 for further mixing or allowing mixing of gas inside the generator 10.

In the current embodiment, the liquid cooling system comprises one or more liquid channels through one or more walls of the generator housing 15. In the current embodiment, at least part of the generator housing is double walled (indicated at reference number 35) allowing liquid to flow between spacing 35 between the walls. The liquid channels of spacing 35 comprise a liquid inlet and a liquid outlet. The liquid inlet and liquid outlet are fluidly coupled to a heat exchanger, for instance a radiator discussed earlier. The radiator and the heat exchanger are in the current embodiment coupled, for providing heat-exchanging contact between the gas of the gas cooling system and liquid of the liquid cooling system. In the current embodiment, a natural circulation is used in the liquid cooling system. The liquid cooling system in the current embodiment thus uses passive cooling. In an alternative embodiment, a pump may be added. Part of the processed liquid which passed the radiator is used to exchange heat with the gas of the gas cooling system via the heat exchanger. The liquid can be further processed in the radiator before returning in the generator housing 15.

In the embodiment of figure 2, an air flow provision 28 is provided through the various tower segments. A desalting inlet 27 is provided for a flow of cooling air 28 is provided as indicated. Thus, a flow of air is provides from a lower part of the upper staicture 2 to the top of the upper structure 2.

It should be noted that in wind turbines of 2-10 MW, a Darrieus type wind turbine has for 5 MW a rotor diameter of between 135-145 meter and a total rotor height of 108- 1 16 (i.e., the sum of the upper and lower rotor). For a 10 MW wind turbine, the rotor diameter will be 192-205 meter and the total height of the sum of the rotors will be 153- 164 meter, (considering an aerodynamic efficiency of 38% and 300-340 W/m ² ).

Figure 3 shows again the wind turbine of figure 2, where the same reference numbers show the same parts. In this embodiment, the first and second shaft are both coupled to a rotation transfer system 30 that drives a generator rotor 50. As mentioned, the rotation transfer system 30 can comprise a transmission. In particular, the transmission comprises a geared transmission or gearbox. In the current embodiment, the geared transmission comprises a planetary transmission 30, here again a 1.5 stage planetary transmission as explained above. In this embodiment, one of the first and second shafts are coupled to the ring gear 31. The other of the first and second shaft is coupled to the planet gears 33, in particular to the planet gear carrier 53. The planet gears are thus not fixed to the housing 34. The sun gear 32 in this embodiment is coupled to the generator rotor 50. In this embodiment, the generator has a generator rotor 50 and a generator stator 51. In this embodiment, the generator has an outer generator rotor 50 and an inner generator stator 51. This may also be reversed. Other types of generators may also be possible, in which a rotor and stator are used.

It will also be clear that the above description and drawings are included to illustrate some embodiments of the invention, and not to limit the scope of protection. Starting from this disclosure, many more embodiments will be evident to a skilled person. These embodiments are within the scope of protection and the essence of this invention and are obvious combinations of prior art techniques and the disclosure of this patent.

Reference numbers

1 wind turbine

2 upper structure/tower 3 upper turbine rotor

4 lower turbine rotor

5 vertical blades

6 rotor stmts

7 lower structure

8 buoyant bodies

9 cables

10 generator

1 1 inner generator rotor

12 outer generator rotor 13 first shaft

14 first flexible coupling

15 generator housing

16 stationary frame

17 tower segment

18 first gear coupling

19 second gear coupling

20 second flexible coupling

21 upper tower segment

22 lower tower segment 23 circumferential bearing

24 circumferential bearing

25 first shaft second end

26 flange

27 air desalting part

28 air flow

29 upper tower segment flange

30 transmission/gearing 31 ring gear

32 sun gear

33 (stepped) planet gears

34 transmission housing

35 liquid cooling system

36 lower tower segment flang

37 second shaft first end

38 second shaft second end 40 power line

50 generator rotor

51 generator stator

52 lower planet gear

53 planet gear carrier

R Rotor rotational axis Rg generator rotational axis