Wind turbine, blade for a wind turbine, segment for a blade for a wind turbine, method for the fabrication and assembly of a wind turbine.

The invention relates to a wind turbine with a tower and blades and a vertical drive shaft, and to a method for the fabrication and assembly of a wind turbine with a tower and blades and a vertical drive shaft.

Wind turbines of the vertical type are disclosed, whereby the drive shaft is oriented vertically, and of the usual horizontal type, whereby the drive shaft is oriented horizontally.

The conventional, most common, type of wind turbine is a wind turbine with a horizontal axis.

The blades (vanes) of this type of wind turbine rotate in a vertical plane, or in a plane approaching the vertical, and experience during rotation great variation in load. The blades, as a consequence of their rotation, are cyclically loaded by gravity (gravitational field).

In these conventional horizontal axis wind turbines, the blades must have a certain minimal stiffness to be able to withstand the large and constantly varying loads on the blades.

Blades with too little stiffness can fail in various ways as a consequence of structural instability (extreme flexure, twist, torque...).

As wind turbines become larger, the aforesaid varying blade loads are greater and the blades must be constructed accordingly stiffer.

The stiffness for conventional blades is required in both main directions, i.e. the flap direction and the edge direction. The flap direction is the direction that coincides with the wind direction. The edge direction is perpendicular to the flap direction, and thus lies in the plane of rotation of the blades. In the flap direction, the gravitational bending moment is relatively small, but the aerodynamic bending moment is large.

In the edge direction the aerodynamic bending moment is relatively small, but the gravitational bending moment is large, and moreover cyclically varying.

In the absence of sufficient stiffness, conventional blades can fail in both aforesaid directions.

As wind turbines become larger it becomes increasingly difficult to fabricate blades with the required stiffness, since the structural volume, and therefore also the quantity of material, increase exponentially.

Since the blades become increasingly heavy, all the other components of the wind turbine are loaded all the more. And it also becomes more difficult to transport the heavier blades and other components and to assemble them into a turbine.

Wind turbines of the vertical type, with a vertical drive shaft, are less common but are known. Wind turbines of the vertical type exist in different in different embodiments, of which the most important are: -A type wherein the blades have such a form that the wind turbine resembles a whisk (so-called Darrieus mills).

-A type wherein the blades are vertically oriented at some distance from the axis (so-called H-style turbines).

When used in these vertical axis turbines the blades also must have a minimal stiffness to prevent undesired distortions.

In the Darrieus type turbine this is necessary, at rest, to prevent undesired sag, and damage, to the blades from gravity, which could also cause problems when starting and stopping the turbine (instability during acceleration and speed reduction). To prevent this undesirable distortion, the blades for this type of turbine are in practice usually pre-stressed (flexed) into the form in which they ultimately must operate on the turbine. This causes, of course, and certainly as turbines become larger, increasing problems of transport.

In H-style turbines, a lack of stiffness causes possible excessive outward flex (and resulting damage) of the blades as a result of centrifugal forces during operation.

In conclusion, it can be stated that both for horizontal and for vertical axis turbines of the disclosed type, the stiffness of the blades required in order to prevent the distortion and even the destruction of the blades increases as the blades become larger since the loads also increase proportionately.

Hereby, it should be understood that structural instabilities of the blades (bending, collapse, twist,...) bring with them considerable safety risk. This all sets considerable limits to the efficiency of disclosed wind turbine designs and sets a structural limit to the practically feasible size of these wind turbines.

One object of the present invention is to provide a wind turbine that reduces one or more of the aforesaid problems.

To this end, the wind turbine, in accordance with the present invention, is characterized in that the wind turbine on a tower top is fitted with protruding arms around the vertical axis to which are attached flexible blades that hang in the vertical when at rest, whereby in operation the blades spread out and assume an angle of deployment that depends on the speed of rotation and increases as the speed of rotation increases.

The flexible blades rotate, in operation, in a constant gravity field. Contrary to conventional horizontal axis turbines, in the preferred embodiment of this invention the blades undergo no alternating loads during their rotation.

Because of the flexibility of the blades, and from the action of constant gravity, and the centrifugal force consequent of rotation, the blades spread out from their vertical (hanging) stationary position.

The angle of deployment (also referred to as camber angle) of the blades is determined automatically by the ratio of gravity and the centrifugal force created by rotation.

The automatically set angle of deployment (camber angle) of the blades is such that no net flap bending moment acts on the blades, and the load thereby in principle is a pure axial tensile load.

"Blades" will also be referred to below as "vanes"; both words consequently refer to the same thing.

As a result of possible variation in rotational speed, the centrifugal force and therefore also the angle of deployment, will vary accordingly, but a net flap bending moment remains absent or very small and the vane load remains thereby in principle a pure axial tensile load, or almost pure. In the same manner, variations in the aerodynamic vane load (lift force) during rotation will translate into cyclic changes of the angle of deployment of the blades, but the vane load remains in all circumstances purely, or almost purely, axial (no net bending moment).

The automatic adju stment of the angle of deployment i s si mpl ified in embodiments by a vane design with a very low flap stiffness (flexboard) and preferably a connecting plate between the vane and the yoke (hub), also with very low flap stiffness (blade root flexboard).

Owing to the suppleness of one or both flexboards, the vanes can spread out to their desired camber angle without taking on any bending stresses.

By analogy with the balance that is established in the flap direction, the rotor design is also preferably such that a similar balance can be established in the edge direction, also characterised by the absence, or near absence, of a net bending moment on the blades in this direction.

For this reason, the turbine is preferably fitted with a "hub drumhead" with central flexboard. The central flexboard assures that the blades can "lead" the hub with such an angle of phase displacement that the rotor torque of the blades to the hub drumhead is transferred by means of the pure, or almost pure, axial tensile load of the vanes (x the lever of the hub drumhead).

In this way, during operation, each of the vanes automatically will assume such an angle of phase displacement in respect of the position of the hub, that once again no net bending moment, or hardly any, shall arise on the blades in the edge direction. The flexboards on the roots of the vanes and the central flexboard of the hub drumhead are preferably characterised by a high axial tensile strength but limited stiffness in flexure.

A high axial tensile strength is favourable for the absorption of the centrifugal force of the blades. A limited flexural strength is favourable for permitting the blades automatically to find their angle of equilibrium (camber angle in the flap direction and angle of phase displacement in the edge direction) without bending stresses being absorbed.

In order to achieve these structural characteristics, these flexboards are preferably fabricated in the form of a sandwich construction with alternating layers of carbon fibre laminate and plastic intermediate layers. The carbon fibre laminate provides the required tensile strength. The plastic intermediate layers are preferably made from "low friction" materials (such as Teflon or Ertalon) that allow the structural carbon fibre layers to warp differentially during the flexure of the panel, with a minimum of mutual frictional resistance.

Since the blades of the preferred turbine embodiment, both at rest and during operation, are chiefly loaded axially and tensilely, they are insensitive to any structural instabilities that may occur in the blades of the aforesaid conventional horizontal and vertical

axis turbines.

Since it is the intention, first of all, that the blades absorb as little flexural loading as possible and chiefly axial tensile load, the preferred structural composition of the vanes is totally the contrary to the composition of conventional vanes. In conventional vanes one is compelled, because of the required stiffness and resistance, to apply structural material as far as possible from the centreline of the vane profile, i.e. the outer surface of the vane profile. This is not a simple task because there are also high requirements (precision) set for the geometry of this outer surface in terms of aerodynamic efficiency. Moreover, the contour of a conventional blade is complex (bent in two directions), which can cause the usual problems when applying the structural laminate (avoiding blistering and delamination). In conventional blades the non-structural material (usually a foam filler) are found in the interior of the profile.

Contrary to conventional blades, in preferred embodiments of the blade and turbine design in accordance with a preferred embodiment of this present invention, the structural materials are not applied to the outer surface, but to the central centreline of the profile in order to achieve the desired suppleness (low stiffness) which is to assure that the vane can assume such a camber and angle of phase displacement that the net vane load is as good as purely axial (pure tensile load).

This can be achieved by applying the structural material for absorbing this axial tensile load to and in the immediate vicinity of the central axis. The structural portion of the vane then has the shape of a board, with low stiffness in flexure, which is why it is called a "flexboard".

It is clear that making such "flexboards" is considerably simpler because of their simple geometry (straight board). This can in principle be done without a mould but on a simple flat lamination table.

The structural laminate can, but need not necessarily, extend over the full width of the vane profile.

In the vane design in accordance with a preferred embodiment of this present invention the intention is precisely to load the vanes only or almost only purely axially and tensilely. The intention is for the vane to function as a pendulum, and at its limit, the structural portion of the vane could be a cable which, in both the flap and edge direction, can have a

stiffness of nearly zero.

Because a minimum necessary torque stiffness is needed such a cable is however not always the best solution (to prevent the twisting of the vane profile around its longitudinal axis). It is, however, not excluded that the width of the flexboard can be reduced (less width than the total width of the the vane profile).

The ideal width of the flexboard must be determined by weighing the desired edge and torque stiffness.

Since, contrary to conventional blades, the structural material is not on the exterior but in the interior, the vane construction in a preferred embodiment is "inverted".

An additional benefit of the vane design in accordance with a preferred embodiment of this present invention is that the remainder of the vane profile, and in particular those parts that determine its contour and thus its true aerodynamic airfoil can be made from non-structural material. This is most important since, in order to achieve good aerodynamic yield, high standards must be set for the geometric precision and smoothness of the outer surface of the vane.

In the vane design in accordance with a preferred embodiment of this present invention, by preference, foam cores are adhered to both sides of the "flexboard".

The contours of the foam cores are preferably cut on a computer controlled precision cutting bench ("hot wire cutting").

Since it is precisely the intention that axial tensile stresses will be absorbed only by the flexboard, it is not a disadvantage, but is even desirable, that the foam cores be built from segments and therefore, in preferred embodiments, not applied continuously and without interruption along the full length of the vane. By applying the foam core segments, preferably provided with intermediate mounting joints, it can be consciously seen that the foam cannot absorb any tensile or flexural loads, which is, of course, the intent.

The possible segmentary construction is of course a great advantage for the prefabrication and application of form core to the flexboard. Finally, the outer layer (skin) of the vane profile will be applied around the foam cores.

Here, too, it is the intent that this skin does not absorb any structural tension but functions solely as a protective sheath for the foam core.

As such, one or more of the following functional requirements are set for this sheath: -Impermeability.

-Smoothness: for an aerodynamic low air resistance. -Erosion resistance: against impact of hail, snow, and rain. -Geometric precision: determined by the precision of the underlying form cores. -Thin-walled: to absorb as little tension as possible, fitted as necessary with expansion joints.

Because of the aforesaid functional requirements, and the presence of the underlying foam core, in embodiments of the vane design in accordance with a preferred embodiment of this present invention the sheathing layer is applied by means of "filament winding", for which no mould ("mould less") is necessary.

This winding technology is in itself known, but is most suited for the vane design in accordance with a preferred embodiment of this present invention, since the intention is to produce vanes with a constant width from the vane root to the vane tip.

This constant vane width is possible since the vane does not need to absorb any flexure.

In conventional vanes a certain amount of taper is necessary, i.e. changing width of the vane, to remain in conformity with the increasing flexural loading in the direction of the vane root.

A winding technology for such conventional vanes is in principle also possible, but much less simple because of the tape and the many larger number of wall thickness required.

For the vane design in accordance with a preferred embodiment of this present invention, the winding technology is highly suited because of the constant vane width and the thin layer required. In conventional vanes, the yield of winding technology is moreover limited because, in addition to the winding laminate, a considerably larger quantity of longitudinal

laminate is required to absorb flexural loading.

This longitudinal laminate cannot be applied using winding technology because of the continuity required (continuous fibres from the vane root to the vane tip).

Since in the vane design in accordance with a preferred embodiment of this present invention this continuity if not required and even is undesirable, the aforesaid winding technology is very suitable (only winding laminate).

The winding laminate is preferably applied using a winding apparatus that rotates the vane around its axis.

The winding laminate (tape) is applied using a running bobbin that moves along the length of the vane at a controlled speed. Simultaneously with the winding, the necessary resins and hardeners are applied to the laminate.

Thereafter, thin metal plates (stainless steel) and a vacuum are applied around the vane. By creating a vacuum, the thin metal plates are pressed by atmospheric pressure against the vane surface and a smooth and precise vane surface is obtained without need to use a mould.

Heat could also be applied to speed up the hardening process.

Since the vane design in accordance with a preferred embodiment of this present invention is such that only axial tensions are absorbed (and as good as no bending stresses), the blades can be made much lighter than conventional blades, making possible wind turbines of a size that, until now, has not been feasible.

Since in the vane design in accordance with a preferred embodiment of this present invention in principle only the flexboard has a structural function, (for absorption of the tensile load), the foam cores and the sheath (skin) need not by definition be present across the full length of the blade. The design also makes it possible, among other things, to fit only the tip portion (with the greatest aerodynamic yield) with a sheath while the root portion of the vane

(with negligible aerodynamic yield) can be made without a sheath (and thus can be only "bare" flexboard).

In the same way, local "interruptions" of the vane profile can be made that will function as local hinges with extra flexibility and which can also can be used handily for supports (rotational bearings) on the winding bench. In the same way, the vane tip can be specially detailed according to need (support point for the winding bench, taps based on vane

geometry )

The bare flexboard also offers the possibility to make splices in a relatively simple way between various vane segments by means of simple lap joints. In conventional blades this is anything but simple to do. This possibility to make simple joins, as well as due to the fact that the vane can have a constant width over its full length, makes the vane design in accordance with a preferred embodiment of this present invention most suited for modular fabrication, i .e. production of blade segments that can be joined together in the yard . In this way, using relatively small and thus still transportable blade elements, very large blade lengths can be achieved at the building site.

This possibility, that is clearly non-obvious for conventional blades, makes this present blade design most suited for larger turbines.

Moreover, the modular vane design offers the possibility to construct vanes from pieces of different lengths as desired . In conventional blades this is, by definition, impossible since the length of the vane is completely determined by mould that is specifically designed for it.

The fact that the flexboard need not necessarily be the full vane width makes it equally possible, in a relatively simple manner, to make notches to fit an aerodynamic tip brake.

An aerodynamic tip brake is a panel that at a normal speed of rotation is concealed within the vane profile, and that emerges upon excessive rotational speeds due to the increased centrifugal force and in this way limits overspeed as a result of increased air resistance.

The flexboard design also offers the opportunity, in a relatively simple way, to integrate all types of conductors, such as: lightning conductors, control cables, fibre optic cables to measure distortion, etc ) In conventional blades this is not so simple to do. Finally, the vane design in accordance with a preferred embodiment of this present invention, because of its far-reaching flexibility, offers many additional benefits since the vane can be easily bent. This feature can be useful in transport (for making sharp turns) and in assembly at the work site (moving the blades from a horizontal to a vertical position).

A further benefit of the turbine design according to this present invention is that the effective part of the blades (the tip portion) is located at a relatively small height

(considerably lower than the tower top). Thereby the turbine design is most suited for large

offshore wind turbines. Offshore sites are usually characterised by "flat" wind profiles, i.e. relatively small increase in wind velocity with height. For this reason it does not make sense for the most part to install high turbines offshore.

The wind turbine design, in accordance with a preferred embodiment of this present invention, makes optimal use of this specific "low altitude" wind profile.

The tower and the foundation bear accordingly less load, which is an additional benefit in respect of conventional horizontal axis turbines for which the thrust point for the wind load is located at the tower top.

Because of the smaller loading, the tower, and the foundation, for the preferred turbine design need not be made as heavy and thus are cheaper.

Preferably, the tower of the preferred turbine embodiment is made as a telescopic construction.

This makes it possible when the tower is in the lowered position to attach a segment of a blade to the arm (yoke) and then to extend the tower and attach the next segment of the blade, then extending the tower still further to attach the following blade segment, and so on until the blades are completely attached.

In this way, it is possible to attach the blades to the wind turbine and to assemble the turbine in its totality without the need of high cranes. This is especially a great benefit for offshore wind turbines or for wind turbines in remote mountainous regions. It is noted that in French patent FR 2345600 a wind turbine is disclosed that is fitted at the tower top with two vanes grosso modo extending in the horizontal plane when viewed from the tower top. These vanes bend towards the tips somewhat due among other reasons to their own weight and thereby form an arc. The blades do not hang, however, vertically from the tower top and therefore must be able to withstand large forces, especially, at the root of the blade, that is, that part that is affixed to the tower. The design of the blades is therefore forced to be more or less a standard design whereby the structural materials are located on the exterior. The weight of the blades themselves causes the blades to bend in the direction of the tips. The strength required of the blades and with that their weight is a great disadvantage. French patent 2 298 707 discloses a number of designs. In one design, a sail or a number of posts hang from a diagonal connector. The sail or the posts are connected by

various cables at top and bottom with the mast. When rotating, these cables form a connection between the mast and the sails and hold the sails more or less in a vertical position. The bottom portion of the sails is not free. The sails and the posts form , in form and function, the equivalent of a Darrieus type turbine. The cables will exert great force on the mast and also cause a considerable loss of energy from air resistance. Furthermore, there is a great risk of the cables breaking, which creates a great hazard. This can be prevented by making the cables sufficiently strong, but this will again cost additional weight and extra wind resistance.

The wind turbine in accordance with a preferred embodiment of this present invention presents and/or reduces these disadvantages. These and further aspects of the invention are here subsequently described and illustrated on the basis of a drawing.

The drawings illustrate:

Figure I A: A known horizontal axis wind turbine.

Figure 1 B: A detail of a blade for the wind turbine of figure 1 A. Figure 2: A well-known construction for a wind turbine of so called Darrieus type.

Figure 3: A further example of a construction for wind turbine of the so called H-type.

Figure 4: A wind turbine accordi ng to the invention, in rest position.

Figure 5: A wind turbine according to the invention, in action.

Figure 6: Details of the rotor hub of the wind turbine of figure 4 and 5.

Figures 7 to 14:Construction procedure for a wind turbine, according to the invention.

Figure 1 5 and 1 6: The construction of a blade for the wind turbi ne, according to the invention.

Figure 1 7 and 1 8: Manufacturing procedure for producing a blade for wind turbine, according to the invention. Figure 1 9: Details of a connection (splice, lap joint) and wing tip.

Figure 20: Detail of the rotor hub of wind turbine, according to the

invention.

Figure 21 : Schematic transportation of a blade for a wi nd tu rbi ne , according to the invention.

The figures are not always drawn to scale. Identical parts are indicated in the line with similar reference numeral. Sizes given in the figures are provided by means of example and should be considered as not limited, unless otherwise indicated.

Figure 1 A shows a wind turbine with tower 1 of the conventional horizontal axis type in front, side and top view. By means of not limited example, several dimensions are indicated in the figure. Blades 2 rotate in an approximately vertical plane, whereby the rotation axis is oriented approximately horizontal as well.

The blades undergo large load variations during their rotation. In the direction of the flap (wind direction), the variations are mainly caused by the aerodynamic load. In the side direction (in the pitch surface), the variations are mainly caused by the gravitation. The wind turbine is also very tall and the resulting wind load on the rotor exerts a load at the height of the arrow F (the rotor center). The resulting bending moment on the foot of the tower and /or on the foundation is large. The tower and the foundation should be constructed to measure up to these loads without any risk of collapse.

Figure 1 B shows a blade of a conventional horizontal axis turbine in section. The blade has a fore side 2A (leading edge) and a back side 2B (trailing edge), an upper part 2C and a lower part 2D which are attached to each other on points 2E.

To withstand the changing loads without any risk of collapse, and to avoid intolerable deformation, these blades should be provided with a necessary rigidity structure.

This means that the structural lamination of these wings should be positioned outwards as far as possible (i.e. on the outer contour of the wing profile) and the wing profiles should be applied with sufficient thickness.

However, thicker wing profiles are not advised because of higher aerodynamic resistance (bear).

The structural and aerodynamic requirements that are simultaneously of importance for the conventional blades are thus contradictory and by definition, correction on one of both aspects leads to another aspect's impairment.

To produce the structural lamination of these blades, taking into account the high geometrical precision requirements which are applicable for the wing profile, these wings can only be made in tailored-manufactured moulds.

This requires highly complex moulds of frequently very huge format, and different moulds for each blade and each blade size.

Besides, by using this manufacture technique, the upper and lower part of the profile are made in separate moulds and stuck together afterwards, adding to the difficulties.

This is not simple to do because the joint connections adhesive must be able to accommodate the pressures and because it is difficult to control the quality of connection adhesion (unreachable for inspection after the gluing).

Besides, it is very difficult in this wing concept to introduce additional elements in the wing such as tip drag mechanisms or conductors (for example, lightning conductor).

Figure 2 shows a well known design for a wind turbine with vertical axis. Such wind turbines are called also Darrieus type wind turbines. The rotation axis 3 is now vertical. In this type, the blades 4 are bent. To keep their form, the blades must have sufficient dimension of rigidity. As the size of the blades 4 becomes larger, a problem occurs also in that the bent blades may deform under their own weight; this is the reason why transversal connections 4a are sometimes applied. However, it is difficult to make big bent blades and even harder to transport them. The resulting rotor load applies approximately at the half of the construction's height. Because of the said disadvantages, this type of wind turbine is not built in big amount yet until today.

Figure 3 shows other type of wind turbine with vertical axis, the so called H- type mill.

In this type of turbine to the axis 3 lateral arms 5 and blades 6 are attached. In this variant, the blades also comprise a protruding part, on top and below the lateral arms.

Therefore, the blades experience a considerable centrifugal moment during the rotation (deflection of both wing extremities). Like other conventional turbines, considerable rigidity is necessary also for these blades, to avoid destruction or excessive deformation.

As the blades become larger, the rigidity should grow proportionally as well. The resulting rotor load is exerted at the height of the location indicated by arrow F.

Figure 4 shows a wind turbine according to the invention. The wind turbine 7 comprises at the top lateral arms 8 (beam) to which blades 9 are attached. In a standstill, the blades hang down under vertically, under the influence of their own weight. In this example, the blades comprise two segments of 10 and 10', linked by a connection portion 1 1 . The 10 and 1 0' blade segments can be subdivided in subsegments which are connected similarly to each other. The segments can be identical for many applications, and in preferred embodiments they are identical. In this example, the two undermost sub segments 1 2 of segment 1 0' are equipped with a brake mechanism. Tower 1 3 has several telescopic tower segments and a central vertical drive shaft 14, and a top portion 1 5 where arms 8, through a preferred central flex board , are provided. The blades 9 are connected to the arms 8, through flexible connections 1 6 (flex boards). Flex boards are preferred. However, the flexible connection 1 6, for example, can also be made with plain bearing.

The foot portion 1 7 is built on the foundation blocks 1 8 upon which a tripod 1 7 is placed. Under the tripod 1 7, an engine room 1 9 is provided. Since the engine room is placed in a low position , there is a simple entrance for those parts of wind turbine that require maintenance or regular inspection. On the upmost part 20 of the tripod, the telescopic tower is placed.

Figure 5 shows a wind turbine, according to the invention, in action. The wind allows blades 9 to rotate, by which a driving torque is generated on the arms 8. Under the rotation the blades spread out.

The invention offers several advantages:

The flexible blades rotate in a horizontal level and therefore experience no alternating gravitation load. By the centrifugal forces, the blades will spread out at an angle with regard to vertical axis (flight angle or angle of deployment). This flight angle or angle of deployment is the angle between the vertical and the rotating blades. Since the blades are loaded with simple axial tension when they are standing still as well as in action, they cannot fail under their own weight (no bending or collapse).

Due to the flexibility of the blades and in preferred embodiments, the presence of the flex boards on the wing foots and central flex board on the rotor hub, the blades are always quasi-axially and under tension loaded.

Changes in the centrifugal force resulting from possible variations in the rotor

revolutions per minute (rpm), and changes of the aerodynamic lift during the revolution, lead to an automatic change of the flight angle, during which, however, the wing load remains mainly axial (tensile load).

Because the blades are axially loaded with tension, and do not have to maintain a specific bent or remain rigidly upright as in conventional turbines, the risk of a collapse, bend or kink in the blades is strongly reduced.

Because the blades have a much lower rigidity than conventional blades, they can be made much lighter, while the necessary safety can yet be achieved.

A further advantage of this invention is that the forces on the tower occur on a lower height level. It is schematically shown in figure 5 by arrow F. This makes it possible to make the tower less heavy. This is mainly advantageous when using the wind turbine in parks on the ocean or lake (offshore).

Above the ocean or lake, measured from the water surface, the wind speed increases rapidly with height, but usually stops increasing after some tens of meters, and it even decreases sometimes above a certain height. Such vertical wind profile is also known as wind shear profile. Very high conventional turbines are not always efficient do to the wind shear profile, but are exposed to very huge bending moments.

The invention makes it possible, at the same power production, to be closer to the water surface. Therefore, according to the invention, a wind turbine makes good and better use of wind shear profile above a water surface, in comparison to conventional wind turbines.

This aspect increases the efficiency of the turbine and decreases the moment which is exercised on the construction, thus allowing less heavy constructions.

Further advantage is that a simple and efficient lightning protection is made possible. Usually, the lightning strikes the highest point of a construction. By installing a lightning conductor on the top of the tower, lightning's strike on the blades is prevented in simple way.

In conventional wind turbines with horizontal axis, the lightning strikes usually in the highest point namely the wing tips. For application on the ocean or lake, eventual sound nuisance and/or view of the wind turbine will be also less disturbing.

In this example, a wind turbine with two blades are shown, but the advantages of the concept remains undiminished in force for any other number of blades, for example 3 or

4 blades. An increase in the number of blades, considering the efficiency of the blades depends on their position with regard to the wind direction, will result in decrease in fluctuation of the delivered power.

The delivered power of a wind turbine of the vertical axis type is not dependent on the wind direction, which makes this type differ from wind turbines with horizontal axis, since vertical axis wind turbines need not be directed toward the wind.

The operation of the turbine can be described as follow: In stand by position (turbine which stands still), the blades hang vertically. This is a possible parking stand also of the blades in case of exceptional strong wind. The position and length of the blades is preferred to be such that they are not running in against the basis (tower foot) in heavy wind conditions.

The wind turbine is booted when there is sufficient wind available. During booting, the turbine generator is briefly used as motor to create sufficient torsion, to let the rotor slowly spin. During the starting phase, energy is briefly drawn from the electricity net to start the turbine. However, the necessary energy is small and is required only until the blades rotate fast enough to generate sufficient aerodynamic moment.

At the moment that sufficient aerodynamic moment is generated, the direction of electric current turns and energy is generated.

The brake mechanism, to protect it against excessive rpm, can be simply integrated in preferred embodiments of the wing concept. In inactive condition and during normal action's rpm, the brake flaps are stowed away in the wing profile and retained in their place by for instance means of elasticity, for instance springs. The springs are metered in such a way that above a critical rotation speed, the centrifugal force on the brake flaps becomes so large, that the established elasticity is overstepped and the brake flaps are going outward. By spreading out the brake flaps, the surface on the wing tips which offers a resistance is enlarged and rotor rpm is slowed down.

In this way, maximal speed of the blades is simple and automatically set. In embodiments one could also use a computer to measure and/or calculate the rotor rpm and install a computer controlled mechanism in the blade which will extend the

brake flaps on the command of the computer.

A balance will be established between the position of the brake flaps and rotation speed of the blades.

The brake mechanism is preferably also present to avoid excessive rpm in case of generator load loss (voltage failure).

In case of such voltage failure, the rotor will keep rotating with spread out brake flaps until the load is returned or until the rotor stops because of wind shortage. The brake mechanism is preferable to have a (fail save) spring mechanism. Hereby, in case of failure of the spri ng mechanism, the brake flaps spread out automatically as a consequence of centrifugal force's action and wind turbine's slow down.

The turbine works at its normal ability in nominal wind speed (rated wind speed).

This wind speed is appropriate for the rotor's optimal rotation speed. The rotor will rotate on a lower rpm for this wind speeds, corresponding with aerodynamic rotor ability for that wind speed optimum.

The required (optimal) rotation speed for particular wind condition is determined by establishing the correct ability/speed proportion on the generator.

For lower rotation speeds, the flight angle namely the inclination angle under which the blades are rotated, will be relatively small. For wind speeds in or higher than the rated wind speed, the rotor is preferably forced, by setting the power/rotational speed ratio on the generator, to the aerodynamically most favourable rotational speed, for the occurring wind speed.

In higher wind speeds, optimal rotation speed will be bigger, as well as the corresponding flight angle of the blades. For wind speeds between the rated wind speed (Vrated) and maximal valid wind speed (Vout), the power/speed ratio of the generator is preferably set in such way that the delivered power by the generator is approximately constant, and the normal designed ability of the generator is not overstepped. The metering of the generator's resistance will result in a decrease and an increase of the rotor speed in step with the fluctuations of the wind speed round Vrated. Due to the variable rotor speed, the blades flight angle will vary as well.

Excessive rotor energy will be stored and regained in the form of kinetic

energy, through the utilization of flywheel effect.

As shown in figure 4, the blades can be made in segments, and connected to each other by the connections 1 1 . The connections can be made next to the wind turbine. This simplifies the transportation of the blades considerably. This is a vital advantage increasing in importance as the wind turbines become bigger.

For conventional designs, the blades become bigger and heavier, as the size of the wi nd tu rbi nes i ncreases, and the transportation and assembling costs increase exponentially.

This is not or to a much lesser extent, the case for a wind turbine according to the invention.

Figure 6 shows a detail of the rotor hub, according to the invention, in resting stand and in action respectively. The wind rotates the blades. As a consequence of high flexibility of the blades, and, in preferred embodiments, because of the presence of flex boards on the wing foots and on the rotor hub, the blades are mainly loaded under axial tension. Other than in well known constructions, the blades experience slight or almost no bend load. The arrows at the ends of the blades schematically indicated that there is a balance established in the flap and edge direction on the blades. Since the blades are flexible and much less rigid, and in addition for embodiments because their structural elements are positioned approximately on the axis length of the blades, the flap wise moment is very low and chance for cracks in the blades due to too high flap wise load is small and much smaller than in existed designs.

A flexible connection 1 6, for instance a laminated flex board, connects the blades with arm 8 in a flexible way. The rotation of the blades rotates the arm. Both arms 8 are in this example connected by a central flex board 21 to the central drum hub. This flexible part provides that the rotational moment exerted by the rotating blades, can be transmitted via the arms through the head 22 on a drive shaft 14 in the tower. This axis controls a generator in the engine room.

Central flex board 21 provides that the blades can 'run onward' with regard to the hub with such a phase angle that the rotor torque of the blades is carried over to the drum hub by means of pure axial tensile load of the wings (x lever of the drum hub). The section (detail sight) indicates that the flexible connections 1 6 and 21 in this example, for example a sandwich panel with alternating carbon material layers and Teflon

(Ertalon) layers, is manufactured from a laminated artificial material . Flex boards made according to this construction provide that the wing loads on the rotor hub are transmitted in a flexible way.

Figures 7 though 14 illustrate a method for assembling a wind turbine. Figure 7 shows a tripod 1 7 with part 20 on which a telescopic tower 1 3 is secured. On the tower there arms 8 are provided with flexible parts 1 6.

In this example first the telescopic parts 23 of the tripod 1 7 are extended, as shown in figure 8.

In figure 9 is shown how scaffolds are placed at two sides of the wind turbine. In this example scaffolds are used, but it may also be different working platforms, such as ships.

On the scaffolds elements or sub-elements of the flexible blades 10 are joined together to form a blade or a partial blade. Step by step the telescopic tower is then extended as shown in figures 1 0 to 1 4. When all elements of the flexible blades are joined together, the entire blade can be lifted up slowly. In certain execution methods it is also possible to join elements and sub-elements of the blades 1 0 during the lifting. In such execution methods the length of the scaffolds can be shortened.

Figure 14 shows the end result.

The shown telescopic construction of the tower in this preferred execution method has, besides the named advantages, some other advantages as well:

In non-extended state, the height of the tower on the base is relatively modest. The base and the tower can therefore be transported more easily. The tripod and tower can be assembled ashore and , in case of offshore applications, then be rolled into the sea or be transported to its destination by ships. It is also possible to mount the base onto floaters (floating construction), transport it to its destination using tugboats, and have it sunk into position.

The height is relatively modest, therefore frequently occurring problems, such as instability during transportation due to strong winds, or being too high to steer under present obstacles (e.g. bridges) are greatly reduced. Figures 7 through 14 illustrate a great advantage of this method. A large crane is not necessary for the assembly of the wind turbine. Especially for offshore applications or for

applications of wind turbines at remote locations, mountain areas for example, it is often difficult, if not impossible, to take a crane with enough lifting capacity to the destination.

The same advantage applies in case the blades need replacing or repairing.

It is obvious that the construction itself is in perfect balance at all times during the assembly of the wind turbine.

When using cranes with a heavy weight, that sometimes causes problems with known constructions.

A great counterweight must be used to maintain the balance of the crane and the load. Figure 1 5 shows an method for manufacturing a blade. The blade contains a part giving it a structural strength all along its length, in this example a so-called "flex board" 24, made of carbon fiber laminate.

This flex board is characterized by a high tensile capacity but low bending stiffness in the direction of the flap. In the example the flex board stretches over the entire width of the wing profile; this is, however, not a must.

The flex board can, if so desired, also have a partial width. In that case the bending stiffness in the edge will be reduced , resulting in a positive effect on the meant operation of the concept.

The flex board contains all the structural material and has a simple shape (board) of a relatively small size and can be made in a relatively simple mould. In its most simple form the flex board can be made on a simple, flat lamination table.

Compared to the very complex and often huge press moulds necessary for conventional blades, this is a big advantage and makes the concept ideal for high capacity turbines. On the flex board 24 foam cores, so-called "hot wire cut foam cores" 25 are fitted (glued). These foam cores can be very precisely cut beforehand on a CNC-operated hot wire cutting bank.

Because the transfer of power through the foam cores is not necessary, even undesired, it is not a disadvantage that foam cores from different elements (blocks) are pieced together. Ideally expansion joints 27 are used between the blocks. This makes structural as well as thermal expansion possible.

Preferably an outer layer 26 (a skin) is fitted, in this case using a filament winding technique.

The winding technique is ideal for the application of this blade concept because this skin only has a sealing and protective function, and ideally, no structural stiffness. The winding laminate is ideal in this application because the fibers are applied at right angles on the axial main load device and therefore cannot cause parasitic stiffness.

With conventional blades, wherein the skin does have a load-bearing function, the vast majority of the fibers are oriented parallel to the axis of the blade. Moreover the structural fibers of these blades must be continuous from the base of the blade to the tip, in order to avoid structural discontinuities.

Therefore the winding technique is much less usable for conventional blades and, by definition, less efficient because only the secondary laminate (in the cross direction) can be wound.

The mai n lami nate mu st sti l l be appl ied usi ng conventional (man ual) techniques.

Neither is it necessary with the blade concept according to the invention, to apply the nonstructural material (foam cores and skin) over the whole blade length.

The blade may contain bare parts 28, without loss of structural load capacity, i.e. only the flex board without the surrounding coating. Such uncovered parts give an extra degree of flexibility to the blade. Such bare sections give, so to speak, an extra degree of security, giving the blade extra bending possibilities at these locations, without the blade getting damaged.

With conventional blades such interruptions are, without a doubt, impossible.

The bare flex parts of the board also make it possible to support the blades at regular distances during the winding process, by using antifriction bearings. These points of support make sure that the blade stays straight during the winding process and is not pulled sideways by the winding spool.

With conventional blades that would be fabricated using the winding technique, such interstitial points of support are very difficult if not impossible to achieve. The bare flex parts of the board also make it possible to give the wing tips a special, for example aerodynamic, rounded shape, with minimal air resistance and also give an

elegant possibility to easily connect several consecutive blade segments (splices, lap joints).

In or on the structural flex board it is also possible to connect conductors, fiber optic cables, power cables or other control cables in an uncomplicated way. With conventional blades, which are built up from two scales glued together, that is not always evident. It is also obvious that the blade, according to the invention, can be significantly thinner than the profile of rotor blades for conventional turbines of similar size.

With conventional blades it is always necessary to seek the highest possible profile thickness, due to the necessary stiffness.

Thick profiles, however, cause a negative aerodynamic efficiency. With the blade concept according to the invention, the profile height is not critical, and limited by the necessary structural thickness of the flex board.

This limited profile thickness decreases, of course, the air resistance and improves the aerodynamic characteristics of the blade.

A comparison to figu re 1 B clarifies the essential difference between a conventional blade and the blade concept according to the invention. With the conventional blades the structural material is placed on the outside of the wing profile, and the nonstructural material on the inside.

With the blade concept according to the invention, this buildup is reversed (inverted). The structural part is centrally located, in the middle, and the nonstructural part (filling material) around it, on the outside.

Figure 1 6 again shows, diagrammatically and as non-limiting example, a blade of a wind turbine according to the invention. The blade segments 10 and 10' together form a blade 9. In this illustration the springs and levers 1 2a for the unfolding of the brake flaps 1 2 are shown as well. The invention makes it possible to integrate the brake mechanism into the blade in a simple manner without negatively affecting the aerodynamic profile of the blade during normal use. Because the structural material is placed inside the flex board it is easy to apply fixtures such as holes to the flex board, for housing and securing parts of the brake mechanism. In conventional blade designs this is much harder because the structural parts also determine the aerodynamic profile and any amendment or change in these parts has

negative aerodynamic and structural consequences.

Figure 1 7 shows a step in the procedure for manufacturing a blade for a wind turbine according to the invention. The blade is supported at the uncovered parts 28, by a rotation device, which allows the blade to rotate during the winding process. Fi g u re 1 8 s h ows a fu rther step in a preferred working method for manufacturing a blade for a wind turbine according to the invention. The blades for known conventional turbines must be pre-formed. This requires using large and complicated moulds.

In the aforementioned blade concept for a wind turbine according to the invention, the structural parts are not on the outside of the blade, but on the central axis. By reversing the positions of the structural and nonstructural materials the construction of the blade in accordance with the invention is, so to speak, "inverted" in comparison to known conventional blades.

This makes it possible to make blades without using press moulds.

Figure 1 8 shows a possible working method. The blade contains a central flex board 24, foam cores 25 and an outer skin 26. Around the blade a vacuum bag 29 is placed, wherein there are two thin stainless steel plates 30.

By drawing a vacuum 31 , 32 the two plates are pressed against the blade by atmospheric pressure, creating a nice, smooth surface. If necessary, heat can be added to accelerate the hardening process. In a preferred execution method the consecutive wing segments of a blade have an equal structural and geometrical buildup. However, the concept also offers the freedom to vary the buildup of the wing along the blade, according to the needs. It is, for example, possible to increase the section of the flex board gradually in the direction of the wing base, due to the increasing traction caused by the lateral jerk. This same way the profile thickness can, if desirable, gradually be adjusted.

Figure 19 shows an example of the possible simple lap joint 34, mutually between several blade segments and a possible geometric shaping of the wing tip 35.

Figure 20 shows in detail an arm 8 of a preferred execution method of a wind turbine according to the invention . The arm 8 contains flexible joints (flex boards) 1 6, whereupon the blades 1 0 are connected. These flex boards 1 6 are, in this example, made of alternately carbon fiber plates and plates of synthetic material (for example Teflon), creating a

sandwich panel resistant to high axial tensions but possessing a relatively low bending stiffness.

The carbon fiber plates give structural strength in the axial direction, while the synthetic plates make a sliding movement possible to neutralize differences in tension over the sandwich.

The flex board 1 6 makes an automatic adjustment of balance between gravity and the lateral jerk possible, resulting in a tension along the flex board which is almost completely axially oriented.

The flex board enables the blades to automatically spread out to their natural camber angle during rotation. In standstill the blades will hang downwards vertically, under the influence of their own weight. During operation the blades spread out wherein the final camber angle will be determined by all forces present (gravity, lateral jerk, aerodynamic forces, forces caused by the tip friction).

The arm furthermore contains a yoke 35, a rotor hub 22 provided with an upper plate 33 and a central flex board 34. The construction of this central flex board is similar to that of the flex boards 1 6.

The central flex board 34 ensures that the blades can "advance" in relation to the hub with such a phase angle that the rotor torque of the blades is transferred by means of pure axial tensile load of the wings (x the lever of the drum hub). An advantage of the blades for a wind turbine according to the invention is that they are extremely flexible and therefore easily bendable. This allows for sharp turns, among other things, that are impossible with conventional blades. Such transport is clearly illustrated in figure 21 .

The same advantage is used to bring the blades from their initial horizontal position to a vertical position for assembly to the turbine.

In a preferred execution method the flex boards at the base of the wing 1 6 and the central flex board 34 are implemented as sandwich panels because such panels can withstand great deformations without any moving parts. In a less preferred implementation the necessary rotational movements could also be achieved by applying conventional plain bearings.

The great advantage of the wing concept for the wind turbine according to the

invention is that the blades are always under tension of traction and never of pressure. For that reason the stiffness can be, and preferably is, modest.

With conventional blades, that must be able to withstand standing positions, pressure tensions act besides the pulling tensions, because of which minimal standards are to be met on the stiffness of these blades.

In the illustrations of the blade concept for the wind turbine according to the invention, the blades in operation are shown as straight elements. In reality the blades may show a certain curvature due to possible variations in weight and stiffness along the length of the blade. In preferred embodiments the blade elements are, however, straight or nearly straight.

The different parts of a wing may be made up the same way, but it is possible to have a variation in the buildup of the parts of the wing. The parts that are closest to the arm will have to endure the highest traction. A modular buildup makes it possible to easily adjust the strength of the flex board (and therefore the weight of the flex board), so the upper modules, meaning the modules close to the arms have a stronger and thicker flex board than modules near the tip. The invention also offers the possibility to vary the profile and therefore the aerodynamic characteristics of a part of the wing, in an easy manner by varying the form of the nonstructural parts. A great advantage hereby is that such variations can be performed fast and easily so fast testing is possible. With conventional wing concepts it is always necessary to make new moulds. The wing concept, according to the invention, therefore also offers a great advantage in the test phase due to the exceptional flexibility.

It is obvious that within the framework of the invention there are many possible variations.