Patent Description:
Dimensions of wind turbines and wind blades are ever increasing, and consequently are increasing the challenges to overcome during the manufacturing processes of such wind turbine rotor blades. Presently, preferred materials used to manufacture wind turbine rotor blades, hereinafter also referred to as the blades, are glass- and/or carbon-fiber reinforced plastics commonly referred to as "composites", which are generally processed through hand lay-up and resin injection molding processes. Larger sections, longer spans, thicker structural components of the blades make the resin flow very complex to design and optimize, and thus posing an increased risk of manufacturing errors such as transverse wrinkles, poor impregnation of the resin, air pockets, large areas with dry fibers, and so on and so forth. These errors can extend over wide areas, can be very time consuming and very costly to repair and can drastically affect the cost and reliability of the final product i.e. the manufactured blade for the wind turbine. Additionally, hand lay-up of composite structures becomes very time-consuming especially with the increase of thicknesses and number of layers required in manufacturing of the spar caps.

Recent developments in the wind turbine industry, as shown in <CIT>, have led to the introduction of pultruded unidirectional fibrous composite strips, i.e. pultruded strips of composite material having unidirectional fibers (UD) reinforcement, mostly in the spar cap constructions, which represent the main load carrying components of the rotor blades.

<FIG> shows a cross-sectional view of an airfoil section of a conventionally known rotor blade <NUM>, hereinafter also referred to as the conventional blade <NUM>, having pultruded strips <NUM> stacked in spar caps <NUM> of the conventional blade <NUM>. One of these structural elements, i.e. the conventionally known pultruded strips <NUM> is schematically depicted in <FIG>. The conventionally known pultruded strip <NUM>, hereinafter also referred to as the conventional strip <NUM> is defined by planar surfaces and generally resembles a longitudinally, i.e. along a longitudinal axis <NUM> of the conventional strip <NUM>, elongated rectangular parallelepiped such as a bar or slab, and has a rectangular shaped cross-section when sectioned normally to the longitudinal axis <NUM>. Such conventional strips <NUM> of <FIG> are stacked atop each other to form a stack of the conventional strips <NUM>.

The conventional strip <NUM> is defined by first and second longitudinally extending sides <NUM>, <NUM> and by first and second longitudinally extending edges <NUM>, <NUM>, thereby resembling shape of a bar or slab. The conventional strip <NUM> has first and second abutment surfaces 251a, 252a on the first and second side <NUM>, <NUM>. The first and second abutment surfaces 251a, 252a are generally limited by the first and second peripheral surfaces 251p, 252p. The first and second abutment surfaces 251a, 252a are spaced apart along a vertical axis <NUM> of the conventional strip <NUM>, and the first and second edges <NUM>, <NUM> are spaced apart along a transverse axis of the strip <NUM>. The axes i.e. the longitudinal axis <NUM>, the vertical axis <NUM> and the transverse axis <NUM> are mutually perpendicular. The first and second abutment surfaces 251a, 252a may be covered with peel ply layers <NUM>. The surface <NUM> of the peel ply layer <NUM> is flush with the peripheral surfaces 251p, 252p. The peel ply layers <NUM> are removed prior to stacking the conventional strips <NUM>. The stack is then resin infused to form the conventional spar cap <NUM>.

As shown in <FIG>, the conventional blade <NUM> includes a shell <NUM>. The shell <NUM> is generally made from two half shells i.e. a leeward shell 21a and a windward shell 21b both moulded generally from glass-fiber reinforced plastics. This is generally referred to as the 'butterfly blade' since it has two separate half shells 21a, 21b that are later assembled with each other to form the complete shell <NUM> for example the two half shells 21a, 21b are glued together to form the shell <NUM>. Alternatively, the blade <NUM> may include a shell <NUM> that is formed integrally i.e. the shell <NUM> does not have the two half shells 21a, 21b but instead is formed in one-part as is done in the well known integral blade construction of Siemens. Parts of the shell <NUM> have a sandwich panel construction and comprise a core (not shown) of lightweight material e.g. polyurethane foam, PET foam, balsa wood, ply-wood, etc. sandwiched between inner and outer surfaces or facesheets of the shell <NUM>. Within the blade <NUM> is a blade cavity <NUM>. The blade <NUM> may include one or more spar caps <NUM>, generally in pairs for example a pair of spar caps <NUM> namely spar caps 230a and 230b, or two pairs of spar caps <NUM> i.e. four spar caps (not shown). Each pair of the spar caps <NUM> i.e. the spar caps 230a, 230b are supported by a shear web <NUM>, also referred to as the web <NUM>, which forms a generally known I-beam shape along with the spar caps 230a, 230b. The spar caps 230a, 230b, are generally embedded in the shell <NUM> either partially or completely. One spar cap <NUM> of each pair is embedded or integrated with the leeward shell 21a and the other spar cap <NUM> of the pair is embedded or integrated with the windward shell 21b.

The spar caps <NUM> have a generally elongated rectangular parallelepiped shape such as a bar or slab, elongated in a span wise direction of the blade <NUM>, i.e. in other words the spar cap <NUM> has a rectangular cross section when sectioned perpendicular to the span of the blade <NUM>. The conventionally known spar cap <NUM> is made up of the stack(s) of prefabricated conventional strips <NUM> of <FIG>. The conventional strips <NUM> are pultruded strips of carbon-fiber reinforced plastic and are substantially flat and have a rectangular cross-section.

During manufacturing of the turbine blade <NUM> a resin-infusion process is used. Various laminate layers of the shell <NUM> are laid up, generally by hand-lay, in a mould cavity, the conventional strips <NUM> are then stacked where the spar caps <NUM> are to be formed i.e. interspersed between parts of the leeward and the windward shells 21a, 21b, and a vacuum is applied to the mould cavity. Resin is, simultaneously from a far side or subsequently, introduced into the mould. The vacuum pressure causes the resin to flow over and around the laminate layers and the strips <NUM> of the stack and to infuse into the interstitial spaces between the laid up layers and between the strips <NUM>. Finally, the resin-infused layup is cured to harden the resin and bond the various laminate layers and the strips <NUM> together and to each other to form the blade <NUM>.

As has been depicted in <FIG> and in <FIG> that schematically depicts a detailed view of a region R of <FIG>, there exists a difference between the shapes, i.e. sectional geometries, of the strips <NUM> and the shell <NUM>. The strips <NUM> are flat, i.e. having planar surfaces <NUM>, <NUM>, whereas the shell <NUM> is curved, particularly the strips <NUM> that form the outermost and the innermost layers of the spar cap <NUM> have different sectional geometry i.e. are planar or flat whereas the shell <NUM> in proximity of these strips <NUM> forming the spar cap <NUM> is curved. This difference can lead to resin rich areas at the interface between the two geometries as shown in region R2 of <FIG> and/or to "puncturing" of the shell <NUM> from the corners of the pultruded conventional strips <NUM>, as schematically shown in regions R1 and R3 of <FIG>. The first defect, i.e. formation of resin rich areas as shown in region R2 can lead to crack initiation at the interface between spar cap <NUM> and the blade shell <NUM> which then can develop in longitudinal cracks and/or delamination of the rotor blade structure. The second defect, i.e. puncturing of the blade shell <NUM> by the corners of the conventional strips <NUM> can result in longitudinal wrinkles in the blade shell fibers, in an obstruction of the resin flow and/or blade shell fibers cut when pressure is applied from vacuum bags during or prior to resin infusion. <CIT> discloses a wind turbine according to the preamble of claim <NUM>.

Thus in a nutshell the stacking of the conventional strips <NUM> during manufacturing of the spar caps <NUM> results into problematic areas such as the regions R1, R3 and/or the region R2 as shown in <FIG>. Therefore there exists a need for a technique that ensures that formation of resin rich areas R2 and/or puncturing of the shell <NUM> in regions R1, R2 is at least partially obviated.

The object of the present invention is to provide a technique that ensures that formation of resin rich areas R2 and/or puncturing of the shell <NUM> in regions R1, R2 is at least partially obviated.

The abovementioned object is achieved by a wind turbine rotor blade according to claim <NUM> and by a method for making a spar cap according to claim <NUM>. Advantageous embodiments of the present technique are provided in dependent claims.

In a first aspect of the present technique useful to understand the invention, a pultruded fibrous composite strip is presented. The pultruded fibrous composite strip, hereinafter also referred to as the strip is for stacking with one or more similar strips to form a spar cap of a wind turbine rotor blade, hereinafter also referred to as the blade. The strip has a substantially constant cross-section defined by first and second mutually opposed and longitudinally extending sides, and by first and second longitudinal edges. The first side includes a first abutment surface and the second side includes a second abutment surface. The first abutment surface and the second abutment surface, hereinafter together referred to as the abutment surfaces, have a non-planar profile. When the strip is stacked with similar strips, in preparation of resin infusion and subsequent curing of the resin to bond the strip with the other similar strips to form the spar cap, the non-planar profile or shape of the abutment surfaces of the strips avoid formation of resin rich pockets or regions at the interface of the shell of the wind turbine rotor blade and the strips, as compared to when conventionally known strips with flat or planar abutment surfaces are embedded into the shell. Furthermore, the non-planar profiles of the abutment surfaces also ensure that sectional geometries of the strips substantially matches the sectional geometry of the region of the shell where the strips are embedded and thus puncturing of the shell by the corners of the strips is at least partially obviated as compared to conventionally known strips with flat or planar abutment surfaces.

The profile of the abutment surface means an outline, silhouette, contour, shape of the surface. The profile of the abutment surface is represented by a curvature of the surface when observed holistically for the surface.

The pultruded fibrous composite strip is a pultruded strip of composite material having unidirectional fibers (UD) reinforcement. The pultruded strips have structural fibers, generally longitudinally running along the strip and hence unidirectional, made of glass, carbon, aramid and/or basalt, while the matrix that keeps the fibers together in the strip and protects them from external agents may be, but not limited to, epoxy, vinylester, polyurethane, polyester, etc..

In different embodiments of the strip, the abutment surfaces have a curved profile, a V-shaped profile, and an open polygon shaped profile, respectively. With these shapes or profiles the strips can be stacked such that the strips are geometrically aligned with or in agreement to the shape of the shell in the region where the strips are integrated i.e. where the spar caps are formed.

The first side further includes two peripheral surface regions - each extending longitudinally. The first abutment surface is limited between the peripheral surface regions of the first side and separated from the first and second longitudinal edges by the peripheral surface regions of the first side. Similarly, the second side further includes two peripheral surface regions - each extending longitudinally. The second abutment surface is limited between the peripheral surface regions of the second side and separated from the first and second longitudinal edges by the peripheral surface regions of the second side. In this embodiment, at least one of the peripheral surface regions is chamfered, i.e. includes a chamfer recess. In another embodiment of the strip, both the peripheral surface regions of at least one of the first and the second sides are chamfered. Due to chamfering the resin flow to the abutment surfaces is facilitated.

In another embodiment of the strip, the strip includes a first peel-ply layer on the first abutment surface and/or a second peel-ply layer on the second abutment surface. The peel-ply layer at least partially covers the abutment surface on which the peel-ply layer is present. The peel-ply layer is present on the abutment surface(s) having the non-planar profile. The peel-ply or the peel-plies may be removed before stacking of the strips and before performing resin infusion and the removal of the peel-ply or the peel-plies provides a roughened surface on the abutment surface from where the peel-ply has been removed.

In a second aspect of the present technique useful to understand the invention, a spar cap for a wind turbine rotor blade is presented. The spar cap includes a plurality of pultruded fibrous composite strips stacked with one or more similar strips to form a stack of the strips. Each of the strips is as described hereinabove for the first aspect of the present technique. In the stack, the strips are oriented such that one of the abutment surfaces of the strip are aligned to or in agreement with the shape of the shell in the region where the strips are embedded, i.e. in other words the strips are oriented such that the contour of the strip generally or substantially follows the contour of the shell in the region where the strips are embedded.

According to the invention, a wind turbine rotor blade as defined in claim <NUM> is presented. The wind turbine rotor blade, hereinafter also referred to as the blade, has at least one spar cap extending longitudinally in a span-wise direction of the blade. The spar cap includes a plurality of pultruded fibrous composite strips stacked with one or more similar strips. Each of the strips is according to the first aspect of the present technique as described hereinabove. Each of the strips is oriented such that the first and the second sides of the strip longitudinally extend along the span-wise direction of the blade and are spaced apart in a flap-wise direction of the blade, and the first and the second edges of the strip longitudinally extend along the span-wise direction of the blade and are spaced apart in a chordwise direction of the blade.

According to the invention, a method for making a spar cap as defined in claim <NUM> for a wind turbine rotor blade is presented.

In the method of the present technique, a plurality of pultruded fibrous composite strips is provided. Each of the strips is according to the first aspect of the present technique described hereinabove. The strips are then stacked in a mould to form a stack of the strips. The strips are stacked such that contour of the strips generally or substantially follows the contour of the shell in the region where the strips are embedded or stacked. Thereafter, in the method, resin is supplied to the stack. Finally in the method, the resin is cured to bond the adjacent strips together and to bond the shell with the strips.

In an embodiment of the method, one or more of the strips include a first peel-ply layer at least partially covering the first abutment surface and/or a second peel-ply layer at least partially covering the second abutment surface. The peel-ply layer is present on the surface having the non-planar profile. In the method the first and/or the second peel plies are removed from their respective abutment surfaces before stacking the strips in the mould to form the stack of the strips.

The above mentioned attributes and other features and advantages of the present technique and the manner of attaining them will become more apparent and the present technique itself will be better understood by reference to the following description of embodiments of the present technique taken in conjunction with the accompanying drawings, wherein:.

Hereinafter, above-mentioned and other features of the present technique are described in details. Various embodiments are described with reference to the drawing, wherein like reference numerals are used to refer to like elements throughout. In the following description, for the purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be noted that the illustrated embodiments are intended to explain, and not to limit the scope of the invention defined by the appended claims.

It may be noted that in the present disclosure, the terms "first", "second", "third" etc. are used herein only to facilitate discussion, and carry no particular temporal or chronological significance unless otherwise indicated.

<FIG> shows an exemplary embodiment of a wind turbine <NUM> of the present technique. The wind turbine <NUM> includes a tower <NUM>, which is mounted on a fundament (not shown). A nacelle <NUM> is mounted on top of the tower <NUM> and rotatable with regard to the tower <NUM> by means of a yaw angle adjustment mechanism <NUM> such as yaw bearings and yaw motors. The yaw angle adjustment mechanism <NUM> functions to rotate the nacelle <NUM> around a vertical axis (not shown) referred to as a yaw axis, which is aligned with the longitudinal extension of the tower <NUM>. The yaw angle adjustment mechanism <NUM> rotates the nacelle <NUM> during operation of the wind turbine <NUM> to ensure that the nacelle <NUM> is appropriately aligned with the current wind direction to which the wind turbine <NUM> is subjected.

The wind turbine <NUM> further includes a rotor <NUM> having at least a rotor blade <NUM>, and generally three rotor blades <NUM>, although in the perspective view of <FIG> only two rotor blades <NUM> are visible. One of the rotor blades <NUM> is schematically depicted in <FIG>. The rotor <NUM> is rotatable around a rotational axis 110a. The rotor blades <NUM>, hereinafter also referred to as the blades <NUM> or as the blade <NUM> when referring to one of the blades <NUM>, are generally mounted at a driving collar <NUM>, also referred to as a hub <NUM>. The hub <NUM> is mounted rotatable with regard to the nacelle <NUM> by means of a main bearing (not shown). The hub <NUM> is rotatable about the rotational axis 110a. Each of the blades <NUM> extends radially with respect to the rotational axis 110a and has an airfoil section <NUM>.

In between the hub <NUM> and each of the rotor blades <NUM>, is provided a blade adjustment mechanism <NUM> in order to adjust the blade pitch angle of the blade <NUM> by rotating the respective blade <NUM> about a longitudinal axis (not shown) of the blade <NUM>. The longitudinal axis of each of the blade <NUM> is aligned substantially parallel with the longitudinal extension of the respective blade <NUM>. The blade adjustment mechanism <NUM> functions to adjust blade pitch angles of the respective blade <NUM>.

The wind turbine <NUM> includes a main shaft <NUM> that rotatably couples the rotor <NUM>, particularly the hub <NUM>, to a generator <NUM> housed within the nacelle <NUM>. The hub <NUM> is connected to a rotor of the generator <NUM>. In an exemplary embodiment (not shown) of the wind turbine <NUM>, the hub <NUM> is connected directly to the rotor of the generator <NUM>, thus the wind turbine <NUM> is referred to as a gearless, direct drive wind turbine <NUM>. As an alternative, as shown in the exemplary embodiment of <FIG>, the wind turbine <NUM> includes a gear box <NUM> provided within the nacelle <NUM> and the main shaft <NUM> connects the hub <NUM> to the generator <NUM> via the gear box <NUM>, thereby the wind turbine <NUM> is referred to as a geared wind turbine <NUM>. The gear box <NUM> is used to convert the number of revolutions of the rotor <NUM> into a higher number of revolutions of the main shaft <NUM>, and consequently of the rotor of the generator <NUM>. Furthermore, a brake <NUM> is provided in order to stop the operation of the wind turbine <NUM> or to reduce the rotational speed of the rotor <NUM> for instance in case of a very strong wind and/or in case of an emergency.

The wind turbine <NUM> further includes a control system <NUM> for operating the wind turbine <NUM> at desired operational parameters, for example at a desired yaw angle, with a desired blade pitch, at a desired rotational speed of the rotor <NUM>, and so on and so forth. The controlling and/or adjusting of the operational parameters are performed to obtain an optimized power generation under the existent conditions for example under existent wind conditions and other weather conditions.

The wind turbine <NUM> may further include different sensors for example a rotational speed sensor <NUM>, a power sensor <NUM>, angle sensors <NUM>, etc that provide inputs to the control mechanism <NUM> or other components of the wind turbine <NUM> to optimize operation of the wind turbine <NUM>.

Furthermore as shown in <FIG>, the rotor blade <NUM> includes a root section <NUM> having a root 11a and an airfoil section <NUM>. Generally, the rotor blade <NUM> includes a transition section <NUM> in between the root section <NUM> and the airfoil section <NUM>. The airfoil section <NUM>, hereinafter also referred to as the airfoil <NUM>, includes a tip section <NUM> having a tip 12a. The root 11a and the tip 12a are separated by a span <NUM>, of the rotor blade <NUM>, which follows the shape of the rotor blade <NUM>. A direction along or parallel to the span <NUM> is referred to as span-wise direction 16d. The tip section <NUM>, including the tip 12a therein, extends from the tip <NUM> towards the root 11a up to a span-wise position of approx <NUM>% (percent), i.e. one third of the total length of the blade <NUM>, as measured from the tip 12a. The tip 12a extends within the tip section <NUM> towards the root 11a up to a span-wise position of approx. The rotor blade <NUM> includes a leading edge section <NUM> having a leading edge 14a, and a trailing edge section <NUM> having a trailing edge 13a. The trailing edge section <NUM> surrounds the trailing edge 13a. Similarly, the leading edge section <NUM> surrounds the leading edge 14a.

At each span-wise position perpendicular to the span <NUM>, a chord line <NUM> that connects the leading edge 14a and the trailing edge 13a can be defined. A direction along or parallel to the chord line <NUM> is referred to as chord-wise direction 17d. <FIG> depicts two such chord lines <NUM> at two different span-wise positions. Furthermore a direction mutually perpendicular to the span-wise direction 16d and to the chord-wise direction 17d is referred to as a flap-wise direction 9d. The rotor blade <NUM> has a shoulder <NUM> that is a section of the rotor blade <NUM> where the chord line <NUM> has maximum chord length, i.e. in example of <FIG> at the chord line <NUM> that is depicted towards the root 11a.

In the wind turbine <NUM>, one or more of the blades <NUM> include one or more spar caps <NUM> shown in <FIG> according to the present technique. In accordance with the invention, the spar cap <NUM> of the present technique includes a component of such a spar cap <NUM> i.e. a pultruded strip <NUM> as shown in <FIG>. The invention also presents a method <NUM> for making such a spar cap <NUM> using the pultruded strip <NUM> of the present technique as shown in <FIG>. Hereinafter, <FIG> in combination with <FIG> and <FIG> have been referred to further explain the present technique. It may be noted that the rotor blade <NUM> of the present technique differs from the conventionally known rotor blade <NUM> as shown in <FIG> only for the spar cap <NUM> and the pultruded strips <NUM>, and other components of the rotor blade <NUM> are same as described hereinabove with reference to <FIG> for the conventional blade <NUM>, for example the web <NUM>, the leeward and windward shells 21a, 21b, etc. The difference between the present invention as compared to the conventionally known techniques is in the geometrical structure of the pultruded strip <NUM> as opposed to the structure of the conventional strip <NUM>, and in the spar cap <NUM> resulting from the use of the pultruded strips <NUM> as opposed to the spar caps <NUM> formed from the conventional strips <NUM>.

<FIG> and <FIG> show exemplary embodiments of the pultruded strip <NUM> of the present technique. As aforementioned, the pultruded strips <NUM>, hereinafter also referred to as the strip <NUM> are pultruded unidirectional fibrous composite strips. The strip(s) <NUM>, depicted in <FIG> is a pultruded strip of composite material having unidirectional fibers (UD) reinforcement i.e. the strips <NUM> have structural fibers, generally longitudinally running along the strip <NUM>, and hence unidirectional, made of glass, carbon, aramid and/or basalt, while the matrix that keeps the fibers together in the strip <NUM> and protects the fibers from external agents may be, but not limited to, epoxy, vinylester, polyurethane, polyester, etc. Each of the strips <NUM> are formed by pultrusion, a continuous process similar to extrusion, in which fibers e.g. glass-fibers or carbon-fibers are pulled through a supply of liquid resin i.e. through the material of the matrix that keeps the fibers together, and through dies that shape the strip <NUM> to the shape according to the present technique. The resin i.e. the matrix material is then cured, for example by heating in an open chamber, or by employing heated dies that cure the resin as the strip <NUM> is pultruded.

The strip <NUM> is used to form the spar cap <NUM> of <FIG> by stacking the strip <NUM> with one or more similar strips <NUM> to form the spar cap <NUM> of the rotor blade <NUM> of the wind turbine <NUM>. As shown in <FIG> and <FIG>, the strip <NUM> has a longitudinal axis <NUM> extending generally in the direction in which the strip <NUM> was pultruded when manufactured, and which is also the direction along which the fibers (not shown) of the strip <NUM> extend. The strip <NUM> has a first side <NUM> and a second side <NUM> opposite to the first side <NUM>, and a first edge <NUM> and a second edge <NUM> opposite to the first edge <NUM>. The strip <NUM> has a substantially constant cross-section, i.e. the strip <NUM> maintains its cross-sectional shape and dimensions at positions along the longitudinal axis <NUM>. The strip <NUM> is defined by the first and the second mutually opposed and longitudinally extending sides <NUM>, <NUM> and by the first and the second longitudinal edges <NUM>, <NUM> i.e. the sides <NUM>, <NUM> and the edges <NUM>, <NUM> extend generally parallelly to the longitudinal axis <NUM> of the strip <NUM>.

The first side <NUM> includes a first abutment surface 51a. The first abutment surface 51a may be the entire surface of the first side <NUM> i.e. covering the entire expanse between the first and the second edges <NUM>, <NUM>. Alternatively, the first abutment surface 51a may be a substantial part of the entire surface of the first side <NUM> and may be limited by borders or peripheral regions 51p, 51p' or peripheral surface regions 51p, 51p' of the first side <NUM> towards the first and the second edges <NUM>, <NUM>, or in other words, the surface of the first side <NUM> has three regions - namely the two peripheral surface regions 51p, 51p' and the first abutment surface 51a sandwiched between the two peripheral surface regions 51p, 51p'. The peripheral surfaces 52p, 52p' separate the second abutment surface 52a from the first and the second edges <NUM>, <NUM>. The width of each of the peripheral surface regions 51p, 51p' i.e. expanse of each of the peripheral surface region 51p, 51p' as measured along the first side <NUM> and perpendicular to the longitudinal axis <NUM> may be between <NUM>% and <NUM>% of a distance between the first and the second edge <NUM>, <NUM> as measured along the first side <NUM> and perpendicular to the longitudinal axis <NUM>. The advantage of having the peripheral regions 51p, 51p' is that presence of the peripheral regions 51p, 51p' allows incorporation of a peel ply (not shown in <FIG> and <FIG>) on the surface of first side <NUM> during the pultrusion process. When a peel ply is incorporated on the surface of first side <NUM> during the pultrusion process, the area or region of the surface of the first side <NUM> covered by the peel-ply is the first abutment surface 51a, and the areas or regions of the surface of the first side <NUM> not covered by the peel-ply are the peripheral surface regions 51p, 51p'. When a peel ply is incorporated on the surface of first side <NUM>, a surface of the peel ply is flush with the peripheral surface regions 51p, 51p'.

Similarly, the second side <NUM> includes a second abutment surface 52a. The second abutment surface 52a may be the entire surface of the second side <NUM> i.e. covering the entire expanse between the first and the second edges <NUM>, <NUM>. Alternatively, the second abutment surface 52a may be a substantial part of the entire surface of the second side <NUM> and may be limited by borders or peripheral regions 52p, 52p' or peripheral surface regions 52p, 52p' of the second side <NUM> towards the first and the second edges <NUM>, <NUM>, or in other words, the surface of the second side <NUM> has three regions - namely the two peripheral surface regions 52p, 52p' and the second abutment surface 52a sandwiched between the two peripheral surface regions 52p, 52p'. The peripheral surfaces 52p, 52p' separate the second abutment surface 52a from the first and the second edges <NUM>, <NUM>. The width of each of the peripheral surface regions 52p, 52p' i.e. expanse of each of the peripheral surface region 52p, 52p' as measured along the second side <NUM> and perpendicular to the longitudinal axis <NUM> may be between <NUM>% and <NUM>% of a distance between the first and the second edge <NUM>, <NUM> as measured along the second side <NUM> and perpendicular to the longitudinal axis <NUM>. The advantage of having the peripheral regions 52p, 52p' is that presence of the peripheral regions 52p, 52p' allows incorporation of a peel ply (not shown in <FIG> and <FIG>) on the surface of second side <NUM> during the pultrusion process. When a peel ply is incorporated on the surface of second side <NUM> during the pultrusion process, the area or region of the surface of the second side <NUM> covered by the peel-ply is the second abutment surface 52a, and the areas or regions of the surface of the second side <NUM> not covered by the peel-ply are the peripheral surface regions 52p, 52p'. When a peel ply is incorporated on the surface of second side <NUM>, a surface of the peel ply is flush with the peripheral surface regions 52p, 52p'.

According to the invention, the first abutment surface 51a and the second abutment surface 52a have non-planar profile. The profiles of the first abutment surface 51a and the second abutment surface 52a, hereinafter together referred to as the abutment surfaces 51a, 52a, are geometrically similar i.e. if the first abutment surface 51a is curved then the second abutment surface 52a is similarly curved, or if the first abutment surface 51a is v-shaped then the second abutment surface 52a is similarly v-shaped, and so on and so forth. Non-planar as used herein means not forming a flat plane or planar surface.

<FIG> and <FIG> show a three-axis coordinate system, formed by the mutually perpendicular longitudinal axis <NUM>, a transverse axis <NUM> and a vertical axis <NUM>, to further explain the non-planar profile the abutment surfaces 51a, 52a. The first and the second edges <NUM>, <NUM> are spaced apart along the transverse axis <NUM>, whereas the first and the second abutment surfaces 51a, 52a are spaced apart along the vertical axis <NUM>, which also defines the thickness of the strip <NUM>. As can be seen in <FIG> and <FIG>, the abutment surfaces 51a, 52a are not parallel to the transverse axis <NUM>, and thus do not form a flat planes. Furthermore, the abutment surfaces 51a, 52a are not parallel to a plane formed by the transverse axis <NUM> and the longitudinal axis <NUM> i.e. in other words each of the abutment surfaces 51a, 52a are mutually non-parallel to the transverse axis <NUM> and the longitudinal axis <NUM>. The difference between the geometrical shape of the conventional strip <NUM> and the strip <NUM> used in the present invention is further explained by comparison of <FIG> showing the conventional strip <NUM> to <FIG> depicting the strip <NUM> of the present technique. As can be seen from <FIG>, the abutment surfaces 251a, 252a of the conventional strip <NUM> are parallel to the transverse axis <NUM> of the conventional strip <NUM>, or in other words mutually parallel to the transverse axis <NUM> and the longitudinal axis <NUM> of the conventional strip <NUM>.

The non-planar profile of the abutment surfaces 51a, 52a of the strip <NUM> can be realized by abutment surfaces 51a, 52a which are curved as depicted in <FIG>, or can be V-shaped as depicted in <FIG>, or can be open polygonal shaped as depicted in <FIG>. When open polygonal shaped, the strips <NUM> are prismatic in shape.

Besides having the abutment surfaces having non-planar profiles, the strips <NUM> may also include a chamfer recess <NUM> as depicted in <FIG>. The chamfer recess <NUM> extends longitudinally i.e. along the longitudinal axis <NUM>. The chamfer recesses <NUM> may present in the peripheral surface regions 51p, 51p' of either one or both of the first and the second sides <NUM>, <NUM>. One or both of the peripheral surface regions 51p, 51p' of any side i.e. the first and/or the second side <NUM>, <NUM>, may be chamfered. The chamfer recesses <NUM> are transitional edges between the abutment surfaces 51a, 52a and the first and the second edges <NUM>,<NUM>, and thus the first and the second edges <NUM>, <NUM> are not aligned perpendicularly to the peripheral surface regions 51p, 51p' when the chamfer recess <NUM> is incorporated in the peripheral surface regions 51p, 51p'.

<FIG> depicts yet another embodiment of the strip <NUM>. In this embodiment the strip <NUM> includes a first peel-ply layer <NUM> on the first abutment surface 51a and/or a second peel-ply layer <NUM> on the second abutment surface 52a. The peel-ply layer <NUM>,<NUM> at least partially covers the abutment surface 51a, 52a on which the peel-ply layer <NUM>,<NUM> is present. The surface <NUM> of the peel ply layer <NUM>,<NUM> is flush with the surface of the peripheral region 51p, 51p', 52p, 52p' of the sides <NUM>, <NUM> of the strip <NUM>. In a preferred embodiment as depicted in <FIG>, the peel-ply layer <NUM> extends to the chamfer recess <NUM>. Thus with the peel-ply layer <NUM>,<NUM> removed and resin injection during manufacturing of the blade <NUM>, the resin flow is facilitated from the chamfer recess <NUM> into the abutment surfaces 51a,52a.

<FIG> show stacks <NUM> formed by placing the strip <NUM> on top of another strip <NUM>. It may be noted that directional terminology, such as 'top', 'bottom', 'front', 'back' etc., is used in <FIG> to <NUM> and in other accompanying FIGs of the present technique with reference to the orientation of the FIG(s) being described. The components used in the invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. For example the stacking of the strips <NUM> may be side by side instead of on top of one another. It may also be noted that although in the stacks of <FIG> only two strips <NUM> are depicted and in <FIG> only three strips <NUM> are depicted, in general the number of strips <NUM> in the stacks may be greater, for example between four and twelve, or more. The number of strips <NUM> to be stacked depends on numerous factors for example, thickness of the strips <NUM>, desired thickness of the spar cap <NUM>, etc. The stack <NUM> of <FIG> shows two identical strips <NUM> of <FIG> stacked. As can be seen the abutment surfaces 51a, 52a of both the strips <NUM> are non-planar. <FIG> and <FIG> show the stacked strips <NUM> with respect to a region of the shell <NUM> of the wind turbine rotor blade <NUM> in which the strips <NUM> are embedded to form the spar cap <NUM>. As can be seen in <FIG>, the strips <NUM> are stacked in such a way that shape or contour of the strips <NUM> is generally in agreement with or aligned with shape or contour of the region of the shell <NUM> of the wind turbine rotor blade <NUM> in which the strips <NUM> are embedded to form the spar cap <NUM>. As can be seen by comparison of <FIG> with <FIG> and <FIG>, due to the non-planar profile of the strips <NUM>, formation of regions similar to the regions R1, R2, and R3 are at least partially obviated in the present technique.

<FIG> depicts a flow chart showing, according to the invention, the method <NUM> for making the spar cap <NUM>, i.e. the one or more of the spar caps 30a, 30b, for the wind turbine rotor blade <NUM>. In the method <NUM>, in a step <NUM> a plurality of the strips <NUM> is provided. Each of the strips <NUM> is as described hereinabove in reference to <FIG>. The strips <NUM> are then stacked in a mould to form a stack of the strips. In the method <NUM>, after the step <NUM> in a step <NUM>, the strips <NUM> are stacked as described hereinabove in reference to <FIG>. After completion of this stage of the method <NUM>, the mould has the stack <NUM> of the strips <NUM> and has components that are placed to form parts of the shell <NUM> of the blade <NUM>. Thereafter, subsequent to the step <NUM> in the method <NUM>, in a step <NUM> resin is supplied to the stack <NUM> and to the other components of the shell <NUM> placed in the mould. The resin flow in the step <NUM> may be achieved by Vacuum Assisted Resin Transfer Molding (VARTM) process. Finally in the method <NUM>, in a step <NUM> the resin is cured to bond the adjacent strips <NUM> together and to bond the strips <NUM> with the components of the shell <NUM>. It may be noted that the supplying of the resin is required creation of partial volume in the mould and pumping in of the resin, and so on and so forth, however the steps are conventionally known in the art of wind turbine blade manufacturing though resin injection and thus not explained herein in further details for sake of brevity.

An embodiment of the method <NUM>, when the strips <NUM> used for the method <NUM> include the first and/or the second peel-ply layers <NUM>, <NUM> as described hereinabove in reference to <FIG>, includes a step <NUM> in which the first and/or the second peel plies <NUM>, <NUM> are removed from their respective abutment surfaces 51a, 52a before the step <NUM> is performed.

It may be noted that the strips <NUM> of the present technique are used for the wind turbine blades <NUM> that have the so-called 'structural shell design' as shown in <FIG> in which the spar caps 30a, 30b, are integrated or embedded within the structure of the shell <NUM>, i.e. the outer shell <NUM>. Furthermore, the number of spar caps 30a, 30b, depicted in <FIG> are for exemplary purposed only, and it may be appreciated by one skilled in the art that the blade <NUM> of the present technique may have two spar caps <NUM> i.e. only one pair of the spar caps <NUM> as shown in <FIG>, or may have four (not shown) or more than four (not shown) spar caps <NUM>, for example six spar caps <NUM> forming three distinct pairs of the spar caps <NUM>.

It may further be noted that the present technique is applicable to the well known 'integral blade' construction of Siemens, where unlike butterfly blade construction the leeward and windward shells are not separately manufactured. In the integral blade construction the entire shell is manufactured in one-part as an integral shell and thus does not have a separately manufactured leeward and windward side.

Claim 1:
A wind turbine rotor blade (<NUM>) having at least one spar cap (<NUM>) extending longitudinally in a span-wise direction (16d) of the wind turbine rotor blade (<NUM>), the spar cap (<NUM>) comprising a plurality of pultruded fibrous composite strips (<NUM>) stacked with one or more similar strips (<NUM>), wherein each of the pultruded fibrous composite strips (<NUM>)
is of substantially constant cross-section defined by first and second mutually opposed and longitudinally extending sides (<NUM>,<NUM>) and by first and second longitudinal edges (<NUM>,<NUM>), the first and second sides (<NUM>,<NUM>) comprising, respectively, first and second abutment surfaces (51a,52a),
wherein the first and the second abutment surfaces (51a) are non-planar,
wherein each of the pultruded fibrous composite strips (<NUM>) is oriented such that:
- the first and the second sides (<NUM>,<NUM>) of the strip (<NUM>) longitudinally extend along the span-wise direction (16d) of the wind turbine rotor blade (<NUM>) and are spaced apart in a flap-wise direction (9d) of the wind turbine rotor blade (<NUM>), and
- the first and the second edges (<NUM>,<NUM>) of the strip (<NUM>) longitudinally extend along the span-wise direction (16d) of the wind turbine rotor blade (<NUM>) and are spaced apart in a chordwise direction (17d) of the wind turbine rotor blade (<NUM>) and characterized in that a the strips are oriented such that one of the abutment surfaces of the strip are aligned to or in agreement with the shape of the shell in the region where the strips are embedded.