GB2530072A

GB2530072A - Improvements relating to the manufacture of wind turbine blades

Info

Publication number: GB2530072A
Application number: GB1416130.1A
Authority: GB
Inventors: Jonathan Smith
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2014-09-12
Filing date: 2014-09-12
Publication date: 2016-03-16
Also published as: GB201416130D0

Abstract

A kit of materials 60 for arranging in a wind turbine blade mould 80 to form part of a wind turbine blade shell includes a base layer 62 of fibrous fabric and a core layer of core (e.g foam) material. The layers of the kit are shaped to form part of a wind turbine blade shell and are attached together such that the kit can be arranged in the blade mould as a single unit. Preferably the kit comprises one or more under-layers and one or more over-layers and the layers of the kit are stitched together. The core layer preferably comprises a plurality of core panels spaced apart to define spanwise channels 68. The core panels may comprise mating features 72a for mating with complementary mating features 72b of core panels on adjacent kits to connect the panels together. A method of making a wind turbine blade preferably comprises pre-assembling a plurality of kits outside the mould 88 and transferring them to the mould. The method may comprise arranging one or more reinforcing structures, such as spar caps, in the spanwise channels between the core panels.

Description

lmr3rovements relating to the manufacture of wind turbine blades

Technical field

The present invention relates to the manufacture of wind turbine blades.

Background

Figure 1 shows atypical wind turbine blade 10 for a utility-scale wind turbine. The blade extends longitudinally from a root end 12 to a tip end 14 in a so-called spanwise' directionS, and transversely between a leading edge 16 and a trailing edge 18 in a so-called widthwise' or thordwise' direction C. Figure 2 is a cross-sectional view of the blade 10 taken along the line A-A in Figure 1.

Referring to Figure 2, the blade 10 comprises a substantially hollow outer shell 20, which is formed from two main parts: a windward half shell 22 and a leeward half shell 24. The respective half shells 22,24 are moulded individually from composite materials, as will be described in further detail below, before being bonded together along their respective leading and trailing edges 26, 28.

A pair of reinforcing structures 30, known as shear webs, are located inside the blade shell. The shear webs 30 are bonded between the windward and leeward half shells 22, 24 and extend longitudinally inside the blade 10. The shear webs 30 reinforce the blade and transfer shear loads from the blade 10 to the wind turbine hub (not shown) in use.

The windward and leeward half shells 22, 24 are each made up from a plurality of materials arranged in various layers. Each half shell 22, 24 comprises an outer skin 32 and an inner skin 34, which are formed from glass-fibre reinforced plastic (GFRP).

Between the skins 32, 34, the half shells 22, 24 comprise longitudinally-extending reinforcing structures 36 known as spar caps' which extend in the spanwise direction S of the blade 10 (i.e. perpendicular to the plane of the page in Figure 2). The spar caps 36 are each made up of a stack of strips 38 of reinforcing material, for example carbon-fibre reinforced plastic (CFRP). The shear webs 30 referred to above are bonded between opposed spar caps 36 of the windward and leeward shells 22, 24, as shown in Figure 2.

Also between the inner and outer skins 34, 32, the half shells 22, 24 comprise panels of lightweight core material 40, typically foam. These are generally provided on either side of the spar caps 36 and between the spar caps 36.

The composition of the half shells 22, 24 varies along the length of the blade 10 depending upon the shape and the structural requirements of the blade 10 at any given position. For example, the blade 10 is very thin and narrow near the tip end 14, and this region of the blade 10 tends to be made up primarily of GFRP, with little or no core material 40 being used.

The half shells 22, 24 are each formed in respective half moulds in accordance with a lay-up process as will now be described briefly with reference to Figures 3a-e.

Referring first to Figure 3a, this is a chordwise section through part of a wind turbine blade mould, specifically a windward half mould 42 for moulding the windward half shell 22. The lay-up process begins with the application of a gelcoat (not shown) to the surface 44 of the mould 42. Next, various glass-fibre fabric layers 45 are arranged one on top of another to form the outer skin 32. Specifically, in this example, a base layer 46 of glass fibre fabric having a triaxial weave (so-called triax') is placed on the gel coat.

The base layer 46 covers substantially the entire surface 44 of the mould 42. The base layer 46 itself may comprise more than one layer of fabric, and the or each layer is typically subdivided into a plurality of sections which are arranged individually on the mould surface 44. A plurality of further layers 48 of glass-fibre fabric are then arranged at various locations on top of the base layer 46. In this example, the further layers 48 include some layers having unidirectional fibres (so-called ud') and other layers having fibres woven together with a biaxial weave (so-called biax').

Referring now to Figure 3b, the lay-up process continues with the various foam panels 40 referred to above being positioned on top of the glass-fibre layers 45. For ease of illustration, the individual glass-fibre layers 46, 48 forming the outer skin 32 are not shown in Figure 3b. The foam panels 40 in this example are positioned on top of the thicker regions of the layers 45 forming the outer skin 32, i.e. on top of the further glass-fibre layers 46 that were arranged previously on top of the base layer 46 (see Figure 3a).

Once the foam panels 40 have been positioned, distinct spanwise channels 50 are defined in between the panels 40.

Referring now to Figure 3c, a plurality of strips 38 of CFRF are then stacked one on top of another in the spanwise channels 50 between the foam panels 40 to form the spar caps 36 shown in Figure 2.

Referring to Figure 3d, once the spar caps 36 have been assembled in the mould 42, a plurality of further layers 52 of glass-fibre fabric are then arranged over the top of the various layers to form the inner skin 34. This completes the lay-up process.

Referring now to Figure 3e, once all of the layers forming the windward shell 26 have been arranged in the mould 42 to form the lay-up, the lay-up is covered with a vacuum film 54, which is sealed against the mould surface using sealing tape 56 to form a sealed region 58 enclosing the lay-up. Air is then removed from the sealed region 58 using a vacuum pump to create a vacuum inside the sealed region 58. Resin is then admitted into the evacuated sealed region 58. The resin infuses between all of the various layers of the lay-up. The resin is then cured, causing it to harden and bond all of the layers together.

A substantially identical lay-up and moulding process is used to form the leeward half shell2B.

Modern wind turbine blades are very large structures, and there is a continual drive to produce blades of increasing size to capture more energy from the wind. Presently, utility scale wind turbine blades are up to 80 metres in length and have a width of more than 5 metres in some places. Given the large size of the blades, it will be appreciated that the lay-up process described above is time-consuming. At present, the lay-up process may take several days or weeks to complete.

In order to meet the increasing demand for wind turbines, and more generally to increase the efficiency of blade manufacture, there is a continual drive to improve the blade manufacturing process to reduce the takt time of blade production.

Summary of the invention

Against this background the present invention provides a kit of materials for arranging in a wind turbine blade mould to form part of a wind turbine blade shell. The kit comprises a base layer of fibrous fabric and a core layer of core material arranged on top of the base layer. The layers of the kit are shaped to form part of a wind turbine blade shell and are attached together such that the kit can be arranged in a blade mould as a single unit.

The present invention allows the various layers forming the blade shell to be pre-kitted together offline, i.e. outside of the blade mould. Accordingly, several layers of the blade shell can be arranged in the mould simultaneously in a single operation, which significantly reduces the time in which the mould is monopolised for making a blade, and hence significantly reduces the takt time of blade production.

The kits comprise at least the base layer, which may form part of the outer skin of the blade, and the core material. Whereas in the prior art lay-up process these layers are assembled individually in the mould, the kit allows the core material to be laid-up simultaneously with the outer skin. Positioning the core material correctly in the mould was a difficult and time consuming process with the prior art lay-up method. The kits allow the time-consuming step of ensuring the correct relative positions of the shell materials to be performed offline, for example in advance of the final lay-up process.

The kit may also include other shell materials. In a preferred embodiment the kit includes one or more under-layers of fibrous fabric arranged between the base layer and the core layer. The kit preferably also includes one or more over-layers of fibrous fabric arranged on top of the core layer. The fibrous fabric is preferably glass-fibre fabric, but may instead comprise other suitable reinforcing fibres such as carbon fibres. The layers of the kit are preferably stitched together. However, other suitable means of attaching the layers together in the kits may be employed, for example the various layers may be held together by means of adhesives, such as adhesive tape.

The core layer preferably comprises a plurality of core panels of core material. The core material is preferably lightweight material such as foam, balsa, polystyrene etc. In a particularly advantageous embodiment, the core panels are spaced apart to define channels between adjacent panels. When the kits are arranged in a mould, longitudinally-extending reinforcing structures such as spar caps can be arranged in the channels. Ensuring the correct position of spar caps in the mould was previously a difficult and time-consuming task. However, the channels conveniently serve to locate the spar caps and thus reduce the time required to position the spar caps correctly in the mould.

The core panels preferably comprise mating features for mating with complementary mating features of core panels of an adjacent kit when the kits are assembled in the mould. The mating features serve to connect the panels together and maintain the alignment between the panels.

In a preferred embodiment, the base layer has a width substantially equal to a chordwise width of the blade mould. Accordingly, the kit may be arranged in the mould in a chordwise direction. The kit advantageously comprises the entire width of the blade shell between the leading and trailing edges of the blade. A plurality of kits may be arranged in the mould, with each kit comprising a spanwise section of the blade shell.

The invention also provides a method of making a wind turbine blade. The method comprises: providing a wind turbine blade mould, the mould extending in a spanwise direction between a root end and a tip end, and the mould extending in a chordwise direction between a leading edge and a trailing edge; and arranging a kit of materials, as described above, in the mould to form part of a shell of the blade.

The method preferably comprises assembling the kit outside the mould and transferring the kit to the mould. Preferably the method comprises assembling the kit on a substantially flat surface, for example on a table or on the factory floor. The method may involve lifting and placing the kit in the mould. The kit may be suspended above the mould, moved into position, and lowered into the mould. The method preferably comprises arranging a plurality of kits in the mould. Preferably the method comprises connecting the respective core layers of adjacent panels together. The method may involve arranging each kit in the mould in a chordwise direction.

The core layer preferably comprises a plurality of core panels spaced apart in a chordwise direction to form spanwise channels in-between. The method may involve arranging one or more longitudinally-extending reinforcing structures on top of the kit, for example in the spanwise channels. The reinforcing structure(s) preferably extend substantially in the spanwise direction of the mould. The one or more reinforcing structures preferably comprise a spar cap. The spar cap may include a plurality of strips of reinforcing material. The method may comprise stacking the strips on top of the kit.

The method may comprise arranging one or more cover patches over the reinforcing structure(s). The cover patches may comprise a plurality of fibrous fabric layers attached together to form a kit. The layers of the cover patches may be similar to the over-layers and preferably overlap the respective over-layers. The method may further involve admitting resin into the mould in a VARTM process.

The invention also provides a wind turbine blade made according to the above method, and a wind turbine comprising such a wind turbine blade.

Brief description of the drawings

Figures 1-3 have already been described above by way of background to the present invention. In order that the present invention may be more readily understood, embodiments of the invention will now be described in further detail, by way of example only, with reference to the following figures, in which: Figures 4(a)-(d) show the various stages involved in assembling a kit according to an embodiment of the present invention; Figure 5 shows a plurality of kits being arranged in a wind turbine blade mould; Figure 6 is a cross-sectional view of the mould showing spar caps being arranged on top of the kits; Figure 7 shows cover patches being arranged on top of the kits; and Figures 8(a) and (b) are schematic cross-sectional views of the cover patches being arranged in overlapping relation with upper layers of the kits.

Detailed description

Figures 4a-4d show various stages in the assembly of a kit 60 for making part of a wind turbine blade shell 20 (see Figure 2) according to an embodiment of the present invention. The kit 60 is suitable for use in the manufacture of the wind turbine blade 10 shown in Figures 1 and 2, the composition of which has already been described above

byway of background.

Referring to Figure 4a, this shows the initial stage of assembling the kit 60 in which a plurality of glass-fibre layers 62, 64 are stacked one on top of another. These layers 62, 64 will ultimately form part of the outer skin 32 of the blade shell 20 (see Figure 2). The kit 60 is assembled on a flat surface such as a table or the factory floor, and comprises a substantially-rectangular base layer 62 comprising one or more layers or plies' of glass-fibre fabric. The base layer 62 has a width indicated by the arrow W and a length indicated by the arrow L. In this example, the width W of the base layer 62 (and hence the width of the kit 60) is greater than its length L. A plurality of glass-fibre fabric mats 64, referred to hereinafter generally as under-layers' 64 are stacked on top of the base layer 62. The under-layers 64 correspond to the further layers 48 described above by way of introduction in relation to Figure 3(a), and may have any suitable composition, for example they may be ud, biax or triax, according to the structural requirements of the blade 10. In this example these layers 64 have substantially the same length as the base layer 62, but are not as wide. The under-layers 64 are arranged in three stacks 66 on top of the base layer 62. The stacks 66 are spaced apart relative to one another in the widthwise direction W of the kit 60 such that a pair of longitudinally-extending channels 68 are defined between the stacks 66.

Referring next to Figure 4b, a plurality of foam core panels 70 are arranged respectively on top of the stacks 66 of under-layers 64. Accordingly, the under-layers 64 are thereby located underneath the core panels 70, i.e. between the core panels 70 and the base layer 62. The foam panels 70 in this example have a length and width similar to the length and width of the under-layers 64. Accordingly, the foam panels 70 serve to increase the height of the three stacks 66 and thereby further define the longitudinal channels 68 between the stacks 66.

The foam panels 70 have connecting features 72a, 72b at each end. Specifically, a first end 73 of the foam panels 70 includes a protruding male connecting member 72a, and a second end 74 of the panels 70 includes a female connecting member 72b in the form of a cut-out portion. In this example, the connecting features 72a, 72b are shaped similar to the connecting features of a jigsaw puzzle. When the kit 60 is arranged in the mould with other kits, the connecting features 72a, 72b enable the foam panels 70 to be connected to other foam panels in adjacent kits.

Referring now to Figure 4c, this shows a plurality of glass-fibre mats 76a-c arranged on top of the foam core panels 70. Specifically, in this example, three mats 76a-c are stacked on top of each of the foam panels 70. These additional layers 76a-c are referred to herein generally as over-layers'. The over-layers 76a-c each have substantially the same length but vary in width. The widest over-layer is the lowermost layer 76a, which is arranged directly on top of the foam panels 70; the narrowest over-layer is the uppermost over-layer 76c; and the intermediate over-layer 76b is of intermediate width. Accordingly, the over-layers 76a-c vary in width in a stepwise fashion, i.e. they become progressively narrower moving up the stack 66.

Referring to Figure 4d, once the base layer 62, under-layers 64, foam panels 70, and over-layers 76a-c have been stacked, the various layers are stitched together along a plurality of stitch lines 78 extending in the widthwise direction W of the kit 60. The stitches serve to hold all of the various layers together in the kit 60 so that the kit 60 can be handled and assembled in the mould as a single unit, as will now be described with reference to Figures 5 to 8.

Referring now to Figures, this shows the kits 60 being positioned in a wind turbine blade mould 80. The kits 60 are arranged side-by-side in the mould 80 moving in a spanwise direction S of the mould 80, with each kit 60 forming a spanwise section of the blade shell. It will be appreciated from Figure 5 that each kit 60 has a width corresponding to the distance over the mould surface 82 between the leading edge 84 and the trailing edge 86 of the mould 80, or in other words the width of each kit 60 comprises the full width of the blade shell.

All of the kits 60 required to form a blade shell are initially stacked on a table 88 adjacent to the blade mould 80. The kits 60 are stacked in the order in which they will be placed into the mould 80, with the first kit 60 being at the top of the pile 89. In order to place a kit in the mould 80, a pair of operators 90 in this example each grasp an edge 92 of the kit 60, i.e. an edge 92 of the base layer 62 in this example. The operators 90 then lift the kit 60 from the pile 89 of kits 60 on the table 88, carry the kit 60 to the mould 80, and place the kit 60 in the appropriate spanwise location in the mould 80. The kits 60 are arranged in a chordwise direction C in the mould 80, i.e. between the leading and trailing edges 84, 86 of the mould 80. In alternative examples of the invention! the kits 60 may be suspended from a gantry above the mould 80 (such as the gantry 102 in Figure 6) and lowered from the gantry into the mould 80 when required. The gantry may be moveable in the spanwise direction of the mould 80 along a set of parallel rails disposed respectively on either side of the mould 80.

As shown in Figure 5, prior to the kit 60 being placed in the mould 80, a third operator 94 applies an adhesive 96 onto the mould surface 82 in the region in which the kit 80 is to be placed. The kit 80 is then placed on top of the adhesive 96, which serves to maintain the kit 80 in position and prevents the kit 80 from sliding down steeply inclined sections of the mould surface 82.

Still referring to Figure 5, once the kit 60 has been arranged in the mould 80, a fourth operator 98 smooths the surface of the kit 60 using a brush 100 or other suitable implement. This forces any wrinkles or folds out of the kit 60 and ensures that the kit 60 is sitting flush against the surface 82 of the mould 80.

As mentioned previously in relation to Figure 4(b), the foam panels 70 are provided with connecting features 72a, 72b. Referring still to Figure 5, as each kit 60 is laid in the mould 80, the male connecting features 72a at the first ends 73 of the foam panels 70 in one kit 60 are connected with the female connecting features 72b in the foam panels 70 of an adjacent kit 60. The connecting features 72a, 72b maintain the relative alignment between the kits 60 and substantially prevent the kits 60 from moving relative to one another in the mould 80.

This process is continued, kit by kit, until substantially the entire mould surface 82 has been covered. As the dimensions of the mould 80 vary along its length, and the structural requirements of the blade shell also vary along its length and width, it follows that the shape, size and composition of the kits 60 also vary accordingly, with each kit 60 having the requisite composition of the blade shell at the particular spanwise location of the blade where the kit is to be arranged.

It was described above in relation to Figure 4(a) and (b), that the kits 60 include longitudinal channels 68 between foam core panels 70. Referring still to Figure 5, when the kits 60 are arranged in the mould 80, these channels 68 are aligned in the spanwise direction S of the mould 80. The channels 68 of adjacent kits 60 are aligned with one another to define spanwise channels 68 in the mould 80.

Referring now to the cross-sectional view of Figure 6, once the kits 60 have been arranged in the mould 80, spar caps 36 are then arranged on top of the kits 60 in the spanwise channels 68. Specifically, in this example, a plurality of pultruded strips 38 of CFRP are stacked one on top of the other in the spanwise channels 68. The pultrusions 38 are suspended from a gantry 102 above the mould 80 and lowered into the spanwise channels 68. The spanwise channels 68 defined by the kits 60 conveniently serve to locate the pultrusions 38 quickly and easily, which is a particular advantage over prior art lay-up methods where it can be difficult to ensure the pultrusions 38 are positioned correctly.

Referring now to Figure 7, once the spar caps 36 have been arranged in the mould 80, a plurality of cover patches 104 are then placed over the spar caps 36 (the spar caps have been omitted from Figure 7 for clarity). The cover patches 104 are each in the form of a kit and comprise a plurality of glass-fibre layers 1 06a-c stitched together. In this example the layers 1 USa-c of the cover patches 104 correspond with the over-layers 76a-c of the kits 60 described above (see Figure 4(c)). Hence, the cover patches 104 in this example each comprise three glass-fibre layers 1 06a-c.

Referring to the schematic cross-sectional view of Figure 8(a), this shows how the cover patch 104 fits against the over-layers 76a-c of the kits 60. The three layers 1 06a-c of the cover patches 104 vary in width in a stepwise manner, and become progressively narrower moving down the stack, i.e. in a reverse stepwise manner compared to the over-layers 76a-c of the kits 60. Accordingly, when the cover patches 104 are arranged over the spar caps, the various layers 1 USa-c of the cover patch overlap the corresponding over-layers 76a-c, as shown schematically in Figure 8(b).

Once all of the kits 60, spar caps 36 and cover patches 104 have been arranged in the mould 80 to form a lay-up, the lay-up is covered with a vacuum film and sealed against the mould surface 82 to form a sealed region enclosing the lay-up. Air is then pumped out of the sealed region using vacuum pumps to form a substantially evacuated sealed region enclosing the lay-up. Resin is then admitted into the substantially evacuated sealed region in a VARTM process. The resin infuses between all of the various layers and components. The resin is then cured, causing it to harden and bond all of the components together to form the blade shell.

By assembling the kits 60 offline in advance of the lay-up process, the present invention provides an easier and more accurate lay-up process than the prior art method described by way of background with reference to Figure 3. Since the core material 70 and other structural layers of the shell are advantageously included in the kit 60, the lay-up process of the present invention involves just a few stages, in comparison to the many stages involved in the prior art method which requires each layer to be arranged in the mould 80 individually. Accordingly, the present invention is also much quicker than the prior art lay-up process and hence significantly reduces the takt time of blade production.

Many modifications may be made to the examples described above without departing from the scope of the present invention as defined in the accompanying claims. In particular the composition of the kits 60 may vary in other embodiments. For example, the kits 60 of other embodiments may involve different numbers of layers in the base layer 62, under-layers 64 and over-layers 76a-c, or may not include under-layers 64 and/or over-layers 76a-c.

Whilst the kits 60 described above generally comprise three discrete stacks 66 of under-layers 64, foam panels 70 and over-layers 76a-c, in other examples the kits 60 may have different configurations. For example there may be greater or fewer than three stacks 66, and/or one or more layers of one stack 66 may simultaneously form part of a neighbouring stack 66 in other embodiments.

Whilst glass-fibre layers have been mentioned above by way of example, the layers may be any other suitable material employed in the construction of blade shells. The layers are not necessarily structural layers and may have other functionality. For example one or more layers in the kit 60 may be part of a lightning conductor system, or part of a radar absorbing system.

Claims

Claims 1. A kit of materials for arranging in a wind turbine blade mould to form pad of a wind turbine blade shell, the kit comprising: a base layer of fibrous fabric; and a core layer of core material arranged on top of the base layer, wherein the layers of the kit are shaped to form part of a wind turbine blade shell and are attached together such that the kit can be arranged in a blade mould as a single unit.
2. The kit of Claim 1, further comprising one or more under-layers of fibrous fabric arranged between the base layer and the core layer.
3. The kit of Claim 1 or Claim 2, further comprising one or more over-layers of fibrous fabric arranged on top of the core layer.
4. The kit of any preceding claim, wherein the layers of the kit are stitched together.
5. The kit of any preceding claim, wherein the core layer comprises a plurality of core panels of core material.
6. The kit of Claim 5, wherein the core panels are spaced apart to define channels between adjacent panels.
7. The kit of Claim S or Claim 6, wherein the core panels comprise mating features for mating with complementary mating features of core panels of an adjacent kit to connect the panels together when the kits are arranged in a wind turbine blade mould.
8. The kit of any preceding claim, wherein the base layer has a width substantially equal to a chordwise width of the mould in which the kit is to be arranged.
9. The kit of any preceding claim, wherein the fibrous fabric is glass-fibre fabric.
10. The kit of any preceding claim, wherein the core material is foam or balsa.
11. A wind turbine blade having a blade shell made from a plurality of kits as claimed in any preceding claim.
12. A method of making a wind turbine blade, the method comprising: providing a wind turbine blade mould, the mould extending in a spanwise direction between a root end and a tip end, and the mould extending in a chordwise direction between a leading edge and a trailing edge; and arranging a kit of materials, as claimed in any preceding claim, in the mould to form part of a shell of the blade.
13. The method of Claim 12, comprising assembling the kit outside the mould and transferring the kit to the mould.
14. The method of Claim 12, comprising assembling the kit on a substantially flat surface.
15. The method of any of Claims 12 to 14, comprising lifting and placing the kit in the mould.
16. The method of any of Claims 12 to 15, comprising suspending the kit above the mould and lowering the kit into the mould.
17. The method of any of Claims 12 to 16, comprising arranging a plurality of kits, as claimed in any of Claims 1 to 11, in the mould.
18. The method of Claim 17, comprising connecting the respective core layers of adjacent panels together.
19. The method of Claim 17 or Claim 18, comprising arranging each kit in the mould in a chordwise direction.
20. The method of any of Claims 12 to 19, comprising arranging one or more longitudinally-extending reinforcing structures on top of the kit, the reinforcing structure(s) extending substantially in the spanwise direction of the mould.
21. The method of Claim 20, wherein the one or more reinforcing structures is a spar cap comprising a plurality of strips of reinforcing material, and the method comprises stacking the strips on top of the kit.
22. The method of Claim 20 or Claim 21, wherein the core layer comprises a plurality of core panels spaced apart in a chordwise direction to form spanwise channels in-between, and wherein the method comprises arranging the reinforcing structure(s) in the spanwise channels between the core panels.
23. The method of any of Claims 20 to 22, further comprising arranging one or more cover patches over the reinforcing structure(s).
24. The method of Claim 23, wherein the cover patches comprise a plurality of fibrous fabric layers attached together to form a kit.
25. The method of any of Claims 11 to 24, comprising admitting resin into the mould in a VARTM process.
26. A wind turbine blade made according to the method of any of Claims 11 to 25.
27. A wind turbine comprising the wind turbine blade of Claim 26.