Improvements relating to wind turbine blades
A family of wind turbine blades with customizable reinforcing arrangements using primary and secondary fiber strips addresses the over-specification issue, optimizing stiffness and cost for varying wind conditions while maintaining performance and reducing manufacturing complexity.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- VESTAS WIND SYSTEMS AS
- Filing Date
- 2025-11-17
- Publication Date
- 2026-05-21
Smart Images
Figure DK2025050206_21052026_PF_FP_ABST
Abstract
Description
[0001] IMPROVEMENTS RELATING TO WIND TURBINE BLADES
[0002] Technical Field
[0003] The present invention relates generally to wind turbine blades, and more specifically to wind turbine blades that are structurally optimised for the conditions at a particular site.
[0004] Background
[0005] The rotor blades of a horizontal axis wind turbine rotate through a substantially vertical plane in use. The weight of the rotor blade itself generates alternating tensile and compression forces along its length as it rotates which results in cyclic loading of each rotor blade. In particular, the alternating tensile and compression forces are experienced along the leading edge of a blade and along the trailing edge of a blade. These loads are commonly referred to in the art as "edgewise loads", or they are sometimes known as "chordwise loads". The edgewise loads are a result of gravitational loading and this edgewise loading increases from the tip of the blade to the root of the blade.
[0006] The rotor blades during operation are also subjected to flapwise loads. "Flapwise" is typically used in the art to refer to the direction substantially normal to the chord of the blade, where the "chord" is the distance between the leading edge and the trailing edge, i.e. the flapwise direction is the direction in which the aerodynamic lift acts. The flapwise direction is perpendicular to the edgewise direction.
[0007] Wind turbine manufacturers usually produce several different wind turbine platforms, each with different power ratings. The blades of each platform are carefully designed with a particular size and shape, e.g. length and aerodynamic profile, that enables the turbine to generate its rated power. At the same time, the wind turbine blades must be able to withstand the various loads experienced in use, including the edgewise and flapwise loads discussed above. These loads will vary from site to site and so the blades are generally built to withstand the maximum loads that may be experienced across all potential sites.
[0008] However, as wind conditions may vary considerably from one site to another, this approach often leads to the blades being over-specified for relatively low wind sites. In other words, the blades may be built to withstand loads that are considerably greater than the loads that will be experienced at a site. Some manufacturers already offer different blades designed for a particular wind turbine platform. The blades may have slightly different lengths or profiles and may be designed to suit different sites or wind conditions. The blades may be produced in different moulds, or in flexible moulds that can be adapted to vary the size or shape of the blades. Whilst these solutions may allow some optimisation for site conditions, they also add considerable cost and complexity to the manufacturing process in view of the need for additional moulds or expensive flexible tooling, which may require additional factory space or additional time to re-configure the tooling between production runs.
[0009] Against this background, the present invention aims to provide a more cost effective and / or simpler solution for producing blades that can be optimised for a particular site.
[0010] Summary of the invention
[0011] According to the present invention there is provided a family of wind turbine blades of substantially equal length and of substantially the same external shape. The family comprises at least a first blade and a second blade, wherein each blade comprises: a blade shell that extends longitudinally in a spanwise direction from a root end to a tip end and transversely in a chordwise direction between a leading edge and a trailing edge, the blade shell being formed from first and second opposing half shells; a first main reinforcing arrangement associated with the first half shell and a second main reinforcing arrangement associated with the second half shell; a first rear reinforcing arrangement associated with the first half shell and spaced from the first main reinforcing arrangement in the chordwise direction towards the trailing edge, and a second rear reinforcing arrangement associated with the second half shell and spaced from the second main reinforcing arrangement in the chordwise direction towards the trailing edge; the first main reinforcing arrangement and the first rear reinforcing arrangement being formed of layers extending longitudinally in the spanwise direction, the layers of the first main reinforcing arrangement being arranged in a plurality of stacks of layers comprising at least an inner stack closest to the trailing edge and an outer stack closest to the leading edge, and / or the layers of the first rear reinforcing arrangement being arranged in a plurality of stacks of layers comprising at least an inner stack closest to the leading edge and an outer stack closest to the trailing edge. Each stack comprises at least: an innermost layer being the layer within the stack that is closest to an interior of the blade; an outermost layer being the layer within the stack that is closest to an exterior of the blade; and optionally one or more intermediate layers between the innermost layer and the outermost layer. Each of the said layers comprises a strip of fibrous composite material. The strips are selected from primary strips and secondary strips, the primary strips being made of fibres having a first Young’s modulus and the secondary strips being made of fibres having a second Young’s modulus lower than the first Young’s modulus.
[0012] At a first spanwise position along the first blade, the said layers of the outer stack of the first main reinforcing arrangement and / or the said layers of the outer stack of the first rear reinforcing arrangement comprise a primary strip. At a corresponding first spanwise position along the second blade, the said layers of the outer stack of the first main reinforcing arrangement and / or the said layers of the outer stack of the first rear reinforcing arrangement comprise a primary strip. At the corresponding first spanwise position along the second blade the inner stack of the first main reinforcing arrangement and / or the inner stack of the first rear reinforcing arrangement comprises a greater number of layers comprising a secondary strip than the inner stack of the corresponding reinforcing arrangement(s) of the first blade at the corresponding first spanwise position of the first blade.
[0013] The present invention enables a family of blades to be produced with different stiffnesses and at different costs such that the blades can be customised for the conditions at a particular wind site. For example, lower stiffness blades can be produced at lower cost for sites having lower wind loads without sacrificing the performance or quality of the blades. The same blade tooling can be used to make different blades within the family thus avoiding the need for additional or reconfigurable blade tooling. The invention also provides an innovative and efficient way of combining different materials within the reinforcing arrangements.
[0014] The first main reinforcing arrangement and the second main reinforcing arrangement may be mutually opposed. The first rear reinforcing arrangement and the second rear reinforcing arrangement may be mutually opposed.
[0015] A reinforcing arrangement may comprise one or more reinforcing structures, for example one or more spar caps or other stiffening structures, such as a stringer. In some embodiments, a reinforcing arrangement may consist of a single reinforcing structure, e.g. a single spar cap. In other embodiments, a reinforcing arrangement may consist of multiple reinforcing structures, e.g. multiple spar caps that are mutually spaced apart in the chordwise direction. For example, a main reinforcing arrangement may comprise two spar caps with a space in-between.
[0016] Each of the said layers may extend in the spanwise direction between a first end facing toward the root end of the blade and a second end facing toward the tip end of the blade. Hence, each of the said strips of fibrous composite material may extend in the spanwise direction between a first end facing toward the root end of the blade and a second end facing toward the tip end of the blade.
[0017] Each layer of the said layers may comprise a single strip of fibrous composite material that extends in the spanwise direction between the first end facing toward the root end of the blade and the second end facing toward the tip end of the blade. Each of the said strips may be continuous along an entire length of the respective layer between its first and second ends. Each of the said strips may be homogenous along an entire length of the respective layer between its first and second ends. Each strip may be homogeneous in the sense that its material composition does not vary along the length of the respective layer. Preferably, each strip is not formed by combining different materials in separate spanwise sections. By ensuring that each strip extends continuously between the first end and the second end and remains homogeneous along its entire length, the reinforcing arrangement provides predictable and uniform mechanical properties along the span of the blade. This eliminates local stiffness discontinuities that could arise from material transitions within a strip, thereby reducing stress concentrations and improving fatigue resistance.
[0018] The fibres of the primary and secondary strips preferably extend predominantly in the spanwise direction. For example, they may comprise mainly unidirectional fibres. Preferably the primary and secondary strips are pultrusions. Pultrusions are readily obtainable and comprise fibres within a cured resin matrix. Pultrusions are easy to store and handle and can be cut to a desired length. Pultrusions can be stacked easily in the blade moulds during the blade production process.
[0019] Aside from pultrusion, the primary and secondary strips could be formed by other methods such as moulding or belt pressing. In an example, the strips forming the first main reinforcing arrangement are pultrusions and the strips forming the first rear reinforcing arrangement are formed by moulding. Compared to a blade where both the strips of the first main reinforcing arrangement and the strips of the first rear reinforcing arrangement are pultrusions, this arrangement may provide a lower cost but still maintain structural benefits.
[0020] An interlayer may be arranged between said layers in the stacks. The interlayers may comprise a glass ply. The interlayers do not comprise the primary strips or the secondary strips. The said layers of the stacks are the strips. In other words, the said layers consist of the strips. The said layers do not include interlayers such as glass plies.
[0021] The primary strips and the secondary strips have different fibre compositions. The primary strips are preferably made exclusively or predominantly from fibres having the first Young’s modulus. The secondary strips are preferably made exclusively or predominantly from fibres having the second Young’s modulus.
[0022] The fibres having the first Young’s modulus are preferably carbon fibres. Accordingly, the primary strips may be made from carbon-fibre reinforced polymer (CFRP). The fibres having the second Young’s modulus are preferably glass fibres. Accordingly, the secondary strips may be made from glass-fibre reinforced polymer (GFRP). Other types of fibres could be used instead, for example aramid fibres.
[0023] Higher modulus fibres tend to be more expensive than lower modulus fibres. Accordingly, the secondary strips may advantageously be cheaper to produce than the primary strips. The incorporation of secondary strips into the reinforcing arrangements enables the cost of the blades to be reduced. The strips forming the reinforcing arrangements represent a significant proportion of the total blade cost, and therefore replacement of more expensive materials with less expensive materials can translate into a significant cost saving in the context of a single blade, and an even greater cost saving in the context of a wind turbine incorporating multiple such blades.
[0024] The second blade may differ from the first blade in that primary strips within inner stacks of the reinforcing arrangements of the first blade are replaced by secondary strips in the same positions within the inner stacks of the corresponding reinforcing arrangements of the second blade. Accordingly, the second blade may be cheaper to produce than the first blade. The first blade is preferably designed for wind loads of a first magnitude, and the second blade is preferably designed for wind loads of a second magnitude that is lower than the first magnitude. The replacement of primary strips with secondary strips enables blades to be produced at a lower cost for sites having lower wind loads.
[0025] The primary strips have a first stiffness in the spanwise direction and the secondary strips have a second stiffness in the spanwise direction, wherein the first stiffness is greater than the second stiffness.
[0026] The stiffness of an element is a measure which is indicative of the extent to which an object resists deformation in response to an applied force. Typically, the stiffness k is quantified as k = F / d, where F is a force and d is a displacement. The stiffness is different from the Young’s modulus of a material, but the stiffness of a given strip or reinforcing arrangement does depend on the Young’s modulus of the material or materials, from which it is made. For example, for an exemplary element the stiffness is k = E x A / L, where E is the Young’s modulus, A is cross-sectional area (transverse to direction of tension / compression) and L is the length of the element.
[0027] Reinforcing arrangements incorporating secondary strips will have a lower stiffness than an equivalent reinforcing arrangement made entirely from primary strips. Stiffness will also generally reduce as the number of secondary strips incorporated in the reinforcing arrangements increases. The incorporation of secondary strips within the reinforcing arrangements therefore allows blades to be made with a reduced stiffness, but without compromising the performance of the blade because the blade will be used at sites having lower wind loads. Accordingly, it is possible to reduce the stiffness of the blade by incorporating secondary strips into the reinforcing arrangements whilst maintaining strain levels in the blade, since the customised blades are built for sites where loads on the blade are expected to be lower.
[0028] The quantity of secondary strips can be selected to optimise a blade for a particular site, with lower wind sites enabling the incorporation of more secondary strips whilst maintaining strain levels in the blade at or below a predetermined level. The present invention therefore allows customised blades to be produced at a reduced cost for lower wind sites. The incorporation of the secondary strips in the inner stacks of the reinforcing arrangements is particularly advantageous because it maximises the edgewise stiffness of the blade in comparison to if the secondary strips were instead incorporated in the outer stacks. Each strip in the reinforcing arrangements contributes to the edgewise stiffness of the blade based upon its modulus and its distance from an edgewise neutral axis. The edgewise neutral axis is generally located between the first main reinforcing arrangement and the first rear reinforcing arrangement and is the axis about which strain levels are zero when the blade bends in the edgewise direction.
[0029] The strips of the inner stacks contribute less towards the edgewise stiffness of the blade than the strips of the outer stacks because they are located closer to the edgewise neutral axis. By incorporating the secondary strips in the inner stacks, the blade can be made cheaper whilst minimising any reduction in edgewise stiffness. The more expensive higher modulus material can be concentrated in the outer stacks where it contributes more significantly to the edgewise stiffness of the blade. At the same time, the less expensive lower modulus material can be concentrated in the inner stacks where it contributes less significantly to the edgewise stiffness of the blade. This arrangement therefore makes the most efficient use of the more expensive higher modulus material in the blade, i.e. the primary strips.
[0030] In each blade of the family, the layers of the first main reinforcing arrangement and / or the layers of the first rear reinforcing arrangement preferably have different lengths and terminate at different spanwise positions. Consequently, the reinforcing arrangements may vary in thickness in different regions of the blade, where different numbers of layers are present in the stacks.
[0031] In each blade of the family, the inner stack of the first main reinforcing arrangement and / or the inner stack of the first rear reinforcing arrangement may comprise a longest layer in said stack. In the second blade, the longest layer in the inner stack of the first main reinforcing arrangement preferably comprises a secondary strip and / or the longest layer in the inner stack of the first rear reinforcing arrangement preferably comprises a secondary strip.
[0032] In the second blade, a secondary strip in the inner stack of the first main reinforcing arrangement and / or a secondary strip in the inner stack of the first rear reinforcing arrangement preferably extends along an entire length of the respective reinforcing arrangement.
[0033] The first blade may comprise a secondary strip in the inner stack of the first main reinforcing arrangement and / or a secondary strip in the inner stack of the first rear reinforcing arrangement. In the first blade, a secondary strip in the inner stack of the first main reinforcing arrangement and / or a secondary strip in the inner stack of the first rear reinforcing arrangement preferably extends along an entire length of the respective reinforcing arrangement.
[0034] Incorporating secondary strips in the longest layers of the stacks is advantageous because it maximises the cost savings and enables the stiffness of the blade to be optimised along the whole length of the blade, or along most of the length of the blade.
[0035] In preferred embodiments, the outermost layers of the stacks are the longest layers in the stacks. Accordingly, at the first spanwise position along the second blade, the outermost layer of the inner stack of the first main reinforcing arrangement preferably comprises a secondary strip and / or the outermost layer of the inner stack of the first rear reinforcing arrangement preferably comprises a secondary strip.
[0036] In the second blade, a secondary strip in the inner stack of the first main reinforcing arrangement and / or a secondary strip in the inner stack of the first rear reinforcing arrangement preferably has substantially the same length and / or width and / or thickness as a primary strip in a corresponding position in the first blade.
[0037] Most preferably the secondary strips in the second blade have substantially identical dimensions to the primary strips in the first blade that they replace. The overall geometry of the reinforcing arrangements in the second blade may therefore be the same as the overall geometry of the reinforcing arrangements in the first blade.
[0038] At the first spanwise position along the first blade and at the corresponding first spanwise position along the second blade, the first main reinforcing arrangement of the first blade and the first main reinforcing arrangement of the second blade preferably have substantially the same cross-sectional area in a chordwise plane. At the first spanwise position along the first blade and at the corresponding first spanwise position along the second blade, the first rear reinforcing arrangement of the first blade and the first rear reinforcing arrangement of the second blade preferably have substantially the same cross-sectional area in a chordwise plane.
[0039] At the first spanwise position along the first blade and at the corresponding first spanwise position along the second blade, the first main reinforcing arrangement of the first blade and the first main reinforcing arrangement of the second blade preferably have the same number of stacks and the same number of layers within each stack.
[0040] At the first spanwise position along the first blade and at the corresponding first spanwise position along the second blade, the first rear reinforcing arrangement of the first blade and the first rear reinforcing arrangement of the second blade preferably have the same number of stacks and the same number of layers within each stack.
[0041] The reinforcing arrangements may therefore have the same geometry in each blade of the family. This advantageously allows the same tooling to be used to make any of the blades within the family.
[0042] At the first spanwise position along the first blade, each of the said layers of the outer stack of the first main reinforcing arrangement preferably comprises a primary strip and / or each of the said layers of the outer stack of the first rear reinforcing arrangement preferably comprises a primary strip. Accordingly, the outer stacks of the main and / or rear reinforcing arrangements of the first blade may be made entirely from primary strips.
[0043] At the first spanwise position along the first blade, each of the said layers of the inner stack of the first main reinforcing arrangement preferably comprises a primary strip and / or each of the said layers of the inner stack of the first rear reinforcing arrangement preferably comprises a primary strip. Accordingly, the inner stacks of the main and / or rear reinforcing arrangements of the first blade may be made entirely from primary strips.
[0044] Forming the reinforcing arrangements of the first blade entirely from primary strips maximises the strength and stiffness of the first blade, making it suitable for sites having relatively high wind loads. At the corresponding first spanwise position along the second blade, each of the said layers of the outer stack of the first main reinforcing arrangement preferably comprises a primary strip and / or each of the said layers of the outer stack of the first rear reinforcing arrangement preferably comprises a primary strip. Accordingly, the outer stacks of the main and / or rear reinforcing arrangements of the second blade may be made entirely from primary strips.
[0045] The outer stacks in the second blade may therefore be the same as the outer stacks in the first blade. In contrast, the inner stacks in the second blade may be modified in comparison to the first blade by including secondary strips in the inner stacks of the second blade in the same positions as primary strips in the inner stacks of the first blade.
[0046] At the corresponding first spanwise position along the second blade the inner stack of the first main reinforcing arrangement and / or the inner stack of the first rear reinforcing arrangement preferably comprises a secondary strip in a layer corresponding to the position of a primary strip in the corresponding reinforcing arrangement(s) of the first blade.
[0047] This arrangement makes efficient use of the more expensive higher modulus material in the second blade since it is concentrated in stacks furthest from the edgewise neutral axis. At the same time, the less expensive lower modulus material may be concentrated in the inner stacks of the second blade thus minimising any resulting reduction in edgewise stiffness since the inner stacks are closest to the edgewise neutral axis.
[0048] In each blade of the family, the first main reinforcing arrangement and / or the first rear reinforcing arrangement may further comprise one or more intermediate stacks of layers between the inner and outer stacks. At the first spanwise position along the blades each layer of the intermediate stack(s) may comprise a primary strip.
[0049] The intermediate stacks are further from the edgewise neutral axis than the inner stacks, and therefore contribute more towards the edgewise stiffness of the blade. It is therefore also desirable for these stacks to contain the higher modulus material, with the lower modulus material being concentrated in the inner stacks, which are closer to the edgewise neutral axis.
[0050] Any number of layers of the inner stacks of the second blade may comprise a secondary strip. When further secondary strips are incorporated in a stack having layers of varying length, these further secondary strips preferably form the second longest layer in the stack, and then the third longest layer and so on, depending upon the number of further secondary strips in the stack.
[0051] Accordingly, in the second blade, a second longest layer of the inner stack of the first main reinforcing arrangement may comprise a further secondary strip. A third longest layer of the inner stack of the first main reinforcement arrangement may comprise a further secondary strip. Similarly, in the second blade, a second longest layer of the inner stack of the first rear reinforcing arrangement may comprise a further secondary strip. A third longest layer of the inner stack of the first rear reinforcement arrangement may comprise a further secondary strip.
[0052] Incorporating further secondary strips in the longest layers of the inner stack is advantageous because it further maximises the cost savings and enables the stiffness of the blade to be optimised along most of the length of the blade.
[0053] The inner stacks of the second blade may also comprise one or more primary strips.
[0054] Accordingly, at the first spanwise position along the second blade, the inner stack of the first main reinforcing arrangement and / or the inner stack of the first rear reinforcing arrangement may comprise one or more primary strips in layers corresponding to the position of one or more primary strips in the corresponding reinforcing arrangement(s) of the first blade.
[0055] If an inner stack includes primary strips, these preferably form layers that are shorter than the layers of that stack comprising secondary strips. In the second blade, a shortest layer of the inner stack of the first main reinforcement arrangement may comprise a primary strip.
[0056] At the first spanwise position along the first blade, the innermost layer of the inner stack of the first main reinforcing arrangement preferably comprises a primary strip, and / or the innermost layer of the inner stack of the first rear reinforcing arrangement preferably comprises a primary strip. Similarly, at the corresponding first spanwise position along the second blade, the innermost layer of the inner stack of the first main reinforcing arrangement preferably comprises a primary strip, and / or the innermost layer of the inner stack of the first rear reinforcing arrangement preferably comprises a primary strip.
[0057] The innermost layer of a stack may be the shortest layer of the stack. The innermost layers of the stacks may also form an interface with a shear web in the case that the reinforcing arrangement is a spar cap. If the innermost layers in each blade of the family are formed of primary strips then the interfaces with shear webs may be unaffected by the incorporation of secondary strips within the reinforcing arrangements. This may facilitate use of substantially identical shear webs across different blades in the family.
[0058] Alternatively, at the corresponding first spanwise position of the second blade, each of the said layers of the inner stack of the first main reinforcing arrangement may comprise a secondary strip and / or each of the said layers of the inner stack of the first rear reinforcing arrangement may comprise a secondary strip. Accordingly, the inner stacks of the main and / or rear reinforcing arrangements of the second blade may be made entirely from secondary strips. Such arrangements allow the second blade to be made considerably cheaper because a significant proportion of less expensive lower modulus material is used in place of the more expensive higher modulus material.
[0059] Each blade of the family may further comprise a main shear web connected between the first and second main reinforcing arrangements and / or a rear shear web connected between the first and second rear reinforcing arrangements. The main shear web in the first blade may have the same height as the corresponding main shear web in the second blade and / or the rear shear web in the first blade may have the same height as the corresponding rear shear web in the second blade.
[0060] By keeping the geometry of the reinforcing arrangements substantially the same for different blades in the family, substantially identical shear webs may be used for different blades in the family. The need to purchase additional web tooling or reconfigure existing web tooling when customising blades for a particular site is therefore advantageously avoided.
[0061] Furthermore, as different blades in the family have substantially equal length and substantially the same external shape, they can be made in the same moulds, or in moulds having the same geometry as each other. Accordingly, the invention also provides a method of making the family of wind turbine blades described above, wherein the method comprises: forming at least part of the blade shell of the first blade in a first mould; and forming at least part of the blade shell of the second blade in a second mould, wherein the second mould is either the same mould as the first mould or is a further mould having the same mould surface geometry as the first mould, such that the first and second blades have substantially equal length and substantially the same external shape.
[0062] Forming at least part of a blade shell may comprise forming an entire half shell, or forming a section of a half shell. For example, the moulds may be configured to form a spanwise section of a blade shell in the case of a split blade that is produced in a number of sections to be connected together.
[0063] The method may further comprise making a main shear web or a rear shear web of the first blade using a first web tool; making a main shear web or a rear shear web of the second blade using a second web tool; wherein the second web tool is either the same web tool as the first web tool or is a further web tool having the same geometry as the first web tool, such that the shear web produced for the first blade is substantially the same as the shear web produced for the second blade.
[0064] Accordingly, the method may involve using the same web tooling or substantially identical web tooling to produce the shear webs for both the first and second blades.
[0065] Brief description of the drawings
[0066] Examples of the present invention will now be described with reference to the accompanying figures, in which:
[0067] Figure 1 shows a wind turbine comprising a plurality of wind turbine blades;
[0068] Figure 2 is an exploded perspective view of a wind turbine blade;
[0069] Figure 3 is a schematic chordwise cross-sectional view of a first wind turbine blade in a family of wind turbine blades; Figure 4 is a schematic spanwise cross-section through a reinforcing arrangement of the first blade;
[0070] Figure 5 is a schematic chordwise cross-sectional view of a second wind turbine blade in the family of wind turbine blades;
[0071] Figure 6 is a schematic spanwise cross-section through a reinforcing arrangement of the second blade;
[0072] Figure 7 schematically shows reinforcing arrangements of a third blade in the family of wind turbine blades; and
[0073] Figure 8 schematically shows reinforcing arrangements of a fourth blade in the family of wind turbine blades.
[0074] Detailed description
[0075] Figure 1 shows a horizontal axis wind turbine 10 comprising a rotor 12 mounted at the top of a tower 14. The rotor 12 comprises a plurality of wind turbine blades 16, three in this example, connected to a central hub 18.
[0076] The wind turbine 10 is optimised for the wind conditions at a particular site by selecting its blades 16 from a family of wind turbine blades, in which each blade in the family has the same external appearance, e.g. the same size and shape, but differs in terms of its strength and stiffness.
[0077] Figure 2 is a schematic exploded view of a wind turbine blade 16. The blade 16 comprises a blade shell that extends longitudinally in a spanwise direction (S) from a root end 20 to a tip end 22 and transversely in a chordwise direction (C) between a leading edge 24 and a trailing edge 26. The blade shell is formed from first and second opposing half shells 28, 30 which join together along their leading and trailing edges 24, 26 to form the blade shell.
[0078] The blade 10 further comprises a plurality of reinforcing arrangements 32a, 32b, 34a, 34b associated with the half shells 28, 30. The reinforcing arrangements 32a, 32b, 34a, 34b extend longitudinally in the spanwise direction (S), along the whole or part of the length of the blade 16. In this example, the reinforcing arrangements 32a, 32b, 34a, 34b are spar caps, which take up bending loads experienced by the blade 16 in use. Specifically, a first main spar cap 32a and a first rear spar cap 34a are associated with the first half shell 28, and a second main spar cap 32b and a second rear spar cap 34b are associated with the second half shell 30.
[0079] The first and second main spar caps 32a, 32b are mutually opposed. Likewise, the first and second rear spar caps 34a, 34b are mutually opposed. The rear spar caps 34a, 34b are spaced from the main spar caps 32a, 32b in the chordwise direction (C) towards the trailing edge 26. The main spar caps 32a, 32b provide the main structural support for the blade 16, whilst the rear spar caps 34a, 34b provide additional support near the trailing edge 26.
[0080] The blade 16 further comprises shear webs 36, 38, which resist shear loads between the half shells 28, 30. The shear webs 36, 38 are bonded between mutually-opposed spar caps 32a, 32b, 34a, 34b to form spars. The shear webs 36, 38 extend longitudinally in the spanwise direction (S). In this example, the blade 16 comprises a main shear web 36, which is bonded between the main spar caps 32a, 32b, and a rear shear web 38, which is bonded between the rear spar caps 34a, 34b.
[0081] Each shear web 36, 38 comprises a web panel 40 disposed between first and second mounting flanges 42, 44. In the assembled blade, the first mounting flanges 42 are bonded to the spar caps 32a, 34a associated with the first half shell 28 and the second mounting flanges 44 are bonded to the spar caps 32b, 34b associated with the second half shell 30.
[0082] Figure 3 is a schematic chordwise cross-sectional view of a first wind turbine blade 16a in the blade family, which is taken at a first spanwise position along the blade, as indicated by the line 3-3 in Figure 1. The blade has an airfoil profile in this location, and it can be seen that the main spar caps 32a, 32b are arranged in the region where the profile has its maximum thickness.
[0083] The spar caps 32a, 32b, 34a, 34b are embedded within the shell of the wind turbine blade, i.e. the blade has a so-called ‘structural shell’ design. More specifically, the spar caps 32a, 32b, 34a, 34b are arranged between an inner skin 46 of the blade and an outer skin 48 of the blade. The inner skin 46 forms an interior surface 50 of the blade, whilst the outer skin 48 forms an exterior surface 52 of the blade. The inner and outer skins 46, 48 are typically made from glass-fibre reinforced polymer (GFRP). In some regions of the blade, core material 54 is also provided between the inner and outer skins 46, 48.
[0084] As shown in Figure 3, the spar caps 32a, 32b, 34a, 34b are formed of layers arranged in a plurality of stacks of layers.
[0085] In each of the first and second main spar caps 32a, 32b, the layers are arranged in three stacks, which are arranged side-by-side in the chordwise direction (C). An inner stack 60 is arranged closest to the trailing edge 26, an outer stack 61 is arranged closest to the leading edge 24, and an intermediate stack 62 is arranged between the inner stack 60 and the outer stack 61.
[0086] In each of the first and second rear spar caps 34a, 34b, the layers are arranged in three stacks, which are arranged side-by-side in the chordwise direction (C). An inner stack 63 is arranged closest to the leading edge 24, an outer stack 64 is arranged closest to the trailing edge 26, and an intermediate stack 65 is arranged between the inner stack 63 and the outer stack 64.
[0087] Each stack comprises an innermost layer 66 and an outermost layer 68, as indicated in Figure 3 by way of example for the first main spar cap 32a. The innermost layer 66 is the layer within a stack that is closest to an interior 70 of the blade. The innermost layers 66 in this example are also the layers within the stacks that are closest to a shear web 36, 38. The outermost layer 68 is the layer within a stack that is closest to the exterior surface 52 of the blade. The stacks also include intermediate layers 72 between the innermost layer 66 and the outermost layer 68. The stacks may include any number of intermediate layers 72 depending on a required thickness of the stack.
[0088] Each of the layers of the stacks comprises a strip 74 of fibrous composite material. The strips 74 extend longitudinally in the spanwise direction (S) (as shown in Figure 4), i.e. perpendicular to the plane of Figure 3. The strips 74 in this example are generally rectangular in transverse cross-section, i.e. in the plane of Figure 3.
[0089] The strips 74 have a length dimension generally in the spanwise direction (S), a width dimension generally in the chordwise direction (C), and a thickness dimension generally perpendicular to the spanwise and chordwise directions. The strips have a great length and a relatively small thickness. For example, the thickness of a strip 74 may be 5 mm, and its length may be 80 metres or more.
[0090] As different parts of the blade may require different levels of reinforcement, the thickness of the spar caps 32a, 32b, 34a, 34b may vary in different regions of the blade. For example, the spar caps may be thinner near the tip 22 and / or root 20 of the blade and thicker in a central region of the blade. This can be achieved by using strips having different lengths such that the layers of the stacks terminate at different spanwise positions, as will now be discussed with reference to Figure 4.
[0091] Figure 4 is a schematic spanwise cross-section through a stack of layers, taken along the line 4-4 in Figure 3. In this example, the stack is the inner stack 60 of the first main spar cap 32a. The layers of the stack 60 have different lengths and terminate at different spanwise positions of the blade. The outermost layer 68 is the longest layer in the stack 60 and extends along an entire length of the spar cap. The innermost layer 66 is the shortest layer in the stack and extends along only part of the length of the spar cap 32a. The intermediate layers 72 have progressively decreasing lengths, moving through the stack 60 from the outermost layer 68 towards the innermost layer 66.
[0092] The other stacks 61, 62 of the spar cap 32a may have the same structure. Accordingly, the spar cap 32a tapers in thickness towards both of its ends, where only the outermost layer 68 is present. The spar cap has a maximum thickness in a central region, where all layers 66, 68, 72 are present. The ends of the strips 74 are also chamfered to provide a smooth tapering of the spar cap that avoids stress concentrations in the blade shell.
[0093] The strips 74 are preferably pultrusions, i.e. strips that are formed in a pultrusion process, as will be familiar to persons skilled in the art. The fibres in the strips preferably extend longitudinally along the length of the strip, i.e. in the spanwise direction (S). Accordingly, the pultrusions are relatively stiff in the spanwise direction and less stiff in the chordwise direction.
[0094] The strips 74 forming the spar caps of the first blade 16a in the family are all so-called ‘primary strips’. In this example, the primary strips are made of carbon fibre reinforced polymer (CFRP). Carbon fibres have a relatively high Young’s modulus, and therefore impart a relatively high spanwise stiffness k) to the strips 74 and hence to the spar caps. Carbon fibres are also advantageously lightweight. The first blade 16a therefore has a high strength to mass ratio. However, carbon fibres are relatively expensive, and therefore the first blade 16a is relatively expensive to produce.
[0095] The all-carbon structure of the spar caps 32a, 32b, 34a, 34b makes the first blade 16a particularly suitable for sites having relatively high loads. However, as wind loads vary from site to site, the first blade 16a may be over specified (i.e. excessively robust) for some wind turbine sites, such as sites where wind loads are lower. For such sites, a different blade within the family may be produced, which has the same size and shape as the first blade 16a, but differs in terms of its strength and stiffness. An example of such a blade will now be described with reference to Figure 5, which shows a second blade 16b within the family.
[0096] Referring to Figure 5, this is a schematic chordwise cross-sectional view of a second wind turbine blade 16b in the blade family, which is taken at the first spanwise position along the blade, as indicated by the line 3-3 in Figure 1. The second blade 16b has the same length and external shape as the first blade 16a. In most respects, the second blade 16b also has the same overall structure as the first blade 16a shown in Figure 3. Accordingly, the above discussion of the structure of the first blade 16a applies equally to the second blade 16b and will not be repeated. The following discussion will focus only on the differences between the second blade 16b and the first blade 16a.
[0097] In the second blade 16b, so-called ‘secondary strips’ 76 are used in place of primary strips 74 in certain positions within the spar caps 32a, 32b, 34a, 34b. The remaining strips of the spar caps are primary strips 74, i.e. the same as in the first blade 16a. The secondary (GFRP) strips 76 are indicated by shading in the figures, whereas the primary (CFRP) strips 74 are unshaded.
[0098] The secondary strips 76 in this example are made from glass-fibre reinforced polymer (GFRP). In this example, each of the spar caps 32a, 32b, 34a, 34b of the second blade 16b includes a GFRP strip 76 in the same position as a CFRP strip 74 in the first blade 16a (shown in Figure 3).
[0099] The GFRP strips 76 in the second blade 16b have the same dimensions as the corresponding CFRP strips 74 that they replace in the first blade 16a. Accordingly, the spar caps 32a, 32b, 34a, 34b of the second blade 16b have the same dimensions as the corresponding spar caps 32a, 32b, 34a, 34b of the first blade 16a. Glass fibres have a lower Young’s modulus than carbon fibres, and therefore the GFRP strips 76 have a lower spanwise stiffness than the corresponding CFRP strips 74 in the first blade 16a. Accordingly, the stiffness of the second blade 16b is reduced slightly in comparison to the stiffness of the first blade 16a. This means that strain levels within the second blade 16b would be increased for the same loads. However, as the second blade 16b will be subjected to lower wind loads than the first blade 16a - since it is designed for use at sites having lower wind loads - the strain levels of the two blades 16a, 16b in use at their respective sites will be similar.
[0100] Glass fibres are considerably cheaper than carbon fibres and so the incorporation of GFRP strips 76 in the spar caps of the second blade 16b makes the second blade less expensive to produce than the first blade 16a.
[0101] In each of the spar caps 32a, 32b, 34a, 34b of the second blade 16b, a GFRP strip 76 is provided in the inner stack 60, 63. This has been found to be the optimum position for incorporating the GFRP strips 76 because it minimises any reduction in the edgewise bending stiffness of the second blade 16b caused by the incorporation of lower modulus material, as will now be discussed.
[0102] Bending stiffness refers to the resistance of an object to bending deformation when subjected to a moment (bending force). Bending stiffness (K) can be quantified as K=E- 1, where E is the Young’s modulus of the object and I is its second moment of area. The second moment of area is a geometric property that reflects how the cross-section of the object is arranged relative to the neutral axis. The neutral axis is a line or plane through the object at which there is zero strain (i.e. no extension or compression) when the object bends about this axis. Each element of an object will contribute to the stiffness of the object based upon the Young’s modulus of the element and its distance from the neutral axis, since the second moment of area increases with the square of the distance of the element from the neutral axis.
[0103] Each strip 74, 76 forming a spar cap 32a, 32b, 34a, 34b therefore contributes to the edgewise stiffness of the blade based upon its Young’s modulus and its distance, at a given cross section, from the edgewise neutral axis N, which is indicated in Figure 5. As the strips in the outer stacks 61, 64 are further from the edgewise neutral axis N than the strips in the inner stacks 60, 63 they will contribute more to the edgewise stiffness of the blade than strips of the same Young’s modulus in the inner stacks 60, 63.
[0104] As the GFRP strips 76 in the second blade 16b have a lower Young’s modulus than the CFRP strips 74 in the first blade 16a that they replace, the edgewise stiffness of the second blade 16b will be slightly reduced in comparison to the first blade 16a. However, this reduction is minimised by locating the GFRP strips 76 in the inner stacks 60, 63 because these are the stacks that are closest to the edgewise neutral axis N.
[0105] The layers of the outer stacks 61, 64 in the second blade 16b each comprise a CFRP strip 74. This is the same arrangement as seen in the first blade 16a. Accordingly, the outer stacks 61, 64 of the second blade 16b are unchanged in comparison to the first blade 16a. Similarly, the layers of the intermediate stacks 62, 65 in the second blade 16b each comprise a CFRP strip 74. This is the same arrangement as seen in the first blade 16a. Accordingly, the intermediate stacks 62, 65 of the second blade 16b are unchanged in comparison to the first blade 16a.
[0106] The more expensive higher-modulus carbon material in the second blade 16b is therefore used in the most efficient positions, i.e. furthest from the edgewise neutral axis N, whilst the less expensive lower-modulus glass material is incorporated as close as possible to the edgewise neutral axis N so that the edgewise stiffness of the second blade 16b is maximised.
[0107] In each of the spar caps 32a, 32b, 34a, 34b of the second blade 16b, the GFRP strip 76 is provided as an outermost layer 68 of the inner stack 60, 63, i.e. the layer closest to the exterior surface 52 of the blade 16b. This is the longest layer of the stack, as can be seen in Figure 6.
[0108] Figure 6 is a schematic spanwise cross-section through the inner stack 60 of the first main spar cap 32a of the second blade 16b, taken along the line 6-6 in Figure 5. The layers of the stack have different lengths and terminate at different spanwise positions of the blade. The GFRP strip 76 forms the outermost layer 68, which is the longest layer in the stack 60. The GFRP strip 76 extends along an entire length of the spar cap 32a. Accordingly, the second blade 16b is optimised for lower load conditions over its entire length, or at least over most of its length. In contrast, if the innermost layer 66 of the stack was instead replaced with a secondary strip, e.g. a GFRP strip, the optimisation would only be seen in a central region of the blade, i.e. where the innermost layer 66 is present within the stack 60.
[0109] It will be appreciated that the configuration of the first main spar cap 32a of the second blade 16b shown in Figures 5 and 6 (i.e. both spanwise and transverse configurations) is the same as the configuration of the first main spar cap 32a of the first blade 16a shown in Figures 3 and 4, except that the longest CFRP strip 74 in the inner stack 60 of the first blade 16a is replaced with a GFRP strip 76 having the same dimensions in the second blade 16b. The same applies to the second main spar cap 32b, and the first and second rear spar caps 34a, 34b.
[0110] As the dimensions of the spar caps 32a, 32b, 34a, 34b do not change, the shear webs in the first and second blades are the same, i.e. they have the same dimensions including the same height. The shear webs 36, 38 for the two blades 16a, 16b in the family can therefore be produced using the same web tooling. This provides a significant manufacturing advantage because it enables customised blades to be produced having different stiffness properties without needing to provide additional tooling or without the need to reconfigure existing tooling. Furthermore, as the blade shell geometry is also the same for the two blades 16a, 16b, the same blade shell moulds can be used to make both blades in the family.
[0111] The two blades 16a, 16b described above are merely two examples of blades within the blade family. Many other blades within the family can be produced by replacing any number of primary strips 74 in one or more of the spar caps with secondary strips 76 having the same dimensions as the primary strips that they replace.
[0112] Further examples will now be described briefly, with reference to Figures 7 and 8, which show schematic representations of the spar arrangements of third and fourth blades within the blade family. The blade shells are omitted from these figures, but they would be the same as the shells shown in Figures 3 and 5.
[0113] Referring to Figure 7, in the third blade 16c the inner stacks 60 of the first and second main spar caps 32a, 32b each include two GFRP strips 76. The two strips 76 form, respectively, an outermost layer 68 and an intermediate layer 72 of the stack 60, the intermediate layer 72 being adjacent to the outermost layer 68. As previously described, the outermost layer 68 is the longest layer in the stack 60. The adjacent intermediate layer 72 in this example is the next longest layer. The rear spar caps 34a, 34b in the third blade 16c are the same as those in the second blade 16b and each include one GFRP strip 76 in the inner stack 63. The remaining strips of all spar caps are CFRP strips 74.
[0114] The third blade 16c is cheaper to produce than the second blade 16b because more of the carbon material in the spar caps is replaced with the cheaper glass material. The third blade 16c also has a lower stiffness than the second blade 16b and is therefore suited to lower wind sites than the second blade 16b.
[0115] Referring to Figure 8, in the fourth blade 16d the first main spar cap 32a is the same as the first main spar cap 32a of the second blade 16b, i.e. it includes a single GFRP strip 76 as the outermost layer 68 of the inner stack 60 - the remaining strips of the inner stack 60 are CFRP strips 74. In the second main spar cap 32b, each layer of the inner stack 60 comprises a GFRP strip 76, i.e. the inner stack is formed entirely by GFRP strips 76.
[0116] Similarly, the first rear spar cap 34a is the same as the first rear spar cap 34a of the second blade 16b, i.e. it includes a single GFRP strip 76 as the outermost layer 68 of the inner stack 63 - the remaining strips of the inner stack 63 are CFRP strips 74. In the second rear spar cap 34b, each layer of the inner stack 63 comprises a GFRP strip 76, i.e. the inner stack 63 is formed entirely by GFRP strips 76.
[0117] Therefore, the fourth blade 16d incorporates more GFRP strips 76 in one side of the blade than in the other. The spar caps 32a, 34a of the first half shell are stiffer than the spar caps 32b, 34b of the second half shell because they include more CFRP strips 74.
[0118] In order to determine the most optimal configuration of the spar caps 32a, 32b, 34a, 34b for a given site, computer modelling may be used. The wind loads at a given site are determined, from which the loads on the blades at that site can be estimated. Strain levels on the blade can be modelled for the estimated loads. Optimizing a blade for a given site may involve maximising the volume of CFRP that is replaced with GFRP whilst maintaining strain levels at or below a predetermined level. This allows cheaper blades to be produced that are customised for a particular site without adversely affecting the performance and longevity of the blade.
[0119] Many modifications may be made to the above examples within the scope of the present invention as set out in the accompanying claims. For example, whilst the reinforcing arrangements 32a, 32b, 34a, 34b in the above examples are spar caps, in other examples, the reinforcing arrangements may comprise or include other stiffening structures such as stringers. Accordingly, shear webs 36, 38 may not necessarily be provided between reinforcing arrangements.
[0120] Whilst the blades 16a, 16b, 16c, 16d in the above examples have a structural shell design in which the spar caps are embedded in the shell structure, the spar caps or other reinforcing arrangements may instead be bonded to an inner surface of the blade shell, or they may be provided as part of a box-spar structure.
[0121] Whilst the strips 74, 76 forming the reinforcing structures are preferably made from CFRP or GFRP, other reinforcing fibres such as aramid fibres could be used. In general, different members of the blade family may be produced by replacing relatively expensive and relatively high stiffness strips (primary strips) with less expensive lower stiffness strips (secondary strips).
[0122] Although lower stiffness strips 76 are incorporated into all of the spar caps of the various blades in the above examples, in other blades of the family only a subset of the spar caps might incorporate the lower stiffness strips, for example only one or two spar caps.
[0123] Whilst the spar caps in the above examples have three stacks of strips, in other examples the intermediate stacks 62, 65 may be omitted or there may be additional intermediate stacks between the inner stacks 60, 63 and the outer stacks. In yet further examples, any of the spar caps may have a distributed structure, for example in which core material may be provided between the inner stacks 60, 63 and the outer stacks 61, 64 or between intermediate stacks 62, 65 of the spar cap.
[0124] Whilst the outermost layer 68 in the stacks is the longest layer in the above examples, in other spar cap configurations the longest layer may be a different layer in the stack, for example the innermost layer 66.
[0125] The first and second main spar caps 32a, 32b may have different constructions from one another, for example, different numbers of layers in their corresponding stacks. Accordingly, the first main spar cap 32a and the second main spar cap 32b may have different thicknesses, and / or different strengths. Similarly, the first and second rear spar caps 34a, 34b may have different constructions from one another, for example different thicknesses and / or different numbers of layers. The rear spar caps may include only a single stack, or even just a single layer.
[0126] The number of layers in the stacks may be different from the examples shown above. For example, within the same spar cap, the number of layers in adjacent stacks may be different.
[0127] The strips 74, 76 may not be pultrusions but could be made by other processes, for example they may be moulded or belt pressed. The strips do not need to have rectangular cross sections. In other examples, the strips 61, 64 may have a different cross-sectional shape, for example square, circular or oval etc.
[0128] Any of these variations may be used in combination.
Claims
Claims1. A family of wind turbine blades (16a, 16b, 16c, 16d) of substantially equal length and of substantially the same external shape, the family comprising at least a first blade and a second blade, wherein each blade comprises:a blade shell that extends longitudinally in a spanwise direction (S) from a root end (20) to a tip end (22) and transversely in a chordwise direction (C) between a leading edge (24) and a trailing edge (26), the blade shell being formed from first and second opposing half shells (28, 30);a first main reinforcing arrangement (32a) associated with the first half shell (28) and a second main reinforcing arrangement (32b) associated with the second half shell (30);a first rear reinforcing arrangement (34a) associated with the first half shell and spaced from the first main reinforcing arrangement (32a) in the chordwise direction towards the trailing edge, and a second rear reinforcing arrangement (34b) associated with the second half shell and spaced from the second main reinforcing arrangement (32b) in the chordwise direction towards the trailing edge;the first main reinforcing arrangement and the first rear reinforcing arrangement being formed of layers extending longitudinally in the spanwise direction, the layers of the first main reinforcing arrangement being arranged in a plurality of stacks of layers comprising at least an inner stack (60) closest to the trailing edge and an outer stack (61) closest to the leading edge, and / or the layers of the first rear reinforcing arrangement being arranged in a plurality of stacks of layers comprising at least an inner stack (63) closest to the leading edge and an outer stack (64) closest to the trailing edge,wherein each stack comprises at least:- an innermost layer (66) being the layer within the stack that is closest to an interior (70) of the blade;- an outermost layer (68) being the layer within the stack that is closest to an exterior of the blade; and- optionally one or more intermediate layers (72) between the innermost layer and the outermost layer,wherein each of the said layers comprises a strip of fibrous composite material, the strips being selected from primary strips (74) and secondary strips (76), the primary strips being made of fibres having a first Young’s modulus and the secondary strips being made of fibres having a second Young’s modulus lower than the first Young’s modulus;wherein at a first spanwise position along the first blade, the said layers of the outer stack of the first main reinforcing arrangement and / or the said layers of the outer stack of the first rear reinforcing arrangement comprise a primary strip; andwherein at a corresponding first spanwise position along the second blade, the said layers of the outer stack of the first main reinforcing arrangement and / or the said layers of the outer stack of the first rear reinforcing arrangement comprise a primary strip; and wherein at the corresponding first spanwise position along the second blade the inner stack of the first main reinforcing arrangement and / or the inner stack of the first rear reinforcing arrangement comprises a greater number of layers comprising a secondary strip than the inner stack of the corresponding reinforcing arrangement(s) of the first blade at the corresponding first spanwise position of the first blade.
2. The family of wind turbine blades of Claim 1 , wherein the first blade is designed for wind loads of a first magnitude, and the second blade is designed for wind loads of a second magnitude that is lower than the first magnitude.
3. The family of wind turbine blades of Claim 1 or Claim 2, wherein the primary strips (74) are made of carbon fibres and the secondary strips (76) are made of glass fibres.
4. The family of wind turbine blades of any preceding claim, wherein in each blade of the family, the layers (66, 68, 72) of the first main reinforcing arrangement (32a) and / or the layers (66, 68, 72) of the first rear reinforcing arrangement (34a) have different lengths and terminate at different spanwise positions.
5. The family of wind turbine blades of any preceding claim, wherein in the second blade, a secondary strip (76) in the inner stack (60) of the first main reinforcing arrangement (32a) and / or a secondary strip (76) in the inner stack (63) of the first rear reinforcing arrangement (34a) has substantially the same length and / or width and / or thickness as a primary strip (74) in a corresponding position in the first blade.
6. The family of wind turbine blades of any preceding claim, wherein in each blade of the family, the inner stack (60) of the first main reinforcing arrangement (32a) and / or the inner stack (63) of the first rear reinforcing arrangement (34a) comprises a longest layer in said stack, and whereinin the second blade, the longest layer in the inner stack of the first main reinforcing arrangement comprises a secondary strip (76) and / or the longest layer in the inner stack (63) of the first rear reinforcing arrangement comprises a secondary strip (76).
7. The family of wind turbine blades of any preceding claim, wherein in the second blade, a secondary strip (76) in the inner stack (60) of the first main reinforcing arrangement (32a) and / or a secondary strip (76) in the inner stack (63) of the first rear reinforcing arrangement (34a) extends along an entire length of the respective reinforcing arrangement.
8. The family of wind turbine blades of any preceding claim, wherein at the first spanwise position along the second blade, the outermost layer (68) of the inner stack (60) of the first main reinforcing arrangement (32a) comprises a secondary strip (76) and / or the outermost layer (68) of the inner stack (63) of the first rear reinforcing arrangement (34a) comprises a secondary strip (76).
9. The family of wind turbine blades of any preceding claim, wherein at the first spanwise position along the second blade, the inner stack (60) of the first main reinforcing arrangement (32a) and / or the inner stack (63) of the first rear reinforcing arrangement (34a) further comprises one or more primary strips (74) in layers corresponding to the position of one or more primary strips (74) in the corresponding reinforcing arrangement(s) of the first blade.
10. The family of wind turbine blades of any preceding claim, wherein at the first spanwise position along the first blade, the innermost layer (66) of the inner stack (60) of the first main reinforcing arrangement (32a) comprises a primary strip (74), and / or the innermost layer (66) of the inner stack (63) of the first rear reinforcing arrangement (34a) comprises a primary strip (74), and wherein at the first spanwise position along the second blade, the innermost layer (66) of the inner stack (60) of the first main reinforcing arrangement (32a) comprises a primary strip (74), and / or the innermost layer (66) of the inner stack (63) of the first rear reinforcing arrangement (34a) comprises a primary strip (74).
11. The family of wind turbine blades of any preceding claim, wherein at the first spanwise position along the second blade, each layer (66, 68, 72) of the inner stack (60) of the first main reinforcing arrangement (32a) comprises a secondary strip (76) and / or each layer (66, 68, 72) of the inner stack (63) of the first rear reinforcing arrangement (34a) comprises a secondary strip (76).
12. The family of wind turbine blades of any preceding claim, wherein in each blade of the family, the first main reinforcing arrangement (32a) and / or the first rear reinforcing arrangement (34a) further comprises one or more intermediate stacks (62, 65) of layers (66, 68, 72) between the inner and outer stacks (60, 61, 63, 64), wherein at the first spanwise position along the blades each layer of the intermediate stack(s) (62, 65) comprises a primary strip (74).
13. The family of wind turbine blades of any preceding claim, wherein each blade of the family further comprises a main shear web (36) connected between the first and second main reinforcing arrangements (32a, 32b) and / or a rear shear web (38) connected between the first and second rear reinforcing arrangements (34a, 34b), and wherein the main shear web in the first blade has the same height as the corresponding main shear web in the second blade and / or the rear shear web in the first blade has the same height as the corresponding rear shear web in the second blade.
14. A method of making the family of wind turbine blades according to any preceding claim, wherein the method comprises:forming at least part of the blade shell of the first blade in a first mould; and forming at least part of the blade shell of the second blade in a second mould, wherein the second mould is either the same mould as the first mould or is a further mould having the same mould surface geometry as the first mould, such that the first and second blades have substantially equal length and substantially the same external shape.
15. The method of Claim 14, further comprising:making a main shear web (36) or a rear shear web (38) of the first blade using a first web tool;making a main shear web or a rear shear web of the second blade using a second web tool;wherein the second web tool is either the same web tool as the first web tool or is a further web tool having the same geometry as the first web tool, such that the shear web produced for the first blade is substantially the same as the shear web produced for the second blade.