WO2018224106A1

WO2018224106A1 - Modular wind turbine blades

Info

Publication number: WO2018224106A1
Application number: PCT/DK2018/050124
Authority: WO
Inventors: Jonathan Smith
Original assignee: Vestas Wind Systems A/S
Priority date: 2017-06-09
Filing date: 2018-06-06
Publication date: 2018-12-13

Abstract

A modular wind turbine blade is described. The modular wind turbine blade comprises first and second blade modules each comprising a proximal end and a distal end, a first side comprising a first aerodynamic surface being a windward surface or a leeward surface, a second side comprising a second aerodynamic surface being the other of the windward surface or the leeward surface, and a tapered end portion having a thickness between the first and second sides that decreases towards an end of the. The tapered end of the first blade module has a thickness that decreases towards the distal end, and that defines a mating surface on the second side of the module that extends between the distal end and the second aerodynamic surface. The second blade module has a tapered end portion having a thickness that decreases towards the proximal end, and that defines a mating surface on the first side of the module that extends between the proximal end and the first aerodynamic surface. The mating surfaces of the first and second blade modules are configured to form a scarf joint between the first and second blade modules. The invention also provides a mould assembly for making the blade modules, and a method of assembling the modules.

Description

Modular wind turbine blades

Background The present invention relates generally to modular rotor blades for wind turbines.

Modern wind turbines are designed and manufactured to capture increasingly more energy from the wind to generate power. One way of increasing the energy capture of a wind turbine is to increase the swept area of the rotor blades, which means increasing the length of the rotor blades.

In general, large wind turbines are assembled on site from components that are transported to the site. Typical components of a wind turbine include a plurality of rotor blades, a rotor hub, a nacelle and a tower. The site may be remote and difficult to access, which makes transportation of large components, in particular the long rotor blades, problematic. To resolve this problem, the rotor blades may be divided into two or more modules that are easier to transport, and which are connected together on site.

One of the key challenges associated with modular wind turbine blades is ensuring that the blade is sufficiently strong across the joint between the blade modules. Another key challenge is ensuring that the blade modules are precisely aligned, particularly where the modules are to be bonded together. Ensuring precise alignment between blade modules can be difficult when assembling the blade in the field, and if the modules are not precisely aligned then this can reduce the strength of the blade across the interface between the blade modules.

Current methods of assembling modular wind turbine blades can be relatively complicated and time-consuming, and hence there is a need for more straightforward assembly procedures that can be performed easily and efficiently on site.

Against this background, the present invention aims to provide an improved modular wind turbine blade, which is both strong and easy to assemble. The invention also aims to provide an associated process for manufacturing blade modules of a modular wind turbine blade. Summary of the invention

According to an aspect of the invention, there is provided a modular wind turbine blade comprising first and second blade modules, the first blade module comprising:

a proximal end and a distal end;

a first side comprising a first aerodynamic surface being a windward surface or a leeward surface;

a second side comprising a second aerodynamic surface being the other of the windward surface or the leeward surface; and

a tapered end portion having a thickness between the first and second sides that decreases towards the distal end, the tapered end portion defining a mating surface on the second side of the module that extends between the distal end and the second aerodynamic surface,

and the second blade module comprising:

a proximal end and a distal end;

a tapered end portion having a thickness between the first and second sides that decreases towards the proximal end, the tapered end portion defining a mating surface on the first side of the module that extends between the proximal end and the first aerodynamic surface.

The mating surfaces of the first and second blade modules are configured to form a scarf joint between the first and second blade modules. The scarf joint provides a large bond area and results in a very strong yet simple connection being formed between the blade modules.

The blade modules comprise spanwise sections of the wind turbine blade. The blade may have two or more blade modules connected together by means of a scarf joint between each pair of modules. The first aerodynamic surface may be a windward surface and the second aerodynamic surface may be a leeward surface, or vice-versa. The proximal end of each blade module is closer to the root of the blade than the distal end of the module, and the distal end of each module is closer to the tip of the blade than the proximal end of the module. In some embodiments, the proximal end of a module may comprise the root of the blade. A distal end of a module may comprise the tip of the blade. For example, the first module may comprise the root of the wind turbine blade and the second module may comprise the tip of the wind turbine blade.

Typically each blade module includes an outer shell, and the outer shell defines the first aerodynamic surface, the second aerodynamic surface, and the mating surface. Each blade module may further comprise first and second mutually-opposed spar caps. Each spar cap may have a tapered end that partially defines the tapered end portion of the blade module. Generally, the first and second spar caps are respectively adjacent to the first and second aerodynamic surfaces of each blade module. For example, the first and second mutually-opposed spar caps may be embedded in the windward and leeward sides of the outer shell, respectively.

Accordingly, the first spar cap of the first blade module may extend further into the tapered end portion of the first blade module than the second spar cap of the first blade module. Similarly, the second spar cap of the second blade module may extend further into the tapered end portion of the second blade module than the first spar cap of the second blade module. As such, the tapered end portions forming the scarf joint may extend over a defined spanwise length of each blade module and one of the two spar caps of each blade module may extend further into the spanwise length of the tapered end portion than the other spar cap. When the first and second modules are assembled, the joint region may extend over a defined spanwise length, and one of the two spar caps of each blade module may extend further into the joint region than the other spar cap.

Preferably, each spar cap comprises a plurality of strips of pre-cured fibre- reinforced composite material. These strips are preferably formed by pultrusion, and are referred to herein as 'pultrusions' or 'pultruded strips'. Carbon fibres are preferred as the reinforcing fibres, due to their high strength-to-weight ratio, and such strips are referred to herein as 'carbon pultrusions'. The strips (e.g. the carbon pultrusions) are preferably arranged in a stack and bonded together by a cured matrix material such as epoxy to form an integrated stack. Accordingly, each spar cap preferably comprises one or more integrated stacks of pre-cured pultruded strips, most preferably carbon pultrusions. Each strip may have a tapered end that partially defines the tapered end of the spar cap. The blade modules preferably further comprise a shear web located between the first and second spar caps. The shear web may have a tapered end that partially defines the tapered end of the blade module. The tapered end of the shear web may comprise a flange arranged in a plane substantially parallel to the mating surface of the blade module.

The shear webs are preferably bonded inside the outer shell of each blade module between mutually-opposed spar structures. The shear webs of each blade module may have an I-shaped cross-section, consisting of a longitudinally-extending web having transverse flanges along its upper and lower edges. The flanges may be bonded respectively to the opposed spar caps of the blade modules.

The tapered end portion of each blade module may have a taper gradient of between 1 /50 to 1 /200, preferably between 1 /75 to 1 /150, more preferably 1 /80 to 1 /120 and most preferably approximately 11\ 00.

In some embodiments, the mating surfaces of the first and second modules comprise alignment features to facilitate alignment between the modules. The alignment features may comprise one or more male features on the mating surface of one module for engaging with one or more female features on the mating surface of the other module.

In embodiments, the alignment features may comprise a ball and a socket, and / or a ball and a slot. Bond spacers may be provided between the mating surfaces of the first and second blade modules. The bond spacers may be configured to maintain the mating surfaces of the first and second modules substantially parallel and spaced apart when the blade modules are connected via the scarf joint. The modular wind turbine blade of the present invention is preferably constructed as a plurality of individual blade modules, which may be assembled on site, e.g. at a wind farm location, prior to being installed on a wind turbine structure. Constructing the blade from individual blade modules facilitates transportation of the wind turbine blade and allows longer blades to be installed, where it would not be feasible to transport such long blades as a single unit by conventional means. Accordingly, another aspect, the present invention provides a method of assembling a modular wind turbine blade from first and second blade modules, wherein the method comprises:

providing first and second blade modules, each blade module comprising a proximal end, a distal end, a first side comprising a first aerodynamic surface being a windward or a leeward surface, a second side comprising a second aerodynamic surface being the other of the windward surface or the leeward surface, and a tapered end portion; wherein the tapered end portion has a thickness between the first and second sides that decreases towards the distal end in the first module and towards the proximal end in the second module, the tapered end portion of the first module defining a mating surface on the second side of the first module that extends between the distal end and an the second aerodynamic surface of the first module, and the tapered end portion of the second module defining a mating surface on the first side of the second module that extends between the proximal end and the first aerodynamic surface of the second module; and

bonding the mating surfaces of the first and second blade modules together to form a scarf joint connecting the two modules.

The step of bonding the modules together may comprise moving the mating end surfaces of the modules together in a direction generally perpendicular to both spanwise and chordwise axes of the blade modules.

The method of assembling a modular wind turbine blade may further comprise supporting the first and second blade modules in a jig during the bonding step and applying a clamping pressure via the jig between the mating surfaces of the blade modules.

The method is preferably performed on-site, for example at or near a wind farm location where the blade is to be installed on a wind turbine structure.

An adhesive is preferably used to bond the mating surfaces of the first and second blade modules together to form a scarf joint connecting the two modules. The method preferably involves applying the adhesive to the mating surface of one of the modules before bringing the two mating surfaces of the modules together. The adhesive is preferably a film adhesive. The method preferably involves applying heat locally to cure the adhesive. The present invention also extends to the individual blade modules of the modular wind turbine blade described above.

Accordingly, in a further aspect of the present invention, there is provided a blade module for a modular wind turbine blade, the blade module comprising:

a tapered end portion having a thickness between the first and second sides that decreases towards an end of the blade module, the tapered end portion defining a mating surface on one side of the module that extends between the end of the blade module and the aerodynamic surface of the said one side of the module,

wherein the mating surface of the module is configured to form a scarf joint with a corresponding mating surface of a second blade module.

Optional and advantageous features discussed above in relation to the invention when expressed in terms of a modular wind turbine blade also of course apply to the invention when expressed in terms of a blade module for a modular wind turbine blade. Repetition of such features is avoided purely for reasons of conciseness.

The invention also provides a new mould assembly for making a modular wind turbine blade, as will now be described in relation to a further aspect of the invention. Accordingly, in another aspect, the invention provides a mould assembly for making a blade module of a modular wind turbine blade, the mould assembly comprising: a first mould half having a mould surface shaped to define a first side of the blade module comprising a first aerodynamic surface being a windward surface or a leeward surface;

a second mould half having a mould surface shaped to define a second side of the blade module comprising a second aerodynamic surface being the other of the windward surface or the leeward surface;

the mould assembly having open and closed configurations, wherein in the closed configuration the first and second mould halves are mutually opposed and define a hollow interior region between their respective mould surfaces; wherein the mould assembly further comprises an inclined end surface in the hollow interior region, the inclined end surface extending substantially between the first and second aerodynamic surfaces defined by the first and second mould halves and being shaped to define a tapered end portion of the blade module.

The inclined end surface may further define male and/or female surface features. These features may be configured such that one or more male features on the mating surface of one module engage with one or more female features on the mating surface of the other module when the modules are assembled to form a scarf joint.

The first and second blade modules of the modular wind turbine blade may be formed in separate mould assemblies. Alternatively, the first and second blade modules are formed in the same mould assembly. Accordingly, the mould surface may have a first portion shaped to form at least part of the outer shell of the first blade module, and a second portion shaped to form at least part of the outer shell of the second blade module. The first portion and the second portion of the mould surface may be located in adjacent spanwise sections of the mould.

The invention also provides a new method of making one or more blade modules of a modular wind turbine blade, as will now be described in relation to a further aspect of the invention.

Accordingly, in a further aspect, the invention provides a method of making one or more blade modules of a modular wind turbine blade, the method comprising:

providing a mould assembly as described above, wherein the inclined end surface is comprised in the first or second mould half;

arranging one or more first layers of fibrous material on the mould surface of each of the first and second mould halves to form a first and second halves of an outer skin of the first blade module;

arranging a spar cap on top of the one or more first layers of each mould half, the spar caps having a tapered portion that partially defines the tapered end portion of the blade module;

arranging one or more second layers of fibrous material on top of the one or more first layers and on top of the spar caps to form an inner skin of the first blade module; integrating the one or more first layers, the one or more second layers and the spar caps by means of a curable matrix material; and curing the matrix material to form the outer shell of the first blade module.

It will be appreciated that the above method results in a blade module having a first and second side, each side comprising one or the other of a leeward and windward aerodynamic surface, and a tapered end portion having a thickness between first and second sides of the blade module that decreases towards an end of the blade module. The tapered end portion defines a mating surface on one side of the module that extends between the end of the blade module and the aerodynamic surface of the said one side of the module.

The above method may therefore be used to form the blade modules discussed above.

The various components of the outer shell may be integrated using any suitable techniques known in the art of composites moulding. For example, infusion or prepreg techniques may be used. Vacuum-assisted infusion is particularly preferred. This involves arranging a vacuum film over the mould surface to create a sealed region encapsulating the various components. Air is then removed from this region and the matrix material is admitted. The matrix material is preferably a suitable resin such as epoxy. This infuses throughout the various layers. The resin hardens when cured to bond the various layers together.

The spar cap is preferably formed from one or more stacks of strips of reinforcing material. For example carbon pultrusions as described previously. The strips may be stacked and bonded together to form the spar structure prior to arranging the spar structure in the mould. Alternatively, the method may comprise forming the spar cap by stacking the strips in the mould.

The tapered end portion of the spar cap is preferably formed by stacking the strips in the mould, the strips extending into the tapered end portion of the blade module to a decreasing or increasing extent in order to define a tapered end portion of each stack.

Preferably the end portions of the strips are also tapered to reduce stress concentrations in the stacked strips.

The strips preferably have a substantially rectangular cross section, e.g. resulting rectangular pultrusion die. The strips typically have a height of a few millimetres. The stacks may comprise any number of strips according to the required strength and thickness of the blade shell. Typically the stack may include five or more strips. The strips may be very long in length, as the pultrusion process allows continuous strips of any length to be formed. The strips preferably extend along a majority of the length of the blade modules. In preferred embodiments, each spar cap may be formed from a plurality of stacks, preferably three, arranged side-by-side.

In preferred embodiments the outer shell is moulded in two halves: a windward half and a leeward half. Each half shell is moulded in a respective mould (i.e. a mould half) of the mould assembly. The mould halves are preferably arranged side by side, and once the respective half shells have been cured, adhesive may be applied to one or both half shells and one of the half moulds may be lifted, turned, and placed on top of the other mould half to bond the respective half shells together. This process is referred to as 'closing the mould'.

The spar caps may be arranged in the respective half shells such that when the half shells are bonded together to form the complete blade module, the spar caps in the windward half shell are located opposite the spar caps in the leeward half shell. The method preferably comprises bonding a shear web to the spar caps. For example the method may comprise bonding the shear web between opposed spar caps of the first and second half shells. For example, prior to bonding the half shells together, e.g. with the mould still open, the method may comprise bonding a shear web to the inner surface of one of the half shells. Adhesive may then be applied along an upper edge of the shear web before closing the mould to bond the shear web to the inner surface of the other half shell at the same time as bonding the two half shells together.

The shear web preferably has a tapered end portion that partially defines the tapered end of the blade module. The tapered end of the shear web may comprise a flange arranged in a plane substantially parallel to the inclined end surface of the mould assembly. The method may advantageously comprise bonding the tapered end of the shear web with the one or more first layers of fibrous material on the inclined end surfaced of the first mould half. Optional features of the method discussed above in relation to the invention when expressed in terms of a modular blade apply equally to the invention when expressed in terms of a mould assembly or a method of making a blade module. Repetition of these features is avoided purely for reasons of conciseness.

Brief description of the drawings

The present invention will now be described in further detail, by way of example only, with reference to the following figures, in which:

Figure 1 is a perspective view of a first and second blade module of a modular wind turbine blade according to the present invention;

Figures 2, 3 and 4 are schematic cross-sectional views of a portion of the first and second blade modules according to the present invention; Figure 5 is a schematic cross-sectional view of a portion of the first and second blade modules according to embodiments of the invention comprising alignment features;

Figures 6a and 6b are perspective views of blade modules according to embodiments of the invention comprising alignment features;

Figure 7 shows first and second blade modules according to an embodiment of the invention arranged to form a scarf joint, the first and second blade modules being supported in a jig structure; and

Figure 8 shows a portion of a mould assembly for making a blade module according to the present invention.

Detailed description

Referring to Figure 1 , this shows a perspective view of a modular wind turbine blade 10 according to a first embodiment of the present invention. The modular wind turbine blade 10 includes first and second blade modules 12, 14, each comprising a tapered end portion 16, 18 defining a mating surface 20, 22 configured to form a scarf joint between the first and second blade modules 12, 14. The first and second blade modules 12, 14 form spanwise (s) sections of the modular wind turbine blade 10. In Figure 1 , the axes s and c indicate respectively the spanwise and chordwise directions of the blade modules 12, 14. In embodiments, the first blade module 12 comprises an inboard section of the blade 10 and the second blade module 14 comprises an outboard section of the blade 10. In embodiments, the first module 12 is an inboard module, and the second module 14 is an outboard module. In the embodiment shown, the second blade module 14 includes the tip 24 of the blade 10. In the embodiment shown, the first blade module 12 includes the root 26 of the blade 10. Alternatively, the modular wind turbine blade 10 may include one or more further blade modules inboard of the first blade module 12 and/or outboard of the second blade module.

Each blade module comprises a proximal end 28 and a distal end 30. In the embodiment shown, the proximal end 28a of the first blade module 12 comprises the root 26, and the distal end 30b of the second blade module 14 comprises the tip 24. The proximal end 28a, 28b of each blade module 12, 14 is closer to the root 26 of the blade 10 than the distal end 30a, 30b of each blade module 12, 14. Each module has a trailing edge 13 and a leading edge 15.

Figures 2 to 4 show schematic cross-sectional views of a portion of the first and second blade modules 12, 14 centred around the scarf joint, according to embodiments of the invention. In these figures, portions of the blade modules including the distal end 30a of the first blade module 12 and the proximal end 28b of the second blade module are shown. Each blade module comprises a first side 33a, 33b and a second side 35a, 35b. The first side 33a, 33b comprises a first aerodynamic surface 32a, 32b and the second side 35a, 35b comprises a second aerodynamic surface 34a, 34b. The first aerodynamic surface 32a, 32b may be one of a windward or leeward surface of the blade module, and the second aerodynamic surface 34a, 34b may be the other of the windward or leeward surface of the blade module. As can be seen in Figure 2, the tapered end portion 16, 18 of each blade module 12, 14 has a thickness t between the first side 33a, 33b and second side 35a, 35b that decreases towards the end of the blade module that comprises the tapered end portion 16, 18. In the embodiment shown, the tapered end portion 16 of the first blade module 12 has a thickness t that decreases towards the distal end 30a of the blade module 12. Accordingly, in the embodiment shown, the tapered end portion 18 of the second blade module 14 has a thickness t that decreases towards the proximal end 28b of the blade module 14. The tapered end portions 16, 18 of each blade module defines a mating surface 20, 22 on one side of the blade module. The mating surface 20, 22 extends between an end 28b, 30a of the blade module and the aerodynamic surface 32, 34 of the side of the blade module that also comprises the mating surface 20, 22. The mating surface 20, 22 is contiguous with the first aerodynamic surface 32a, 32b and contiguous with the second aerodynamic surface 34a, 34b, in that the mating surface 20, 22 shares a common border with these surfaces. In the embodiment shown, the tapered end portion 16 of the first module 12 defines a mating surface 20 on the second side 35a of the first blade module 12. This mating surface 20 extends between the distal end 30a of the first blade module 12 and the second aerodynamic surface 34a of the first blade module 12. In other words, the second side 35a of the first blade module 12 comprises the second aerodynamic surface 34a and the mating surface 20 of the first blade module 12, and the first side 33a of the first blade module 12 comprises the first aerodynamic surface 32a of the first blade module 12.

Accordingly, the tapered end portion 18 of the second blade module 14 defines a mating surface 22 on the first side 33b of the second blade module 14. This mating surface 22 extends between the proximal end 28b of the second blade module 14 and the first aerodynamic surface 32b of the second blade module 14. In other words, the first side 33b of the second blade module 14 comprises the first aerodynamic surface 32b and the mating surface 22 of the second blade module 14, and the second side 35b of the second blade module 14 comprises the second aerodynamic surface 34b. The mating surfaces 20, 22 of the first and second blade modules 12, 14 are configured to form a scarf joint between the first and second blade modules 12, 14. That is, the mating surfaces 20, 22 fit together such that when the modules are assembled, a scarf joint is formed between the two mating surfaces 20, 22. The tapered end portions 16, 18 of the first and second blade modules 12, 14 extend over a certain length / of the modules in a spanwise direction s. The length / of the tapered end portions 16, 18 extends between an imaginary line (see vertical dashed lines 17a, 17b in Figures 2 to 4) at the spanwise location where the module begins to taper and the end of the module where the mating surface 20, 22 of one side 33, 35 of the module reaches the aerodynamic surface 32, 34 of the other side 33, 35 of the module. Accordingly, when the first and second blade modules 12, 14 are assembled to form a scarf joint between the mating surfaces 20, 22 of the modules, the spanwise length of the scarf joint corresponds to the spanwise length / of the tapered end portions 16, 18 of the first and second blade modules 12, 14. The mating surfaces 20, 22 of the modules 12, 14 are inclined relative to the aerodynamic surfaces 32a, 34a, 32b, 34b of the respective modules. Accordingly, the tapered end portion 16, 18 varies in thickness t along the length / of the tapered end portion 16, 18. The thickness t is the distance between the first side 33a, 33b and the second side 35a, 35b, perpendicular to the spanwise (s ) and chordwise (c) directions. In Figures 2 to 4, this corresponds to the distance along the y axis between the first side 33a, 33b and the second side 35a, 35b, where the x axis corresponds to the spanwise direction and the z axis corresponds to the chordwise direction.

The tapered end 16 of the first module 12 decreases in thickness t towards the distal end 30a of the module 12. The tapered end 18 of the second module 14 decreases in thickness t towards the proximal end 28b of the second module 14.

In embodiments, the tapered end portion 16, 18 of each blade module 12, 14 has a taper gradient of between 1 /50 to 1 /200. In other words, the thickness t of the tapered end portions 16, 18 decreases by one unit every 50 to 200 units of spanwise length of the tapered end portion 16, 18. In preferred embodiments, the tapered end portion 16, 18 of each blade module 12, 14 has a taper gradient of between 1/75 and 1/150. In some preferred embodiments, the tapered end portion 16, 18 of each blade module 12, 14 has a taper gradient of between 1 /80 and 1/120, most preferably approximately 1/100. In embodiments, the tapered end portion 16, 18 of each blade module 12, 14 has a taper gradient of at least 1/50, 1 /75, or 1/80, and at most 1/200, 1/150, or 1/120.

In embodiments, the first aerodynamic surface 32a, 32b is a windward surface and the second aerodynamic surface 34a, 34b is a leeward surface. Accordingly, the mating surface 20 of the first module 12 may extend substantially between the leeward surface 34a and the windward surface 32a such that the thickness t of the tapered end portion 16 decreases such that the mating surface 20 becomes closer to the windward surface 32a along the length / of the tapered end portion 16, towards the distal end 30a of the module 12. Accordingly, the mating surface 22 of the second module 14 may extend substantially between the leeward surface 34b and the windward surface 32b such that the thickness t of the tapered portion 18 decreases such that the mating surface 22 becomes closer to the leeward surface 34b along the length / of the tapered end portion 18, towards the proximal end 28b of the module 14.

Alternatively, the first aerodynamic surface 32a, 32b may be a leeward surface and the second aerodynamic surface 34a, 34b may be a windward surface. Accordingly, the mating surface 20 of the first module 12 may extend substantially between the leeward surface 32a and the windward surface 34a such that the thickness t of the tapered end portion 16 decreases such that the mating surface 20 becomes closer to the leeward surface 32a along the length / of the tapered end portion 16, towards the distal end 30a of the module 12. Accordingly, the mating surface 22 of the second module 14 may extend substantially between the leeward surface 34b and the windward surface 32b such that the thickness t of the tapered portion 18 decreases such that the mating surface 22 becomes closer to the windward surface 34b along the length / of the tapered end portion 18, towards the proximal end 28b of the module 14.

As the skilled person would understand, the chordwise dimension (referred to as 'width', along the z axis in Figures 2 to 4) of the first and second modules 12, 14 may vary along the spanwise length / of the tapered end portions 16, 18, and between the first and second modules 12, 14. Therefore, as can be seen in Figure 1 , the mating surface 20 of one of the modules (in this case the first module 12) may not extend over the full width of the module 12 over the whole spanwise length / of the tapered end portion 16. Instead, the mating surface 20 of the first module 12 (in the embodiment shown) extends over the width of the first module 12 only to an extent corresponding to the width of the mating surface 22 of the narrower second module 14. The width of the mating surfaces 20, 22 may vary along the length / of the tapered end portion 16, 18, as can be seen in Figure 1 .

As further explained below, the mating surfaces 20, 22 may comprise surface features such as indents or protrusions. Such features may be ignored for the purposes of determining the thickness t of the tapered end portion 16, 18. Accordingly, the thickness t of the tapered end portions 16, 18 of the blade modules 12, 14 is measured between the first or second aerodynamic surface (as the case may be) and an imaginary continuous plane corresponding to the mating surface 20, 22 ignoring surface features.

In the embodiment shown in Figure 3, the mating surfaces 20, 22 are configured to form a nibbed scarf joint between the first and second blade modules 12, 14. Therefore, the tapered end portions 16, 18 of the first and second modules 12, 14 may have a thickness between the first and second sides that abruptly decreases to define a first minor part 21 a, 21 b of the mating surface 20, 22 then gradually decreases over a major surface 23a, 23b of the mating surface 20, 22. The thickness may then stay constant over a second minor part 25a, 25b of the mating surface 20, 22. In other words, seen from the cross-sectional view of Figure 3, the profile of the mating end surfaces 20, 22 would include a major angled portion and a minor straight portion on one (not shown) or both sides (as shown in Figure 3) of the major angled portion.

Referring now to Figure 4, each blade module 12, 14 comprises an outer shell 36 defining a generally hollow interior 37 of the blade 10. The outer shell 36 is formed primarily from glass-fibre-reinforced plastic (GFRP), and has a laminate structure comprising an outer skin 38 defining an outer surface 39 of the blade 10, and an inner skin 40 partially defining an interior surface 41 of the blade 10. The outer surface 39 of the first blade module 12 comprises the first aerodynamic surface 32a, the second aerodynamic surface 34a, and the mating surface 20. The outer surface 39 of the second blade module 14 comprises the first aerodynamic surface 32b, the second aerodynamic surface 34b, and the mating surface 22. As the skilled person would understand, once the first and second blade modules 12, 14 are connected, the mating surfaces 20, 22 will form an internal part of the blade structure.

In other words, the first and second blade modules 12, 14 each comprise an outer shell 36 having a windward surface 32a, 32b (or 34a, 34b) and a leeward surface 34a, 34b (or 32a, 32b). The outer shell 36 defines an end portion 16, 18 of the blade module that is tapered substantially between the windward and the leeward surfaces 32a, 32b, 34a, 34b to define a mating end surface 20, 22 of the blade module 12, 14. The first and second blade modules 12, 14 are configured to be connected together via a scarf joint in which the respective mating surfaces 20, 22 of the first and second modules 12, 14 overlap. As such, the blade 10 is modular in the spanwise direction, and the scarf joint connects a module that is on the root side of the joint (while not necessarily comprising the root of the blade), and a module that is on the tip side of the joint (while not necessarily comprising the tip of the blade).

The inner and outer skins 40, 38 may each comprise a plurality of layers of glass-fibre reinforcing fabric embedded in cured epoxy resin. Core material, such as foam panels may be provided between the inner and outer skins 40, 38 in regions of the blade 10 where increased stiffness is required. A plurality of longitudinally-extending spar caps 42a, 42b, 44a, 44b may be embedded in the laminate structure of the outer shells 36 of the respective blade modules 12, 14, e.g. between the inner and outer skins 40, 38. Referring still to Figure 4, each blade module in this embodiment comprises first and second mutually-opposed spar caps (42a and 44a in the first module 12 and 42b and 44b in the second blade module 14). The first spar cap 42a, 42b of each blade module 12, 14 is embedded in the outer shell 36 on the first side of the blade module 12, 14, adjacent to the first aerodynamic surface 32a, 32b of the module. The second spar cap 44a, 44b of each blade module 12, 14 is embedded in the outer shell 36 on the second side of the blade module 12, 14, adjacent to the second aerodynamic surface 34a, 34b of the module.

Each spar cap 42a, 42b, 44a, 44b has a tapered end 45 that partially defines the tapered end portion of the blade module. The tapered end 45 of each spar cap 42a, 42b, 44a, 44b defines an angled surface that is substantially parallel to the mating surface 20, 22 to which it is adjacent. As such, the tapered end 45 of the spar caps 42a, 42b, 44a, 44b may have a taper gradient of between 1/50 to 1/200, or any preferred value as specified above in relation to the tapered end 16, 18 of the blade modules 12, 14. As shown in Figure 4, in this embodiment, the first spar cap 42a of the first blade module 12 extends further into the tapered end portion 16 of the first blade module 12 than the second spar cap 44a of the first blade module 12. Conversely, the second spar cap 44b of the second blade module 14 extends further into the tapered end portion 18 of the second blade module 14 than the first spar cap 42b of the second blade module 14. In other words, when the modules 12, 14 are assembled, the scarf joint formed between the mating surfaces 20, 22 extends over a defined spanwise portion of the blade 10, referred to herein as the joint region, and one spar cap 42a, 42b, 44a, 44b of each module 12, 14 will extend further into the joint region than the other spar cap of the same module. In embodiments, each blade module 12, 14 may include more than one parallel spar cap 42a, 42b on a first side 33a, 33b of the blade module and more than one spar cap 44a, 44b on a second side 35a, 35b of the blade module. Each spar cap 42a, 42b, 44a, 44b may have a tapered end portion 45 that partially defines the tapered end portion 16, 18 of the blade module 12, 14. For example, a pair of side-by-side spar caps may be located on each side 33, 35 of the module 12, 14. In this embodiment, each spar cap 42a, 42b, 44a, 44b comprises a stack of pultruded strips 46. The strips are preferably made of CFRP, and are referred to generally as carbon pultrusions. Alternatively, the strips may comprise glass-fibre reinforced plastic. Referring still to Figure 4, each strip has a tapered end 49 that partially defines the tapered end of the spar cap. An end of the strips 46 tapers such that the angled surface of the tapered end of each strip is substantially parallel to the mating surface 20, 22 to which it is adjacent.

In other words, the end of the strips 46 taper such that the resulting stack of strips tapers to form an angled surface that is substantially parallel to the mating surface 20, 22 to which it is adjacent. In the second spar cap 44a of the first module 12 , each strip 46 extends further into the tapered end portion 16 of the module 12 than the preceding strip 46, going from the strip that is closest to the second aerodynamic surface 34a to the strip 46 that is furthest from the second aerodynamic surface 34a. Similarly, in the first spar cap 42b of the second module 14, each strip 46 extends further into the tapered end portion 18 of the module 14 than the preceding strip 46, going from the strip that is closest to the first aerodynamic surface 32b to the strip 46 that is furthest from the first aerodynamic surface 32b.

Conversely, in the first spar cap 42a of the first module 12, each strip 46 extends less into the tapered end portion 16 of the module 12 than the preceding strip 46, going from the strip that is closest to the first aerodynamic surface 32a to the strip 46 that is furthest from the first aerodynamic surface 32a. Similarly, in the second spar cap 44b of the second module 14 each strip 46 extends less far into the tapered end portion 18 of the module 14 than the preceding strip 46, going from the strip that is closest to the second aerodynamic surface 34b to the strip 46 that is furthest from the second aerodynamic surface 34b.

As shown in Figure 4, each blade module 12, 14 may include a longitudinally-extending shear web 48a, 48b located inside the outer shell 36, between the first and second spar caps 42a, 42b, 44a, 44b. The shear webs 48a, 48b are bonded along their longitudinal edges between opposed pairs of spar caps 42a, 42b, 44a, 44b on the respective first and second sides of the blade modules 12, 14. The shear webs 48a, 48b have a tapered end 50 that partially defines the tapered end of the blade module 12, 14. An end 50 of the shear webs 48a, 48b tapers such that the angled surface of the tapered end 50 of the shear web is substantially parallel to the mating surface 20, 22 to which it is adjacent. As such, the tapered end 50 of the shear webs 48a, 48b may have a taper gradient of between 1/50 and 1 /200, or any preferred value as specified above in relation to the tapered end 16, 18 of the blade modules 12, 14.

In embodiments (not shown), the tapered end 50 of the shear webs 48a, 48b may comprise a flange arranged in a plane substantially parallel to the mating surface of the blade module. The tapered end 50 of the shear webs 48a, 48b is typically bonded to the inner surface 41 of the outer skin 38 of the module 12, 14 in the region of the mating surface 20, 22. The presence of the flange allows for a sturdier bond to be obtained. Further, the flange helps to support the mating surface 20, 22 and facilitates bond formation between the two parts of the shear web in the respective modules.

In the embodiment shown in Figure 4, the mating surface 20, 22 of the module is formed as part of the outer skin 38. Therefore, the outer skin 38 covers the tapered end 45 of the spar caps 42a, 42b, 44a, 44b and the tapered end 50 of the shear webs 48a, 48b. For example, the tapered end 45 of the spar caps 42a, 42b, 44a, 44b and the tapered end 50 of the shear webs 48a, 48b may be bonded to the inner surface of the outer skin 38 of the module.

Figure 5 is a schematic cross-sectional view of a portion of the first and second blade modules 12, 14 according to embodiments of the invention. In the embodiment shown, the mating surfaces 20, 22 of the first and second modules 12, 14 additionally comprise alignment features 52, 54 to facilitate alignment between the modules 12, 14. The alignment features 52, 54 may comprise one or more male features 52 on the mating surface 20 of one module (shown as the first module 12 in Figure 5) for engaging with one or more female features 54 on the mating surface of the other module (shown as the second module 14 in Figure 5).

In embodiments, a mating surface 20, 22 may comprise both male 52 and female 54 alignment features for engagement with corresponding female and male alignment features on the mating surface of the other module 12, 14.

The male and female alignment features may take any suitable form. For example the male alignment features 52 may comprise protrusions such as domes or balls. The female alignment features may comprise slots, grooves or sockets, for example. A particular example is shown in the perspective view of Figure 6a, which shows the mating surface 22 of a blade module provided with first and second female alignment features, which in this example are in the form of a slot 56 and a socket 60 respectively. The slot 56 and socket 60 are spaced apart from each other on the mating surface 22.

The other blade module (not shown) comprises first and second male alignment features, which in this example are each in the form of dome-shaped protrusions (one of which is shown schematically in the schematic sectional view labelled χ in Figure 6a). The male alignment features are arranged to be received respectively within the female alignment features (i.e. the slot 56 and socket 60 respectively in this example) when the mating surfaces 22 of the respective modules are brought together.

The mating alignment features constrain relative movement between the mating surfaces of the two modules, ensuring a straightforward and precise alignment between the two modules. In this example, the first male dome-shaped feature (not shown) is received within the socket 60. The dome may form a close fit with the socket 60. With the dome received in the socket 60, translational movement between the modules substantially in the plane of the mating surfaces 22 is prevented. If only a single set of alignment features was provided (e.g. just the dome and socket 60 in this example) the two modules could still rotate relative to one another generally in the plane of the mating surfaces 22. The combination of first and second spaced-apart alignment features prevents such rotation. In this example, the second dome shaped protrusion 58 (see schematic sectional view χ in Figure 6a) is received within the slot 56. In combination with the first set of alignment features 60, rotation between the modules in the plane of the mating surfaces 22 is substantially prevented. The slot 56 extends slightly in a chordwise / widthwise direction of the mating surface 22, which provides some tolerance in this direction and allows the dome 58 to move laterally in the slot 56 to facilitate initial engagement between the respective alignment features.

In other embodiments, the mating surfaces 20, 22 of the first and second modules 12, 14 may comprise male and female surface features 52, 54 of arbitrary geometry. In the example shown in Figure 6b, a mating surface 20 comprises a male feature in the form of a three dimensional triangle (or wedge) (not shown) that fits within a corresponding recess 57 defined in the other mating surface 22. This arrangement also facilitates alignment between the modules. Referring again to Figure 5, the modular wind turbine according to embodiments of the invention may further comprise bond spacers 62 between the mating surfaces 20, 22 of the first and second blade modules 12, 14. The bond spacers 62 are configured to maintain the mating surfaces 20, 22 of the first and second modules 12, 14 substantially parallel when the blade modules 12, 14 are connected via the scarf joint. In other words, the bond spacers control the thickness of the bond, that is, they maintain a substantially constant distance between the mating surfaces 20, 22, over the surface of the joint, by maintaining a known bond thickness over the surface of the joint. The bond spacers also constrain the movement of the modules 12, 14 relative to each other by rotation around the spanwise (x) axis.

The novel design of the blade modules of the present invention facilitates assembly of the modular wind turbine blade on site. In particular, the scarf joint between the blade modules provide a simple means of assembling the module that does not require precise manoeuvring of the modules to bring connecting structures into alignment. Further, the alignment features provide convenient and reliable means of finely aligning the blade modules together. Ensuring the correct alignment between blade modules is of paramount importance and is greatly facilitated by these alignment features.

The modular wind turbine blade 10 is typically assembled from its constituent blade modules 12, 14 on site, for example at or near a wind farm where the blade 10 is to be installed. The assembly process involves bonding the mating surfaces 20, 22 of the first and second blade modules 12, 14 together to form a scarf joint connecting the two modules or each pair of modules 12, 14. This typically involves applying adhesive on one or both of the mating surfaces 20, 22 of the blade modules 12, 14, followed by curing of the adhesive if necessary (for example using heater pads). Any suitable adhesive may be used, for example a film adhesive or paste adhesive. Alternatively, a local infusion may be used. The first and second blade modules 12, 14 are then moved relative to each other in order to move the mating surfaces 20, 22 relative to each other in a direction generally perpendicular to both spanwise and chordwise axes of the blade module (i.e. along axis y in Figures 5 and 6). For example, the second blade module 14 shown in Figures 2 to 5 may be supported by a structure and the first blade module 12 may be positioned with its mating surface 20 vertically above the mating surface 22 of the second blade module. The first blade module 12 may then be lowered onto the second blade module 14 so as to bring their bonding surfaces (i.e. mating surfaces 20, 22 and alignment features 52, 54, if present, with the applied adhesive) in contact with each other. Moving the mating surfaces 20, 22 of the modules into alignment for bonding may further comprise engaging male alignment features on a mating surface 20, 22 with corresponding female alignment features on the other mating surface 20, 22.

Assembling the first and second modules 12, 14 may further comprise providing bond spacers (e.g. at least three bond spacers 62) between the mating surface 20, 22 of the first and second modules 12, 14, in order to maintain the surfaces 20, 22 substantially parallel.

The bonded joint is easy to inspect and may be tested at this stage using any suitable nondestructive testing techniques known in the art. The bonding process described above is straightforward and the wind turbine blade is accordingly easy to assemble on site.

In other words, a method of assembling a modular wind turbine blade 10 according to embodiments of the invention comprises providing and bonding first and second blade modules 12, 14. Each module comprises an outer shell 36 defining an end 16, 18 of the blade module 12, 14 that is tapered substantially between the windward and the leeward surfaces 32a, 32b, 34a, 34b of the respective module 12, 14 to define a mating end surface 20, 22 on each of the blade modules 12, 14. The mating end surfaces 20, 22 are configured to overlap to form a scarf joint connecting the two modules 12, 14.

Figure 7 shows first and second blade modules 12, 14 according to embodiments of the invention arranged to form a scarf joint 64. The first and second blade modules 12, 14 are supported in a jig structure 66. The jig structure 66 may be used to support a blade module while the other blade module is being connected to the supported blade module. In embodiments, the jig structure may be used to support both blade modules 12, 14 during the bonding step and to apply a clamping pressure on the bond.

The outer shells 36 of the respective blade modules 12, 14 may each be formed as separate half shells in respective first and second (windward and leeward or vice-versa) half moulds of a mould assembly. The half shells may thereafter be bonded together by applying adhesive along the edges of the shells 36 and closing the mould, e.g. placing the leeward mould on top of the windward mould. Shear webs are also bonded inside the blade between opposed spar caps 42a, 42b, 44a, 44b. Figure 8 shows a portion of a mould assembly 68 for making a blade module 12, 14 of the modular wind turbine blade 10. The mould assembly of Figure 8 will be described by reference to the first blade module 12 although the skilled person would understand that the same considerations apply for the second blade module 14, and are not repeated herein simply for the sake of conciseness.

The mould assembly 68 comprises two mould halves: a first half mould 70 and a second half mould 72. The first mould half 70 has a surface shaped to define a first side of the blade module 12 comprising a first aerodynamic surface 32a being a windward surface or a leeward surface. The second mould half 72 has a surface shaped to define a second side of the blade module comprising a second aerodynamic surface being the other of the windward or the leeward surface. The mould assembly has an open and a closed configuration. Figure 8 shows the mould assembly in a transition between the open and closed configuration (as indicated by the arrow 73), the second mould half is moved onto the first mould half. In the closed configuration, the first and second mould halves 70, 72 are mutually opposed and define a hollow interior region between their respective mould surfaces. The mould assembly further comprises an inclined end surface 74 in the hollow interior region. The inclined end surface 74 may extend substantially between the first and second aerodynamic surfaces 32a, 34a defined by the first and second mould halves 70, 72. The inclined end surface 74 defines a tapered end portion 16 of the blade module having a thickness between the first and second aerodynamic surfaces of the module 12 that decreases towards an end 30a of the blade module 12.

As explained above, the inclined end surface may extend over a major section of the distance between the first and second aerodynamic surfaces, with substantially straight minor sections on one or both sides of the inclined surface, such that the tapered end portion of the blade module 12 is configured to form a nibbed scarf joint.

In embodiments, the inclined surface 74 may define male and / or female surface features configured for engagement with corresponding features on the second module 14. The first and second blade modules 12, 14 of the modular wind turbine blade 10 may be formed in separate mould assemblies 68. Alternatively, in embodiments, the first and second blade modules 12, 14 are formed in the same mould assembly. Accordingly, the mould surface may have a first portion shaped to form at least part of the outer shell 36 of the first blade module 12, and a second portion shaped to form at least part of the outer shell 36 of the second blade module 14. The first portion and the second portion of the mould surface may be located in adjacent spanwise sections of the mould.

A moulding process according to the present invention for making blade modules will now be described in further detail with reference to Figure 8. The process will be described by reference to the first module 12, although the skilled person would understand that a similar process applies to the second module 14.

After setting up the mould assembly 68, the next stage in the process involves applying a gel coat (not shown) to the first mould half surface 75 and second mould half surface 77. Following application of the gel coat, one or more first layers comprising glass-fibre plies may be arranged in the mould halves 70, 72 to form the outer skin 38 of the blade module. The one or more first layers are arranged to cover the inclined surface 74 of the mould assembly 68.

After the outer skin layers have been arranged in the mould halves 70, 72, the spar caps 42a, 44a are laid up. This process involves stacking a plurality of carbon pultrusions 46 in the mould halves 70, 72. In the example shown in Figure 8, each stack comprises three carbon pultrusions stacked on top of one another. Any suitable number of pultrusions may be used in practice. Each of the carbon pultrusions preferably has a tapered end 49, and the pultrusions in each spar cap 42a, 44a are arranged such that the tapered end 49 of the pultrusions are aligned to be substantially parallel to the inclined surface 74 of the mould in the first mould half 70 and in the second mould half 72.

Accordingly, the method of laying up the spar caps 42a, 42b may involve arranging the pultrusions successively in the mould halves 70, 72 in order to obtain stacks that have tapered ends 45. This results in the spar caps 42a, 44a having tapered ends 45 corresponding to the inclined surface 74 of the mould assembly 68. The gradient of the taper of the carbon pultrusions in each stack 94 and the arrangement of the successive pultrusions in a stack are selected such that the tapered end 45 of the spar caps 42a, 42b tapers substantially parallel and adjacent to the outer skin 38 on the inclined surface 74 of the mould, when the mould is in a closed configuration. Once the pultrusions have been arranged in the mould halves 70, 72 to form the spar caps 44a, 44b, foam panels (not shown) may be arranged in the mould adjacent to the stacks of pultrusions, if required. One or more second layers comprising glass-fibre plies are arranged in the mould halves 70, 72 over the pultrusions 46 forming the spar caps 42a, 44a, and over the foam panels (if used). The second layers form an inner skin 40 of the respective outer shells 36 of the first and second sides of the blade module 12. Once the second layers forming the inner skins 40 have been arranged in the moulds 70, 72, the shell layup is complete. The mould assembly 68 is then covered with a vacuum film (not shown), which is sealed to form a sealed region encapsulating the shell layup. Air is withdrawn from the sealed region to form an effective vacuum inside the sealed region. The layup is then subject to a resin-infusion process, whereby epoxy resin is admitted into the evacuated sealed region. Resin inlets are provided in the vacuum film in both halves 70, 72 of the mould assembly 68. The epoxy resin flows throughout the layup, between the inner skin 40 and outer skin 38 layers, the spar cap pultrusions 46, and the foam panels (if used). Heat is then applied to cure the resin and integrate the various shell components together. The vacuum film is then removed.

The next step in the manufacture of the blade modules 12 involves loading the shear web 48a into one of the mould halves (illustrated as the second mould half 72 in Figure 7). The shear web 48a extends longitudinally in a spanwise direction and may have an I-shaped cross-section comprising a vertical web disposed between upper and lower horizontal flanges (not shown), wherein horizontal and vertical refer to the x-z and x-y planes, respectively, in Figure 8. Prior to loading the shear web 48a, adhesive is applied to the inner skin 40 of the second half shell (in the embodiment illustrated in Figure 8) in the region of the spar cap 44a. The shear web 48a is then positioned directly over the embedded spar cap 44a and lowered onto the adhesive. The lower flange (not shown) of the shear web 48a is thereby bonded to the spar cap 44a.

As explained above, the shear web 48a has a tapered end 50 that tapers at an angle corresponding to the gradient of the outer skin 38 on the inclined surface 74. The tapered end 50 of the shear web 48a preferably has a return flange, which is arranged in abutment with the outer skin 38 in the region of the inclined surface. Adhesive is applied to the outer skin 38 of the second half shell or to the tapered end 50 / flange of the shear web 48a prior to loading the shear web 48a into the mould half 72. The adhesive serves to bond the shear web 48a to the outer skin 38.

Once the shear web 48a has been bonded to one of the half shells, further adhesive is provided along the upper flange of the shear web 48a. Adhesive is also applied along the leading and trailing edges (not shown) of at least one of the half shells.

The mould assembly is then closed by lifting and turning the first mould half 70 and positioning it on top of the second mould half 72. In this position, the two half shells of the blade module (the first blade module 12 being illustrated in Figure 7) are bonded together. The upper flange (not shown) of the shear web 48a is bonded to the spar cap 42a of the first half shell. This completes the blade module production process.

Once the two half shells of the blade module 12 have been bonded together, and a similar process has been performed to produce the second blade module 14, the first and second blade modules 12, 14 are removed from their (common or respective) mould assembly. As a result of the moulding process described above, the blade modules 12, 14 each include a moulded tapered end 16, 18 in their outer shells 36, partially defined or supported by the tapered ends 45 of the spar caps 42a, 42b, 44a, 44b and shear webs 48a, 48b.

The blade modules 12, 14 are separate parts, which are suitably-sized to facilitate transportation to an assembly site, such as a wind farm location. On site, the blade modules 12, 14 may be bonded together, in the same way as described previously with reference to Figure 6, such that the mating surface 20 of the first blade module 12 overlaps with the mating surface 22 of the second blade module 14 to form a scarf joint.

Many modifications may be made to the above embodiments without departing from scope of the present invention as defined in the following claims.

Claims

1 . A modular wind turbine blade (10) comprising first and second blade modules (12, 14), the first blade module (12) comprising:

a proximal end (28a) and a distal end (30a);

a first side (33a) comprising a first aerodynamic surface (32a) being a windward surface or a leeward surface;

a second side (35a) comprising a second aerodynamic surface (34a) being the other of the windward surface or the leeward surface; and

a tapered end portion (16) having a thickness between the first and second sides that decreases towards the distal end, the tapered end portion defining a mating surface (20) on the second side of the module (35a) that extends between the distal end and the second aerodynamic surface, the second blade (14) module comprising:

a proximal end (28b) and a distal end (30b);

a first side (33b) comprising a first aerodynamic surface (32b) being a windward surface or a leeward surface;

a second side (35b) comprising a second aerodynamic surface (34b) being the other of the windward surface or the leeward surface; and

a tapered end portion (18) having a thickness between the first and second sides that decreases towards the proximal end, the tapered end portion defining a mating surface (22) on the first side (33b) of the module that extends between the proximal end and the first aerodynamic surface, wherein the mating surfaces (20, 22) of the first and second blade modules (12, 14) are configured to form a scarf joint between the first and second blade modules. 2. The modular wind turbine of Claim 1 , wherein each blade module (12, 14) comprises an outer shell (36), and wherein the outer shell defines the first aerodynamic surface (32a, 32b), the second aerodynamic surface (34a, 34b), and the mating surface (20, 22). 3. The modular wind turbine blade of Claim 1 or Claim 2, wherein each blade module (12, 14) further comprises first (42a, 42b) and second (44a, 44b) mutually-opposed spar caps, and wherein each spar cap has a tapered end (45) that partially defines the tapered end portion (16, 18) of the blade module.

4. The modular wind turbine blade of Claim 3, wherein the first spar cap (42a) of the first blade module (12) extends further into the tapered end portion (16) of the first blade module (12) than the second spar cap (44a) of the first blade module, and wherein the second spar cap (44b) of the second blade module (14) extends further into the tapered end portion (18) of the second blade module (14) than the first spar cap (42b) of the second blade module.

5. The modular wind turbine blade of Claim 3 or Claim 4, wherein each spar cap (42, 44) comprises a stack of pultruded strips, each strip having a tapered end that partially defines the tapered end of the spar cap. 6. The modular wind turbine blade of any preceding claim, wherein each blade module (12, 14) further comprises a shear web (48a, 48b) located between the first and second spar caps, the shear web having a tapered end (50) that partially defines the tapered end of the blade module. 7. The modular wind turbine blade of Claim 6, wherein the tapered end (50) of the shear web (48a, 48b) comprises a flange arranged in a plane substantially parallel to the mating surface of the blade module.

8. The modular wind turbine blade of any preceding claim, wherein the tapered end portion (16, 18) of each blade module has a taper gradient of between 1 /50 to 1/200, preferably between 1 /75 to 1 /150, more preferably 1 /80 to 1 /120 and most preferably approximately 1/100.

9. The modular wind turbine blade of any preceding claim, wherein the mating surfaces (20, 22) of the first and second modules comprise alignment features (52, 54) to facilitate alignment between the modules, wherein the alignment features comprise one or more male features on the mating surface of one module for engaging with one or more female features on the mating surface of the other module. 10. The modular wind turbine blade of any preceding claim, wherein bond spacers (62) are provided between the mating surfaces of the first and second blade modules, the bond spacers being configured to maintain the mating surfaces of the first and second modules substantially parallel when the blade modules are connected via the scarf joint.

1 1 . The modular wind turbine blade of any preceding claim, wherein the first blade module comprises a root (26) of the blade and the second blade module comprises a tip

(24) of the blade.

12. A method of assembling a modular wind turbine blade (10) from first and second blade modules (12, 14), wherein the method comprises:

providing first and second blade modules (12, 14) , each blade module comprising a proximal end (28a, 28b) , a distal end (30a, 30b), a first side (33a, 33b) comprising a first aerodynamic surface (32a. 32b) being a windward or a leeward surface, a second side (35a, 35b) comprising a second aerodynamic surface (34a, 34b) being the other of the windward surface or the leeward surface, and a tapered end portion (16, 18); wherein the tapered end portion has a thickness between the first and second sides that decreases towards the distal end in the first module and towards the proximal end in the second module, the tapered end portion of the first module defining a mating surface (20) on the second side of the first module that extends between the distal end and the second aerodynamic surface of the first module, and the tapered end portion of the second module defining a mating surface (22) on the first side of the second module that extends between the proximal end and the first aerodynamic surface of the second module; and

bonding the mating surfaces of the first and second blade modules together to form a scarf joint connecting the two modules. 13. The method of Claim 12, wherein the step of bonding the modules together comprises moving the mating surfaces (20, 22) of the modules together in a direction generally perpendicular to both spanwise and chordwise axes of the blade modules.

14. The method of Claim 12 or Claim 13, further comprising supporting the first and second blade modules (12, 14) in a jig (66) during the bonding step and applying a clamping pressure via the jig between the mating surfaces of the blade modules.

15. A mould assembly (68) for making a blade module of a modular wind turbine blade, the mould assembly comprising: a first mould half (70) having a mould surface shaped to define a first side of the blade module comprising a first aerodynamic surface being a windward surface or a leeward surface;

a second mould half (72) having a mould surface shaped to define a second side of the blade module comprising a second aerodynamic surface being the other of the windward surface or the leeward surface;

the mould assembly having open and closed configurations, wherein in the closed configuration the first and second mould halves (70, 72) are mutually opposed and define a hollow interior region between their respective mould surfaces;

wherein the mould assembly further comprises an inclined end surface (74) in the hollow interior region, the inclined end surface extending substantially between the first and second aerodynamic surfaces defined by the first and second mould halves and being shaped to define a tapered end portion of the blade module.