Efficient wind turbine blades, wind turbine blade structures, and associated systems and methods of manufacture, assembly and use

TECHNICAL FIELD

0001The present disclosure is directed generally to efficient wind turbine blades and wind turbine blade structures, including lightweight, segmented and/or otherwise modular wind turbine blades, and associated systems and methods of manufacture, assembly, and use.

BACKGROUND

0002As fossil fuels become scarcer and more expensive to extract and process, energy producers and users are becoming increasingly interested in other forms of energy. One such energy form that has recently seen a resurgence is wind energy. Wind energy is typically harvested by placing a multitude of wind turbines in geographical areas that tend to experience steady, moderate winds. Modern wind turbines typically include an electric generator connected to one or more wind-driven turbine blades, which rotate about a vertical axis or a horizontal axis.

0003In general, larger (e.g., longer) wind turbine blades produce energy more efficiently than do short blades. Accordingly, there is a desire in the wind turbine blade industry to make blades as long as possible. However, long blades create several challenges. For example, long blades are heavy and therefore have a significant amount of inertia, which can reduce the efficiency with which the blades produce energy, particularly at low wind conditions. In addition, long blades are difficult to manufacture and in many cases are also difficult to transport. Accordingly, a need remains for large, efficient, lightweight wind turbine blades, and suitable methods for transporting and assembling such blades.

SUMMARY OF INVENTION

0004According to the present invention there is provided a wind turbine blade, comprising: an external aerodynamic surface having a longitudinally-extending spanwise axis, a chordwise axis extending transverse to the spanwise axis, and a thickness axis extending transverse to both the chordwise and spanwise axes; and a plurality of longitudinally-extending spars providing internal support for the aerodynamic surface, wherein at least one of the spars includes a laminate of precured composite material, the laminate of precured composite material including: a plurality of precured composite layers; and a plurality of adhesive layers interposed between adjacent precured composite layers.

0005Preferably each of the precured composite layers includes a precured fiber-reinforced resin product. Each of the precured composite layers may include a precured composite pultrusion.

0006The aerodynamic surface defines an airfoil cross-section, and the plurality of longitudinally-extending spars may include a pressure spar and a suction spar spaced apart from each other along the thickness axis, and an aft spar spaced apart from both the pressure and suction spars along the chordwise axis, and wherein each of the pressure, suction and aft spars are comprised of a laminate of precured composite pultrusions.

0007The wind turbine blade may further comprise a plurality of longitudinally spaced-apart ribs, and wherein the at least one spar is attached to the ribs.

0008A strap may be clamped circumferentially around the plurality of precured composite layers.

0009The wind turbine blade may further comprise: a plurality of longitudinally spaced-apart ribs; and a plurality of truss attachment members, wherein each of the truss attachment members includes a first piece and a corresponding second piece, wherein each of the first pieces is attached to the corresponding second piece to clamp a portion of the precured composite layers together therebetween, and wherein at least one of the first piece and the second piece of each truss attachment member is attached to one of the longitudinally spaced apart ribs.

BRIEF DESCRIPTION OF THE DRAWINGS

0010<ul id="ul0001" list-style="none"><li><figref idref="f0001">Figure 1</figref> is a partially schematic, isometric illustration of a wind turbine system having blades configured in accordance with an embodiment of the disclosure.</li><li><figref idref="f0002">Figure 2A</figref> is a partially schematic, side elevation view of a wind turbine blade having a hybrid truss/non-truss structure in accordance with an embodiment of the disclosure.</li><li><figref idref="f0002">Figure 2B</figref> is an enlarged illustration of a portion of the wind turbine blade shown in <figref idref="f0002">Figure 2A</figref>.</li><li><figref idref="f0003">Figures 2C-2F</figref> are schematic cross-sectional illustrations of wind turbine blade portions having truss structures in accordance with several embodiments of the disclosure.</li><li><figref idref="f0004">Figure 3</figref> is a partially schematic, isometric illustration of a portion of a wind turbine blade having three spars that form part of a truss structure in accordance with an embodiment of the disclosure.</li><li><figref idref="f0004">Figure 4</figref> is a partially schematic, isometric illustration of a portion of a wind turbine blade having a non-truss internal structure in accordance with an embodiment of the disclosure.</li><li><figref idref="f0005">Figure 5A</figref> is a partially schematic, isometric illustration of an internal portion of a wind turbine blade having truss attachment members configured in accordance with an embodiment of the disclosure.</li><li><figref idref="f0005 f0006">Figures 5B-5C</figref> are enlarged isometric illustrations of a truss attachment member configured in accordance with an embodiment of the disclosure.</li><li><figref idref="f0006 f0007">Figures 5D-5F</figref> illustrate several views of an internal portion of a wind turbine blade having a truss structure secured at least in part with truss attachment members configured in accordance embodiments of the disclosure.</li><li><figref idref="f0008">Figure 6A</figref> is a partially schematic, side elevation view of a spar having multiple portions, each with layers that terminate at staggered positions to form a non-monotonically varying bond line.</li><li><figref idref="f0009">Figure 6B</figref> is an illustration of an embodiment of the structure shown in <figref idref="f0008">Figure 6A</figref> with clamps positioned to prevent or limit delamination in accordance with an embodiment of the disclosure.</li><li><figref idref="f0009">Figure 6C</figref> is an enlarged illustration of a portion of the spar shown in <figref idref="f0009">Figure 6B</figref>.</li><li><figref idref="f0010">Figures 6D-6G</figref> are partially schematic illustrations of spars having joints configured in accordance with further embodiments of the disclosure.</li><li><figref idref="f0011">Figure 7A</figref> is a partially schematic, isometric illustration of a spar having layers that fan out at a hub attachment region in accordance with an embodiment of the disclosure.</li><li><figref idref="f0011">Figure 7B</figref> is a partially schematic, isometric illustration of a spar connected to fan-shaped transition plates at a hub attachment region in accordance with another embodiment of the disclosure.</li><li><figref idref="f0012">Figure 8A</figref> is a partially schematic, side elevation view of a wind turbine blade structure subassembly configured in accordance with an embodiment of the disclosure, and <figref idref="f0012">Figure 8B</figref> is an enlarged, partially schematic end view of a rib from the subassembly of <figref idref="f0012">Figure 8A</figref>.</li><li><figref idref="f0013 f0014">Figures 9A-9C</figref> are partially schematic, not-to-scale isometric views of inboard, midboard, and outboard spar portions configured in accordance with embodiments of the disclosure.</li><li><figref idref="f0015">Figures 9D and 9E</figref> include partially schematic, cut-away side elevation views of the inboard and midboard spar portions of <figref idref="f0013">Figures 9A</figref> and <figref idref="f0014">9B</figref>, respectively, and <figref idref="f0016">Figure 9F</figref> is a partially schematic, side elevation view of a joint between adjacent end portions of the inboard spar portion and the midboard spar portion of <figref idref="f0013">Figures 9A</figref> and <figref idref="f0014">9B</figref>, configured in accordance with several embodiments of the disclosure.</li><li><figref idref="f0017">Figures 10A</figref> and <figref idref="f0019">10C-10E</figref> are a series of partially schematic, side elevation views of a portion of a blade subassembly illustrating various stages in a method of manufacturing a blade spar in accordance with an embodiment of the disclosure, and <figref idref="f0017">Figure 10B</figref> is an enlarged end view of a portion of a representative rib illustrating another stage in the method of blade manufacture.</li><li><figref idref="f0019 f0020 f0021">Figures 11A-11C</figref> are an enlarged isometric view of a portion of a wind turbine blade structure, an end view of a representative rib, and an isometric view of the wind turbine blade structure, respectively, illustrating various aspects of a spar manufactured in accordance with an embodiment of the disclosure.</li><li><figref idref="f0022">Figure 12A</figref> is an isometric view of a compressing apparatus configured in accordance with an embodiment of the disclosure, and <figref idref="f0023">Figure 12B</figref> is a partially exploded isometric view of the compressing apparatus of <figref idref="f0022">Figure 12A</figref>.</li><li><figref idref="f0024">Figures 13A and 13B</figref> are enlarged isometric views of opposing end portions of a first tool portion of the compressing apparatus of <figref idref="f0022">Figures 12A</figref> and <figref idref="f0023">12B</figref>.</li><li><figref idref="f0025">Figure 14A</figref> is an isometric view of a second tool portion of the compressing apparatus of <figref idref="f0022">Figures 12A</figref> and <figref idref="f0023">12B</figref>, and <figref idref="f0025">Figure 14B</figref> is a partially exploded isometric view of the second tool portion of <figref idref="f0025">Figure 14A</figref>.</li><li><figref idref="f0026">Figure 15</figref> is an enlarged, cross-sectional end view of a laminated blade spar being compressed by the compressing apparatus of <figref idref="f0022">Figures 12A</figref> and <figref idref="f0023">12B</figref> during an adhesive curing cycle in accordance with an embodiment of the disclosure.</li><li><figref idref="f0026">Figure 16</figref> is a partially schematic isometric view of a lay-up tool illustrating various stages in a method of manufacturing a wind turbine blade spar in accordance with another embodiment of the disclosure.</li></ul>

DETAILED DESCRIPTION

0011The present disclosure is directed generally to efficient wind turbine blades, wind turbine blade spars and other structures, and associated systems and methods of manufacture, assembly, and use. Several details describing structures and/or processes that are well-known and often associated with wind turbine blades are not set forth in the following description to avoid unnecessarily obscuring the description of the various embodiments of the disclosure. Moreover, although the following disclosure sets forth several embodiments, several other embodiments can have different configurations or different components than those described in this section. In particular, other embodiments may have additional elements or may lack one or more of the elements described below with reference to <figref idref="f0001 f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009 f0010 f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018 f0019 f0020 f0021 f0022 f0023 f0024 f0025 f0026">Figures 1-16</figref>. In <figref idref="f0001 f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009 f0010 f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018 f0019 f0020 f0021 f0022 f0023 f0024 f0025 f0026">Figures 1-16</figref>, many of the elements are not drawn to scale for purposes of clarity and/or illustration.

0012<figref idref="f0001">Figure 1</figref> is a partially schematic, isometric illustration of an overall system 100 that includes a wind turbine 103 having blades 110 configured in accordance with an embodiment of the disclosure. The wind turbine 103 includes a tower 101 (a portion of which is shown in <figref idref="f0001">Figure 1</figref>), a housing or nacelle 102 carried at the top of the tower 101, and a generator 104 positioned within the housing 102. The generator 104 is connected to a shaft or spindle having a hub 105 that projects outside the housing 102. The blades 110 each include a hub attachment portion 112 at which the blades 110 are connected to the hub 105, and a tip 121 positioned radially or longitudinally outwardly from the hub 105. In an embodiment shown in <figref idref="f0001">Figure 1</figref>, the wind turbine 103 includes three blades connected to a horizontally-oriented shaft. Accordingly, each blade 110 is subjected to cyclically varying loads as it rotates between the 12:00, 3:00, 6:00 and 9:00 positions, because the effect of gravity is different at each position. In other embodiments, the wind turbine 103 can include other numbers of blades connected to a horizontally-oriented shaft, or the wind turbine 103 can have a shaft with a vertical or other orientation. In any of these embodiments, the blades 110 can have structures configured in accordance with the arrangements described in further detail below with reference to <figref idref="f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009 f0010 f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018 f0019 f0020 f0021 f0022 f0023 f0024 f0025 f0026">Figures 2A-16</figref>.

0013<figref idref="f0002">Figure 2A</figref> is a partially schematic, partially cut-away illustration of one of the blades 110 shown in <figref idref="f0001">Figure 1</figref>. The blade 110 extends outwardly in a radial or longitudinal direction from an inner region 113 that includes the hub attachment portion 112, to an outer region 114 that includes the tip 121. The hub attachment portion 112 can include one or more hub attachment elements, e.g., a ring with a bolt circle, one or more bearings, fasteners, and/or other elements. The internal structure of the blade 110 can be different at the inner region 113 than at the outer region 114. For example, the inner region 113 can include a truss structure 140 formed from a plurality of longitudinally or radially extending beams or spars 170, chordwise extending ribs 142, and truss members 143 connected among the spars 170 and the ribs 142. The truss structure 140 can be surrounded by a skin 115 (most of which is removed in <figref idref="f0002">Figure 2A</figref>) that presents a smooth, aerodynamic surface to the wind during operation. The outer region 114 can include a non-truss structure, which will be described in further detail later with reference to <figref idref="f0004">Figure 4</figref>. As used herein, the term "truss structure" refers generally to a load-bearing structure that includes generally straight, slender members forming closed shapes or units (e.g., triangular units). The term "non-truss structure" refers generally to a load-bearing structure having an arrangement that does not rely on, or does not primarily rely on, straight slender members forming closed-shape units for strength. Such structures may include, for example, monocoque and semi-monocoque structures. Accordingly, the skin 115 of the inner region 113 is generally non-load bearing, and the skin 115 at the outer region 114 is load bearing.

0014In a particular aspect of an embodiment shown in <figref idref="f0002">Figure 2A</figref>, the blade 110 includes three segments 116, shown as a first segment 116a, a second segment 116b, and a third segment 116c. The first and second segments 116a, 116b can each have the truss structure 140 described above, and the third segment 116c can have a non-truss structure. Accordingly, the blade 110 can have a truss structure for the inner two-thirds of its span, and a non-truss structure for the outer one-third. In other embodiments, these values can be different, depending, for example, on the size, shape and/or other characteristics of the blade 110. For example, in one embodiment, the truss structure 140 extends outwardly over a majority of the span or length of the blade 110, but by an amount less than or greater than two-thirds of the length. The segments 116 can be manufactured individually and then connected to each other at a manufacturing facility, or at an end user installation site. For example, the segments 116 can each be sized to fit in a 53-foot or other suitably sized container for shipment. In other embodiments, one or more of the segments (e.g., the first segment 116a and the second segment 116b) can be built entirely at the installation site.

0015In still further embodiments, the blade 110 can include other numbers of segments 116 (e.g., two or more segments). In any of these embodiments, individual segments 116 can include ribs 142, truss members 143, and portions of the spars 170 that extend for the length of the segment 116. The segments 116 can be joined to each other by joining adjacent spar portions, e.g., as discussed later with reference to <figref idref="f0008 f0009">Figures 6A-6C</figref> and <figref idref="f0012 f0026">8A-16</figref>. For example, the first segment 116a can include one or more first spar segments that are joined to corresponding second spar segments of the second segment 116b. The resulting joined spars can extend along corresponding generally smooth, continuous longitudinal axes. In any of these embodiments, the skin 115 can be laid up on the truss structure 140 with or without forming a joint at the interface between adjacent segments 116. For example, the spar portions can be joined at a location between two neighboring ribs 142, and a relatively small panel of skin 115 can be laid over the spar joint and the two neighboring ribs 142. The neighboring ribs 142 can be spaced apart by about one meter in one embodiment, and by other values in other embodiments. Larger panels of the skin 115 can be laid inboard and outboard of the small panel. In another embodiment, the skin 115 can have no spanwise joints and can be laid up as a continuous element. In any of these embodiments, the skin 115 can be attached (e.g., adhesively bonded or ultrasonically bonded) to the ribs 142 alone, or to the ribs 142 and the spars 170. In any of these embodiments, the truss structure 140 can serve as primary structure for carrying shear and bending loads in the blade 110.

0016<figref idref="f0002">Figure 2B</figref> is a partially schematic, isometric illustration of a portion of the blade 110 shown in <figref idref="f0002">Figure 2A</figref>, taken at a location where the internal structure of the blade 110 is a truss structure 140. Accordingly, the truss structure 140 can include multiple spars 170 (four are shown in <figref idref="f0002">Figure 2B</figref>) attached to spaced-apart ribs 142. Truss members 143 can be connected between neighboring spars 170, for example, using techniques described later with reference to <figref idref="f0005 f0006 f0007">Figures 5A-5F</figref>.

0017<figref idref="f0003">Figures 2C-2F</figref> are schematic, cross-sectional illustrations of blades 110 having truss arrangements configured in accordance with a variety of embodiments. <figref idref="f0003">Figure 2C</figref> illustrates a blade 110 having four spars 170 positioned in a generally rectangular arrangement. <figref idref="f0003">Figure 2D</figref> illustrates a blade 110 having six spars 170, including four spars 170 positioned in a generally rectangular arrangement, and two additional spars 170, one positioned forward of the generally rectangular arrangement, and one positioned aft of the generally rectangular arrangement. <figref idref="f0003">Figure 2E</figref> illustrates a blade 110 having four spars 170 positioned in a generally diamond-shaped arrangement, and <figref idref="f0003">Figure 2F</figref> illustrates a blade 110 having three spars 170 positioned in a triangular arrangement. In other embodiments, the blade 110 can include spars 170 having other arrangements.

0018<figref idref="f0004">Figure 3</figref> is an isometric illustration of an internal portion of a blade 110 having a truss structure 140 that includes a triangular arrangement of spars 170, generally similar to that shown in <figref idref="f0003">Figure 2F</figref>. The blade 110 extends in a longitudinal radial, or spanwise direction along a spanwise axis S, and extends fore and aft along a transverse chordwise axis C. Accordingly, the blade 110 can have a forward leading edge region 117 with a leading edge 117a and an aft trailing edge region 118 with a trailing edge 118a. The thickness of the blade 110 can be measured relative to a thickness axis T transverse to both the spanwise axis S and the chordwise axis C.

0019In a particular embodiment shown in <figref idref="f0004">Figure 3</figref>, the blade 110 can include three spars 170, including a first spar 170a and a second spar 170b, both positioned at the leading edge region 117 and/or toward the leading edge 117a and spaced apart from each other along the thickness axis T. The blade 110 can further include a third spar 170c positioned at the trailing edge region 118 and/or toward the trailing edge 118a and spaced apart from both the first spar 170a and the second spar 170b along the chordwise axis C. Each of the spars 170a-170c is attached to a plurality of ribs 142 (one of which is visible in <figref idref="f0004">Figure 3</figref>) which are in turn spaced apart from each other along the spanwise axis S. Each of the spars 170a-c can have a generally rectangular cross-section. The forward spars 170a, 170 can have a chordwise dimension greater than a thickness dimension, and the aft spar 170c can have a thickness dimension greater than a chordwise dimension. The third spar 170c can extend over a majority of the thickness dimension of the blade 110 and in a particular embodiment, can extend over the entirety or nearly the entirety of the thickness dimension. For example, the third spar 170c can have a dimension in the thickness direction that is about the same as the dimension of the rib 142 in the thickness direction.

0020One feature of the arrangement shown in <figref idref="f0004">Figure 3</figref> is that it can include a single spar (the third spar 170c) at the trailing edge region 118. For example, the truss structure 140 can include only three longitudinally extending spars 170 at any given longitudinal location, with only one of the spars 170 at the trailing edge region 118. This arrangement can allow the third spar 170c to be positioned a greater chordwise distance away from the first and second spars 170a, 170b than some arrangements that include four spars (e.g., the arrangement shown in <figref idref="f0002 f0003">Figures 2B-2C</figref>). By spacing the third spar 170c further away from the first and second spars 170a, 170b, the ability of the truss structure 140 to handle large loads in the chordwise direction C is enhanced. This can be particularly important for wind turbine blades mounted to a horizontal shaft because such blades are subjected to significant gravity loads in the chordwise direction C when the blades are at the 3:00 and 9:00 positions described above with reference to <figref idref="f0001">Figure 1</figref>. Accordingly, it is expected that this arrangement may be lighter and/or better able to withstand significant loads in the chordwise direction C than at least some arrangements having four spars. At the same time, it is expected that this arrangement will be simpler, lighter and/or less costly than arrangements that include more than four spars e.g., the arrangement described above with reference to <figref idref="f0003">Figure 2D</figref>.

0021The internal structural components described above can be manufactured from suitable composite and/or non-composite materials. For example, the spars 170 can be formed from a laminate of layers that each include unidirectional fiberglass, carbon fibers, and/or other fibers in a matrix of suitable thermoset and/or thermoplastic resins. The fibers can be oriented generally parallel to the spanwise axis S over most of the length of the blade 110, and can have other orientations at specific locations, as described further below with reference to <figref idref="f0008 f0009 f0010 f0011">Figures 6A-7A</figref>. In other embodiments, composite spars can also be fabricated by infusion, prepreg, pultrusion, or press molding. In still further embodiments, the spars 170 can be formed from metallic materials, including machined, forged or cast alloys, metallic laminates, sandwich structures, as well as metal/composite hybrids (e.g., composite facesheets with metallic core, e.g., honeycomb core), etc. The truss members 143 can be formed from aluminum (e.g., 2024-T6 aluminum) or another suitable metal, composite, or other material. The ribs 142 can be formed from a composite of fiberglass and foam or balsa, e.g., a balsa core sandwiched between fiberglass faceplates. In other embodiments, the ribs 142 can be formed from fiberglass alone, without a foam or balsa core, or the ribs 142 can be formed with other techniques and/or components. For example, the ribs 142 can have a corrugated or beaded construction. The ribs 142 can be formed from a single panel, or two spaced apart panels, with no core structure between the two panels. The ribs 142 can also be made from metal; from composite materials such as fiberglass, carbon fibers, and/or other fibers in a matrix of thermoset and/or thermoplastic; and/or from (unreinforced) plastic materials (e.g., resin without fibers). For example, composite ribs can be fabricated by wet lamination, infusion, prepreg, sprayed chopped fiber, press molding, vacuum forming, and/or other suitable mass production techniques.

0022<figref idref="f0004">Figure 4</figref> is a partially schematic illustration of a portion of the wind turbine blade 110 located at the outer region 114 described above with reference to <figref idref="f0002">Figure 2A</figref>. In this embodiment, the internal structure of the wind turbine blade 110 at the outer region 114 is not a truss structure. For example, the structure can instead include a relatively thin web 119 oriented generally parallel to the thickness axis T and extending along the spanwise axis S. The web 119 can be connected to or formed integrally with flanges 120 extending in the chordwise direction C. Spanwise-extending spars 470a, 470b are attached to each of the flanges 120 and are in turn connected to a skin 115, a portion of which is shown in <figref idref="f0004">Figure 4A</figref>. In one embodiment, the structure can include spaced-apart ribs 142 positioned in the trailing edge region 118. In other embodiments, such ribs 142 can extend into the leading edge region 117 as well. The skin 115 can be formed from a fiberglass-balsa-fiberglass sandwich, or a fiberglass-foam-fiberglass sandwich. In other embodiments, the skin 115 can be formed from composite materials fabricated by wet lamination, infusion, prepreg, sprayed chopped fiber, press molding, vacuum forming, and/or other mass production techniques. The skin 115 can have the same construction in both the outer region 114 shown in <figref idref="f0004">Figure 4</figref>, and the inner region 113 shown in <figref idref="f0004">Figure 3</figref>. The ribs 142 can have a similar construction. The web 119 and flanges 120 can be formed from fiberglass, e.g., unidirectional fiberglass. In other embodiments, any of the foregoing components can be formed from other suitable materials. The spars 470a, 470b located in the outer region 114 can be bonded to corresponding spars at the inner region 113 (<figref idref="f0002">Figure 2A</figref>) using a variety of techniques including, but not limited to, those described later with reference to <figref idref="f0008 f0009">Figures 6A-6C</figref> and <figref idref="f0012 f0026">8A-16</figref>. In any of these embodiments, the spars 470a, 470b located in the outer region 114 can extend along the same generally smooth, continuous longitudinal axes as the counterpart spars in the inner region 113 to efficiently transfer loads from the outer region 114 to the inner region 113.

0023One feature of the arrangement described above with reference to <figref idref="f0002 f0003 f0004">Figures 2A-4</figref> is that the blade 110 can include both truss and non-truss internal structures. An advantage of this arrangement is that it can be more structurally efficient than a design that includes either a truss structure alone or a non-truss structure alone. For example, the truss structure can be used at the inner region 113 (e.g., near the hub) where bending loads are higher than they are near the tip 111, and where the blade 110 is relatively thick. At the outer region 114, the non-truss structure can be easier to integrate into this relatively thin portion of the blade 110. The non-truss structure in this region is also expected to be more structurally efficient than a truss structure, which tends to lose efficiency when the aspect ratio of the closed shapes formed by the truss members becomes large.

0024<figref idref="f0005">Figure 5A</figref> is a partially schematic, isometric illustration of a portion of a representative truss structure 140 configured in accordance with a particular embodiment of the disclosure. In this embodiment, the truss structure 140 includes three spars 170, identified as a first spar 170a, a second spar 170b and a third spar 170c. In other embodiments, the truss structure 140 can have other numbers and/or arrangements of spars 170. In any of these embodiments, the truss structure 140 can include truss members 143 and ribs 142, in addition to the spars 170. Truss attachment members 150 can connect the truss members 143 to the spars 170. For example, truss members 143 can include a first attachment feature 151a (e.g., a first mounting hole) that is aligned with a second attachment feature 151b (e.g., a second corresponding mounting hole) carried by the truss attachment member 150. When the two attachment features 151a, 151b include corresponding holes, they can be connected via an additional fastening member 157, e.g., a rivet or threaded fastener. In other embodiments, the attachment features 151a, 151b can be connected directly to each other, for example, if one feature includes an expanding prong and the other includes a corresponding hole.

0025<figref idref="f0005">Figure 5B</figref> illustrates a representative portion of the truss structure 140 described above with reference to <figref idref="f0005">Figure 5A</figref>. As shown in <figref idref="f0005">Figure 5B</figref>, a representative truss attachment member 150 is positioned along the second spar 170b so as to receive and attach to multiple truss members 143. Each of the truss members 143 can include a slot 145 which receives a flange-shaped truss attachment portion 154 of the truss attachment member 150. In this embodiment, the attachment features 151a, 151b include corresponding holes 158a, 158b that are connected with the fastening members 157 described above with reference to <figref idref="f0005">Figure 5A</figref>.

0026<figref idref="f0006">Figure 5C</figref> is an enlarged isometric illustration of one of the truss attachment members 150 shown in <figref idref="f0005">Figures 5A-5B</figref>. In this embodiment, the truss attachment member 150 includes a spar attachment portion 152 (e.g. having a channel 153 in which the corresponding spar 170 is positioned), and one or more truss attachment portions 154 (two are shown in <figref idref="f0005">Figure 5B</figref>). The truss attachment portions 154 can have a flat, flange-type shape in which the second attachment features 151b (e.g., the mounting holes 158b) are positioned. In a particular embodiment shown in <figref idref="f0005">Figure 5B</figref>, the truss attachment member 150 is formed from two complementary components or pieces: a first component or piece 156a and second component or piece 156b. The first piece 156a includes two first flange portions 155a, and the second piece 156b includes two second flange portions 155b. When the two pieces 156a, 156b are placed together, the first flange portions 155a mate with corresponding second flange portions 155b to form two flange pairs, each of which forms one of the truss attachment portions 154. Accordingly, each first flange portion 155a can be in surface-to-surface contact with the corresponding second flange portion. The first and second portions 155a, 155b can have aligned mounting holes configured to receive a corresponding fastener. The two pieces 156a, 156b also form the channel 153. In a particular aspect of this embodiment, the first piece 156a and the second piece 156b are sized so that, when placed together, the resulting channel 153 is slightly smaller than the cross section of the spar around which it is placed. Accordingly, when the two pieces 156a, 156b are forced toward each other, the truss attachment member 150 can be clamped around the corresponding spar, thus securing the truss attachment member 150 in position. For example, when second attachment feature 151b includes a mounting hole, the manufacturer can pass a fastener 157 through the mounting hole to both attach the truss attachment member 150 to the corresponding truss member 143 (<figref idref="f0005">Figure 5A</figref>), and also clamp the truss attachment member 150 around the corresponding spar 170 (<figref idref="f0005">Figure 5A</figref>).

0027In other embodiments, the truss attachment members 150 can be formed using other techniques. For example, the truss attachment members 150 can be extruded, molded, cast, or machined. In any of these embodiments, the truss attachment member 150 can be formed from a light-weight material, e.g. a metal such as aluminum or steel, or a suitable composite. In other embodiments, the truss attachment members 150 can be formed from other materials that readily accommodate the attachment features 151b. The truss attachment members 150 can be secured to the corresponding spars using the clamping technique described above, and/or other techniques, including but not limited to adhesive bonding or co-curing.

0028The truss attachment members 150 can have other shapes and/or configurations in other embodiments. For example, the spar attachment portion 152 need not extend around the entire circumference of the corresponding spar 170, but can instead extend around only a portion of the spar 170. In some embodiments for which an adhesive joint between the truss attachment member 150 and the spar 170 provides sufficient strength, the truss attachment member 150 can have only a relatively small surface contacting the spar 170. The truss attachment member can include other numbers of truss attachment portions 154, e.g., only one truss attachment portion 154, or more than two truss attachment portions 154.

0029In still further embodiments, the truss attachment members 150 can be formed from other materials. For example, the truss attachment members 150 can be formed from a composite material. In a particular example, the truss attachment member 150 is formed by wrapping strands (e.g., plies of strands) around the spar 170, and overlapping the ends of the strands (or plies) to form one or more flanges. The strands are attached to the spar 170 with an adhesive, or via a co-curing process. The corresponding truss member 143 attached to the truss attachment member 150 can have a slot 145 that receives the flange and is secured to the flange with an adhesive.

0030One feature of an embodiment of the truss attachment member 150 described above with reference to <figref idref="f0005 f0006">Figures 5A-5C</figref> is that it does not require holes in the spar 170 to provide an attachment between the spar 170 and the corresponding truss members 143. Instead, the truss attachment member 150 can be clamped or otherwise secured to the spar 170 and the holes can be located in the truss attachment member 150 rather than in the spar 170. This arrangement can be particularly beneficial when the spar 170 includes composite materials, as it is typically more difficult to form mounting holes in such materials, and/or such holes may be more likely to initiate propagating fractures and/or create stress concentrations in the spar 170.

0031<figref idref="f0006 f0007">Figures 5D-5F</figref> illustrate other views of the truss structure 140 described above with reference to <figref idref="f0005">Figure 5A</figref>. <figref idref="f0006">Figure 5D</figref> is a side view of a portion of the truss structure 140, illustrating a representative rib 142. The rib 142 includes a web 146 and a flange 147 extending around the web 146. The web 146 can include one or more cut-outs 148 (three are shown in <figref idref="f0006">Figure 5D</figref>) that accommodate the corresponding spars 170a-170c. In a particular embodiment shown in <figref idref="f0006">Figure 5D</figref>, the cut-out 148 accommodating the third spar 170c can extend entirely through the thickness of the rib 142. As a result, a trailing edge portion 141 of the rib 142 is discontinuous from the rest of the web 146 of rib 142. Accordingly, the flange 147 of the rib 142 can secure the trailing edge portion 141 of the rib 142 to the rest of the rib 142.

0032<figref idref="f0007">Figure 5E</figref> is a view of the truss structure 140 from a position forward of and above the leading edge region 117, and <figref idref="f0007">Figure 5F</figref> is a view of the truss structure 140 from a position above the trailing edge region 118. As is shown in both <figref idref="f0007">Figures 5E and 5F</figref>, the truss members can include first truss members 143a and second truss members 143b. The first truss members 143a can be positioned adjacent to the web 146 of a corresponding rib 142, and can be joined to the web 146, in particular, via an adhesive or other bonding technique. Accordingly, the first truss members 143a in combination with the truss attachment members 150 can secure the ribs 142 to the spars 170a-170c. The second truss members 143b can extend transversely (e.g., diagonally) between neighboring ribs 142 and/or spars 170 to increase the overall strength and stiffness of the truss structure 140.

0033<figref idref="f0008">Figure 6A</figref> is a partially schematic, side elevation view of a joint between two portions 171 of a spar 170. The two portions can include a first portion 171a and a second portion 171b, and the joint can be formed along a non-monotonically varying (e.g., zig-zagging) bond line 176. Such a bond line 176 is expected to produce a stronger bond between the first and second portions 171a, 171b than is a straight or diagonal bond line. The first and second portions 171a, 171b may each form part of a different neighboring segment of the overall spar 170, as described above with reference to <figref idref="f0002">Figure 2A</figref>. For example, the first portion 171a can be part of the first segment 116a shown in <figref idref="f0002">Figure 2A</figref>, and the second portion 171b can be part of the second segment 116b.

0034The first portion 171a can include multiple, stacked, laminated first layers 172a, and the second portion 171b can include multiple, stacked, laminated second layers 172b. In a particular embodiment, the layers 172a, 172b can be formed from a unidirectional fiber material (e.g., fiberglass or a carbon fiber) and a corresponding resin. Each of the layers 172a, 172b can be formed from a single ply or multiple plies (e.g., six plies). The layers 172a, 172b can be prepreg layers, hand lay-ups, pultrusions, or can be formed using other techniques, e.g., vacuum-assisted transfer molding techniques. The first layers 172a terminate at first terminations 173a, and the second layers 172b terminate at second terminations 173b. Neighboring terminations 173a, 173b located at different positions along the thickness axis T can be staggered relative to each other to create the zig-zag bond line 176. This arrangement produces projections 174 and corresponding recesses 175 into which the projections 174 fit. In a particular aspect of this embodiment, each layer has a termination that is staggered relative to its neighbor, except where the bond line 176 changes direction. At such points, two adjacent layers can be terminated at the same location and bonded to each other, to prevent a single layer from being subjected to increased stress levels.

0035During a representative manufacturing process, each of the first layers 172a are stacked, bonded and cured, as are each of the second layers 172b, while the two portions 171a, 171b are positioned apart from each other. The layers 172, 172b are pre-cut before stacking so that when stacked, they form the recesses 175 and projections 174. After the two portions 171a, 171b have been cured, the recesses 175 and/or projections 174 can be coated and/or filled with an adhesive. The two portions 171a, 171b are then brought toward each other so that projections 174 of each portion are received in corresponding recesses 175 of the other. The joint region can then be bonded and cured.

0036<figref idref="f0009">Figure 6B</figref> is an illustration of a spar 170 having a bond line 176 generally similar to that described above with reference to <figref idref="f0008">Figure 6A</figref>. As is also shown in <figref idref="f0009">Figure 6B</figref>, the spar 170 can include one or more clamps or straps 177 that are positioned at or near the bond line 176. The clamps 177 can be positioned to prevent or halt delamination that might result between any of the layers in the composite spar 170. For example, as shown in <figref idref="f0009">Figure 6C</figref>, if a potential delamination 178 begins between two layers 172a, the compressive force provided by the clamp 177 can prevent the delamination 178 from spreading further in a spanwise direction. The clamp 177 can be positioned where it is expected that the potential risk of delamination is high, e.g., at or near the termination 173 of the outermost layers 172a, 172b shown in <figref idref="f0009">Figure 6B</figref>. In other embodiments, the function provided by the clamps 177 can be provided by other structures. For example, the truss attachment members 150 described above can perform this function, in addition to providing attachment sites for the truss members.

0037<figref idref="f0010">Figures 6D-6G</figref> are a series of partially schematic, side elevation views of spars 670a-670d, respectively, illustrating various joints that can be formed between adjacent spar portions 671 in accordance with other embodiments of the disclosure. The spars 670 can be at least generally similar in structure and function to the spar 170 described in detail above. For example, as shown in <figref idref="f0010">Figure 6D</figref>, the spar 670a can include a first portion 671a having multiple, stacked, laminated first layers 672a, and a second portion 671b having multiple, stacked, laminated second layers 672b. In addition, the first portion 671a can be joined to the second portion 671b along a bond line 676a that is non-monotonically varying (e.g., zigzagging) along the thickness axis T. In this particular embodiment, however, the first layers 672a and the second layers 672b have first terminations 673a and second terminations 673b, respectively, that are not parallel to the chordwise axis C. That is, the terminations 673 are beveled or slanted relative to the chordwise axis C. The bevels can have the same direction and extent for each layer, or these characteristics can vary from one layer to the next. For example, as shown in <figref idref="f0010">Figures 6D and 6E</figref> in dashed lines, the layer below the topmost layer can be beveled in the opposite direction as the topmost layer. Bevels in neighboring layers can be positioned directly above and below each other, as shown in <figref idref="f0010">Figures 6D and 6E</figref>, or the bevels in neighboring layers can be offset in a spanwise direction so as not to overlay each other.

0038Referring next to <figref idref="f0010">Figure 6E</figref>, the spar 670b can be at least generally similar in structure and function to the spar 670a described in detail above. For example, the spar 670b can include a first portion 671c having multiple, stacked, laminated first layers 672a, and a second portion 671 d having multiple, stacked, laminated second layers 672b. In this particular embodiment, however, the first layers 672a have first terminations 673c that form a projection 674a, and the second layers 672b have second terminations 673d that form a recess 675a. The projection 674a is received in the recess 675a to form a bond line 676b that is non-monotonically varying along both the thickness axis T and the chordwise axis C.

0039Referring next to <figref idref="f0010">Figure 6F</figref>, the spar 670c is at least generally similar in structure and function to the spar 670a described in detail above. In this particular embodiment, however, the first layers 672a include first terminations 673e, and the second layers 672b include second terminations 673f, that form alternating projections 674b and recesses 675b along the chordwise axis C. This results in a bond line 676c that is non-monotonically varying along the chordwise axis C but not along the thickness axis T.

0040Referring next to <figref idref="f0010">Figure 6G</figref>, in this particular embodiment the first layers 672a include first terminations 673g, and the second layers 672b include terminations 673h, that form alternating projections 674c and recesses 675c along the chordwise axis C, and alternating projections 674d and recesses 675d along the thickness axis T. As the foregoing discussion illustrates, there are a wide variety of non-monotonically varying, staggered, zigzagging, overlapping, and/or other bond lines that can be used to efficiently and strongly join spar portions together in accordance with the present disclosure. Accordingly, the present disclosure is not limited to bond lines having any particular configuration.

0041One feature of embodiments described above with reference to <figref idref="f0008 f0009 f0010">Figures 6A-6G</figref> is that they can include spar portions connected to each other along a bond line that has a zig-zag shape, or otherwise varies in a non-monotonic manner. An expected advantage of this arrangement is that the bond line will be stronger than a simple vertical or diagonal bond line. In addition, it is expected that forming the bond line can be simplified because it does not require the use of a significant number of additional fastening elements, and can instead employ a bonding technique generally similar to the technique used to bond the individual layers of the two portions. Still further, the bond between the spar portions may be formed with no heating, or only local heating, which avoids the need to heat the entire blade. The foregoing characteristics can in turn facilitate the ease with which a manufacturer and/or installer forms a large wind turbine blade that is initially in multiple segments (e.g., the segments 116 described above with reference to <figref idref="f0002">Figure 2A</figref>), which are then joined to each other, for example, at an installation site. Further details of suitable manufacturing techniques are described later with reference to <figref idref="f0012 f0013 f0014 f0015 f0016 f0017 f0018 f0019 f0020 f0021 f0022 f0023 f0024 f0025 f0026">Figures 8A-16</figref>.

0042In other embodiments, the spar 170 can include other configurations and/or materials. For example, selected plies can be formed from metal or carbon fiber rather than glass fiber. The plies need not all have the same thickness. Accordingly, the dimensions and materials selected for each ply can be selected to produce a desired strength, stiffness, fatigue resistance and cost.

0043<figref idref="f0011">Figure 7A</figref> is a partially schematic illustration of a hub attachment portion 112 configured in accordance with an embodiment of the disclosure. For purposes of illustration, <figref idref="f0011">Figure 7A</figref> illustrates only the hub attachment portion 112, and in particular, the transition between the longitudinally extending spars 170 and a hub attachment element, e.g., a circumferentially extending hub attachment ring 180. The ring 180 can include a non-composite structure, e.g., a metallic element, and can have a relatively short spanwise direction as shown in <figref idref="f0011">Figure 7A</figref>, or a longer spanwise dimension in other embodiments. The ring 180 or the hub attachment portion 112 can be circumferentially continuous, or formed from multiple sections arranged circumferentially. For example, the hub attachment portion 112 can include one circumferential section for each spar 170, with each section connected to a continuous ring 180. Other hub attachment elements that may be included in the hub attachment region 112 are not shown in <figref idref="f0011">Figure 7A</figref>. The hub attachment portion 112 can include a transition to four spars 170 (as shown in <figref idref="f0011">Figure 7A</figref>) or other numbers of spars 170 (e.g., three spars 170, as shown in <figref idref="f0004">Figure 3</figref>).

0044Each of the spars 170 can include a laminate composite of layers 172, and each of the layers 172 can in turn include multiple plies. For example, in a particular embodiment, each of the spars 170 can include a laminate of fifteen layers 172, each having a total of six plies, for a total of ninety plies. Each of the plies can have fibers that are oriented unidirectionally, for example, in alignment with the spar axis S. Accordingly, such fibers have a 0° deviation from the spar axis S. The layers 172 can be stacked one upon the other, each with fibers oriented at 0° relative to the spar axis S, and can be cut so as to have the shape shown in <figref idref="f0011">Figure 7A</figref>. The number of plies oriented at 0° relative to the spar axis S can be reduced in a direction extending toward the ring 180. For example, the number of such plies can be reduced from ninety at the right side of <figref idref="f0011">Figure 7A</figref> (where the spars 170 have a generally fixed, rectangular cross-sectional shape) to twenty at the ring 180 on the left side of <figref idref="f0011">Figure 7A</figref> (where the structure has thinner, arcuate shape). The seventy deleted layers 172 can be terminated in a staggered fashion so that the overall thickness of the structure is gradually reduced from right to left

0045As the 0° orientation layers 172 are dropped off, the manufacturer can add layers that are oriented at other angles relative to the spar axis S. For example, the manufacturer can add layers having fibers oriented at +45° and -45° relative to the spar axis S. In a particular embodiment, twenty to thirty such plies can be added, so that the total number of plies at the ring 180 is between forty and fifty, as compared with ninety plies at the right side of <figref idref="f0011">Figure 7A</figref>. By adding the +45°/-45° oriented plies to the structure at the hub attachment portion 112, the load carried by the spars 170 can be spread out in a circumferential direction and distributed in a more uniform fashion at the ring 180. To further enhance this effect, the load path can be "steered" by providing a different number of +45° plies as compared with -45° plies. This arrangement can accordingly reduce or eliminate the likelihood that individual bolts passing through bolt holes 182 in the ring 180 will experience significantly higher loads than other bolts located at different circumferential positions. As a result, this arrangement is expected to not only provide a smooth transition from the airfoil-shaped cross section of the blade 110 to the circular cross-section shape at the hub attachment portion 112, but is also expected to more evenly distribute the loads than do existing structures.

0046<figref idref="f0011">Figure 7B</figref> is another illustration of a hub attachment portion 112 in which the spar 170 includes layers 172 of unidirectionally extending fibers, aligned with the spar axis S. In this embodiment, individual layers 172 terminate at terminations 173. One or more termination elements 179 (e.g., plates), each having a curved, fan-type shape, can be butted up against the spar 170, and can include recesses that receive the terminated layers 172. In a particular embodiment shown in <figref idref="f0011">Figure 7B</figref>, this arrangement includes three transition elements 179, two of which are visible in <figref idref="f0011">Figure 7B</figref>. The two visible transition elements 179 each accommodate multiple layers 172 (e.g., four or more layers 172). A gap 183 between the two transition elements 179 receives a third transition element (not shown in <figref idref="f0011">Figure 7B</figref> for purposes of clarity) that in turn receives the remaining layers 172. Each of the transition elements 179 can then be attached to the ring 180, which is in turn connected to a pitch bearing 181. The pitch bearing 181 is used to vary the pitch of the wind turbine blade 110 in use. Each of the transition elements 179 can have a generally arcuate cross-sectional shape where it connects to the ring 180, and a generally flat, rectangular or rectilinear cross-sectional shape at its furthest point from the ring 180, where it connects to the spar 170.

0047In other embodiments, the transition region between the hub attachment ring 180 or other attachment feature, and the rest of the blade 110 can have other arrangements. For example, the general arrangement of fan-shaped plies or plies in combination with transition elements can be applied to other blade structures that may not include the spars described above. In another example, the arrangement of +45°/-45° plies described above can be used to "steer" loads (e.g., to more evenly distribute loading at the boltholes 182) in blades 110 that do not include the spars 170, or in blades 110 that include spars or other structures arranged differently than is described above.

0048<figref idref="f0012">Figure 8A</figref> is a partially schematic, side elevation view of a manufacturing assembly 801 of the turbine blade 110 configured in accordance with an embodiment of the disclosure, and <figref idref="f0012">Figure 8B</figref> is an enlarged end view taken along line 8B-8B in <figref idref="f0012">Figure 8A</figref> illustrating a representative rib 142 supported by a tool stanchion 802. Referring to <figref idref="f0012">Figures 8A and 8B</figref> together, the manufacturing assembly 801 includes a plurality of ribs 142 supported by individual tool stanchions 802 at the appropriate spanwise locations. As discussed above, the turbine blade 110 includes an inboard or first blade segment 116a, a midboard or second blade segment 116b, and an outboard or third blade segment 116c. In the illustrated embodiment, the second spar 170b (e.g., the lower or "pressure" spar) has been assembled onto the ribs 142. The spar 170b includes an inboard or first spar portion 871a, a midboard or second spar portion 871b, and an outboard or third spar portion 871c.

0049Referring next to <figref idref="f0012">Figure 8B</figref>, as explained above with reference to <figref idref="f0006">Figure 5D</figref>, the ribs 142 include a plurality of cutouts 148 configured to receive corresponding truss attachment members 150. More particularly, in the illustrated embodiment the representative rib 142 includes a first cutout 148a configured to receive the first spar 170a (e.g., the suction spar; not shown in <figref idref="f0012">Figures 8A or 8B</figref>), a second cutout 148b configured to receive the second spar 170b (e.g., the pressure spar), and a third cutout 148c configured to receive the third spar 170c (e.g., the aft spar; also not shown in <figref idref="f0012">Figures 8A or 8B</figref>). As described in greater detail below, in various embodiments one or more of the spars 170 can be manufactured by laminating a plurality of prefabricated composite layers or "pultrusions" together in position on the manufacturing assembly 801. Further details of these embodiments are described in greater detail below with respect to <figref idref="f0013 f0014 f0015 f0016 f0017 f0018 f0019 f0020 f0021 f0022 f0023 f0024 f0025 f0026">Figure 9A-16</figref>.

0050<figref idref="f0013 f0014">Figures 9A-9C</figref> are a series of partially schematic, enlarged isometric views of the inboard spar portion 871a, the midboard spar portion 871b, and the outboard spar portion 871c configured in accordance with embodiments of the disclosure. Referring first to <figref idref="f0013">Figure 9A</figref>, in the illustrated embodiment the spar 170b can be manufactured from a plurality of layers 972 (identified individually as layers 972a-o) that are bonded or otherwise laminated together in place on the manufacturing assembly 801 (<figref idref="f0012">Figure 8A</figref>). In particular embodiments, the layers 972 can include prefabricated composite materials, such as pultrusions or "planks" of pultruded composite materials. As is known, composite pultrusion is a manufacturing process that creates fiber-reinforced polymer or resin products having relatively consistent shape, strength and resilience characteristics. In a typical pultruding process, the reinforcement material (e.g., unidirectional fibers, tows, roving, tape etc. of glass fibers, aramid fibers, carbon fibers, graphite fibers, Kevlar fibers, and/or other material) is drawn through a resin bath (e.g., a liquid thermosetting resin bath of epoxy resin, vinylester resin, polyester resin, plastic). The wet, fibrous element is then pulled through a heated steel die, in which accurate temperature control cures the resin and shapes the material into the desired profile. The pultrusions can then be cut to the desired length for use. Strength, color and other characteristics can be designed into the profile by changes in the resin mixture, reinforcement materials, die profiles, and/or other manufacturing parameters.

0051In the illustrated embodiment, the layers 972 can be formed from pultruded planks having generally rectangular cross sections. In one embodiment, for example, the layers 972 can have cross-sectional widths of from about 2 inches to about 12 inches, or from about 4 inches to about 10 inches, and cross-sectional thicknesses of from about .10 inch to about .5 inch, or about .25 inch. In other embodiments, the layers 972 can have other shapes and sizes. In particular embodiments, the layers 972 can be provided by Creative Pultrusions, Inc., of 214 Industrial Lane, Alum Bank, PA 15521. In other embodiments, the layers 972 can be comprised of other types of pultruded materials as well as other types of composite materials including both prefabricated and hand-laid composite materials. In yet other embodiments, the methods of manufacturing turbine blade spars described herein can be implemented using other types of laminated materials. Such materials can include, for example, wood (e.g., balsa wood, plywood, etc.), metals (e.g., aluminum, titanium, etc.) as well as combinations of wood, metals, composites, etc.

0052Referring still to <figref idref="f0013">Figure 9A</figref>, the inboard spar portion 871a includes an inboard end portion 979a and an outboard end portion 979b. Each of the end portions includes a staggered arrangement of layers 972. For example, with reference to the outboard end portion 979b, each of the layers 972 includes a corresponding termination 973 (identified individually as terminations 973a-o) which is staggered relative to adjacent terminations 973 to form projections 974 and corresponding recesses 975. In addition, in various embodiments the layers 972 can be tapered toward the terminations 973 at the end portions 979. As described in greater detail below, this arrangement of alternating projections 974 and recesses 975 facilitates joining the first spar portion 871 a to the second spar portion 871 b in a very efficient overlapping joint with a zigzag bond line.

0053Referring next to <figref idref="f0014">Figure 9B</figref>, the second spar portion 871b is also comprised of a plurality of layers 972 having terminations 973 that are staggered to create an alternating arrangement of projections 974 and corresponding recesses 975. Like the first spar portion 871a, the second spar portion 871b includes an inboard end portion 979c and an outboard end portion 979d. As illustrated in <figref idref="f0014">Figure 9B</figref>, however, the second spar portion 871b becomes thinner (i.e., it tapers in thickness) toward the outboard end portion 979d. In the illustrated embodiment, this is accomplished by successive termination of the outer layers 972 as they extend outwardly from the inboard end portion 979c. This gradual tapering of the spar 170b can be done to reduce weight and/or tailor the strength of the spar 170b for the reduced structural loads that occur toward the tip of the turbine blade 110.

0054Referring next to <figref idref="f0014">Figure 9C</figref>, the third spar portion 871c includes an inboard end portion 979c and a corresponding outboard end portion 979f. As this view illustrates, the spar 170b continues to taper toward the outboard end portion 979f by terminating various layers 972 as they approach the end portion 979f.

0055<figref idref="f0015">Figures 9D and 9E</figref> include partially schematic, enlarged side views illustrating additional details of the first spar portion 871a and the second spar portion 871b configured in accordance with an embodiment of the disclosure. In addition, these Figures also illustrate various features of the end portions of some of the layers 972. As shown in <figref idref="f0015">Figure 9D</figref>, the outboard end portion 979b of the first spar portion 871a includes a plurality of alternating projections 974 and corresponding recesses 975 formed by the staggered terminations 973 of the respective layers 972. As this view further illustrates, the end portions of the layers 972 can be gradually tapered toward the termination 973 to further facilitate and shape the projections 974/recesses 975 into gradually transitioning recesses/projections. For example, in the illustrated embodiment, the last 2 to 6 inches, or about the last 4 inches of each layer 972 can have a double-sided taper (if, e.g., an inner layer 972) or a single-sided taper (if, e.g., an outer layer 972) to a termination 973 of from about 0.0 inch to about .07 inch, or about .04 inch.

0056Referring next to <figref idref="f0015">Figure 9E</figref>, the inboard end portion 979c of the second spar portion 871b includes a plurality of projections 974 configured to fit into corresponding recesses 975 of the outboard end portion 979b of the first spar portion 871a. Similarly, the inboard end portion 979c also includes a plurality of recesses 975 configured to receive corresponding projections 974 of the outboard end portion 979b of the first spar portion 871a. For example, during manufacture of the spar 170b, the first projection 974a on the outboard end portion 979b of the first spar portion 871a is fit into the corresponding first recess 975a on the inboard end portion 979c of the second spar portion 871b. Although the respective end portions 979 are fit together in this manner during assembly of the spar 170b on the manufacturing assembly 801 of <figref idref="f0012">Figure 8A</figref>, the mating end portions 979 are not actually bonded together at this time, so that the blade sections 116 (<figref idref="f0012">Figure 8A</figref>) can be separated after manufacture and individually transported to the installation site.

0057As shown in <figref idref="f0016">Figure 9F</figref>, when the outboard end portion 979b of the first spar portion 871a is ultimately joined to the inboard end portion 979c of the second spar portion 871b at the installation site, the alternating projections 974 and recesses 975 create an overlapping or a zigzag bond line 976. As is known to those of ordinary skill in the art, this is a very efficient structural joint, and can avoid or at least reduce the need for further structural reinforcement of the joint between the first spar portion 871a and the second spar portion 871 b.

0058<figref idref="f0017">Figures 10A</figref> and <figref idref="f0018 f0019">10C-10E</figref> are a series of partially schematic side elevation views of a portion of the manufacturing assembly 801 of <figref idref="f0012">Figure 8A</figref>, illustrating various stages in a method of manufacturing the spar 170b in situ on the truss structure of the turbine blade 110 in accordance with an embodiment of the disclosure. <figref idref="f0017">Figure 10B</figref> is an enlarged end view taken along line 10B-10B in <figref idref="f0017">Figure 10A</figref>, further illustrating aspects of this spar manufacturing method. Referring first to <figref idref="f0017">Figures 10A and 10B</figref> together, the ribs 142 have been secured to their corresponding tool stanchions 802, and a plurality of truss members 143 have been installed (at least temporarily) between corresponding truss attachment members 150. Each truss attachment member 150 of the illustrated embodiment includes a first piece 1056a and a mating second piece 1056b. As shown in <figref idref="f0017">Figure 10A</figref>, only the first piece 1056a is attached to the truss structure during build-up of the spar 170b. As discussed in more detail below, after all of the spar layers 772 have been properly arranged on the first piece 1056a of the truss attachment member 150, the second piece 1056b is fit into position and secured to the first piece 1056a.

0059Referring next to <figref idref="f0018">Figure 10C</figref>, the individual spar layers 772 are sequentially placed into position on the first piece 1056a of the truss attachment member 150 of each rib 142. As the spar layers 772 are placed on top of each other, the terminations 773 are positioned as shown in <figref idref="f0011">Figures 7A-7E</figref> to produce the desired spar profile. A layer of adhesive (e.g., epoxy adhesive, thermosetting resin adhesive, etc.) can be applied to one or both of the mating surfaces of adjacent layers 772. The spar layers 772 can be temporarily held in position during the stacking process with clamps 1002 (e.g., C-clamps and/or other suitable clamps known in the art).

0060Referring next to <figref idref="f0018">Figure 10D</figref>, once all of the layers 772 have been properly arranged on the first pieces 1056a of the truss attachment members 150, the layers 772 can be compressed during the adhesive curing cycle using a suitable clamping tool, such as the compressing apparatus 1090 described in greater detail below. More particularly, a plurality of the compressing apparatuses 1090 can be positioned on the spar portion 871 between the ribs 142 to compress the layers 972 together during the curing process. The compressing apparatus 1090 is described in greater detail below with reference to <figref idref="f0022 f0023 f0024 f0025 f0026">Figures 12A-15</figref>.

0061Referring next to <figref idref="f0019">Figure 10E</figref>, once the adhesive between the layers 972 has cured, the second pieces 1056b of each of the truss attachment members 150 can be installed on the truss structure and joined to the corresponding first pieces 1056a with threaded fasteners and/or other suitable methods. In one embodiment, adhesive can be applied between the mating surfaces of the first piece 1056a and the spar portion 871, and/or the second piece 1056b and the spar portion 871, to bond the spar portion 871 to the respective truss attachment members 150. In other embodiments, such adhesive can be omitted.

0062<figref idref="f0019">Figure 11A</figref> is an enlarged isometric view of a portion of the truss structure of the turbine blade 110, and <figref idref="f0020">Figure 11B</figref> is an end view of a representative rib 142 illustrating aspects of the installed spars 170. In one embodiment, the second piece 1056b of the truss attachment member 150 can be mated to the first piece 1056a by sliding the second piece 1056b sideways into the cutout 148. For this procedure, the end portions of the truss members 143 can be temporarily detached from corresponding truss attachment portions 1154 of the truss attachment member 150. Once both pieces 1056 of the truss attachment member 150 are in their respective positions, the end portions of the truss members 143 can be rejoined to the truss attachment portions 1154. In one embodiment, the end portions of the truss members 143 and the corresponding truss attachment portions 1154 can be pilot drilled undersize, and then drilled full size during final assembly. Moreover, the end portions of the truss numbers 143 can be attached to the truss attachment portions 1154 by fasteners 859 that are frozen before installation in the corresponding fastener holes so that they expand to a press fit after installation. In other embodiments, the truss members 143 can be attached to the truss attachment members 150 using other suitable methods known in the art.

0063<figref idref="f0021">Figure 11C</figref> is a partially schematic isometric view of a portion of the manufacturing assembly 801 after the spar 170b has been fully assembled and installed on the truss structure of the turbine blade 110. Referring to <figref idref="f0019">Figures 11A</figref> and <figref idref="f0021">11C</figref> together, although the mating end portions 979 of the second spar portion 871b and the third spar portion 871c are assembled in place to ensure that they will fit neatly together during final assembly, the end portions 979 are not bonded during truss manufacture. This enables the second blade section 116b and the third blade section 116c to be separated from each other at the manufacturing facility for transportation to the installation site. Accordingly, in the illustrated embodiment the end portions 979 of the spar portions 871 are not bonded together during the manufacturing process, but instead form separation joints 1120 where the spars 170 will be joined together when the turbine blade 110 is assembled on site. In one embodiment, the spars can be joined together on site using the systems and methods described in detail in <patcit id="pcit0001" dnum="US61180816A"><text>U.S. Provisional Patent Application No. 61/180,816, filed May 22, 2009</text></patcit> and incorporated herein in its entirety by reference. The blade segments can be transported to the site using systems and methods described in detail in <patcit id="pcit0002" dnum="US61180812A"><text>U.S. Provisional Patent Application No. 61/180,812, filed May 22, 2009</text></patcit> and incorporated herein in its entirety by reference.

0064<figref idref="f0022">Figure 12A</figref> is an isometric view of the compressing apparatus 890 configured in accordance with an embodiment of the disclosure, and <figref idref="f0023">Figure 12B</figref> is a partially exploded isometric view of the compressing apparatus 1090. Referring to <figref idref="f0022">Figures 12A</figref> and <figref idref="f0023">12B</figref> together, the compressing apparatus 1090 includes a first tool portion 1250a and a second tool portion 1250b. In the illustrated embodiment, the tool portions 1250 are mirror images of each other, or are at least very similar to each other. Each tool portion 1250 includes a support plate 1254 and opposing side flanges 1256 (identified individually as a first side flange 1256a and a second side flange 1256b) extending therefrom. As described in greater detail below, the tool portions 1250 are configured to fit together in a clamshell arrangement around a portion of the laminated spar 170 to compact and compress the spar layers (e.g., the layers 772) together while the adhesive between the layers cures. More particularly, each of the tool portions 1250 includes one or more expandable members 1258 configured to expand inwardly from the support plate 1254 to thereby compress the corresponding spar section during the curing process. In the illustrated embodiment, the first side flange 1256a is somewhat wider than the second side flange 1256b, so that the mating flanges 1256 can overlap and be temporarily held together with fasteners 1252 (e.g., threaded fasteners, such as bolts, screws, etc.) during the compressing and curing process. Each tool portion 1250 can also include a first end portion 1261 and an opposing second end portion 1262. Handles 1253 can be provided on the end portions 1261 and 1262 to facilitate manual placement, installation and/or removal of the tool portions 1250. The tool portions 1250 can be manufactured from various materials having sufficient strength, stiffness, and manufacturing characteristics. For example, in one embodiment the tool portions 1250 can be formed from aluminum that is machined, welded, or otherwise formed to the desired shape. In other embodiments, the tool portions 1250 can be fabricated from other suitable metals including steel, brass, etc., as well as suitable non-metallic materials such as composite materials.

0065<figref idref="f0024">Figure 13A</figref> is an exploded isometric view of the first end portion 1261 of the first tool portion 1250a, and <figref idref="f0024">Figure 13B</figref> is an enlarged isometric view of the second end portion 1262. Referring first to <figref idref="f0024">Figure 13A</figref>, each tool portion 1250 includes a manifold 1360 for filling and unfilling the expandable members 1258 with a fluid (e.g., compressed air). In the illustrated embodiment, a conduit 1368 (identified individually as conduits 1368a-c) extends between each expandable member 1258 and a fill/drain fitting 1366. The fill/drain fitting 1366 can include a threaded orifice 1370 or other feature (e.g., a high-pressure air coupling) configured to receive a corresponding fitting for flowing fluid into the respective expandable members 1258 through the conduits 1368. In one embodiment, for example, the expandable members 1258 can be filled with compressed air to inflate the expandable members 1258 and thereby compress the layers of the spar 170 together during the curing cycle. In other embodiments, the expandable members 1258 can be filled with other types of gas or liquids (e.g., water, oil, etc.) to inflate the expandable members 1258 and compress the spar layers together.

0066The proximal end portions of the expandable members 1258 can include an end closure 1364 to seal the expandable member 1258 and maintain pressure. In the illustrated embodiment, the end closures 1364 can include two or more plates that sandwich the end portion of the expandable member 1258 therebetween to prevent leakage. In other embodiments, other structures and systems can be used to seal the proximal end portions of the expandable members 1258. As shown in <figref idref="f0024">Figure 13B</figref>, the distal end portions of the expandable members 1258 can be closed off and sealed with a suitable end closure plate 1365 that is fastened to the support plate 1254 with a plurality of fasteners 1352. In other embodiments, the end portions of the expandable members 1258 can be secured to the tool portion 1250 and/or closed off and sealed using other suitable means.

0067<figref idref="f0025">Figure 14A</figref> is an enlarged isometric view of the second tool portion 1250b, and <figref idref="f0025">Figure 14B</figref> is a partially exploded isometric view of the second tool portion 1250b. With reference to <figref idref="f0025">Figure 14B</figref>, each of the expandable members 1258 can include a flexible tubular structure comprised of an outer layer 1430 and an inner layer 1432. The outer layer 1430 can include a suitable material to provide strength to the expandable member 1258, and the inner layer 1432 can include a suitable material for sealing the expandable member 1258. For example, the inner sealing layer 1432 can include a rubber liner, and the outer layer 1430 can include woven nylon, fiberglass, etc. Accordingly, in one embodiment the expandable member 1258 can include a structure that is at least generally similar in structure and function to a fire hose. In other embodiments, the expandable members 1258 can include other materials and have other structures.

0068<figref idref="f0026">Figure 15</figref> is an enlarged end view taken substantially along line 15-15 in <figref idref="f0018">Figure 10D</figref> illustrating use of the compressing apparatus 1090 in accordance with an embodiment of the disclosure. In this view, the spar layers 972 have been appropriately positioned on the truss substructure, with bonding adhesive between the layers. The first tool portion 1250a has been positioned on one side of the spar 170, and the second tool portion 1250b has been positioned on the other side. Each first flange 1256a of each tool portion 1250 overlaps the corresponding second flange 1256b of the opposing tool portion 1250. Once the two tool portions 1250 have been properly positioned, the tool portions 1250 are temporarily attached with the fasteners 1252. A pressure source (e.g. a source of compressed air) is then attached to the manifold 1360 on each tool portion 1250, and the expandable members 1258 are inflated to a sufficient pressure. As they expand, the expandable members 1258 provide an even, distributed pressure over the laminated spar 170. The pressure can be modulated as required to provide a desired level of compaction and compression during the curing process. Moreover, a suitable vacuum bag or other thin film protective layer can be wrapped around the spar 170 to avoid getting adhesive on the compressing apparatus 1090. After the spar 170 has suitably cured, the compressing apparatus 1090 can be disassembled by relieving the pressure in the expandable members 1258 and removing the fasteners 1252.

0069The methods and systems described in detail above can be used to assemble a wind turbine blade spar in situ on a manufacturing subassembly in accordance with embodiments of the disclosure. More particularly, several embodiments of the disclosure have been described in detail above for manufacturing laminated spars using pultruded composite materials, such as pultruded composite "planks." There are a number of advantages associated with some of these embodiments. These advantages can include, for example, lower cost and lower weight wind turbine blades as compared to conventional manufacturing techniques. Moreover, use of pultrusions can reduce dimensional variations in the finished parts.

0070In certain embodiments, other turbine blade structures, such as outer skins, ribs, truss members, etc. can be formed from pultruded composite materials. For example, in one embodiment skins can be formed from one or more pultruded composite members (e.g., sheets) that are laminated together. In other embodiments, truss members can be formed from composite pultrusions. Accordingly, the methods and systems disclosed herein for forming turbine blade structures from pultruded materials are not limited to use with turbine blade spars or spar caps, but can be used to form other turbine blade structures.

0071In other embodiments, however, turbine blade spars and/or other blade structures, such as the spars 170 described herein, can be manufactured from pultruded composite materials using a suitable production tool. <figref idref="f0026">Figure 16</figref>, for example, illustrates a tool 1610 having a mold surface 1612 with an appropriate contour for the spar 170b. To manufacture the spar 170b on the tool 1610, the layers 972 (e.g., pultruded planks) are sequentially positioned on the mold surface 1612. Tooling pins 1614 and/or other locaters can be used to accurately position the layers 972. The layers 972 can be precut to the appropriate lengths so that when arranged on the tool surface 1612, the respective end portions 979 form the desired zigzagging joint or overlapping fingers. Although no adhesive is used between the mating end portions 979 at this time, each layer 972 is covered with adhesive prior to installation on the tool 1610. After all the layers 972 have been placed on the tool surface 1612, the lay up can be vacuum-bagged to extract the air from the laminate and compress the layers 972 together. The spar can be cured at room temperature, or heat can be applied via an autoclave or other means if desired for the particular adhesive used.

0072From the foregoing, it will be appreciated that specific embodiments have been described herein for purposes of illustration, but that the invention maybe include other embodiments as well. For example, features described above with reference to <figref idref="f0011">Figure 7A</figref> in the context of four spanwise extending spars can be applied to wind turbine blades having other numbers of spars, including three spars. In addition, the truss structures described above can have arrangements other than those specifically shown in the Figures. The attachments between spars, ribs, and truss members can have arrangements other than those described above. Certain aspects of the disclosure described in the context of particular embodiments may be combined or eliminated in other embodiments. Further, while advantages associated with certain embodiments have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the disclosure. Accordingly, the invention can include other embodiments not explicitly shown or described above. Therefore, the invention is not limited, except as by the appended claims.

0073Aspects of the present disclosure may be defined by the following numbered clauses: <ol id="ol0001" ol-style=""><li>1. A wind turbine system, comprising: <ul id="ul0002" list-style="none" compact="compact"><li>a wind turbine blade having a radially inner region and a radially outer region, wherein: <ul id="ul0003" list-style="none" compact="compact"><li>the inner region includes a hub attachment element, an internal load-bearing truss structure extending longitudinally outwardly from the hub attachment element, and an external skin carried by the internal truss structure; and</li><li>the outer region is positioned longitudinally outwardly from the internal truss structure, is attached to the internal truss structure, and has an internal load-bearing structure that does not include a load-bearing truss structure, the outer region further including a blade tip.</li></ul></li></ul></li><li>2. The system of clause 1 wherein the wind turbine blade has an overall length, and wherein the internal truss structure extends from the hub attachment element to a point approximately two-thirds of the overall length from the hub attachment element.</li><li>3. The system of clause 1 wherein the outer region includes a longitudinally extending spar, multiple ribs spaced along the spar, and a portion of the external skin is carried by the spar and the ribs.</li><li>4. The system of clause 1 wherein the truss structure of the inner region includes a plurality of longitudinally extending spars, multiple ribs spaced along the spars, and generally straight, slender truss members connected between the spars.</li><li>5. The system of clause 1 wherein the outer region has a monocoque structure.</li><li>6. The system of clause 1 wherein the outer region has a semi-monocoque structure.</li><li>7. The system of clause 1 wherein the truss structure of the inner region includes a first number of longitudinally extending spars, and wherein the outer region includes a second number of longitudinally extending spars, the second number being less than the first number.</li><li>8. The system of clause 1 wherein the truss structure of the inner region includes only three longitudinally extending spars, and wherein the outer region includes two longitudinally extending spars.</li><li>9. The system of clause 1 wherein the truss structure of the inner region includes a first longitudinally extending spar, and wherein the outer region includes a second longitudinally extending spar, and where the first and second spars extend along a generally smooth, continuous longitudinal axis.</li><li>10. The system of clause 1 wherein the inner region includes a first segment and a second segment positioned radially outwardly from the first segment, the first segment having a first spar segment, the second segment having a second spar segment joined to the first spar segment and positioned radially outwardly from the first spar segment.</li><li>11. A method for manufacturing a wind turbine blade, comprising: <ul id="ul0004" list-style="none" compact="compact"><li>forming a radially inner region of a wind turbine blade to have a load-bearing truss structure;</li><li>applying a skin to the truss structure;</li><li>forming a radially outer region of the wind turbine blade to have a non-truss structure; and</li><li>connecting the inner region of the wind turbine blade and the outer region of the wind turbine blade to each other.</li></ul></li><li>12. The method of clause 11 wherein forming the radially outer region of the wind turbine blade includes forming the radially outer region of the wind turbine blade to have a monocoque structure.</li><li>13. The method of clause 11 wherein forming the radially outer region of the wind turbine blade includes forming the radially outer region of the wind turbine blade to have a semi-monocoque structure.</li><li>14. The method of clause 11 wherein forming the radially inner region of the wind turbine blade includes forming a first radially inner segment and a second radially inner segment, and wherein the method further comprises: <ul id="ul0005" list-style="none" compact="compact"><li>connecting the first radially inner segment to the second radially inner segment at an installation site;</li><li>connecting the radially outer region to the second radially inner segment at the installation site to form a radially extending wind turbine blade, with the second radially inner segment positioned between the first radially inner segment and the radially outward region; and</li><li>mounting the wind turbine blade to a wind turbine hub at the installation site.</li></ul></li><li>15. A method for operating a wind turbine, comprising: <ul id="ul0006" list-style="none" compact="compact"><li>rotating a wind turbine shaft carrying multiple wind turbine blades;</li><li>transmitting loads from an individual wind turbine blade to the shaft via a radially inner region of the blade and a radially outer region of the blade, the radially inner region including an internal load-bearing truss structure and an external skin carried by the internal truss structure, the radially outer region including a load-bearing skin position around a non-truss structure; and</li><li>subjecting the individual wind turbine blade to cyclically varying gravitational loads by rotating the shaft about a generally horizontal axis.</li></ul></li><li>16. The method of clause 15 wherein transmitting loads includes transmitting loads from the outer region of the blade to the shaft via the inner region of the blade.</li><li>17. The method of clause 15 wherein transmitting loads includes transmitting loads from the outer region of the blade across a spar joint to the inner region of the blade, and then to the shaft.</li><li>18. A wind turbine system, comprising: <ul id="ul0007" list-style="none" compact="compact"><li>a wind turbine blade having a leading edge and a trailing edge, the wind turbine blade including a truss structure with: <ul id="ul0008" list-style="none" compact="compact"><li>a longitudinally extending first spar positioned toward the leading edge;</li><li>a longitudinally extending second spar positioned toward the leading edge and spaced apart from the first spar;</li><li>a single, longitudinally extending third spar positioned toward the trailing edge;</li><li>a plurality of spaced-apart ribs, with individual ribs connected to each of the first, second and third spars;</li><li>a plurality of truss members connected among the first, second and third spars; and</li><li>an external skin attached to and carried by the spars, the ribs, or both the spars and the ribs.</li></ul></li></ul></li><li>19. The system of clause 18 wherein the wind turbine blade includes an inner region having a generally circular hub attachment element, and an outer region positioned longitudinally outwardly from the inner region.</li><li>20. The system of clause 18 wherein the first, second and third spars are the only longitudinally extending spars of the wind turbine blade at a given longitudinal location along the truss structure.</li><li>21. The system of clause 18 wherein the wind turbine blade has an overall longitudinal length, and wherein the first, second and third spars are the only longitudinally extending spars of the wind turbine blade over a majority of the longitudinal length of the blade.</li><li>22. The system of clause 18 wherein the wind turbine blade has an overall longitudinal length, and wherein the first, second and third spars are the only longitudinally extending spars of the wind turbine blade over approximately two thirds of the longitudinal length of the blade.</li><li>23. The system of clause 18 wherein the first, second and third spars are the only longitudinally extending spars of the truss structure.</li><li>24. The system of clause 18 wherein an individual rib includes a first cut-out positioned to receive the first spar and a second cut-out positioned to receive the second spar.</li><li>25. The system of clause 18 wherein an individual rib has first web portion connected to the third spar and positioned forward of the third spar in a chordwise direction, and wherein the individual rib has a second web portion positioned aft of the third spar in the chordwise direction, the first and second web portions being discontinuous.</li><li>26. The system of clause 18 wherein the first spar has a rectangular cross-sectional shape with a chordwise dimension that is greater than its thickness dimension, and wherein the third spar has a rectangular cross-sectional shape with a chordwise dimension that is less than its thickness dimension.</li><li>27. The system of clause 18 wherein the first, second and third spars are each formed from a laminate of composite materials.</li><li>28. The system of clause 18 wherein a cross-section of the wind turbine blade has a chordwise dimension and a thickness dimension, and wherein the single third spar extends over a majority of the thickness dimension.</li><li>29. The system of clause 18 wherein the wind turbine blade is a first wind turbine blade, and wherein the system further comprises: <ul id="ul0009" list-style="none" compact="compact"><li>a hub carrying the first wind turbine blade;</li><li>a second wind turbine blade carried by the hub; and</li><li>a third wind turbine blade carried by the hub, wherein each of the first, second and third wind turbine blades has only three longitudinally extending, load bearing spars at all portions of the blade having a truss structure.</li></ul></li><li>30. A method for operating a wind turbine, comprising: <ul id="ul0010" list-style="none" compact="compact"><li>rotating a wind turbine shaft carrying multiple wind turbine blades; and</li><li>transmitting loads from an individual wind turbine blade to the shaft via an internal truss structure of the individual wind turbine blade that includes two longitudinally extending, load bearing spars toward a leading edge of the blade and a single longitudinally extending load bearing spar toward a trailing edge of the blade.</li></ul></li><li>31. The method of clause 30 wherein rotating the shaft includes rotating the shaft about a generally horizontal axis, and wherein the method further comprises subjecting the individual wind turbine blade to cyclically varying gravitational loads as the shaft rotates.</li><li>32. The method of clause 30 wherein rotating the shaft includes rotating the shaft about a generally horizontal axis, and wherein the method further comprises subjecting the individual wind turbine blade to cyclically varying gravitational loads in a chordwise direction as the shaft rotates.</li><li>33. A method for manufacturing a wind turbine blade, comprising: <ul id="ul0011" list-style="none" compact="compact"><li>forming a truss structure having only three longitudinally extending spars including a first spar toward a leading edge of the wind turbine blade, a second spar toward the leading edge of the wind turbine blade and a third spar positioned toward a trailing edge of the wind turbine blade;</li><li>connecting truss members between the longitudinally extending spars;</li><li>connecting ribs to the longitudinally extending spars; and</li><li>connecting an external skin to the ribs, at least one of the spars, or both the ribs and at least one of the spars.</li></ul></li><li>34. The method of clause 33 wherein connecting ribs to the longitudinally extending spars includes receiving the first spar in a first cutout of at least one of the ribs, and receiving the second spar in a second cutout of the at least one rib.</li><li>35. The method of clause 33 wherein connecting ribs to the longitudinally extending spars includes connecting a first portion of at least one rib to the third spar so as to extend in a forward chordwise direction, and positioning a second portion of the at least one rib aft of the third spar, the first and second portions being discontinuous from each other.</li><li>36. The method of clause 33 wherein forming the truss structure includes forming the truss structure with a single third spar that extends in a thickness direction over a majority of the thickness of the wind turbine blade.</li><li>37. A wind turbine system, comprising: <ul id="ul0012" list-style="none" compact="compact"><li>a wind turbine blade including: <ul id="ul0013" list-style="none" compact="compact"><li>a plurality of longitudinally extending spars;</li><li>a plurality of longitudinally spaced-apart ribs, with individual ribs attached to the longitudinally extending spars;</li><li>a plurality of truss attachment members, with individual truss attachment members connected to a spar, a rib, or both a spar and rib without the use of a hole in the respective spar, the rib or both the spar and the rib; and</li><li>a plurality of truss members, with individual truss members connected between corresponding pairs of truss attachment members.</li></ul></li></ul></li><li>38. The system of clause 37 wherein: <ul id="ul0014" list-style="none" compact="compact"><li>the spars are formed from a composite material, and wherein the truss attachment members include a spar attachment portion and a truss attachment portion, the spar attachment portion extending circumferentially around a spar and clamped to the spar, the truss attachment portion including a flange extending away from the spar and having a first attachment hole; and</li><li>at least one of the truss members includes a second attachment hole; and wherein the system further comprises: <ul id="ul0015" list-style="none" compact="compact"><li>a fastener extending through the first and second attachment holes but not into the spar.</li></ul></li></ul></li><li>39. The system of clause 38 wherein the truss member has a slot in which the flange of the truss attachment member is received.</li><li>40. The system of clause 37 wherein an individual truss attachment member is attached to a spar, and wherein the truss attachment member is formed from a metal and the spar is formed from a composite material.</li><li>41. The system of clause 37 wherein an individual truss attachment member is attached to a spar, and wherein both the truss attachment member and the spar are formed from a composite material.</li><li>42. The system of clause 41 wherein the spar and the truss attachment member are adhesively bonded.</li><li>43. The system of clause 41 wherein the spar and the truss attachment member are co-cured.</li><li>44. The system of clause 37 wherein the truss attachment member includes a first component extending circumferentially around a first portion of the spar, a second component extending circumferentially around a second portion of the spar, and at least one fastener connecting the first and second components and clamping the spar between the first and second components.</li><li>45. The system of clause 44 wherein the fastener is positioned to both clamp the spar between the first and second components and attach one of the truss members to the truss attachment member.</li><li>46. The system of clause 37 wherein: <ul id="ul0016" list-style="none" compact="compact"><li>the spars are formed from a composite material, and wherein the truss attachment members include a first component extending circumferentially around a first portion of the spar and a second component extending circumferentially around a second, complementary portion of the spar, the first component having two first flanges, one extending outwardly from the spar in first direction, and the other extending outwardly from the spar in a second direction different than the first direction, the second component having two second flanges, one extending outwardly from the spar in the first direction and positioned surface-to-surface against one of the first flanges of the first component, and the other of the second flanges extending outwardly in the second direction and positioned surface-to-surface against the other first flange of the first component, each of the first flanges having a first fastener opening, each of the second flanges having a second fastener opening aligned with a corresponding one of the first fastener openings;</li><li>a first truss member having a slot in which the first flanges are received;</li><li>a second truss member having a slot in which the second flanges are received;</li><li>a first fastener passing through the first truss member, one of the first fastener openings, and the corresponding aligned second fastener opening to secure the first truss member to the truss attachment member and clamp the first and second components around the spar; and</li><li>a second fastener passing through the second truss member, the other of the first fastener openings, and the corresponding aligned second fastener opening to secure the second truss member to the truss attachment member and clamp the first and second components around the spar; wherein</li><li>neither the first nor the second fasteners pass into the spar.</li></ul></li><li>47. The system of clause 37 wherein at least one of the truss members is attached to one of the individual ribs and to one of the truss attachment members to provide an attachment between one of the spars and the individual rib.</li><li>48. The system of clause 47 wherein the rib has a web and a flange, and the truss attachment member is attached to the web of the rib.</li><li>49. The system of clause 37 wherein the truss attachment member is attached to one of the individual spars, and extends around only a portion of the spar.</li><li>50. The system of clause 37 wherein the truss attachment member is adhesively attached to one of the individual spars.</li><li>51. A method for making a wind turbine blade, comprising: <ul id="ul0017" list-style="none" compact="compact"><li>positioning a plurality of ribs to be longitudinally spaced-apart from each other, the ribs including a first rib and a second rib;</li><li>positioning first and second longitudinally extending spars proximate to the ribs;</li><li>connecting a first truss attachment member to the first spar, the first rib, or both the first spar and the first rib without the use of a hole in the respective first spar, the first rib or both the first spar and the first rib;</li><li>connecting a second truss attachment member to the second spar, the second rib, or both the second spar and the second rib without the use of a hole in the respective second spar, the second rib or both the second spar and the second rib; and</li><li>connecting a truss member between the first and second truss attachment members.</li></ul></li><li>52. The method of clause 51 wherein the first truss attachment member includes a first component and a second component and wherein connecting the first truss attachment member includes clamping the first and second components around the first spar.</li><li>53. The method of clause 51 wherein the truss member is a first truss member and wherein the first truss attachment member includes a first component and a second component, the first component having two first flanges, one extending outwardly from the spar in first direction, and the other extending outwardly from the spar in a second direction different than the first direction, the second component having a two second flanges, one extending outwardly from the spar in the first direction and the other of the second flanges extending outwardly from the spar in the second direction, and wherein connecting the first truss attachment member includes: <ul id="ul0018" list-style="none" compact="compact"><li>positioning the first component to extend around a first circumferential portion of the first spar;</li><li>positioning the second component to extend around a second circumferential portion of the first spar;</li><li>placing one of the first flanges to face toward one of the second flanges to form a first flange pair;</li><li>placing the other of the first flanges to face toward the other of the second flanges to form a second flange pair;</li><li>receiving the first flange pair in a slot of the first truss member;</li><li>receiving the second flange pair in a slot of a second truss member;</li><li>both clamping the first and second components around the spar and attaching the first truss member to the first truss attachment member by passing a first fastener through the first truss member and the first flange pair; and</li><li>both clamping the first and second components around the spar and attaching the second truss member to the first truss attachment member by passing a second fastener through the second truss member and the second flange pair.</li></ul></li><li>54. The method of clause 51 wherein connecting the first truss attachment member includes connecting the first truss attachment member to the first spar, and wherein connecting the second truss attachment member includes connecting the second truss attachment member to the second spar, and wherein the method further comprises connecting the first rib to the truss member.</li><li>55. The method of clause 54 wherein connecting the first rib to the truss member includes connecting the first rib to the truss member with an adhesive.</li><li>56. The method of clause 54 wherein the first rib includes a web and a flange, and wherein connecting the first rib to the truss member includes connecting the web of the first rib to the truss member.</li><li>57. The method of clause 51 wherein connecting the first truss attachment member includes adhesively bonding the first truss attachment member to the first spar.</li><li>58. The method of clause 51 wherein the first truss attachment member and the first spar are formed from composite materials, and wherein connecting the first truss attachment member includes co-curing the first truss attachment member and the first spar.</li><li>59. A wind turbine system, comprising: <ul id="ul0019" list-style="none" compact="compact"><li>a wind turbine blade including: <ul id="ul0020" list-style="none" compact="compact"><li>a generally arcuate hub attachment element;</li><li>an external aerodynamic surface having a longitudinal axis, a chordwise axis transverse to the longitudinal axis, and a thickness axis transverse to both the chordwise and longitudinal axes; and</li><li>a spar extending along the longitudinal axis, the spar including a plurality of layers stacked relative to each other at a location spaced apart from the hub attachment element, wherein the plurality of layers transition from a rectangular cross-sectional shape to an arcuate cross-sectional shape at the hub attachment element.</li></ul></li></ul></li><li>60. The system of clause 59 wherein the layers include a first number of layers having generally unidirectional fibers aligned with the longitudinal axis at a first location positioned a first distance from the hub attachment element, and second number of layers having unidirectional fibers aligned with the longitudinal axis at a second location positioned a second distance from the hub attachment portion, the second distance being less than the first distance, the second number being less than the first number.</li><li>61. The system of clause 60, further comprising a third number of layers oriented at a non-zero, positive value relative to the longitudinal axis at the second location, and a fourth number of layers oriented at a non-zero negative value relative to the spanwise axis at the second location.</li><li>62. The system of clause 61 wherein the third number is different than the second number.</li><li>63. The system of clause 59 wherein the spar is one of three spars, each having stacked layers that transition from a rectangular cross-sectional shape to an arcuate cross-sectional shape at the hub attachment element.</li><li>64. The system of clause 59 wherein the hub attachment element includes a ring.</li><li>65. The system of clause 64 wherein the ring includes a bolt holes positioned to attach the wind turbine blade to a hub.</li><li>66. The system of clause 59 wherein the spar is a first spar and forms a portion of a truss structure, the truss structure further including a second spar, a third spar, a plurality of ribs positioned transverse to the spars, and a plurality of truss members connected between the spars and the ribs.</li><li>67. A wind turbine system, comprising: <ul id="ul0021" list-style="none" compact="compact"><li>a wind turbine blade including: <ul id="ul0022" list-style="none" compact="compact"><li>an external aerodynamic surface having a longitudinal axis, a chordwise axis transverse to the longitudinal axis, and a thickness axis transverse to both the chordwise and longitudinal axes;</li><li>a spar extending along the longitudinal axis, the spar including a plurality of layers stacked relative to each other;</li><li>a generally arcuate hub attachment element; and</li><li>a transition element attached to the hub attachment element and to the layers of the spar, the transition element having recesses in which the layers are received, at least part of the transition element having an arcuate cross-sectional shape.</li></ul></li></ul></li><li>68. The system of clause 67 wherein the hub attachment element includes a generally circular ring, and wherein the transition element is attached to the generally circular ring.</li><li>69. The system of clause 68 wherein the transition element includes a transition plate having a generally rectilinear cross-sectional shape at an interface with the layer, and a generally arcuate shape at an interface with the generally circular ring.</li><li>70. The system of clause 67 wherein the transition element is one of two transition plates, each having recesses in which layers of the spar are received, with a first one of the transition plates receiving first layers and a second one of the transition plates receiving second layers different than the first, the first transition plate being positioned radially inwardly from the second transition plate.</li><li>71. The system of clause 67 wherein the spar is one of multiple spars extending along the longitudinal axis, with each spar including a plurality of layers stacked relative to each other, and wherein the transition element is one of a plurality of transition plates, each having recesses in which the layers of a corresponding one of the spars are received.</li><li>72. The system of clause 67 wherein the layers are composite layers.</li><li>73. The system of clause 67 wherein the spar is a first spar and forms a portion of a truss structure, the truss structure further including a second spar, a third spar, a plurality of ribs positioned transverse to the spars, and a plurality of truss members connected between the spars and the ribs.</li><li>74. A method for manufacturing a wind turbine blade, comprising: <ul id="ul0023" list-style="none" compact="compact"><li>positioning a spar to extend in a longitudinal direction, the spar including a plurality of stacked layers and having a generally rectangular cross-sectional shape;</li><li>positioning an arcuate hub attachment element proximate to the spar;</li><li>mechanically attaching the spar to the hub attachment element via a transition portion that transitions between the generally rectangular cross-sectional shape at the spar and an arcuate shape at the hub attachment element.</li></ul></li><li>75. The method of clause 74 wherein mechanically attaching includes shaping individual layers of the spar to have an increased circumferential extent and an increasingly arcuate shape as the individual layers extend toward the hub attachment element.</li><li>76. The method of clause 75 further comprising selecting first individual layers of the spar to have an increased circumferential extent and an increasingly arcuate shape as the first individual layers extend toward the hub attachment element, and selecting second individual layers to terminate at a location spaced apart from the hub attachment element.</li><li>77. The method of clause 75 further comprising: <ul id="ul0024" list-style="none" compact="compact"><li>selecting first individual layers of the spar to have an increased circumferential extent and an increasingly arcuate shape as the first individual layers extend toward the hub attachment element;</li><li>selecting second individual layers to terminate at a location spaced apart from the hub attachment element; and</li><li>adding third layers in place of at least some of the second layers, wherein the first layers have fibers with a first directional orientation, the second layers have fibers with a second directional orientation, and the third layers have fibers with a third directional orientation different than the second directional orientation.</li></ul></li><li>78. The method of clause 77, further comprising orienting fibers of the second layers to be generally parallel to the longitudinal direction, and orienting fibers of the third layers non-parallel to the longitudinal direction.</li><li>79. The method of clause 74 wherein mechanically attaching the spar to the hub attachment element includes: <ul id="ul0025" list-style="none" compact="compact"><li>positioning a transition element between the spar and the hub attachment element;</li><li>receiving layers of the spar in corresponding recesses of the transition element;</li><li>attaching the received layers to the transition element; and</li><li>attaching an arcuate portion of the transition element to the hub attachment element.</li></ul></li><li>80. The method of clause 79 wherein the transition element is a first transition element, and wherein receiving layers includes receiving first layers, and wherein the method further comprises: <ul id="ul0026" list-style="none" compact="compact"><li>positioning a second transition element between the spar and the hub attachment element;</li><li>receiving second layers of the spar in corresponding recesses of the second transition element;</li><li>attaching the received layers to the second transition element; and</li><li>attaching an arcuate portion of the second transition element to the hub attachment element, with the second transition element being positioned radially outwardly from the first transition element.</li></ul></li><li>81. The method of clause 79 wherein the transition element is a first transition element, and the spar is a first spar, and wherein the method further comprises: <ul id="ul0027" list-style="none" compact="compact"><li>positioning a second spar to extend generally in the longitudinal direction, the second spar including a plurality of stacked layers and having a generally rectangular cross-sectional shape;</li><li>positioning a second transition element between the second spar and the hub attachment element;</li><li>receiving layers of the second spar in corresponding recesses of the second transition element;</li><li>attaching the received layers to the second transition element; and</li><li>attaching an arcuate portion of the second transition element to the hub attachment element at a different circumferential location than where the first transition element is attached to the hub attachment element.</li></ul></li><li>82. The method of clause 74 wherein the transition element includes a plate that tapers from an arcuate cross-sectional shape at the hub attachment element to a generally rectilinear cross-sectional shape at an interface with the spar.</li><li>83. The method of clause 74 wherein the spar is a first spar, and wherein the method further comprises: <ul id="ul0028" list-style="none" compact="compact"><li>positioning a second spar to be spaced apart from the first spar;</li><li>positioning a third spar to be spaced apart from the first and second spars positioning a plurality of ribs transverse to the spars; and</li><li>connecting a plurality of truss members between the spars and the ribs.</li></ul></li><li>84. A wind turbine blade comprising: <ul id="ul0029" list-style="none" compact="compact"><li>an external aerodynamic surface having a longitudinally-extending spanwise axis, a chordwise axis transverse to the spanwise axis, and a thickness axis transverse to both the chordwise and spanwise axes; and</li><li>a plurality of longitudinally-extending spars, wherein at least one of the spars includes: <ul id="ul0030" list-style="none" compact="compact"><li>a longitudinally extending first spar portion having a plurality of laminated first layers, wherein individual first layers terminate at different longitudinal locations to form a first end portion having a plurality of first projections and first recesses, with individual first projections alternating with individual first recesses along the thickness axis;</li><li>a longitudinally extending second spar portion having a plurality of laminated second layers, wherein individual second layers terminate at different longitudinal locations to form a plurality of second projections and second recesses, with individual second projections alternating with individual second recesses along the thickness axis; and</li><li>wherein individual second projections are received in corresponding first recesses, and individual first projections are received in corresponding second recesses, to join the first spar portion to the second spar portion.</li></ul></li></ul></li><li>85. The wind turbine blade of clause 84 wherein the individual second projections are bonded to the corresponding first recesses, and the individual first projections are bonded to the corresponding second recesses, to join the first spar portion to the second spar portion along a bondline having a location that varies in a non-monotonic manner.</li><li>86. The wind turbine blade of clause 84 wherein the individual second projections are bonded to the corresponding first recesses, and the individual first projections are bonded to the corresponding second recesses, to join the first spar portion to the second spar portion along a bondline having a zig-zag shape.</li><li>87. The wind turbine blade of clause 84 wherein the plurality of laminated first layers includes a plurality of first precured composite layers, and wherein the plurality of laminated second layers includes a plurality of second precured composite layers</li><li>88. The wind turbine blade of clause 84, further comprising a plurality of longitudinally spaced-apart ribs, and wherein the at least one spar is attached to the ribs.</li><li>89. The wind turbine blade of clause 84, further comprising a web, and wherein the at least one spar is attached to the web.</li><li>90. The wind turbine blade of clause 84, further comprising: <ul id="ul0031" list-style="none" compact="compact"><li>a first strap clamped circumferentially around the first layers; and</li><li>a second strap clamped circumferentially around the second layers.</li></ul></li><li>91. The wind turbine blade of clause 84, further comprising: <ul id="ul0032" list-style="none" compact="compact"><li>a plurality of longitudinally spaced-apart ribs; and</li><li>a first truss attachment member, wherein the first truss attachment member includes a first piece and a corresponding second piece, wherein the first piece is attached to the second piece to clamp the individual first layers of the first spar portion therebetween, and wherein at least one of the first piece and the second piece of the first truss attachment member is attached to a first one of the longitudinally spaced apart ribs; and</li><li>a second truss attachment member, wherein the second truss attachment member includes a third piece and a corresponding fourth piece, wherein the third piece is attached to the fourth piece to clamp the individual second layers of the second spar portion therebetween, and wherein at least one of the third piece and the fourth piece of the second truss attachment member is attached to a second one of the longitudinally spaced apart ribs.</li></ul></li><li>92. A wind turbine blade comprising: <ul id="ul0033" list-style="none" compact="compact"><li>an external aerodynamic surface having a longitudinally-extending spanwise axis, a chordwise axis transverse to the spanwise axis, and a thickness axis transverse to both the chordwise and spanwise axes; and</li><li>a longitudinally extending first spar portion having a plurality of laminated first layers that form a first spar end portion with a plurality of first projections and first recesses along the chordwise axis;</li><li>a longitudinally extending second spar portion having a plurality of second laminated layers that form a second spar end portion having plurality of second projections and second recesses along the chordwise axis; and</li><li>wherein individual second projections are received in corresponding first recesses, and individual first projections are received in corresponding second recesses, to join the first spar end portion to the second spar end portion.</li></ul></li><li>93. The wind turbine blade of clause 92 wherein all the first layers terminate in first end portions and all the second layers terminate in second end portions, and wherein all the first end portions have a first shape and all the second end portions have a second shape.</li><li>94. The wind turbine blade of clause 92 wherein all the first layers terminate in first end portions and all the second layers terminate in second end portions, wherein individual first end portions have corresponding individual first shapes that define the corresponding first projections and the first recesses along the chordwise axis, and wherein individual second end portions have individual second shapes that define the corresponding second projections and the second recesses along the chordwise axis.</li><li>95. The wind turbine blade of clause 92 wherein all of the first layers terminate in first end portions having a first zig-zag shape along the chordwise axis, and wherein all of the second layers terminate in second end portions having a second zig-zag shape along the chordwise axis that compliments the first zig-zag shape.</li><li>96. An apparatus for compressing a plurality of precured composite material layers together for lamination, the apparatus comprising a first tool portion including: <ul id="ul0034" list-style="none" compact="compact"><li>a first support base;</li><li>a first expandable member carried by the first support base; and</li><li>a first fitting in fluid communication with the first expandable member; and</li><li>a second tool portion including: <ul id="ul0035" list-style="none" compact="compact"><li>a second support base;</li><li>a second expandable member carried by the second support base; and</li><li>a second fitting in fluid communication with the second expandable member, wherein the second support base is configured to be operably coupled to the first support base with the plurality of composite material layers positioned between the first and second expandable members, and wherein the first and second fittings are configured to transfer fluid into the first and second expandable members to expand the expandable members and compress the composite material layers therebetween.</li></ul></li></ul></li><li>97. The apparatus of clause 96 wherein the first and second tool portions are configured to be fit together in a clamshell arrangement around the composite material layers.</li><li>98. The apparatus of clause 96 wherein the first tool portion includes first and second side flanges extending outwardly from opposite sides of the first support base, wherein the second tool portion includes third and forth side flanges extending outwardly from opposite sides of the second support base, and wherein the first side flange is configured to overlap the third side flange, and the second side flange is configured to overlap the fourth side flange, when the first tool portion is operably coupled to the second tool portion with the plurality of composite material layers positioned therebetween.</li><li>99. The apparatus of clause 96: <ul id="ul0036" list-style="none" compact="compact"><li>wherein the first tool portion further comprises: <ul id="ul0037" list-style="none" compact="compact"><li>at least a third expandable member positioned adjacent to the first expandable member; and</li><li>a first manifold extending from the fitting to the first and third expandable members; and</li><li>wherein the second tool portion further comprises: <ul id="ul0038" list-style="none" compact="compact"><li>at least a fourth expandable member positioned adjacent to the second expandable member; and</li><li>a second manifold extending from the fitting to the second and fourth expandable members, wherein the first fitting is configured to transfer fluid into the first and third expandable members via the first manifold to expand the first and third expandable members against one side of the composite material layers, and wherein the second fitting is configured to transfer fluid into the second and fourth expandable members via the second manifold to expand the second and fourth expandable members against the opposite side of the composite material layers to compress the composite material layers therebetween.</li></ul></li></ul></li></ul></li><li>100. A method of manufacturing a wind turbine blade, the method comprising: <ul id="ul0039" list-style="none" compact="compact"><li>moving fibers through a resin bath to wet the fibers with resin;</li><li>moving the wet fibers through a heated die to cure the resin and shape the resin and fibers into an elongate composite pultrusion;</li><li>cutting the elongate composite pultrusion into individual pieces to form a plurality of pultruded composite pieces;</li><li>laminating the plurality of pultruded composite pieces together to form a first wind turbine blade structure; and</li><li>attaching the first wind turbine blade structure to a second wind turbine blade structure to form a portion of a wind turbine blade truss structure.</li></ul></li><li>101. The method of clause 100 wherein laminating the plurality of pultruded composite pieces together to form a first wind turbine blade structure includes forming an elongate spar.</li><li>102. The method of clause 100 wherein the wind turbine blade includes an external aerodynamic surface having a longitudinally-extending spanwise axis, a chordwise axis transverse to the spanwise axis, and a thickness axis transverse to both the chordwise and spanwise axes, wherein laminating the plurality of pultruded composite pieces together to form a first wind turbine blade structure includes forming a spar portion, and wherein attaching the first wind turbine blade structure to a second wind turbine blade structure includes orienting the spar portion along the spanwise axis and fixedly attaching the spar portion to a plurality of ribs extending along the chordwise axis.</li><li>103. The method of clause 100: <ul id="ul0040" list-style="none" compact="compact"><li>wherein the wind turbine blade includes an external aerodynamic surface having a longitudinally-extending spanwise axis, a chordwise axis transverse to the spanwise axis, and a thickness axis transverse to both the chordwise and spanwise axes;</li><li>wherein laminating the plurality of pultruded composite pieces together to form a first wind turbine blade structure includes laminating a first plurality of pultruded composite layers together to form a first spar portion having a first spar end portion with a plurality of first projections and first recesses along the chordwise axis, and laminating a second plurality of pultruded composite layers together to form a second spar portion having a second spar end portion with a plurality of second projections and second recesses along the chordwise axis; and</li><li>wherein attaching the first wind turbine blade structure to a second wind turbine blade structure includes inserting individual first projections into corresponding second recesses, and inserting individual second projections into corresponding first recesses, to join the first spar end portion to the second spar end portion.</li></ul></li><li>104. A method of manufacturing a wind turbine blade having an external aerodynamic surface with a longitudinally-extending spanwise axis, a chordwise axis transverse to the spanwise axis, and a thickness axis transverse to both the chordwise and spanwise axes, the method comprising: <ul id="ul0041" list-style="none" compact="compact"><li>positioning a plurality of turbine blade ribs in a manufacturing assembly, wherein individual ribs are aligned with the chordwise axis and are spaced apart from each other along the spanwise axis;</li><li>positioning a first elongate layer of composite material across the plurality of ribs along the spanwise axis;</li><li>applying a layer of adhesive to the first layer of composite material;</li><li>positioning a second elongate layer of composite material on the layer of adhesive;</li><li>compressing the first and second elongate layers of composite material together; and</li><li>curing the adhesive to laminate the second layer of composite material to the first layer of composite material and form a spar portion extending along the spanwise axis between the plurality of ribs.</li></ul></li><li>105. The method of clause 104 wherein positioning a first elongate layer of composite material across the plurality of ribs includes positioning a first layer of precured composite material across the ribs, and wherein positioning a second elongate layer of composite material on the layer of adhesive includes positioning a second layer of precured composite material on the layer of adhesive.</li><li>106. The method of clause 104 wherein positioning a first elongate layer of composite material across the plurality of ribs includes positioning a first pultruded layer across the ribs, and wherein positioning a second elongate layer of composite material on the layer of adhesive includes positioning a second pultruded layer on the layer of adhesive.</li><li>107. The method of clause 104 wherein each of the individual ribs includes a cutout, and wherein positioning a first elongate layer of composite material across the plurality of ribs includes positioning portions of the first elongate layer of composite material into each of the cutouts.</li><li>108. The method of clause 104 wherein each of the individual ribs includes a cutout, and wherein the method further comprises: <ul id="ul0042" list-style="none" compact="compact"><li>positioning individual fittings in each of the individual cutouts;</li><li>attaching the individual fittings to the corresponding ribs; and</li><li>attaching a corresponding portion of the spar portion to each of the individual fittings.</li></ul></li><li>109. The method of clause 104, further comprising: <ul id="ul0043" list-style="none" compact="compact"><li>positioning a plurality of additional elongate layers of composite material on the first and second elongate layers; and</li><li>terminating the individual layers of composite material at different longitudinal locations to form a spar end portion having a plurality of projections and recesses, with individual projections alternating with individual recesses along the thickness axis.</li></ul></li><li>110. The method of clause 104 wherein curing the adhesive to laminate the second layer of composite material to the first layer of composite material and form a spar portion includes forming a spar end portion having a plurality of projections and recesses, with individual projections alternating with individual recesses along the chordwise axis.</li><li>111. The method of clause 104 wherein the plurality of turbine blade ribs is a plurality of first turbine blade ribs, wherein curing the adhesive to laminate the second layer of composite material to the first layer of composite material and form a spar portion includes forming a first spar portion having a first spar end portion with a plurality of first projections and first recesses, and wherein the method further comprises: <ul id="ul0044" list-style="none" compact="compact"><li>positioning a plurality of second turbine blade ribs in a second manufacturing assembly, wherein individual second ribs are aligned with the chordwise axis and are spaced apart from each other along the spanwise axis;</li><li>positioning a third elongate layer of composite material across the plurality of second ribs along the spanwise axis;</li><li>applying a second layer of adhesive to the third layer of composite material;</li><li>positioning a fourth elongate layer of composite material on the second layer of adhesive;</li><li>compressing the third and fourth elongate layers of composite material together;</li><li>curing the second layer of adhesive to laminate the third layer of composite material to the fourth layer of composite material and form a second spar portion extending along the spanwise axis between the plurality of second ribs, the second spar portion including a second spar end having a plurality of second projections and second recesses;</li><li>applying adhesive to the first spar end portion and the second spar end portion;</li><li>inserting individual first projections into corresponding individual second recesses, and inserting individual second projections into corresponding first recesses, to join the first spar portion to the second spar portion.</li></ul></li><li>112. The method of clause 104 wherein compressing the first and second elongate layers of composite material together includes: <ul id="ul0045" list-style="none" compact="compact"><li>removably coupling a plurality of compressing apparatuses to the first and second layers of composite material between individual turbine blade ribs; and</li><li>operating the compressing apparatuses to compress the first and second layers of composite material together.</li></ul></li><li>113. The method of clause 104 wherein compressing the first and second elongate layers of composite material together includes: <ul id="ul0046" list-style="none" compact="compact"><li>positioning a first tool portion on one side of the first and second layers of composite material, the first tool portion having an expandable member;</li><li>positioning a second tool portion on the opposite side of the first and second layers of composite material;</li><li>coupling the first tool portion to the second tool portion; and</li><li>expanding the expandable member to compress the first and second layers of composite material together.</li></ul></li><li>114. The method of clause 104 wherein compressing the first and second elongate layers of composite material together includes: <ul id="ul0047" list-style="none" compact="compact"><li>positioning a first tool portion on one side of the first and second layers of composite material, the first tool portion having an expandable member;</li><li>positioning a second tool portion on the opposite side of the first and second layers of composite material;</li><li>coupling the first tool portion to the second tool portion; and</li><li>inflating the expandable member to compress the first and second layers of composite material together.</li></ul></li><li>115. The method of clause 104 wherein compressing the first and second elongate layers of composite material together includes: <ul id="ul0048" list-style="none" compact="compact"><li>positioning a first tool portion on one side of the first and second layers of composite material, the first tool portion having a first expandable member;</li><li>positioning a second tool portion on the opposite side of the first and second layers of composite material, the second tool portion having a second expandable member;</li><li>coupling the first tool portion to the second tool portion; and</li><li>expanding the first and second expandable members to compress the first and second layers of composite material together.</li></ul></li><li>116. A method for making a wind turbine blade having a longitudinally extending spanwise axis, a chordwise axis transverse to the spanwise axis, and a thickness axis transverse to both the chordwise and spanwise axes, the method comprising: <ul id="ul0049" list-style="none" compact="compact"><li>laminating a plurality of first material layers together to form a longitudinally-extending first spar portion, wherein individual first material layers terminate at different longitudinal locations to form a plurality of first projections and first recesses, with individual first projections interleaved with individual first recesses along the thickness axis;</li><li>laminating a plurality of second material layers together to form a longitudinally-extending second spar portion, wherein individual second material layers terminate at different longitudinal locations to form a plurality of second projections and second recesses, with individual second projections interleaved with individual second recesses along the thickness axis;</li><li>engaging the first projections of the first spar portion with corresponding second recesses of the second spar portion and engaging the second projections of the second spar portion with corresponding first recesses of the first spar portion; and</li><li>fixing the first projections in the second recesses and fixing the second projections in the first recesses.</li></ul></li><li>117. The method of clause 116 wherein laminating a plurality of first material layers together includes laminating a plurality of first composite material layers together, and wherein laminating a plurality of second material layers together includes laminating a plurality of second composite materials together.</li><li>118. The method of clause 116 wherein laminating a plurality of first material layers together includes laminating a plurality of first precured composite material layers together, and wherein laminating a plurality of second material layers together includes laminating a plurality of second precured composite materials together.</li><li>119. The method of clause 116 wherein laminating a plurality of first material layers together includes laminating a plurality of first pultruded composite layers together, and wherein laminating a plurality of second material layers together includes laminating a plurality of second pultruded composite materials together.</li><li>120. A method for making a wind turbine blade having a longitudinally extending spanwise axis, a chordwise axis transverse to the spanwise axis, and a thickness axis transverse to both the chordwise and spanwise axes, the method comprising: <ul id="ul0050" list-style="none" compact="compact"><li>laminating a plurality of first composite material layers together to form a longitudinally-extending first spar portion, wherein the first spar portion includes a first spar end portion having a plurality of first projections and first recesses;</li><li>laminating a plurality of second composite material layers together to form a longitudinally-extending second spar portion, wherein the second spar portion includes a second spar end portion having a plurality of second projections and second recesses;</li><li>engaging the first projections of the first spar portion with corresponding second recesses of the second spar portion and engaging the second projections of the second spar portion with corresponding first recesses of the first spar portion; and</li><li>bonding the first projections in the second recesses and bonding the second projections in the first recesses.</li></ul></li><li>121. The method of clause 116, wherein laminating a plurality of first composite material layers together includes laminating a plurality of first precured composite material layers together, and wherein laminating a plurality of second composite material layers together includes laminating a plurality of second precured composite material layers together.</li><li>122. The method of clause 116, wherein laminating a plurality of first composite material layers together includes laminating a plurality of first pultruded layers together, and wherein laminating a plurality of second composite material layers together includes laminating a plurality of second pultruded layers together.</li><li>123. The method of clause 116 wherein laminating a plurality of first composite material layers together includes forming a first spar end portion having individual first projections interleaved with individual first recesses along the chordwise axis, and wherein laminating a plurality of second composite material layers together includes forming a second spar end portion having individual second projections interleaved with individual second recesses along the chordwise axis.</li></ol>