Patent Publication Number: US-2018051672-A1

Title: Jointed rotor blade for wind turbine

Description:
BACKGROUND 
     The present application relates generally to a jointed rotor blade of a wind turbine, and more particularly, to a spar cap assembly for a jointed rotor blade of a wind turbine. 
     Wind power is considered as one of the cleanest and environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from the wind and transmit the kinetic energy through rotational energy to turn a shaft that couples the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the rotational energy to electrical energy that may be deployed to a utility grid. 
     Rotor blades of the wind turbine generally include a shell body formed by two shell halves, generally made of a composite material. The individual shell halves are generally manufactured using molding processes and are then coupled together along the corresponding edges of the rotor blade. In general, the shell body is relatively light in weight and the structural properties (e.g., stiffness, buckling resistance and strength) of the shell body may not be able to withstand the bending moments and other loads exerted on the rotor bade during operation. To increase the stiffness, buckling resistance and strength of the rotor blade, the shell body is typically reinforced using spar caps that engage the inner surfaces of the shell halves. As such, flap-wise or span-wise bending moments and loads, which cause a rotor blade tip to defect towards the wind turbine tower, are generally transferred along the rotor blade through the spar caps. 
     In recent years, sizes of the wind turbines for wind power generation have increased to improve power generation efficiency and the absolute power generated. Along with the increase in size of wind turbines for wind power generation, wind turbine rotor blades have also increased in length. For example, an average blade length of a newer generation wind turbine may be  40  meters or more. When the wind turbine rotor blade is increased in length as described above, various challenges occur. For example, difficulties may arise in integral manufacture and in securing roads and trucks for conveyance. Therefore, it is desirable to construct wind blades as segments to enable manufacture of a rotor blade in a modular manner For example, longitudinal segments of a wind blade may be manufactured separately for ease of handling and transportation and then assembled into full length rotor blades at a wind farm site. 
     Different designs and methods have been investigated in the past to join two blade segments and to rebuild the blade to full length at site. Joining two blade segments may incur additional cost, weight, field assembly time and reliability. For example, a joint generally adds weight to the rotor blade. The additional weight due to the joint in a rotor blade increases the weight of the blade, and impacts static moment, inertia and Eigen frequencies of the rotor blade, resulting in a system load increase. 
     Generally, spars and spar caps contribute to a major part of the rotor blade mass. Accordingly, there is a need for a spar cap design that allows for a reduction in blade mass and/or material costs without sacrificing the performance of the rotor blade. 
     BRIEF DESCRIPTION 
     In one aspect, a spar cap assembly for a jointed rotor blade of a wind turbine is disclosed. The spar cap assembly includes a root spar cap assembly and a tip spar cap assembly. The root spar cap assembly includes a root tensile spar cap and a root compressive spar cap, and is formed from a first composite material. The tip spar cap assembly includes a tip tensile spar cap and a tip compressive spar cap, and is formed from a second composite material. The second composite material is different from the first composite material. The thickness of a joining end of the root tensile spar cap is different from the thickness of a joining end of the tip tensile spar cap, and the thickness of a joining end of the root compressive spar cap is different from the thickness of a joining end of the tip compressive spar cap. 
     In another aspect, a jointed rotor blade of a wind turbine is disclosed. The jointed rotor blade includes a root blade segment joined to a tip blade segment at a joint and a spar cap assembly at the joint. The spar cap assembly includes a root spar cap assembly and a tip spar cap assembly. The root spar cap assembly includes a root tensile spar cap and a root compressive spar cap, and is formed from a first composite material. The tip spar cap assembly includes a tip tensile spar cap and a tip compressive spar cap, and is formed from a second composite material that is different from the first composite material. The tip tensile spar cap is adjacent to the root tensile spar cap at the joint, and the tip compressive spar cap is adjacent to the root compressive spar cap at the joint. The thickness of a joining end of the root tensile spar cap is different from the thickness of a joining end of the tip tensile spar cap. Further, the thickness of a joining end of the root compressive spar cap is different from the thickness of a joining end of the tip compressive spar cap. 
     In yet another aspect, a wind turbine is disclosed. The wind turbine includes a jointed rotor blade. The jointed rotor blade includes a root blade segment joined to a tip blade segment at a joint and a spar cap assembly at the joint. The spar cap assembly includes a root spar cap assembly and a tip spar cap assembly. The root spar cap assembly includes a root tensile spar cap and a root compressive spar cap, and is formed from a first composite material. The tip spar cap assembly includes a tip tensile spar cap and a tip compressive spar cap, and is formed from a second composite material that is different from the first composite material. The tip tensile spar cap is adjacent to the root tensile spar cap at the joint, and the tip compressive spar cap is adjacent to the root compressive spar cap at the joint. The thickness of a joining end of the root tensile spar cap is different from the thickness of a joining end of the tip tensile spar cap. Further, the thickness of a joining end of the root compressive spar cap is different from the thickness of a joining end of the tip compressive spar cap. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings. 
         FIG. 1  is an illustration of an exemplary wind turbine. 
         FIG. 2  is an exemplary illustration of a jointed rotor blade having a root blade segment and a tip blade segment, in accordance with some embodiments of the present disclosure. 
         FIG. 3A  is a perspective view of a joining end of the root blade segment of the jointed rotor blade, in accordance with some embodiments of the present disclosure. 
         FIG. 3B  is a perspective view of a joining end of the tip blade segment of the jointed rotor blade, in accordance with some embodiments of the present disclosure. 
         FIG. 4  is a perspective view of a section of the tip blade segment of the jointed rotor blade, in accordance with an example of the present disclosure. 
         FIG. 5  is a perspective view of a section of the root blade segment of the jointed rotor blade, in accordance with an example of the present disclosure. 
         FIG. 6  is a perspective view of the assembly of the jointed rotor blade, in accordance with an example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     To more clearly and concisely describe and point out the subject matter, the following definitions are provided for specific terms, which are used throughout the following description and the appended claims, unless specifically denoted otherwise with respect to particular embodiments. The terms “wind blade” and “rotor blade” are used interchangeably in the present disclosure. As used herein, a “jointed rotor blade” is a rotor blade that includes at least one joint. A “spar cap assembly” is a combination of different spar caps present in the rotor blade. A spar cap that is present in a side of the rotor blade that experiences tensile force during rotation is termed as a tensile spar cap, and a spar cap that is in the side of the rotor blade that experiences compression during rotation is termed as a compressive spar cap. A “root spar cap assembly” is a combination of spar caps present in the root blade segment, and a “tip spar cap assembly” is a combination of spar caps present in the tip blade segment of the jointed rotor blade. A “joining end” is an end that is exposed to the joint. In a chord-wise joint, a joining end of the root blade segment faces the joining end of the tip blade segment at the joint at a specific span length of the jointed blade. A “thickness of a joining end of the root tensile spar cap” is defined as the thickness between the inner face of the root tensile spar cap and the inner surface of the body shell at the joining end of the root blade segment. A “thickness of a joining end of the root compressive spar cap” is defined as the thickness between the inner face of the root compressive spar cap and the inner surface of the body shell at the joining end of the root blade segment. A “thickness of a joining end of the tip tensile spar cap” is defined as the thickness between the inner face of the tip tensile spar cap and the inner surface of the body shell at the joining end of the tip blade segment. A “thickness of a joining end of the tip compressive spar cap” is defined as the thickness between the inner face of the tip compressive spar cap and the inner surface of the body shell at the joining end of the tip blade segment. 
       FIG. 1  is a side view of an exemplary wind turbine  10 . In  FIG. 1 , the wind turbine  10  is a horizontal-axis wind turbine. Alternatively, the wind turbine  10  may be a vertical-axis wind turbine. In some embodiments, the wind turbine  10  includes a tower  12  that extends from a support surface  14 , a nacelle  16  mounted on the tower  12 , a generator  18  positioned within the nacelle  16 , a gearbox  20  coupled to the generator  18 , and a rotor  22  that is rotationally coupled to the gearbox  20  with a rotor shaft  24 . The rotor  22  includes a rotatable hub  26  and at least one rotor blade  28  coupled to and extending outward from the rotatable hub  26 . As shown, the rotor blade  28  includes a blade root end  17  and a blade tip end  19 . The rotor  22  herein includes three rotor blades  28 . However, in an alternative embodiment, the rotor  22  may include more or less than three rotor blades  28 . Additionally, the tower  12  may be any suitable type of tower having any suitable height. The rotor blades  28  may be spaced about the hub  26  to facilitate rotating the rotor  22  to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. Specifically, the hub  26  may be rotatably coupled to the electric generator  18  to permit electrical energy to be produced. 
     In general, the present disclosure is directed to a jointed rotor blade  29  having a spar cap assembly that includes a root spar cap assembly and a tip spar cap assembly. In particular, the present disclosure discloses spar caps of the root blade segment and the tip blade segment formed from different composite materials, which have differing thicknesses depending on the mechanical properties of the respective composite materials. For example, when the specific strength and/or modulus of elasticity of a first composite material is lower than the specific strength and/or modulus of elasticity respectively of a second composite material, the thickness of the spar cap having the first composite material may be increased and the thickness of the spar cap having the second composite material may be decreased, as compared to a pair of symmetrical spar caps having same composite material, without sacrificing the bending strength, stiffness or buckling resistance of the rotor blade. In some embodiments, the observed decrease in weight, and decreased cost of the rotor blade is efficiently used to over compensate the observed increase in cost of the rotor blade by introducing a second composite material. In certain embodiments, an overall reduction in material costs and blade mass is be achieved by altering the composite material and, thereby, the thickness of the tip spar cap assembly with respect to the root spar cap assembly. 
       FIG. 2  further illustrates a perspective view of the jointed rotor blade  29  having a root blade segment  30  and a tip blade segment  32 , in accordance with an example of the present disclosure. The root blade segment  30  and the tip blade segment  32  extend in opposite directions from a joint  34 . In the jointed rotor blade  29 , the root blade segment  30  and the tip blade segment  32  are connected by at least one supporting inner structure, such as, for example, a spar, extending into both blade segments  30 ,  32  to facilitate joining of the blade segments  30 ,  32 . 
     A body shell  38  of the jointed rotor blade  29  generally extends to the root blade segment  30  and the tip blade segment  32  along a longitudinal axis  40 . The body shell  38  may generally serve as the outer casing/covering of the jointed rotor blade  29  and may define a substantially aerodynamic profile, such as by defining a symmetrical or cambered air foil-shaped cross-section. The body shell  38  may also define a pressure side  42  and a suction side  44  extending between leading edge  46  and trailing edge  48  of the jointed rotor blade  29 . Further, the jointed rotor blade  29  may also have a span  50  defining the total length between the blade root end  17  and the blade tip end  19  and a chord  52  defining the total length at a particular point along the span between the leading edge  46  and the trailing edge  48 . As is generally understood, the chord  52  may generally vary in length with respect to the span  50  as the jointed rotor blade  29  extends from the blade root end  17  and the blade tip end  19 . The joint  34  joins the root blade segment  30  to the tip blade segment  32  at the joining end  54  of the root blade segment and the joining end  56  of the tip blade segment. The joint  34  may be at any distance from the root end  17  along the span  50  of the jointed rotor blade  29 . In some embodiments, the joint  34  is at a span in a range from about 50% to about 90% from the root end  17  of the jointed rotor blade  29 . In some specific embodiments, the joint  34  is at a span in a range from about 65% to about 80% from the root end  17  of the jointed rotor blade  29 . While the joint  34  in  FIG. 2  is illustrated herein as a chord-wise joint, other kinds of joints may be envisaged for joining the tip blade segment  32  to the root blade segment  30 . 
     In several embodiments, the body shell  38  of the jointed rotor blade  29  may be formed from a plurality of shell components. For example, the body shell  38  may be manufactured from a first shell half (not shown) generally defining the pressure side  42  of the jointed rotor blade  29  and a second shell half (not shown) generally defining the suction side  44  of the jointed rotor blade  29 , with such shell halves being secured to one another at the leading and trailing edges  46 ,  48  of the jointed rotor blade  29 . In some embodiments, the body shell  38  is separately molded to the tip blade segment  32  and the root blade segment  30 , and joined at the time of joining the tip and root blade segments. In some other embodiments, the body shell  38  is molded to the jointed rotor blade  29  after joining inner structures of the tip blade segment  32  and the root blade segment  30 . The body shell  38  may generally be formed from any suitable material. For instance, in some embodiments, the body shell  38  may be formed entirely from a laminate composite material, such as a carbon fiber reinforced composite or a glass fiber reinforced composite. Alternatively, one or more portions of the body shell  38  may be configured as a layered construction and may include a core material, formed from a lightweight material such as wood (e.g., balsa), foam (e.g., extruded polystyrene foam) or a combination of such materials, disposed between layers of composite material. 
     The jointed rotor blade  29  (illustrated in  FIG. 2 ) may also include one or more longitudinally extending structural components configured to provide increased stiffness, buckling resistance and/or strength to the jointed rotor blade  29 . These structural components may also be joined by joining the joining end  54  of the root blade segment  30  to the joining end  56  of the tip blade segment  32  at the joint  34 .  FIG. 3A  illustrates a perspective view, along the axis  40 , of an embodiment of the joining end  54  of the root blade segment  30  and  FIG. 3B  illustrates a perspective view, along the axis  40 , of an embodiment of the joining end  56  of the tip blade segment  32 , of the jointed rotor blade  29  at the joint  34  illustrated in  FIG. 2 . Referring to  FIG. 3A , the joining end  54  of the root blade segment  30  of the jointed rotor blade  29  may include a root spar cap assembly  60  including a pair of longitudinally extending spar caps  62 ,  64  configured to be engaged (positioned) against the opposing inner surfaces  66 ,  68  of the pressure and suction sides  42 ,  44  respectively of the body shell  38  (illustrated in  FIG. 2 ). Additionally, one or more root spars  70  may be disposed between the spar caps  62 ,  64  for load-bearing. Referring to  FIG. 3B , the joining end  56  of the tip blade segment  32  of the jointed rotor blade  29  may include a tip spar cap assembly  80  including a pair of longitudinally extending spar caps  82 ,  84  configured to be engaged against the opposing inner surfaces  86 ,  88  of the pressure and suction sides  42 ,  44  respectively of the body shell  38  (illustrated in  FIG. 2 ). Additionally, one or more tip spars  90  may be disposed between the spar caps  82 ,  84  so as to bear the load. 
     The spar caps  62 ,  64  of the root blade segment  30  and spar caps  82 ,  84  of the tip blade segment  32  may generally be designed to control the bending stresses and/or other loads acting on the rotor blade in a generally span-wise direction (a direction parallel to the span  50  of the jointed rotor blade  29  illustrated in  FIG. 2 ) during operation of a wind turbine. For instance, bending stresses may occur on a jointed rotor blade  29  when the wind loads directly on the pressure side  42  of the jointed rotor blade  29 , thereby subjecting the pressure side  42  to span-wise tension and the suction side  44  to span-wise compression as the rotor blade  29  bends in the direction of the wind turbine tower. 
     Thus, the spar cap  62  disposed on the pressure side  42  of the root blade segment is termed as the root tensile spar cap  62  and spar cap  82  disposed on the pressure side  42  of the tip blade segment is termed as the tip tensile spar cap  82 . The root tensile spar cap  62  and the tip tensile spar cap  82  may generally be configured to withstand the span-wise tension occurring as the jointed rotor blade  29  is subjected to various bending moments and other loads during operation. Similarly, the spar cap  64  disposed on the suction side  44  of the root blade segment is termed as the root compressive spar cap  64  and spar cap  84  disposed on the suction side  44  of the tip blade segment is termed as the tip compressive spar cap  84 . The root compressive spar cap  64  and the tip compressive spar cap  84  disposed on the suction side  44  of the jointed rotor blade may generally be configured to withstand the span-wise compression occurring during operation of the wind turbine  10 . 
     The spar caps may be designed to have any advantageous shapes and cross-sectional areas. In an exemplary embodiment of the root tensile spar cap  62 , the tip tensile spar cap  82 , root compressive spar cap  64  and the tip compressive spar cap  84  having approximately rectangular cross-section, the spar caps  62 ,  64 ,  82 ,  84  may include a cross-sectional area equal to a product of a spar cap thickness and a chord-wise width of each individual spar cap  62 ,  64 ,  82 ,  84 , as measured along the chord  52  defined between the leading edge  46  and the trailing edge  48 . The spar cap thicknesses and/or the chord-wise width of the root tensile spar cap  62 , the root compressive spar cap  64 , the tip tensile spar cap  82 , and the tip compressive spar cap  84  may vary along the span  50  of the jointed rotor blade  29 . For example, the spar cap thickness may be less at the blade root end  17  end, may increase as the span of the rotor blade increases, may have a maximum (not shown) at a particular span and may be less again at the blade tip end  19  end of the jointed rotor blade  29 . Depending on the location of the joint  34  at the span  50 , the maximum of the spar cap thickness may be in the root blade segment  30  or at the tip blade segment  32 . The increment and the decrease in the spar cap thicknesses are gradual in some embodiments, and is in a stepwise manner in some other embodiments. 
     For example, as shown in  FIG. 3A , the root tensile spar cap  62  may generally have a root tensile spar cap thickness  102  (thickness between the inner face  106  of the root tensile spar cap  62  and the inner surface  66  of the body shell  38 ) at the joining end  54 , and a chord-wise, root tensile spar cap width  108  at the joining end  54 . Additionally, the root compressive spar cap  64  may generally have a root compressive spar cap thickness  104  (thickness between the inner face  110  of the compressive spar cap  84  and the inner surface  68  of the body shell  38 ) at the joining end  54 , and a chord-wise, root compressive spar cap width  112  at the joining end  54 .  FIG. 3B  illustrates the tip tensile spar cap  82  having a tip tensile spar cap thickness  122  (thickness between the inner face  126  of the tip tensile spar cap  82  and the inner surface  86  of the body shell  38 ) at the joining end  56 , and a chord-wise, tip tensile spar cap width  128  at the joining end  56 . Additionally, the tip compressive spar cap  84  is having a tip compressive spar cap thickness  124  (thickness between the inner face  130  of the tip compressive spar cap  84  and the inner surface  88  of the body shell  38 ) at the joining end  56 , and a chord-wise, tip compressive spar cap width  132  at the joining end  56 . A slight curvature at the inner faces  66 ,  68 ,  86 ,  88  of the body shell  38  and/or at the inner surfaces  106 ,  110 ,  126 ,  130  of the inner faces of the spar caps may cause a slight change in the thickness  102 ,  104 ,  122 ,  124  of the spar caps when measured along the widths  108 ,  112 ,  128 ,  132 . However, these changes in the thickness are considered as incidental and for comparison between thicknesses of any two spar caps, maximum thickness of those two spar caps may be considered. 
     Depending on the properties of the material utilized to form the spar caps of the root blade segment  30  and the tip blade segment  32 , the tensile and compressive spar caps of the root blade segment and the tip blade segment may generally be configured to define differing thicknesses and cross-sectional areas without any adverse effects on performance 
     The material and design of the spars and spar caps of the jointed rotor blades play a significant role in controlling the rotor blade mass. One design consideration for a rotor blade is the static moment of the blade. Lightweight and high stiffness materials, such as for example, carbon, are desired to be used in load-bearing structures such as the root and tip spars  70 ,  90 , and the spar caps. However, most of the commonly known lightweight and high stiffness materials are expensive and limit cost effective application when the spar and spar caps of entire blade are constructed of a single material. The static moment benefit obtained by deploying lightweight and high stiffness materials towards the blade tip end  19  end of the blade is greater compared to the benefit obtained by deploying these materials at blade root end  17  end. Combining different materials of spars and spar caps as a function of span position can be effectively used for increasing the cost and performance benefits. A jointed rotor blade  29  provides a prospect to deploy different materials at the root blade segment  30  and the tip blade segment  32  of the jointed rotor blade  29 . 
     In some aspects of the present disclosure, a spar cap assembly for a jointed rotor blade of a wind turbine is disclosed. The spar cap assembly includes a root spar cap assembly and a tip spar cap assembly. The root spar cap assembly  60  includes a root tensile spar cap and a root compressive spar cap, and is formed from the first composite material. The tip spar cap assembly  80  includes a tip tensile spar cap and a tip compressive spar cap, and is formed from the second composite material. The second composite material is different from the first composite material. The thickness of a joining end of the root tensile spar cap is different from the thickness of a joining end of the tip tensile spar cap, and the thickness of a joining end of the root compressive spar cap is different from the thickness of a joining end of the tip compressive spar cap. 
     In some aspects of the present disclosure, the root spar cap assembly  60  consists essentially of the first composite material, and the tip spar cap assembly  80  consists essentially of the second composite material. In some aspects, the material of the root spar  70  and the tip spar  90  are formed of same materials, irrespective of the materials used in the root spar cap assembly  60  and the tip spar cap assembly  80 . However, in some other aspects, the material of the root spar  70  is similar to the material of the root spar cap assembly  60 , and the material of the tip spar  90  is similar to the material of the tip spar cap assembly  80 . In some embodiments, the material, design, thickness, width, or any combinations thereof of the root tensile spar cap  62  may vary from the respective aspects of the root compressive spar cap  64 . Similarly, the material, design, thickness, width, or any combinations thereof of the tip tensile spar cap  82  may vary from the respective aspects of the tip compressive spar cap  84 . In a specific aspect, the root tensile spar cap  62 , the root compressive spar cap  64 , and the root spar  70  are formed of the first composite material, and the tip tensile spar cap  82 , the tip compressive spar cap  84 , and the tip spar  90  are formed of the second composite material. The second composite material is different from the first composite material. 
     The specific strength and/or modulus of elasticity and the thickness of the spar caps may be effectively used to change thickness of the spar caps, without sacrificing the mechanical properties of the jointed rotor blade, when different composite materials are used in the root blade segment  30  and the tip blade segment  32 . In some embodiments of the present disclosure, the root spar cap assembly  60  and the tip spar cap assembly  80  are formed from different composite materials. The thickness  102  of the joining end  54  of the root tensile spar cap  62  is different from the thickness  122  of the joining end  56  of the tip tensile spar cap  82 , and the thickness  104  of the joining end  54  of the root compressive spar cap  64  is different from the thickness of the joining end  56  of the tip compressive spar cap  84 . 
     In some embodiments, the tip spar cap assembly  80  is formed by the second composite material that has higher specific strength and/or modulus of elasticity from the first composite material forming the root spar cap assembly  60 . In these embodiments, the thickness of the spar caps  82 ,  84  of the tip spar cap assembly  80  at the joining end  56  is decreased as compared to spar caps  62 ,  64  of the root spar cap assembly  60  at the joining end  54 , without sacrificing the mechanical properties, such as, for example, bending strength, stiffness or buckling resistance of the jointed rotor blade  29 . Thus, in some embodiments, the thickness  102  of the joining end  54  of the root tensile spar cap  62  is greater than the thickness  122  of the joining end  56  of the tip tensile spar cap  82 , and the thickness  104  of the joining end  54  of the root compressive spar cap  64  is greater than the thickness  124  of the joining end  56  of the tip compressive spar cap  84 . 
     In some embodiments, depending on the material characteristics of the first composite material and the second composite material, the specific strength and/or modulus of elasticity of the first composite material may be significantly different from the specific strength and/or modulus of elasticity respectively of the second composite material. This significant difference in the specific strength and/or modulus of elasticity permits a significant change in the thickness of the tensile and compressive spar caps. In some embodiments, specific strength of the second composite material is at least 30% greater than the specific strength of the first composite material. In some embodiments, elastic modulus of the second composite material is at least 30% greater than the elastic modulus of the first composite material. 
     In some embodiments, the thickness  102  of the joining end  54  of the root tensile spar cap  62  is at least 30% greater than the thickness  122  of the joining end  56  of the tip tensile spar cap  82 . Similarly, in some embodiments, the thickness  104  of the joining end  54  of the root compressive spar cap  64  is at least 30% greater than the thickness  124  of the joining end  56  of the tip compressive spar cap  84 . In certain embodiments, the thickness  102  of the joining end  54  of the root tensile spar cap  62  is at least 50% greater than the thickness  122  of the joining end  56  of the tip tensile spar cap  82 . In some embodiments, the thickness  104  of the joining end  54  of the root compressive spar cap  64  is at least 50% greater than the thickness  124  of the joining end  56  of the tip compressive spar cap  84 . In some specific embodiments, the thickness  102  of the joining end  54  of the root tensile spar cap  62  is at least 70% greater than the thickness  122  of the joining end  56  of the tip tensile spar cap  82 . In some specific embodiments, the thickness  104  of the joining end  54  of the root compressive spar cap  64  is at least 70% greater than the thickness  124  of the joining end  56  of the tip compressive spar cap  84 . 
     The cross sectional area (not shown) of the root tensile spar cap  62 , root compressive spar cap  64 , tip tensile spar cap  82 , and tip compressive spar cap  84  may vary from each other. In some embodiments, wherein the thicknesses of the spar caps vary from each other as referred to above, the width of the spar caps may or may not differ across the joint  34 . In some embodiments, the width  108  of the joining end  54  of the root tensile spar cap  62  is greater than the width  128  of the joining end  56  of the tip tensile spar cap  82 , and width  112  of the joining end  54  of the root compressive spar cap  64  is greater than the width  132  of the joining end  56  of the tip compressive spar cap  84 . 
     In some embodiments, the first composite material of the spar cap assembly of the jointed rotor blade  29  includes a matrix and a reinforcement. In some embodiments, the first composite material of the spar cap assembly of the jointed rotor blade  29  includes a reinforcement of fiberglass. The fiberglass may include E-glass, S-glass, R-glass or any combinations thereof. In some embodiments, the first composite material is reinforced with fiberglass. In some embodiments, the other materials that may be present as a part of the reinforcement are only incidental material impurities present in a concentration less than about 2 weight % of the reinforcement. In some embodiments, the second composite material of the spar cap assembly of the jointed rotor blade  29  includes a matrix and a reinforcement. In some embodiments, the reinforcement is selected from carbon, aramid, basalt, mixtures of carbon and aramid, mixtures of carbon and basalt, or mixtures of aramid and basalt. In some embodiments, the reinforcement is selected from mixtures of carbon and fiberglass, mixtures of aramid and fiberglass, mixtures of basalt and fiberglass, mixtures of carbon and fiberglass along with another reinforcement material, mixtures of aramid and fiberglass along with another reinforcement material, or mixtures of basalt and fiberglass along with another reinforcement material. In some embodiments, the reinforcement includes mixtures of carbon, aramid, basalt, and fiberglass. In some embodiments, the second composite material of the spar cap assembly of the jointed rotor blade  29  includes a reinforcement of carbon fiber, aramid fiber, or a combination of carbon and aramid fibers. In some embodiments, the second composite material is reinforced with carbon fiber, aramid fiber, or a combination thereof. Other materials may be present as a part of the reinforcement, or as incidental material impurities in a concentration less than about 2 weight % of the reinforcement. In certain embodiments, the first composite material is reinforced with fiberglass and the second composite material is reinforced with carbon fiber, aramid fiber, or a combination of carbon and aramid fibers. In one specific embodiment, the first composite material is reinforced with fiberglass and the second composite material is reinforced with carbon fiber. In another specific embodiment, the first composite material is reinforced with fiberglass and the second composite material is reinforced with aramid fiber. In some exemplary embodiments, the first composite material is reinforced with one type of fiberglass and the second composite material is reinforced with another type of fiberglass that has a different composition and higher strength as compared to the fiberglass reinforcement of the first composite material. The matrix materials of the first composite material and the second composite material may include thermosetting polymers or thermoplastics. Some examples of the thermoset polymers that may be used as a matrix for the first composite material and/or the second composite material include epoxies, polyesters, and vinylesters, 
     Changing the composite material of the tip blade segment  32  of the jointed rotor blade  29  from the commonly used glass fiber reinforced plastic (GFRP) to, for example, carbon fiber reinforced plastic (CFRP), can over compensate the increase in weight due to the joint  34 , while maintaining the bending stiffness of the blade. Further, the capability of changing the composite material of the tip blade segment  32  enables formation of the jointed rotor blade  29  using any rotor blade as the baseline blade. Furthermore, using this technology, stronger and/or longer rotor blades may be formed for sites with wind conditions that are above the existing limit. 
     The use of multiple materials along the rotor blade minimizes cost of the rotor blade and of the turbine system by providing the lowest cost balance of weight, moment, and performance For example, the calculated benefit in moment of high performance materials applied to a  30  meters&#39; span is ten times that at a  3  meters&#39; span as measured from the root end  17 . As a consequence, such materials become more cost effective when employed at the tip. Multiple materials can be employed along the span using mechanical or bonded joints, different material pultrusions or fiber mats within the spar or spar caps. 
     In certain aspects, a spar cap assembly for a jointed rotor blade  29  of a wind turbine includes a root spar cap assembly  60  and a tip spar cap assembly  80 . The root spar cap assembly  60  includes a root tensile spar cap  62  and a root compressive spar cap  64 , and is formed from a composite reinforced with fiberglass. The tip spar cap assembly  80  includes a tip tensile spar cap  82  and a tip compressive spar cap  84 , and is formed from a composite reinforced with carbon fiber, aramid fiber, or a combination thereof. The thickness  102  of a joining end  54  of the root tensile spar cap  62  is at least 30% greater than the thickness  122  of a joining end  56  of the tip tensile spar cap  82 . The thickness  104  of a joining end  54  of the root compressive spar cap  64  is at least 30% greater than the thickness  124  of a joining end  56  of the tip compressive spar cap  84 . 
     In some embodiments, a method of forming a spar cap assembly is provided. The method includes forming a root spar cap assembly  60  that includes a root tensile spar cap  62  and a root compressive spar cap  64 , from a first composite material, to engage a root spar  70  of a root blade segment  30 . The method further includes forming a tip spar cap assembly  80  that includes a tip tensile spar cap  82  and a tip compressive spar cap  84 , from a second composite material that is different from the first composite material, to engage a tip spar  90  of a tip blade segment  32 . When formed, the thickness  102  of a joining end  54  of the root tensile spar cap  62  is different from the thickness  122  of a joining end  56  of the tip tensile spar cap  82 , and the thickness  104  of the joining end  54  of the root compressive spar cap  64  is different from the thickness of the joining end  56  of the tip compressive spar cap  84 . In some embodiments, the method further includes forming the root spar cap assembly  60  from a composite reinforced with fiberglass and forming the tip spar cap assembly from a composite reinforced with carbon fiber, aramid fiber, or a combination thereof. The root blade segment and the tip blade segments having the formed spar cap assemblies may be transported to the required assembly sites and joined in the assembly sites, thereby reducing the transportation cost. 
     In some aspects, a jointed rotor blade  29  (illustrated in  FIG. 2 ) of a wind turbine is disclosed. The jointed rotor blade  29  includes a root blade segment  30  joined to a tip blade segment  32  at a joint  34  and a spar cap assembly ( 60  and  80  together) at the joint  34 . The spar cap assembly includes a root spar cap assembly  60  and a tip spar cap assembly  80 . The root spar cap assembly  60  includes a root tensile spar cap  62  and a root compressive spar cap  64 , and is formed from a first composite material. The tip spar cap assembly  80  includes a tip tensile spar cap  82  and a tip compressive spar cap  84 , and is formed from a second composite material that is different from the first composite material. The tip tensile spar cap  82  is adjacent to the root tensile spar cap  62  at the joint  34 , and the tip compressive spar cap  84  is adjacent to the root compressive spar cap  64  at the joint  34 . In certain embodiments, the tip tensile spar cap  82  is joined to the root tensile spar cap  62  at the joint  34 , and the tip compressive spar cap  84  is joined to the root compressive spar cap  64  at the joint  34 . The thickness  102  of a joining end  54  of the root tensile spar cap  62  is different from the thickness  122  of a joining end  56  of the tip tensile spar cap  82 , and the thickness  104  of a joining end  54  of the root compressive spar cap  64  is different from the thickness  124  of a joining end  56  of the tip compressive spar cap  84 . 
     In some embodiments, the thickness  102  of the joining end  54  of the root tensile spar cap  62  of the jointed rotor blade  29  is at least 30% greater than the thickness  122  of the joining end  56  of the tip tensile spar cap  82 , and the thickness  104  of the joining end  54  of the root compressive spar cap  64  of the jointed rotor blade  29  is at least 30% greater than the thickness  124  of the joining end  56  of the tip compressive spar cap  84 . In some embodiments, the root blade segment  30  and the tip blade segment  32  extend in opposite directions from a chord-wise joint  34  as illustrated in  FIG. 2 . 
     In some aspects, a wind turbine having a jointed rotor blade  29  (illustrated in  FIG. 2 ) is disclosed. The jointed rotor blade  29  of the wind turbine  10  includes a root blade segment  30  joined to a tip blade segment  32  at a joint  34  and a spar cap assembly ( 60  and  80  together) at the joint  34 . The spar cap assembly includes a root spar cap assembly  60  and a tip spar cap assembly  80 . The root spar cap assembly  60  includes a root tensile spar cap  62  and a root compressive spar cap  64 . Both the root tensile spar cap  62  and a root compressive spar cap  64  are formed from a first composite material. The tip spar cap assembly  80  includes a tip tensile spar cap  82  and a tip compressive spar cap  84 . Both the tip tensile spar cap  82  and a tip compressive spar cap  84  are formed from a second composite material that is different from the first composite material. The tip tensile spar cap  82  is adjacent to the root tensile spar cap  62  at the joint  34 , and the tip compressive spar cap  84  is adjacent to the root compressive spar cap  64  at the joint  34 . In certain embodiments, the tip tensile spar cap  82  is joined to the root tensile spar cap  62  at the joint  34 , and the tip compressive spar cap  84  is joined to the root compressive spar cap  64  at the joint  34 . The thickness  102  of a joining end  54  of the root tensile spar cap  62  is different from the thickness  122  of a joining end  56  of the tip tensile spar cap  82 , and the thickness  104  of a joining end  54  of the root compressive spar cap  64  is different from the thickness  124  of a joining end  56  of the tip compressive spar cap  84 . 
     In some embodiments, the thickness  102  of the joining end  54  of the root tensile spar cap  62  of the jointed rotor blade  29  is at least 30% greater than the thickness  122  of the joining end  56  of the tip tensile spar cap  82 , and the thickness  104  of the joining end  54  of the root compressive spar cap  64  of the jointed rotor blade  29  is at least 30% greater than the thickness  124  of the joining end  56  of the tip compressive spar cap  84 . In some embodiments, the root blade segment  30  and the tip blade segment  32  extend in opposite directions from a chord-wise joint  34  as illustrated in  FIG. 2 . 
     Different methods may be deployed to join the tip blade segment  32  to the root blade segment  30  at the joint  34  of the jointed rotor blade  29  including methods of physical joining, chemical joining, or mechanical joining. In some embodiments, the tip blade segment  32  is mechanically joined to the root blade segment  30 . In some specific embodiments, the tip blade segment  32  has a spar structure that is joined to a specifically designed spar structure of the root blade segment  30  in a chord-wise joint. In some exemplary embodiments, the spar structure of the tip blade segment is joined to the spar structure of the root blade segment using bolt joints, as illustrated in  FIGS. 4-6 . The mechanical joining may include, without limitation, embedding, adhesive joining, capping, and attaching by using nut and bolts, or rivets. 
       FIG. 4  illustrates a perspective view of a section of the tip blade segment  32  in accordance with an example of the jointed rotor blade  29 . The tip blade segment  32  includes a tip beam structure  140  that forms a portion of the tip spar  90  and extends lengthways for structurally connecting with the root blade segment  30 . The beam structure  140  forms a part of the tip blade segment  32  having an extension protruding from a tip spar  90 , thereby forming an extending spar section. The tip beam structure  140  includes a shear web  144  engaged by the tip tensile spar cap  82  and the tip compressive spar cap  84 . Thus, in some embodiments, the tip spar cap assembly  80  (shown in  FIG. 3B ) engages the tip spar  90  of the tip blade segment  32 . 
     Further, the tip blade segment  32  includes one or more first bolt joint tubes located at a first end  154  of the tip beam structure  140 . In a non-limiting example, the bolt joint tube includes a pin that is in a tight interference fit with a bush. As shown, the one or more bolt joint tubes includes one bolt joint tube  152  located on the beam structure  140 . As shown, the bolt joint tube  152  is oriented in a span-wise direction. The tip blade segment  32  also includes one bolt joint slot  150  located on the beam structure  140  proximate to the chord-wise joint  34 . This bolt joint slot  150  is oriented in a chord-wise direction. In one example, there may be a bushing within the bolt joint slot  150  arranged in a tight interference fit with a bolt tube or pin (shown as pin  153  in  FIG. 6 ). Further, the tip blade segment  32  includes a plurality of second bolt joint tubes  156 ,  158  located at the chord-wise joint  34 . The plurality of second bolt joint tubes  156 ,  158  include a leading edge bolt joint tube  156  and a trailing edge bolt joint tube  158 . Each of the leading edge bolt joint tube  156  and the trailing edge bolt joint tube  158  is oriented in a span-wise direction. In one example, each of the plurality of second bolt joint tubes  156 ,  158  include multiple flanges  155 ,  157  respectively that are configured to distribute compression loads at the chord-wise joint  34 . 
     In certain embodiments, the jointed rotor blade  29  includes one or more first bolt joint tubes  152  located at the first end  154  of the tip beam structure  140  for connecting with the receiving section of the root blade segment  30 , and a plurality of second bolt joint tubes  156 ,  158  located at the chord-wise joint  34 , wherein the first bolt joint tubes  152  located at the first end  154  of the tip beam structure  140  are separated span-wise with the plurality of second bolt joint tubes  156 ,  158  located at the chord-wise joint  34 . It is to be noted that the first joint bolt tube  152  located at the first end of beam structure  140  is separated span-wise with the plurality of second bolt joint tubes  156 ,  158  located at the chord-wise joint  34  by an optimal distance D. This optimal distance D may be such that the chord-wise joint  34  is able to withstand substantial bending moments caused due to shear loads acting on the chord-wise joint  34 . In one non-limiting example, each of the bolt joints connecting the root blade segment  30  and the tip blade segment  32  may include an interference-fit steel bushed joint. 
       FIG. 5  is a perspective view of a section of the root blade segment  30  at the chord-wise joint  34  in accordance with an example of the present disclosure. The root blade segment  30  shows a receiving section  160  extending lengthways within the root blade segment  30  for receiving the beam structure  140  of the tip blade segment  32  (illustrated in  FIG. 4 ). In certain embodiments, the tip spar  90  of the tip blade segment  32  comprises a tip beam structure  140  extending lengthways and structurally connecting with the root blade segment  30  at a receiving section  160  of the spar of the root blade segment  30 . The receiving section  160  includes multiple root spar structures  166  as a part of the root spar  70 , that extend lengthways for connecting with the tip beam structure  140  of the tip blade segment  32 . As shown, the root blade segment  30  further includes bolt joint slots  162 ,  164  for receiving bolt joint tubes  156 ,  158  (shown in  FIG. 4 ) of the tip blade segment  32  and forming tight interference fittings. Thus, in certain embodiments, the receiving section  160  of the root blade segment  30  includes the plurality of root spar structures  166  extending lengthways and connecting with the tip beam structure  140  of the tip blade segment  32  through the second bolt joint tubes in the chord-wise direction. 
     In one example, each of the multiple bolt joint slots  162 ,  164  include multiple flanges  161 ,  163  respectively that are configured to distribute compression loads at the chord-wise joint  34 . The multiple root spar structures are engaged by the root tensile spar cap  62  and the root compressive spar cap  64 . Thus, in some embodiments, the root spar cap assembly  60  engages a root spar  70  of the root blade segment  30 . In certain embodiments, the tip spar cap assembly  80  engages a tip spar  90  of the tip blade segment  32  and the root spar cap assembly  60  engages a root spar  70  of the root blade segment  30 . 
       FIG. 6  shows a perspective view of the exemplary jointed rotor blade  29  at the joint  34 , wherein the tip spar  90  of the tip blade segment  32  includes a tip beam structure  140  extending lengthways and structurally connecting with the root blade segment  30  at a receiving section of the root spar  70  of the root blade segment  30 . As shown, a pair of root spar structures  166  is configured to receive the beam structure  140  and includes bolt joint slots  182 ,  184  that are aligned with the bolt joint slot  150  of the beam structure  140  through which a bolt tube or pin  153  is inserted and remains in a tight interference fit such that root spar structures  166  and the beam structure  140  are joined together by during assembling.  FIG. 6  also shows the rectangular fastening element  172  that includes a bolt joint slot  186  configured for receiving the bolt tube  152  of the beam structure  140  forming a tight interference fit bolted joint. Further, the pair of root spar structures  166  is joined together at one end  188  using a suitable adhesive material or an elastomeric seal. In one example, a sensor element  151  is disposed in the pin or bolt tube  152 . The sensor element may help in receiving and sending signals to a control unit (not shown) of the wind turbine, which signals may enable sensing multiple parameters including blade loads or stresses. This may help in effective operation of the wind turbine. 
     Advantageously, the present disclosure ensures efficient reduction of connecting loads, leading to simplified moment flow between the multiple supporting structures of the wind blade. Further, the present disclosure ensures low cost, reliable, and scalable connections. Due to the customizable blade geometry and segmented blade parts, there is reduction in transportation costs. Furthermore, the easy handling and assembling of the wind blade leads to reduction of turbine down time during wind blade maintenance. 
     Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. Similarly, the various features described, as well as other known equivalents for each such feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure, and are presumed to be covered herein. Further, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.