Wind turbine blades with layered, multi-component spars, and associated systems and methods

A wind turbine blade system, comprising:

• first and second blade segments positioned at different locations along a longitudinal axis and joined together to form at least a portion of a wind turbine blade, the first blade segment including a first spar element and the second blade element including a second spar element;
• wherein
• the second spar element is elongated along the longitudinal axis and includes multiple second planks, with individual second planks including at least one first layer having a first composition, at least one second layer having a second composition different than the first composition, and an adhesive between the first and second layers, the adhesive having an adhesive composition different than the first and second compositions;
• and wherein
• the first blade segment is elongated along the longitudinal axis and includes multiple first planks, with individual first planks including at least one third layer having a third composition different than the first and second compositions.

A wind turbine blade system, comprising:

• a first blade segment having a longitudinal axis, the first blade segment including at least one first spar element that is elongated along the longitudinal axis, the at least one first spar element including multiple first planks, with individual first planks having a first thickness T1 and a first elastic modulus E1;
• and
• a second blade segment having at least one second spar element joined to the at least one first spar element at a spar joint and extending along the longitudinal axis, the at least one second spar including multiple second planks joined to corresponding first planks at the spar joint, with individual second planks having a second thickness T2 and including at least one first layer having a first layer thickness T2a and first composition with an elastic modulus of E2a, and at least one second layer having a second layer thickness T2b and a second composition different than the first composition with an elastic modulus of E2b, and wherein
• (E1×T1) is approximately equal to (E2a×T2a)+(E2b×T2b).

A wind turbine blade, comprising:

• a first blade segment having a first spar cap portion, the first spar cap portion including a plurality of laminated first planks, wherein individual first planks are formed from unidirectional fiberglass, have a first thickness, and 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 a thickness axis;
• and
• a second blade segment having a second spar cap portion, the second spar cap portion including a plurality of laminated second planks, wherein individual second planks are formed from biaxial fiberglass strips attached to carbon strips, and 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;
• wherein the individual second planks have a second thickness at least approximately the same as the first thickness at the corresponding second projections, and have a third thickness less than the second thickness at an intermediate location spaced apart from the corresponding second projections;
• wherein a thickness of the fiberglass strips decreases to zero at the intermediate location;
• and
• 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.

A method for designing a wind turbine blade system, comprising:

• selecting a first spar element of a first blade segment to include first planks having a first thickness and a first plank composition;
• selecting a second spar element of a second blade segment to include second planks having a second thickness and a second plank composition different than the first plank composition;
• sizing the first planks to join with the second planks;
• and
• selecting the first and second thicknesses, and the first and second compositions so that an overall product of thickness and elastic modulus of the first planks is approximately equal to an overall product of thickness and elastic modulus for the second planks.