Current technical evolution within the wind energy industry seems to indicate an increase in the installed power per tower, therefore leading to a need to progressively increase the length of the wind turbine blades. Nevertheless, wind turbine blades going over 45 meters in length do introduce extreme challenges in the transport, both onshore and offshore, building up processes that require expensive cranes and manufacturing repeatability. Modular blades could provide a feasible response to current limitations:

  • Avoiding the implementation of satellite plants for blade manufacturing since logistic costs during manufacturing process and transportation can be reduced.
  • Allowing new large blades to access wind farms with limited road dimensions.
  • Enabling the development of blade families with the same blade root and various blade tips which will be chosen depending on the wind class.
  • Allowing the fast replacement of blade tips for maintenance requirements or for the installation of new blade tips with improved design.

The IndeModular joint system is an innovative new joint system for modular blades. It is a bolted connection which consists of several cells units located in the spar cap of the blade, each cell unit comprising four metallic inserts bonded to the spar cap, their respective bolts and nuts, and an intermediate plate. After all the cell units are assembled, they are pre-stressed resulting in the cell units being under compression loads that allow high fatigue resistance.

The IndeModular joint system system does have the following advantages:

  • The innovative geometry accommodates a large number of bolts per cap width, in order that a high load density is achieved and lightweight and very strong connections are provided.
  • As a result of the particular architecture of the joint system, stresses affecting both the intermediate plate and the blade laminate around the inserts are dramatically lower than in other conventional solutions.
  • The neutral line of the intermediate plate, bolts and blade laminate is perfectly aligned, defining a very structurally effective connection.
  • Due to its modular design, the joint system can be integrated into any different blade architectures (e.g. spar box, single and double spar webs)and blade lengths by simply adding more or less cell units.
  • The joint system can be easily assembled and disassembled from outside the blade and there are no restrictive assembly tolerances: hence, in-field blade assembly time is reduced and accuracy of the assembly is guaranteed.
  • The joint system does not invade the aerodynamic surface of the blade, and power produced by the blade is therefore not affected.

The IndeModular joint system has been successfully tested in a full-scale mechanical test for its validation under Germanischer Lloyd guidelines and supervision. The impact in cost and weight of implementing IndeModular in a blade is less than 10% of the total cost and weight of the monolithic blade. Furthermore, there is no significant impact on the dynamic behaviour of the wind turbine since natural frequencies of both monolithic and modular blades are very similar.