relate these stresses by means of a suitable failure theory. It is also necessary to rigorously relate blade material and geometry to beam-like stiffnesses. In turn, the stiffness and mass must be combined with suitable aerodynamic models to determine structural dynamic response in the rotating field of the rotor. This type of analysis will help to assess the benefits of active control as well as passive (such as by elastic tailoring) load relief systems. Most of these tools either exist or are being developed in the aerospace industry. They are largely developed under government systems procurements and should be extracted and adapted to the special needs of the wind turbine rotor.
Emerging technologies in active and passive control of both the rotor and the generator need to be studied on an overall system basis considering the probable gains in structural efficiency and reduction in blade life-cycle cost.
Two emerging manufacturing processes, resin transfer molding, and pultrusion, offer significant opportunities for cost reduction but with attendant limitations on blade design freedom. A feasibility study should be conducted to evaluate each of these processes in a real application and at a reasonable scale, allowing realistic design and cost trade studies to be accomplished. For example, the cost of a geometrically simple pultruded blade can be little more than the cost of the materials, thus making it appreciably less costly than the curved and shaped wind turbine blades currently employed. However, while less costly, such blades are also less efficient aerodynamically. Thus, from a life-cycle economics perspective, it is not clear that the attendant reduction in the initial cost of the wind turbine can compensate for the associated decrease in energy production over the wind turbine lifetime.