GEC has been studying advanced blade design that utilises bend-twist coupling, which lowers loads on the entire turbine structure in response to turbulent gusts. The design combines stiff carbon fibres with relatively flexible fibreglass materials to achieve the proper twist and bend in blades under stress, says GEC's Dayton Griffin. Bending and twisting of the blade naturally occurs along the length of a blade, but "it is most important near the blade tip." About 2% of the anticipated cost of energy reductions are attributed to the twist-coupling and the remainder to other features of the blade's aerodynamic and structural design.
GEC's design incorporates carbon into the blade skins on a bias with the fibreglass as a way to control the twist. The inclusion of carbon in the structural spars also allows the blade to be more slender than a 100% fibreglass blade, which also lightens loads. The combination reduces loading on the entire structure, which allows cost reduction in other components, such as tower wall thickness. The ultimate goal of the SBIR project is to test 30-35-metre blades for commercial use, but initial tests by GEC and TPI will be done with a nine metre prototype developed under a separate program with Sandia National Laboratories.