Choosing an appropriate timber for a small wind turbine blade: A comparative study

Despite the use of composite materials, timber is still widely used in the wind energy industry and especially in small wind turbine blades. Four species of timber namely alder, ash, beech and hornbeam which are grown in Iran were tested for their suitability for use in small blades. A solid blade is easiest to manufacture and is interesting from the structural aspect but its high inertia could delay starting since small turbines have no pitch mechanism to optimize the blade angles of attack during starting. We describe the design and optimization of solid and hollow blades for a small horizontal axis turbine via genetic algorithms. In order to maximize the power coefficient and minimize the starting time, the optimization algorithm tries to find the external/internal geometry of the blades while the resultant stresses do not exceed the allowable stress of the timbers. Regardless of the type of timbers, the optimization results show that the power coefficient of all the optimal blades is sufficiently high but the starting performance requires choosing an appropriate timber. More specifically, the alder solid blade would be better than the beech, hornbeam and ash. For the hollow blades, the alder and beech timbers could be used for windy areas and all four timbers are very promising for operation in low wind speed regions where starting behavior is more important.