Rotor blades for wind power installations are generally known and can be seen to a great extent at any wind power installation. Those rotor blades are of an external shape which takes account of the particular aerodynamic demands involved. In order to save on material and weight the rotor blades generally comprise a first internal carrier structure and a surface which encloses that first carrier structure and which is of an aerodynamically favourable configuration.
In the case of large wind power installations the rotor blades are of considerable dimensions, for aerodynamic reasons. That has an effect on the one hand on manufacture and transportation and on the other hand on the loads which act on the wind power installation in operation. They arise in particular out of the blade surface area which automatically increases with increasing size, and also the increased area swept by the rotor blades.
Wind power installations have to be designed in accordance with predetermined guidelines for given load situations. They are on the one hand the loads which occur in operation (referred to as operating loads) and on the other hand what are referred to as extreme load situations. Such extreme load situations are derived from given situations or disturbances such as for example a power network failure, a fault in blade adjustment, an extraordinarily strong gust of wind (a once-in-50-years gust etc).
In that respect it will be appreciated that the loads transmitted to the installation by the rotor blades substantially depend on the rotor blade surface area which is exposed to the wind. For calculating the extreme load, it is assumed that the entire rotor blade surface area is exposed to a maximum wind. All subsequent components such as the drive train, machine carrier, pylon, foundations etc have to be appropriately designed.
This means that, the smaller the surface area on which the wind acts, that is to say in particular the rotor blade surface area, the correspondingly lower is the load level for which the installation has to be designed. That also signifies a lower level of material expenditure and thus lower costs.
It will be appreciated however that in conflict with those considerations are a minimum surface area size required for aerodynamic reasons, in order to be able to apply the necessary forces for operation of the wind power installation—for rotating the generator. In that respect, the known rotor blades suffer from the disadvantage that, in particular in the region near the blade root, the rotor blade depth required also increases with an increasing rotor blade size. That rotor blade depth in that case becomes so great that on-road transport of such a rotor blade is already no longer possible or is possible only at incomparably high cost.