Laddermill, a novel concept to exploit the energy in the airspace

Abstract A very significant amount of wind energy is contained in the movements of air at high altitudes. A particular invention (Laddermill Patent Ned. 1004508. Nov. 1996 applications Europe and USA), named “laddermill”, is described that allows exploiting this energy using the winds up to possibly the tropopause. A “laddermill” is a self-supporting system that consists of an endless cable connected to a series of high-lifting wings or kites moving up in a linear fashion, combined with a series of low-lifting wings or kites going down. The cable drives an energy generator placed on the ground. Dutch measured wind statistics are presented that show the immense power source at high altitudes. Some general physical considerations are given for the laddermill. Three simulation programmes were developed independently by different institutions. The results give a good consistency of the laddermill shape and power production. Design solutions are indicated for the wing attitude control and stability and a concept for the ground station is presented providing wing and cable handling. Adaptation to weather is given by flexible retrieval and deployment capability. Comparisons are shown with existing wind turbines. An operational model and related cost model have been made that include an operation strategy that optimises the economical effectiveness of the wings, cable and ground station. This operational model has been applied to the actual wind measurements over a period of 10 years. The results show, in comparison to the existing horizontal axes wind turbines, (i) a potential for significantly larger amount of wind energy production and (ii) an indication that this can be done at significantly lower cost. The public acceptance has been assessed, resulting in a positive perception of elegance of the low speed and silent movements combined with the excitement from reaching impressive altitudes. Safety and potential aviation interference are also addressed.