The Laddermill: work in progress

The Laddermill is a new concept that provides a method for exploiting the wind energy at high altitudes (1-10km). The laddermill could enable wind energy generation in the order of 50 MW per Laddermill, an order of magnitude larger than current conventional windmills. The principle combines kite properties with that of airplanes. Kites go up while driving a ground based generator, and go down flying like an airplane. Development of a demonstrator of the Laddermill is one of the projects at the new chair AeroSpace Sustainable Engineering and Technology (ASSET), created under an agreement between the European Space Agency and the Delft University of Technology. ASSET promotes a general vision towards an optimistic sustainable future using hi-tech aerospace developments. Two distinct Laddermill types are presented. The first type presented is one in which the wings are attached to a continuously rotating tether shaped as an endless loop. The kites attached to the ascending side of the loop are configured for high lift. At the top of the loop, the kites change attitude to allow them to glide down to the ground station. The second type is the pumping Laddermill, in which the kites are attached to a single tether that goes up and down alternately, in a linear motion. Both types will feature a ground station where the generator is located. In general, the tether will provide the ground station with mechanical power at low speeds (1/3 of the wind speed), thus with high forces. Each Laddermill type will enforce several different requirements upon the ground station. These are mechanically analyzed and an early assessment is presented. Also several types of kites are analyzed and compared. A fully 3-D, 6 degrees of freedom simulation software package was developed. The software allows for an analysis of the dynamics of a multitude of attached kites. It is demonstrated that the Laddermill can be designed such that it is stable in a wide range of wind profiles and timely variations, including wind shear. The wind energy at high altitudes is considerable (average 9 Beaufort at 9 km in Holland). Kite like structures are light and inexpensive and enjoy a general cultural acceptance.