Design of a 100 MW laddermill for wind energy generation from 5 km altitude

This paper presents the design of a 100 MW Laddermill. The Laddermill is a novel concept to generate electricity from high altitude winds. The concept allows very large single unit powers. It generates electricity by pulling a rope from a generator, with lift generated by kites. For a 100 MW Laddermill 50 kites are distributed evenly in the top 5 km of a 6.5 km long rope. 500 m of the rope is wound around the generator. The kites pull the 500 m of rope from the generator, thus driving it. Subsequently the kites fly down in a configuration that generates significantly less lift than during the ascent. This way the tether is retrieved and the process is repeated. The 50 kites required for a 100 MW Laddermill each have the wing surface of two soccer fields, or 13.000 m2. Large controllable kites are thus an enabling technology for the Laddermill. Preliminary results including a practical demonstration exist. The tether will be tapered, with a diameter of 24 cm at ground level to 4 cm at the altitude of the highest kite. The groundstation will feature a large drum for the cable, a gearbox and some cable guidance equipment. The whole groundstation can be rotated to align with the wind direction. The groundstation is connected to 2000 tons of ballast which prevents the kites from lifting the groundstation from the ground. This paper discusses several design options considered for the Laddermill concept and the groundstation. It also reports on the results of tests that are performed in which the Laddermill principle is demonstrated and the first Laddermill electricity is produced.