Dutch ex-astronaut and Physicist Dr Wubbo Ockels successfully demonstrated his Laddermill in a field near the university city of Groningen, The Netherlands, on August 29th. His radio-controlled high-flying energy kite, created 10.5kW of electrical energy. The experiment was carried out along the northern coastline of The Netherlands where there's usually more than enough wind to raise the gigantic kites. The Laddermill is designed to capture the energy contained in the airspace at altitudes as high as 10 km.
Description of the principle of operation of the Laddermill as it appears on the Laddermill website:
The Laddermill consists of a series of wings or kites all connected to a cable that forms a huge loop. Like the wings of an airplane will the wind cause an upward lift force to the wings. By changing the attitude of the wing (angle of attack with respect to the wind) can the lift force be made larger or smaller. The wings on one side of the cable loop are all placed such that they produce the maximum lift force, while the wings on the other side of the loop will give a much smaller lift that in fact is just sufficient to support their own weight and the weight of the cable. The result is a large difference in force between the two ends at the ground. When the cable loop is guided around a wheel on the ground the force difference will drive the wheel. By connecting the wheel to a generator electricity will be produced. The wind energy aloft has thus been transferred to electricity on the ground.
Cost calculations have been made that include the cable and wing constructions as well as the ground station mechanisms, power conversion and storage. These calculations lead to an expected installation cost of FL 1000.- or 400 US$ per kilowatt. A 10 megawatt Laddermill system would thus cost 8 million guilders and would provide an average of 3.5 megawatt electrical power. This leads to 5 cent/kWh when amortizing the investment over 4-5 years.
This concept like those of Magenn and Sky WindPower, may lead to sources of wind power that can be located almost anywhere, because of their ability to capture power at high altitudes where the wind is stronger and more consistent. The Laddermill is the first of these systems to actually fly and generate power, so it may have a leg up. All of them use technology that will require a lot of development if they are ever to be commercial. Tyler at Clean Break has a recent post on Magenn, its changes in management and financial concerns.