Comparison of Concepts for High-altitude Wind Energy Generation with Ground Based Generator

Lansdorp’s article compares the advantages and disadvantages of two different methods for power generation using high altitude kites. The first method is the Laddermill. The Laddermill has a tether connected in a loop, which holds an array of wings. The lift of the wings causes the tether to move upwards in one direction and downwards in the other. The tether’s motion spins the generator. The wings are arranged so that the ascending wing’s lift causes the motion of the tether, while the descending wings only create enough lift to keep the wing afloat. The second method is the Pumping Mill. The Pumping Mill method differs from the Laddermill in that the Pumping Mill’s tether is not connected in a loop, but rather a single line. The wings create a lift, which causes the tether to extend. Once the maximum height has been reached, the wings are adjusted so that the tether retracts. This motion is continually repeated to create power.

Lansdorp discusses how different conditions affect both the Laddermill and Pumping Mill systems. The Laddermill benefitted from continuous power production, the ability to adjust the wings due to changing weather, and the ability to inspect individual wings without interrupting power production. Conversely, the Pumping Mill benefitted from the ability to optimize the wings and tethers and that only a small length of tether would interact with the generator. Next, numerical simulations for 5MW Laddermill and Pumping Mill systems were done. The simulations compared the size of the wings, tethers, and generators needed to produce 5MW of power. The results showed that the Laddermill has more massive wings than the Pumping Mill, which Lansdorp believes is due to the extra optimization done for the Pumping Mill. The results imply that it may be cheaper to produce a smaller Pumping Mill system than a Laddermill system. Finally, Lansdorp mentions a modification to the systems that utilizes crosswind power. Some numerical simulations were done to compare the crosswind power to the regular method, but the simulations were only done for the Pumping Mill method. The results showed about a 40% reduction in the necessary masses of the wings when crosswind power was utilized.
What is Noteworthy:

Lansdorp does an interesting comparison of Laddermill and Pumping Mill methods. Various aspects of each system were discussed to show the benefits and any complications that the systems have. Also, the numerical analyses that were done give a size to both systems needed to produce 5MW of power. Finally, Lansdorp introduces a modification that uses crosswind power and does a basic comparison with the original Pumping Mill system.

The author’s comparison of the two methods is very detailed and explains how different aspects affect both the Laddermill and Pumping Mill systems. The numerical analyses also provide a nice size to the system. However, the paper does not go into much detain on crosswind power simulation. The paper only performed the simulation with the Pumping Mill system. The simulation should also be repeated for the Laddermill system to see how crosswind power affects it. The paper is also mainly theoretical with some simulations, which can provide an upper bound for the power produced. Experimental research should be done in the future to determine the actual power that can be produced from the Laddermill and Pumping Mill methods.