More thoughts about kite-generators

[Jed Rothwell]

I do not think those gigantic kites would require ultra-strong tethers. They would not pull on the tether much. Most of the energy of the wind is dissipated either in lifting the kite or turning the electric generators. The kites would work like autogyros. (See: http://www.jefflewis.net/autogyros.html)

The tether has to overcome drag. If a high-altitude balloon were tethered to the earth, and it had on-board wind turbines, I think it would require a very strong and heavy tether. A balloon or airship has enormous drag. With the kite, drag is low. In other words, the tether supplies as much force as the motor in the autogyro, and if the wind produces much more lift than the kite needs to stay in place at a fixed altitude, the extra energy is converted to electricity and sent down to the ground. When the wind drops off too much and the kite begins to fall, power is sent back up to the kite to turn the rotors and keep it up.

The New Scientist recently described a scheme to use gigantic kites to pull freight ships, to augment the diesel engines. Look up SkySails for more information. 19th-century freight ships carried sails long after they also had onboard steam engines. Some people nowadays imagine this was foolish and redundant, but actually it was economical. Sails and slow steam engines together worked well. Also, the early marine steam engines were not reliable. If the engine, paddle wheel or the propeller shaft broke in the middle of the ocean they needed the sails to get back home. Paddle wheels were too fragile for ocean-going ships. They were often damaged in storms.

- Jed