Laddermill

A Laddermill is a hypothetical airborne wind turbine consisting of a long string or loop of power kites. The loop or string of kites (the "ladder") would be launched in the air by the lifting force of the kites, until it is fully unrolled, and the top reaches a height determined by designers and operators; some designers have considered heights of about 30,000 feet (9144 meters), but the concept is not height-dependent. The laddermill method may use one endless loop, two endless loops, or more such loops.

As of 2008, wind power is one of the fastest-growing power sources in the world. The bulk of this growth has been in the form of conventional, three-bladed, horizontal-axis wind turbines, with vertical axis wind turbines accounting for a small remainder. Converting the kinetic energy of the wind into useful electricity requires converting the linear horizontal motion of wind into the rotational motion of a shaft in an electrical generator. In every case this requires some method of maintaining a static force against the motion of the wind, to keep the wind-collection apparatus from simply blowing away. Conventional wind turbines accomplish this by mounting rotors rigidly on towers, relatively close to the ground. This arrangement works reliably, but is relatively expensive, requires large amounts of structural material, and cannot tap the much stronger winds often present at higher altitudes.

Humans have flown kites for thousands of years. Kites can readily fly to great heights. Over the years this has led several inventors to propose various schemes for using kites to convert the linear horizontal motion of wind into rotational motion which can drive an electrical generator. As of 2008, few such schemes have even reached the working prototype stage, and none have reached commercial operation. However, progress in enabling technologies such as the computer control of power kites may someday lead to practical airborne wind turbines of the aerodynamic variety.

In a 2007 "road map" report on renewable energy adopted by the European Parliament, laddermill technology was listed among various "promising and challenging" new energy sources into which revenue from emissions trading could be reinvested. [1]

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