Long-stroke "yo-yo" reeling is nearing the end of its early proof-of-concept usefulness in AWES R&D, as modes emerge that better conserve airspace and output smoother power. Two leading superior modes are Short-Stroke pumping and Crosswind Cableway travel. These are current KiteLab Group AWES down-selects.

Short-Stoke AWES for electrical generation, involves a high-ratio step-up transmission to convert kite "grunt" power into high generator speed. Insofar as the kite sweeps "approximately transverse to the wind" during the stroke, this is "crosswind kite power", as defined by Loyd. One limitation is that the kite cannot be maintained aloft in lulls by back-driving the system. The transmission requirement is a significant capital cost or life-cycle issue. This is a single anchor solution, so scaling requires going longer and higher with a bigger kite or kite stacks or trains.

The crosswind cableway AWES was documented by Dave Lang, as conceived by Joe Hadzicki (DF 2004). A kite buggy hauls a crosswind cable back and forth to turn a generator at high-speed, without need of a step-up transmission. KiteLab replaces the buggy with a flying "pod". In principle, the crosswind cableway can be back-driven to tow the kite back and forth in lulls. As the prevailing wind direction shifts (i.e., around weather front passage), the cableway needs to be rotated, or perhaps the kite moves to an upwind crosswind leg of a polygonal layout. Capital cost can be kept low, but maintenance and operational overhead is fairly high. To scale up the crosswind cableway, many kites can operate side-by-side, driving the cableway as a gang-line.

Either AWES option can be favored, depending on particular conditions. Land foot-print and airspace utilization seems like the major factor of which to choose in a given context. Important secondary factors include kite control preferences. Capital cost variation does not seem to be the major decision driver between Low Complexity AWES options like these.

• CC BY NC SA        ~Dave Santos         18March2013          AirborneWindEnergy/message/8832

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  • Land footprint for some crosswind-cableway AWES could approach zero.   ~JoeF  18March2013