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Wind Power Land Use Intensity

"Airspace Infill Factor" is a basic constraint on kitefarm capacity closely linked to land footprint. Conventional windfarms provide a performance baseline of land use to compare with our AWECS projections. We are temporarily limited to altitudes under 2000 ft by regulatory an practical restriction. Tapping this low altitude wind above towers is better, but not enough to make every AWE concept a clear winner over conventional wind towers by watts per acre. Several AWE starts (like SoarEn, OrthoKiteBunch, and KiteLab Group) are working on high airspace/land-use intensity concepts.

Many AWE starts (like Makani & Joby) show large loose sweep patterns that barely tap encompassed wind, both in practice & simulation. A looping kite's swept area is not easily comparable to a conventional turbine disc with its multi blades & far less power spilling through its center. A looping kite suffers from tether drag, plus induced drag off its inner wingtip, that a conventional turbine escapes by its cleanness & extending wing across its hub. Worst of all is marginal wind when a heavy looping flygen kiteplane must burn electricity struggling up its loop or loitering, with two-way transmission losses.

A new Makani claim is that its future 1-MW rated system will exceed the space intensity performance of a conventional windfarm, with a higher capacity factor to boot. They hope for 90% availability, which is very optimistic compared to commercial or even military aviation norms, but even so is much lower than the > 98% availability of the best current HAWTs. The company presumes 1000 m spacing in all directions between 100 m diameter turbines (10 x 10 spacing), but this is an exaggeration of actual spacing averages closer to 3 x 7. This AWEA page covers conventional; spacing:
Basic Principles of Wind Resource Evaluation

AWE schemes that sweep widely from a single anchor point require either very wide spacing or truly reliable sweep synch to avoid collisions between neighbors. Common micrometeorological events, like a small vertical vortex (gustnado/dust-devil) or down-burst crossing the kitefield can cause kite-windows of overly close kites to intersect.

All these considerations led KiteLab Ilwaco to reject array configurations of single anchor-point AWECS in favor of far denser solutions like kite arches & novel 3D crosslinked aerial string structures. Methods have been found to tightly constrain sweep while still enjoying true crosswind power. Runaway prevention (which KiteGen also recognizes as important) is another reason for multiline structure. Varied foundational experiments over the last three years have validated these concepts.


Unlike square grid geometry of conventional windfarms, a kitefarm (of hemispheric tether scope zones) best maximizes land with a hexagonal grid layout.

There is a tiny clear-zone between circular AWEC cells where a conventional HAWT can operate without interfering. AWE and conventional turbines could thus share land.

Noise is a land intensity issue. Flygen Kiteplane noise is conceded to be comparable to existing turbines by db, but the frequencies and modulations are perceptually more distracting.

A new concept in conventional wind farms is to infill space between colossal wind towers with smaller systems. VAWT promoters hope this niche will favor them, but small HAWTs suspended from cables strung under the big turbines would better serve.

Early kitefarms of high mass flygen kiteplanes will require human no-go zones, bunkers, and/or tunnels while conventional windfarms are safe enough for dual-use like conventional agriculture.

FairIP/CoopIP                       ~Dave Santos            July 19, 2010        M1832

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