| 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.
==notes==
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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