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Photo Credit: California Institute of Technology
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The quest to derive energy from wind may soon be getting some help from
California Institute of Technology (Caltech) fluid-dynamics expert John
Dabiri-and a school of fish.
As head of Caltech's Biological Propulsion Laboratory, Dabiri studies
water- and wind-energy concepts that share the theme of bioinspiration: that
is, identifying energy-related processes in biological systems that may provide
insight into new approaches to-in this case-wind energy.
"I became inspired by observations of schooling fish, and the
suggestion that there is constructive hydrodynamic interference between the
wakes of neighboring fish," says Dabiri, associate professor of
aeronautics and bioengineering at Caltech. "It turns out that many of the
same physical principles can be applied to the interaction of vertical-axis
wind turbines."
The biggest challenge with current wind farms is lack of space. The
horizontal-axis wind turbines most commonly seen-those with large
propellers-require a substantial amount of land to perform properly. "Propeller-style wind turbines suffer in performance as they come in
proximity to one another," says Dabiri.
In the Los Angeles
basin, the challenge of finding suitable space for such large wind farms has
prevented further progress in the use of wind energy. But with help from the
principles supplied by schooling fish, and the use of vertical-axis turbines,
that may change.
Vertical turbines-which are relatively new additions to the wind-energy
landscape-have no propellers; instead, they use a vertical rotor. Because of
this, the devices can be placed on smaller plots of land in a denser pattern.
Caltech graduate students Robert Whittlesey and Sebastian Liska researched the
use of vertical-axis turbines on small plots during a class research project supervised
by Dabiri. Their results suggest that there may be substantial benefits to
placing vertical-axis turbines in a strategic array, and that some
configurations may allow the turbines to work more efficiently as a result of
their relationship to others around them-a concept first triggered by examining
schools of fish.
In current wind farms, all of the turbines rotate in the same direction.
But while studying the vortices left behind by fish swimming in a school,
Dabiri noticed that some vortices rotated clockwise, while others rotated
counter-clockwise. Dabiri therefore wants to examine whether alternating the
rotation of vertical-axis turbines in close proximity will help improve
efficiency. The second observation he made studying fish-and seen in Whittlesey
and Liska's simulation-was that the vortices formed a "staircase"
pattern, which contrasts with current wind farms that place turbines neatly in
rows.
Whittlesey and Liska's computer models predicted that the wind energy
extracted from a parcel of land using this staggered placement approach would
be several times that of conventional wind farms using horizontal-axis
turbines. Once they've identified the optimal placement, Dabiri believes it may
be possible to produce more than 10 times the amount of energy currently
provided by a farm of horizontal turbines. The results are sufficiently
compelling that the Caltech group is pursuing a field demonstration of the
idea.
Dabiri has purchased two acres of land north of Los Angeles, where he is establishing the
Caltech Field Laboratory for Optimized Wind Energy (FLOWE). The pilot program at
the site will feature six vertical turbines on mobile platforms.
Dabiri and his team will systematically move the turbines around, testing
various configurations to find the most efficient patterns.
"Our goal is to demonstrate a new
technology that enables us to extract significantly more wind energy from a
given parcel of land than is currently possible using existing methods,"
says Dabiri. "We want to take advantage of constructive aerodynamic interference
between closely spaced vertical-axis wind turbines. Our results can potentially
make better use of existing wind farms, allow for wind farms to be located
closer to urban centers-reducing power transmission costs-and reduce the size
of offshore installations."
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Photo Credit: California Institute of Technology
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Three of Dabiri's turbines are being
provided in partnership with Windspire Energy. In exchange for the use of the
turbines, Dabiri will share his research results with the company. Each
Windspire turbine stands approximately 30 feet tall and 4 feet wide, and can
generate up to 1.2 kW of power.
"This leading-edge project is a great
example of how thinking differently can drive meaningful innovation," says
Windspire Energy President and CEO Walt Borland. "We are very excited to
be able to work with Dr. Dabiri and Caltech to better leverage the unique
attributes of vertical-axis technology in harvesting wind
energy."
Three turbines from another manufacturer
have been purchased; the six turbines give the pilot facility a total power
capacity of 15 kW, enough to power several homes.
"This project is unique in that we
are conducting these experiments in real-world conditions, as opposed to on the
computer or in a laboratory wind tunnel," says Dabiri. "We have
intentionally focused on a field demonstration because this can more easily
facilitate a future expansion of the project from basic science research into a
power-generating facility. Our ability to make that transition will depend on
the results of the pilot program."
The initial phase of the study will attempt
to demonstrate which configuration of units will improve power output and
performance relative to a horizontal-axis wind turbine farm with a similar
sized plot of land.
"In the future, we hope to transition
to power-generation experiments in which the generated power can be put to use
either locally or via a grid connection," Dabiri says.
The American Recovery and Reinvestment Act
provided partial funding for this project.
For more information on FLOWE, visit: http://dabiri.caltech.edu/research/wind-energy.html.
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