I thought some of you guys would enjoy this article, which discusses
the use of kites as energy-generating platforms. click through for
Do Flying Wind Turbines Make Sense?
By Climate Guest Blogger on Jun 3, 2012 at 10:47 am
Time lapse photo of Makani’s tethered wing flying in a circle (Photo:
by Jonathan Koomey excerpted from his blog
I like site visits—there’s nothing like seeing a company’s innovations
in person. In the case of Makani Power, I harbored some core
misconceptions about their technology, and the visit set me straight.
Corwin Hardham, CEO and one of the co-founders of Makani, invited me
to visit in Fall 2011. An intern of his was taking the class I taught
that semester, and he heard me mention the company’s efforts in
lecture, so he put Corwin in touch with me. Things have been so busy
that I wasn’t able to arrange a visit until a few weeks ago, but I’m
sure glad I stopped by.
When I drove up to Makani’s building, which formerly housed the
control tower for the Alameda Naval Air Station, the first thing I saw
was three rusted artillery guns. That was a jarring sight, but the
location makes sense. Corwin explained that this site was the largest
available open space in the Bay Area and was perfect for building and
testing Makani’s prototypes.
Others had told me about Makani’s technology, and the words “kite” and
“high altitude” always come up, but these terms are misleading. When
I think of kites, I think of Ben Franklin flying the traditional
diamond-shaped kite with a tail. The Makani turbine is a carbon fiber
wing with propellers (see photo), which Ben Franklin wouldn’t have
known what to do with.
And the words “high altitude” made me think of kites flying in the
path of airplanes at 10,000 feet, which isn’t at all right. Makani’s
turbines fly at about 300 m (roughly 1000 feet) above the ground.
Instead, imagine building and operating just the most important part
of the wind turbine, the outer part of the turbine blade (which
generates most of the power) without the rest of the supporting
structure. In essence, that’s what Makani’s tethered flying wing
is—the end of a turbine blade that flies in a circle and generates
power. The initial prototype generates 20 kW— the next version should
generate 600 kW, assuming they get the money to build it.
The wing itself (without the generators and propellers) is incredibly
light—I could easily pick it up with both hands, even though it’s
about 20 feet long. That’s the beauty of carbon fiber. Super strong,
without much weight for the wing itself.
The wing has four propellers mounted perpendicular to plane of the
wing. Each is attached to a generator that can reverse itself to
serve as a motor. This capability is needed because the wing starts
from a cradle on the ground and lifts itself off to achieve the needed
altitude, then switches to generator mode once the wing starts its
normal circular path. If the wing needs to come down for maintenance,
the process works in reverse (and the wing can go from normal flight
to sitting in its cradle in less than 5 minutes, which means that it
can safely avoid adverse conditions on the ground.
The full wing in flight here showing the four generators/ propellers
(Photo: Makani Power)
Complex computer control technology is critical to the wing’s
functioning. My friend Saul Griffith, one of the cofounders of
Makani, told me that the control technology was similar in complexity
to found in missile guidance systems. It’s sophisticated enough to
keep the wing on a path with meter level precision, and that’s awfully
Power is sent down the tethers. Better to move electrons than to
worry about mechanical parts in such a complex environment.
Because the wing flies at higher altitudes than a typical wind
turbine, and because it can operate at lower wind speeds, the capacity
factor for a Makani turbine will be more like 50-60% (instead of
30-40% for new traditional wind turbines in good sites). And with
capital costs typically half of a traditional turbine, the Makani
technology should have a significant economic advantage over
traditional wind power plants (and competing fossil technologies).
Makani’s technology is yet another example of what I call substituting
smarts for parts. It’s a form of dematerialization that allows us to
do more clever things using substantially fewer materials but with
better performance than traditional efforts.
Makani’s technology is also a beautiful case study of the power of
whole system design. Focusing on incremental changes in the design of
traditional turbines can yield cost reductions, and we’ve seen that
occur since the 1970s (with recent increases in the cost per kW
attributable to scaling up to larger turbines with higher capacity
factors, among other things). But to create game changing innovation,
it takes a comprehensive rethinking of the problem starting with a
clean sheet redesign, and that’s exactly what Makani’s innovations
I started out as a skeptic about this technology, but my visit, and
conversations with Saul and others convinced me that it holds the real
promise of revolutionizing the production of electricity from the
wind. My friend Gil Masters, emeritus professor at Stanford and one
of the giants in the renewable energy world, wholeheartedly agrees (we
just had lunch this week).
– Dr. Jonathan Koomey was a researcher and scientist at Lawrence
Berkeley National Laboratory (LBNL) for more than two decades. This
was excerpted from his blog with permission.
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