The wind blowing through the streets of Manhattan couldn't power the city,
but wind machines placed thousands of feet above the city theoretically
could.
The first rigorous, worldwide study of high-altitude wind power estimates
that there is enough wind energy at altitudes of about 1,600 to 40,000 feet
to meet global electricity demand a hundred times over.
The very best ground-based wind sites have a wind-power density of less than
1 kilowatt per square meter of area swept. Up near the jet stream above New
York, the wind power density can reach 16 kilowatts per square meter. The
air up there is a vast potential reservoir of energy, if its intermittency
can be overcome.
Even better, the best high-altitude wind-power resources match up with
highly populated areas including North America's Eastern Seaboard and
China's coastline.
"The resource is really, really phenomenal," said Christine Archer of Cal
State University-Chico, who co-authored a paper on the work published in the
open-access journal Energies."There is a lot of energy up there, but it's
not as steady as we thought. It's not going to be the silver bullet that
will solve all of our energy problems, but it will have a role."
For centuries, we've been using high-density fossil fuels, but peaking oil
supplies and climate concerns have given new life to green technologies.
Unfortunately, renewable energy is generally diffuse, meaning you need to
cover a lot of area to get the energy you want. So engineers look for
renewable resources that are as dense as possible. On that score,
high-altitude wind looks very promising.
Wind's power -- energy which can be used to do work like spinning magnets to
generate electricity -- varies with the cube of its speed. So, a small
increase in wind speed can lead to a big increase in the amount of
mechanical energy you can harvest. High-altitude wind blows fast, is spread
nicely across the globe, and is easier to predict than terrestrial wind.
These properties have led inventors and scientists to cast their hopes
upward, where strong winds have long been known to blow, as Etzler's dreamy
quote shows. During the energy shocks of the 1970s, when new energy ideas of
all kinds were bursting forth, engineers and schemers patented several
designs for harnessing wind thousands of feet in the air.
The two main design frameworks they came up with are still with us today.
The first is essentially a power plant in the sky, generating electricity
aloft and sending it down to Earth via a conductive tether. The second is
more like a kite, transmitting mechanical energy to the ground, where
generators turn it into electricity. Theoretically, both approaches could
work, but nothing approaching a rigorous evaluation of the technologies has
been conducted.
The Department of Energy had a very small high-altitude wind program, which
produced some of the first good data about the qualities of the wind up
there, but it got axed as energy prices dropped in the 1980s and Reagan-era
DOE officials directed funds elsewhere.
The program hasn't been restarted, despite growing attention to renewables,
but that's not because it's considered a bad idea. Rather, it is seen as
just a little too far out on the horizon.
"We're very much aimed these days at things that we can fairly quickly
commercialize, like in the next 10 years or so," said National Renewable
Energy Laboratory spokesperson George Douglas.
Startups like KiteGen, Sky Windpower, Magenn, and Makani (Google's secretive
fundee) have come into the space over the last several years, and they seem
to be working on much shorter timelines.
"We are not that far from working prototypes," Archer said, though she noted
that the companies are all incredibly secretive about the data from their
testing.
Magenn CFO Barry Monette said he expects "first revenue" next year when they
sell "two to four" working prototypes of their blimpy machine, which will
operate at much lower altitudes.
"We do think that we're going to be first [to market], unless something
happens," Monette said.
In the long term, trying to power entire cities with machines like this
would be difficult, largely because even in the best locations, the wind
will fail at least 5 percent of the time.
"This means that you either need backup power, massive amounts of energy
storage, or a continental- or even global-scale electricity grid to assure
power availability," said co-author Ken Caldeira, an ecologist at Stanford
University. "So, while high-altitude wind may ultimately prove to be a major
energy source, it requires substantial infrastructure."
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