Sky High Wind Power

Wind power at 30,000 feet is what the start-up Sky WindPower is proposing.  They would use clusters of Flying Electric Generators (FEGs), on the end of a current carrying tether, in the jet stream at 15,000 to 30,000 feet.  The company has done wind tunnel tests and low altitude tests to prove their idea.  They are hoping to build a 200 kw model, flying at 15,000 ft, somewhere in a remote area of the U.S.

They envision a commercial FEG will have four or eight rotors each generating 2.5 MW.  Clusters of FEG's could provide as much power as need for a given site.

The FEG would fly up into the sky, with its rotors powered by electricity off the grid, pulling up its tether.  Once it at its desired altitude it would change the pitch on its rotors and start generating power from the wind.  GPS technology would be used to assure that the rotorcraft stays within a few feet both horizontally and vertically of where it is programed to be and a computer would control the rotorcraft's attitude, i.e. pitch, roll and yaw. 

The amount of power that you can produce in a wind turbine varies as the cube of the velocity and linearly as the density.  So although the density decreases with an increase in altitude, the increase in velocity that you gain with higher altitudes more than makes up for the decrease in density.  This further explains the advantage that FEG's have flying at high altitudes and allows the rotors to be smaller in diameter.  The wind speed, in addition to being higher, is more uniform.

It is much more steady, blowing at high, useful velocities a much greater percent of the time than do winds at ground level.  This gives FEGs the advantage of having a higher capacity factor.  Capacity factor is the percentage of energy actually captured relative to what would be captured if the wind turbines were operating at full capacity all the time. Ground based sites that can produce a capacity factor of 35% are hard to find.  Capacity factors in the jet stream range from about 70% in the southern parts of the U.S to over 90% in the north.  At a capacity factor of 90%, FEGs could become the nation's cheapest source of electricity, with an estimated cost per kilowatt hour of less than 2 cents, about half the price of coal.

Also the wind tends to blow from one direction and when it changes direction it changes slowly.  The air is free from turbulence caused by friction and ground protuberances, but is subject to high altitude turbulence.  This is moderated by the ability of the FEG to sway on its tether rather than being attached to a ridged tower.  The FEG can move up and down on its tether the same way an airplane does to avoid turbulence.

The use of tethers to position objects in the sky is not unknown.  Balloons tethered at altitudes up to 15,000 feet exist now at fifteen sites along the southern borders of the United States carrying radar equipment to detect illegal flights from the south trying to smuggle drugs. These sites are shown on all aeronautical charts, as restricted spaces, and are well known to pilots. By reserving less than one four hundredth (0.4%) of U.S. air space, located at relatively remote locations, not on airway routes, all the nations electrical energy needs could be met. The strength to weight ratio of new tether materials has improved over time so much that tethers now available are no longer too heavy to be held up by flying energy generating devices at the needed high altitudes.  Tether technology is not simple, but a number of vendors now compete in this field selling primarily to the military and NASA.  The FEG would be able to moved up or down on its tether to seek the best wind conditions or to move out of excessively turbulent air space.

Resources:

Sky WindPower, San Diego, CA, http://www.skywindpower.com
Windmills in the Sky, Popular Science, September, 2005 
Windmills in the Sky, Wired News, 4/6/05
Flying windmills, Urban Renaissance Institute, 3/19/05 (free registration required)

Technocrati tags: wind power, renewable energy, flying electric generators, Sky Windpower

Comments

[JesseJenkins]

I discovered Sky Power myself a few weeks ago (right before it got all the press in Wired and Popular Science) and this idea seems (almost literally) pie in the sky but if they can pull it off, I'd welcome it. Obviously there is tremendous wind potential in high elevations and it would be incredible if we could harvest this resource.

A similar idea would be to sink ocean current powered turbines teathered to the sea floor to harvest the tremendous current potential of the gulf stream or other major currents (also much more consistent and high velocity than normal current areas). It seems like it would be easier to float such turbines in the water at the correct depth than to get these autogyros reliably flying at 30,000 feet (not to mention it would pose much less of a navigation hazard - not NEARLY as many submarines cruzing around at those depths than there are airplanes at 30,000 ft) but perhaps both ideas will eventually be explored and utilized. I dont know of any companies trying to comercialize this idea but it certainly seems as feasable as Sky Power's idea.

On a final note, as a friend of mine once noted, the concept of an autogyro is, impossibly cool! Cheers...

Jessie,

I try to publish posts on subjects that are interesting and imaginative, if I think that they have any possibility of fruition. Some of them I hope will be the ones that have a big payoff. We have a serious problem in developing low cost technology to replace oil. Many of our greatest inventions were dismissed when first suggested. While this one may seem to be pretty far out, it is claimed to be a very low cost total replacement for our electrical generating needs and has some engineering basis. Even if it fails it may spark an idea for someone else. I am glad to do my small part in spreading the word on these ideas.

Jim for The Energy Blog

[Michael Cain]

I would worry less about air traffic and more about severe weather. Large portions of Europe are off limits to overflights, and they seem to do just fine. Airline navigation is certainly good enough to avoid areas where such devices are tethered. General aviation -- ie, small low-flying private aircraft -- may be more of a problem.

OTOH, most areas of the US are subject to large thunderstorms at some point in the year. The largest of these easily reach above 30,000 feet, and come with heavy-duty turbulence, lightning, and the ability to deposit large amounts of ice on exposed surfaces. No one, aside from hurricane chasers in specially fitted planes, messes with the inside of a big thunderstorm.

Mike,

FEGs are designed to be winched down to the ground if weather conditions are serious enough. They have to have this capability for maintence also. I would think that weather condititions would be a large factor in determining the siting of FEGs. Their certainly is some experience with the 15 craft that are looking for drug trafic that would be applicable. Initially I would think they would be locacted in areas having the least severe weather and then as they gain experience and improve reliability they could expand their area of deployment. Although the concept sounds nice their would be a long learning curve to go through which will cost a lot of money that they do not have now. Their sucess will depend on how well financed they can be and how well the first few flights perform. They say they need only $4 million dollars to build their prototype, which is not a lot of money for venture capitalists these days, the expenses for testing and modifying the prototype could well add another $2-$4 million and then they have to prototype their larger production model, etc - what they need right now appears to be a good business plan.

Jim for The Energy Blog

[Don Bongaards]

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