Untethered airborne wind energy systems

Power can be stored via batteries, chemistry or kinetic energy. Whichever you choose, the energy amount is quite limited due to weight constraints. This method is only useful for powering something to remain airborne for extended periods, and this something must be combineable with the physical stress required for dynamic soaring flight. I think at the very most we are looking at a niche market here. Most probably just a nifty idea without much practical use

For a personal use I envisage a storage by battery which seems to be more suitable. Using kinetic energy storage would lead to undergo some gyroscopic effect that is not desirable for the flight. Dynamic soaring could allow harnessing energy exceeding that required for flight by improving the energy-to-mass ratio of the electrochemical storage.

Persistent flight tech has a red-hot R&D market in high tech communications and surveillance. Its naturally presumed the market will be huge, even if AWE is not yet widely seen as key.

The popular solar-electric architectures soar well. We already classed them as hybrid untethered AWES, on the Old Forum.

An energy system comprising small terminals placed everywhere at ground, why not on aerostats, and allowing the UAV (drones) to discharge their respective batteries and return to exploit the wind gradient anywhere it is.

The energy density of batteries has evolved (100-265 Wh/kg ):

Also about supercapacitors:

The fabricated supercapacitor exhibits a very high energy/power density of 206 Wh/kg (59.74 Wh/L)/496 W/kg at a current density of 0.25 A/g, and a high power/energy density of 32 kW/kg (9.8 kW/L)/9.58 Wh/kg at a current density of 50 A/g; it also operates in a voltage range of 0~4 V with excellent cyclic stability of more than 20,000 cycles.

Below you will find an overview with some measurements of UAV for dynamic soaring.
https://oatao.univ-toulouse.fr/14558/13/Bonnin_14588.pdf

Did interest in this thread utilizing the Dr G. Dobos’ approach to wind energy harvesting lead to a dead end due to physics limitations?

Or was it killed off by the climatologists paper referenced on Wikipedia, Miller, et,all…

Naysayer climatologists’ publication can be found referenced on Wikipedia under Jet Stream scroll down to “Possible future power generation” heading shown as Reference #42… a colleague and I are still trying to digest their “doomsday” analysis.

https://en.wikipedia.org/wiki/Jet_stream

or one can download it directly from Wikipedia’s link to…

https://esd.copernicus.org/articles/2/201/2011/esd-2-201-2011.pdf

Just watched a youTube presentation (posted Oct 2018 by Richard Starke on “Air Freight / Cargo” via a jet stream dynamic soaring glider scheme…

Please bear with me as this is my first post to AWES and I am still figuring out the intricacies of this forum…

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Welcome to the forum @WalterPOk ,

No AWES has reached the stage of commercialization at utility scale, whether tethered or untethered.

Concerning Dr. G. Dobos’ approach and more generally dynamic soaring for harnessing wind energy, the specific difficulty is the capacity of storage onboard.

You can linked any YouTube video on a comment on this forum. An example below, by copy/paste the web address:

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More on the youTube presentation (posted Oct 2018 by Richard Starke on “Air Freight / Cargo” via a jet stream dynamic soaring glider scheme…

Pertinent time stamps…

14:35 He cities a 2006 publication by Saks & Costa (??), “Dynamic Soaring in the Shear Wind Region Associated with the Jet Stream”

15:20 Gives “Break-Even” magnitude for EATA (??) glider wind gradient as, dv/dz = 0.012 (1/sec)

16:30 Graph showing magnitude of jet stream wind gradient from weather balloon data which was found on Edwards AFB (Dryden) website

The actual youTube title is: “Autonomous Dynamic Soaring Cargo Motorglider Concept” - Richard Starke

https://www.youtube.com/watch?v=6ednH7Fmlc4

I note a few more of what are perhaps the pertinent posts from the DSUTWP archive…

http://www.energykitesystems.net/DSUTWP/index.html

Post #59 from JoeFaust regarding: Soaring Sink Calculations by Taras Kiceniuk in 2001

Post #60 from Dr. G. Dobos regarding his frustration to convince others of the feasibility of the soaring concept. I ditto that and I am willing to discuss only off forum for the present as I first wish to discuss with others. What comes to mind is a famous quote by Oliver Heaviside to those critical of his use of his “un-rigorous” Operational Calculus, Shall I refuse my dinner because I do not fully understand the process of digestion?

Post #68 from Dr. G. Dobos regarding wind gradient, dv/dz=50 (1/s) appears to have the correct units but he must be referring to a wind speed as he is responding to post #66 by Pierre Benhaiem who mentions a wind speed of 50 (m/s).

Post #73 from Dr. G. Dobos regarding his Pascal computer program written to calculate soaring flight energy. I presume that his calculation follows the analysis techniques outlined in Etkin, Bernard, “Dynamics of Atmospheric Flight”. I purchased a copy a few weeks ago as it was referenced in a colleague’s thesis (Raspet Flight Laboratory - Mississippi State University) dealing with the feasibility of soaring flight in the jet stream. My colleague calculated a “Break-Even” wind gradient requirement of dv/dz = 0.06 to 0.07 (1/s). His calculations did not attempt to optimize flight path or glider configuration.

I thought that I read in one of Dr. Dobos’ DSUTWP posts a mention of a “Break-Even” wind gradient required by conventional man-carrying glider would be dv/dz = 0.012 (1/s). Perhaps I am confusing myself with the youTube presentation of Richard Starke.

From PierreB 's post #17 of this Untethered AWE thread…

and on:
https://www.researchgate.net/publication/273491576_Energy_extraction_from_wind_shear_Reviews_of_dynamic_soaring

I think the biggest problem is the chemical or battery storage on board. It is the reason why I envisage an individual use to begin.

Does anyone have a copy of (or has read) this review of energy extraction via. soaring flight?

Gao, Guo, Chenl-2015-Energy extraction from wind shear: Reviews of dynamic soaring, Proceedings of Institute Mechanical Engineers

I suggested to Gabor on the old AWE forum, build a model version and show the world how well it works. Unlike most AWE ideas, an RC glider can be bought off the shelf. So can folding propellers, batteries, whatever anyone might need to build and run a demo. The “professor crackpots” of the world would often rather talk a concept to death, rather than try it. That way they can blame it all on “naysayers”, without ever trying even the most rudimentary demo. Gabor was advocating compressed air storage. That would involve high storage losses, but a demo could use batteries, so the whole thing could be mostly off-the-shelf. The problem with some ideas is when you start seriously looking at building and running one, it starts to look increasingly like not such a great idea. Well, who knows, but talk is easy, doing a demo takes at least a little effort. So probably nobody will ever bother.

Mr. Selsam,

Proof of Concept is definitely of importance. Sometimes this can only be achieve through thought experiments / paper studies. But I have thought of a few means of demonstrating the feasibilty of the concept in order to help in the promotion of the Dobos IFO concept. Since I do not know the personalities of the AWES forum members at this point, I prefer to respond via private eMail messages at this point. Please share your eMail address with me.

I also wish to share these thoughts of yours (and my response) with pierreB if you are agreeable.

Are you located in the USA?

Much Thanks,

-Walter P. Okhuysen

P.S. my eMail address is

(firstInitial)(middleInitial)(fullLastName)(at)bellsouth(dot)net

Hi @WalterPOk and welcome to the forum. I stand by my comments a few years back. Though intriegueing, harvesting power through untethered flight does not seem a reasonably valid idea for a means of producing significant energy.

Maybe for keeping a thing airborne for extended periods of time, though for that application I dont have much to add

There are a million ways to make some power from the wind at some cost.
The idea is to get it below 3 or 4 cents/kWh for utility-scale power.

Gao (2015) Energy extraction from wind shear - Reviews of dynamic soaring doi 10.1177_0954410015572267.pdf (788.6 KB)

Study authors are also usually willing to email a copy of their study upon request.

Won’t you be needing to fly doubly as fast at half the air density at higher altitude compared to sea level, therefore also needing to double the needed wind gradient?

At 20 kilometers up, air density is only 70 grams per cubic meter, so that would give you 0.07/1.2 = 6 percent of the lift you could get at sea level, if the relationship is one to one. And your wind gradient to do dynamic soaring would need to be 17 times higher, if I am right.

I think the dv/dz = 0.012 (1/sec) shown by Starke is the “break-even” value for wind gradient necessary to DS at “steady state” in jet stream using air property values at high altitude. This is of same order of magnitude for early partly optimized jet stream calculations by Vrana, dv/dz = 0.015-0.017 (1/sec), quoting from Rais-Rohani’s MS Thesis. Rais-Rohani calculated a non-optimized jet stream value of dv/dz = 0.06-0.07 (1/sec).

As to the wind gradient available in the jet stream Starke’s graph is not promising at all; for it is of same magnitude with hardly any to spare.

I searched for a the Dryden weather balloon data Starke mentions and came up empty. We need weather data for jet stream wind gradient. Or alternatively jet stream wind speed vs altitude from which we can estimate wind gradient.

Anyone know where to find jet stream data?

Well all those “really smart people” who have now wasted over a billion dollars to have nothing running on a regular basis, started out with a “mascot” to represent participation from official academia, a very nice lady named Cristina Archer, who is, if memory serves, a meteorologist of some sort. Her role in AWE has been, for maybe 14 years now, to verify (or reassure) the AWE people, and “investors” (donors) that there is indeed wind up there in the sky, just in case anyone had any doubts. It is possible that she might have some info on wind shear proximate the jet streams. It could be worth checking.
You might also check with some “really smart people” who can model the costs of running a fleet of automated airplanes taking off for the jest stream, (hmm, I think I’ll leave that typo intact!) flying their energy-collecting “mission”, then coming down for a landing to “unload” their “valuable” cargo of energy collected from miles in the sky. They should figure out how much energy is likely, at what cost, and determine whether such a system would be worth the effort and cost, compared to the value of the energy delivered in usable form. So far, such an analysis has been lacking in AWE. Despite repeated promises to “power X hundred homes by date Y at location Z”, AWE has yet to deliver anything running commercially on a regular basis.

Dynamic Soaring in Shear Wind Regions Associated with Jet Streams

Gotfried Sachs and Orlando da Costa1
Technische Universität München
Boltzmannstr. 15, 85747 Garching, Germany
sachs@lfm.mw.tum.de
Presented at the XXVIII OSTIV Congress, Eskilstuna, Sweden, 8-15 June 2006

https://journals.sfu.ca/ts/index.php/ts/article/viewFile/172/157

Abstract
Dynamic soaring enables an energy gain by transferring energy from the moving air in a horizontal shear wind region to the saiplane. There are shear wind regions associated with jet streams, extending from the jet stream core with its high wind speed to the altitude where the air is at rest. The possibility of utilizing this energy gain is considered for the dynamic soaring of sailplanes. An efficient optimization procedure is used to determine the minimum shear wind strength which is required for the dynamic soaring flight manoeuvre, applying a realistic mathematical model for describing the dynamics of a sailplane. It turns out that the minimum shear wind strength is smaller than the values which can be encountered in existing shear wind regions associated with jet streams. As a result, the performance capability of modern sailplanes offers the possibility for dynamic soaring in these jet stream regions.

Conclusions
There are shear wind regions associated with jet streams,
covering wide areas and extending over huge distances. The
possibility of utilizing these regions for dynamic soaring is
investigated. For this purpose, energy-neutral dynamic soaring
trajectories are determined which require the smallest shear
wind strength in terms of the minimum wind gradient with
respect to the altitude. It turns out that modern sailplanes with
a high aerodynamic efficiency need shear wind gradients
which are smaller than those of existing shear winds. As a
result, high-performance sailplanes offer the possibility to
conduct dynamic soaring in shear wind regions associated with
jet streams.

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The publication linked in the previous comment indicates in page 14:

Results are presented in Fig. 2 which shows measured data of the shear wind region associated with a jet stream. The data presented in Fig. 2 suggest for a large part of the altitude range that a linear dependence of the wind speed with the altitude can be used as a realistic mathematical model for describing the shear wind characteristics. In this region, the shear wind gradient amounts to a value of about dVW / dh =0.019 s-1.

In page 15:

Mathematical model of sailplane
Data of a high-performance sailplane are used in the numerical investigation for determining the optimal dynamic soaring trajectory requiring the minimum shear wind gradient min (dVW /dh)min. It is similar to the Eta sailplane in its aerodynamics and size characteristics.
The following data are applied for the reference wing area and the mass:
975 kg
18.6 m²

Page 16:

Comparison to the measured shear wind data with 1 dVW /dh = 0.019 s-1 (Fig. 2) shows that required minimum shear wind gradient is significantly smaller.
Properties of the optimal dynamic soaring trajectory with which requires the minimum shear wind gradient (dVW /dh) = 0.012 s-1 are graphically illustrated in the following figures.

But according to another source on Analyzing Jet Stream Circulations :

A jetstream is defined by the following attributes:

  • intense: at least 30 m/s for upper troposphere, at least 15 m/s for lower troposphere
  • narrow: one-half to one of magnitude less in width than in length
  • strong vertical wind shear: at least 5 - 10 m/s per km, one-half to one order of magnitude greater than the synoptic scale shear

10 m/s per km (1000 m) would lead to a value of 0.01, which is somewhat lower than the minimum required wind shear gradient of 0.012 for the glider mentioned above, and almost twice as low as the measured wind shear data of 0.019.

So a huge gradient seems to be required, and seems to be a limit for the development of dynamic soaring for harnessing wind energy in jet-streams apart that required for the flight. It is perhaps a reason why there is no significant results, knowing that the paper linked previously is dated 2006.

In contrast wind gradients appear to be higher but in thinner layers close to the ground or sea where albatrosses use them, and behind hills blocking wind and used by fast gliders:

So I see perhaps some possibilities with small and light gliders being not penalized by the weight due to the scale, and harnessing the wind gradient close to the ground, for an individual use.

Airborne solar wind energy systems (ASWES) are evoked on
Airborne solar wind energy systems (ASWES) and on

The several kilometer long electrified tethers are a perhaps insurmountable problem: huge weight and drag, tensions on the balloon due to the taking of very powerful winds and requiring a solid and heavy construction, security in case of storms or too strong winds as the system is connected to the ground…

Free balloons flying in the stratosphere between about 15 km and 25 km has been realized or studied:

Stratobus’s power enables it to counter winds of this force, and remain stationary.

Loon deployed its high-altitude balloon network into the stratosphere, between altitudes of 18 km and 25 km. The company stated that the particular altitude and layer of the stratosphere is advantageous for the balloons because of its low wind speeds, which are usually recorded between 5 mph and 20 mph (10 km/h to 30 km/h). The layer is also an area of minimal turbulence.

Wind speed decreases in the stratosphere above jet-streams, and becomes low.

I think a large thermal and photovoltaic balloon could perhaps be used, not being subjected to the force of the wind and convection leading to the cooling of the contained air.

The black solar e-film of 60 g / m² and 2000 W / kg could be used for both thermal (for buoyancy) and photovoltaic (for electricity generation) uses:

Stratospheric solar (thermal) balloon are already in use:

Untethered airborne wind energy systems (untethered AWES) such as discussed on the current topic, cannot be mixed with untethered airborne solar energy systems (untethered ASES) where the relative wind speed is cancelled and not wanted.

It remains to store (batteries?) during the day and deliver at night, which is a thorny problem shared with untethered AWES. Another smaller balloon, this time inflated with hydrogen or helium, could make the round trips, discharging its charged batteries in the factory and taking back batteries not yet charged to repeat the cycle, its role being somewhat comparable to the tugs of ships.

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