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Interactive Commentary on " Improving mid-altitude mesoscale wind speed forecasts using LiDAR-based observation nudging for Airborne Wind Energy Systems "

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Interactive Commentary on " Improving mid-altitude mesoscale wind speed forecasts using LiDAR-based observation nudging for Airborne Wind Energy Systems "

Abstract

We have observed a large number of scientific and patent publications focused on high-altitude wind exploitation, reflecting a truly exponential trend. KiteGen, as the first global entity to produce energy using this revolutionary method, finds itself in a difficult position following the massive amount of material produced by third parties and the consequential technical inaccuracies desperately needing rectification. The latter has a detrimental effect on the potential acceptance of the concept and occasionally leads to technological nonsense, weakening the potential for widespread common awareness of this powerful technology that has the potential to enable global transition from fossil fuel energy sources. We have observed that, due to the absolute originality and novelty of this concept, there is a lack of qualified peer review, and blatant errors have been propagated and transferred, undisturbed, from one poorly informed publication to another, with no-one critically re-analyzing their stratified assumptions. We have also observed that these same errors have confused the informal competition that has grown over time around our project, among what seems a hundred actors, leading to the copious physical development of low TPL and/or unfeasible or extremely deficient alternative architectures.
1
Interactive Commentary onImproving mid-altitude
mesoscale wind speed forecasts using LiDAR-based observation
nudging for Airborne Wind Energy Systems
1
Author: Massimo Ippolito
Institution: KiteGen Research
Released: April 2019
Author’s Note
Former Director of Respira Interdepartmental Laboratory of Polytechnic of Torino
Founder and CEO of KiteGen Research srl
Correspondence to: m.ippolito@kitegen.com
1 Markus Sommerfeld1, Curran Crawford1, Gerald Steinfeld2, and Martin Dörenkämper
(2019) DOI: 10.5194/wes-2019-7
https://www.wind-energ-sci-discuss.net/wes-2019-7/wes-2019-7.pdf
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 2
Table of content
Table of content
Abstract
Interactive Commentary on “Improving Mid-altitude Mesoscale Wind Speed Forecasts Using
LiDAR-based observation nudging for Airborne Wind Energy Systems”
Method
High-Altitude Wind Equipment, Design And Architectures.
Text quoted from page 2 paragraph 5:
Accurate Data of High Altitude Wind; Is It required?
Text quoted from page 2 paragraph 10:
Stronger and Constant High Altitude Wind Isn’t the Original Enabling Factor
Text quoted from page 2 paragraph 10:
Finally Some Positive Remarks Regarding the Technology
Text quoted from page 16 paragraph 5:
Text quoted from page 24 paragraph 10:
Optimal Operating Altitude and Power Production: Is It Really Required?
Text quoted from page 22 paragraph 5:
References
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 3
Abstract
We have observed a large number of scientific and patent publications focused on
high-altitude wind exploitation, reflecting a truly exponential trend. KiteGen, as the first global
entity to produce energy using this revolutionary method, finds itself in a difficult position
following the massive amount of material produced by third parties and the consequential
technical inaccuracies desperately needing rectification. The latter has a detrimental effect on the
potential acceptance of the concept and occasionally leads to technological nonsense, weakening
the potential for widespread common awareness of this powerful technology that has the
potential to enable global transition from fossil fuel energy sources. We have observed that, due
to the absolute originality and novelty of this concept, there is a lack of qualified peer review,
and blatant errors have been propagated and transferred, undisturbed, from one poorly informed
publication to another, with no-one critically re-analyzing their stratified assumptions. We have
also observed that these same errors have confused the informal competition that has grown over
time around our project, among what seems a hundred actors, leading to the copious physical
development of low TPL and/or unfeasible or extremely deficient alternative architectures.
2
KiteGen has long refrained from scientific communication due to the absolute certainty
of our original and long-established architectural and scientific consistency, but having the devil
hiding in the details of the technological issues, this certainty has correctly governed and become
involved daily in our developmental activities.
If it could be agreed as true that KiteGen is now the premier exercise in applied technology and
good engineering practices, it would ensure the large-scale production of generating equipment
and the resulting sustainable energy therefrom. Obviously, we do not claim that everything has
been perfected; further improvements are probable and desirable, but
in classic Pareto
progression. The subject paper, despite the voluminous data and formal processes involved, is an
example of a misguided effort that fails to produce significant forward progress in this scientific
and technological domain and risks becoming completely out of sync and out of the dynamic
range of most of the architectures and technology cited in block by the article. We hope that our
position will be widely accepted through reading and understanding the comments we make
available in this paper, accompanied by the appreciation of the articulation of this logical, albeit
rare, thinking in professional and strategic energy planning.
Keywords:
Lidar, Sodar, troposphere, altitude, wind, KiteGen, electrical, energy, baseload,
storage, HAWES, Capacity Factor.
2 Technology Performance Level, the most useful parameter assessing and comparing new energy concepts.
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 4
Interactive Commentary on “Improving Mid-altitude Mesoscale Wind Speed Forecasts Using
LiDAR-based observation nudging for Airborne Wind Energy Systems”
Method
The article is certainly of good quality, providing precious original data and measurements, that
can be profitably added to the collection of previous work in general to state definitively and
positively that high-altitude wind must be considered a new and inexhaustible source of energy
that also totally solves the energy storage issue. However, the wind turbine-minded mindset of
the authors should be noted, which emphasizes wind stability classes rather than the opportunity
to increase the capacity factor by exploiting the freedom choose the various operational heights
of tropospheric wind. While the site’s location regarding wind stability is important for wind
turbines, not only for productivity but also for structural resistance evaluation, it is completely
negligible for effective High Altitude Wind Energy System (HAWES) architectures where
dynamic lightness and swiftly responsive numerical control allow for immediate feedback and
adaptive strategies. Furthermore, the authors’ over-simplified model of HAWES leads to
inappropriate recommendations and the invalid/improper use of this valuable data-set, resulting
in several orders of magnitude out of the dynamic of the devices[4], resulting in unfortunate and
useless, though sophisticated, elaboration of their findings. The difference of the article’s
evaluations from reality is so great that it prevents us from going further in any analysis; in the
meantime recommending giving up on data massaging or model nudging, at least in the HAWES
domain.
As a suggestion for further investigation that your skilled team may conduct, we believe that
your work would be very useful in validating the assumptions made by Archer C., Caldeira K.
(2009) [3], at mid-altitude mesoscale, regarding competitive or collaborative comparisons
between the array of traditional systems, and the opportunities to exploit the naturally-stored
energy in geostrophic wind by means of High Altitude Wind Energy Systems. LiDAR-based
observations from two or more geographically-distant locations would assess the capability of
the winds in the troposphere to provide at least minimally-required power 99.9% of the time
when two appropriately-distanced power harvesting devices are interconnected and
simultaneously utilized as one.
High-Altitude Wind Equipment, Design And Architectures.
Text quoted from page 2 paragraph 5:
“Unlike conventional wind energy which has converged to a single concept with three blades
and conical tower, several different AWES designs are under investigation by numerous
companies and research institutes worldwide (Cherubini et al., 2015). Various concepts from
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 5
ring shaped aerostats, to rigid wings and soft kites with different sizes, rated power and altitude
ranges compete for entry into the marketplace. Since this technology is still in an early stage,
none are commercially available.”
Kitegen financed this (Cherubini et al. 2015) [2] study, as reported in the acknowledgments of
the same, without exerting any pressure on the authors regarding the content, in the conviction
it would enable the reader to make an independent comparison among the different technology
proposals. To any skilled technician in the art capable to evaluate, the differences and various
advantages of the architecture proposed by KiteGen are blatantly clear. We have already
experienced several learned opinions that confirm KiteGen has not only the best architecture,
but also the only one feasible on an industrial scale while simultaneously fulfilling grid
requirements. Other available meta-indicators show an overwhelming convergence toward the
concepts patented by KiteGen, such as the number of new patent applications replicating our
approach, and the numerous independent scientific publications addressing our architecture.
Surprisingly, the requisite technological skills needed to guide and discern among alternatives
don’t seem widely evident among academia and researchers, even in works/papers like this one
where our interactive commentary is addressed despite revealing volumes of good data and
astute formal processes.
KiteGen, as a pioneer, first in producing energy with this new concept, fully patented, and first
completing the research, including a 10-year continuous assessment of the architectures,
cannot anymore accept, without some reaction, the informal competition around our proprietary
technology and the misguided “information” delaying its understanding and acceptance .
From (Cherubini et al. 2005), the classification of flygen and groundgen is clear, as the different
wings or wind-harnessing devices, propeller adopted or different rotokite concepts.
The inadequate buoyancy of helium-filled blimps, a few N per cubic meter unit, cannot withstand
the very high horizontal force of the wind, correctly reported and highlighted in the article, which
implies the altitude cannot be arbitrarily chosen by the control of such devices. Other
dysfunctions will occur for rigid flat wings that cannot structurally withstand the forces without
unacceptable weight (longeron beam) or flexible fabric wings that cannot maintain sufficient
aerodynamic efficiency or survive the forces and aerodynamic stress required for energy
production. In particular, there is the recent demonstration corresponding to the conclusion of
the applied research conducted by KiteGen, which delivers the complete and validated
projection of generators on an industrial scale, which will put an end to architectural speculation,
as this development demonstrates adherence to the best possible specifications in terms of
LCA and energy quality, outperforming the matured wind turbines both in onshore and offshore
applications by a thousand times.
It seems impossible to avoid the (false, but overwhelming
) politically-correct urge to set
aside/ignore the comparisons or architecture adoption to the focus on the most promising
concept. There remains the need to stress, in any case, the introduction of robust scientific
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 6
criteria, stated with certainty and generally requiring that such an analysis must be specifically
tailored to each of the architectures and harnessing strategies depicted, instead of generically
considering the domain as a whole. Each architecture has different requirements and behavior
within wind forces and speeds and different capacity factors. For example, the paper’s authors
deduced and recommended an ideal and quite precise operating altitude of 200-400 m with a
computed wing of 28 of gliding factor. Such a wing, in a pumping kite architecture, will fly in
crosswinds at speeds of 100m/s and over. The suggested altitude provides a very tight cone of
operation, which would require the wing to maintain an excessively tight direction-changing path
in airspace and an impractical few seconds to complete a stroke inside the lemniscate (the
characteristic “eight”-shaped path).
Accurate Data of High Altitude Wind; Is It required?
Text quoted from page 2 paragraph 10:
“Developers and operators of large conventional wind turbines, AWES and drones require
accurate wind data to estimate power and mechanical loads.”
This statement is absolutely wrong, and risks concealing one of the primary architectural
advantages of KiteGen. The KiteGen design concept is totally different because it does not have
fixed structures that have to withstand the worst weather conditions that occur once in decades.
It starts from an arbitrary design choice of the nameplate power of the generator, without having
to take into account historical wind data. Thus, the structural cost of the generator is merely a
linear function of the chosen design power specifications, not the imposed safety factor for a
structure that must withstand all weather conditions.
Currently, our 100 sqm wing is equipped with a 16 mm diameter 3GPa ultimate tensile-strength
line. The force may reach up to 600 kN before breaking[4]. When the wind is strong enough,
the wing may exert forces certainly greater than the line’s ultimate tensile strength. The order of
magnitude of such exceptional forces can raise the power of a single-wing high-altitude wind
generator close to 900 MW; thus 30MN of traction, as also stated in the subject article preprint,
confirming this finding. This is valid and generally correct only from a physical and geometrical
point of view. Obviously, the technology cannot follow those requirements so closely. Another
issue is the Capacity Factor of the machines which needs to be maximized for weak winds
rather than preventively over-engineered for optimization in strong winds.
Thus, it is not practical to apply the features of wing/wind system interaction to the specifications
of the generator. It is better to find a compromise with reduced power that is more easily
manageable and can be engineered/produced with a greater Capacity Factor because it
requires less wind speed.
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 7
Following such design guidelines, it is the generator that shapes the dynamics of operation,
controlling the lines through its system of pulleys. It is not necessary nor useful to have a full
wing-speed-and-force profile dependent on the available natural resource. The arbitrarily
chosen 3 MW nameplate generator will currently manage up to 300 kN of force (50% of the
maximum load of the line ) when the wind speed does not exceed 15 m/s. By regulating the
operating altitude and wing flying position/orientation (pose) relative to the wind direction,
sporadic stronger winds can be avoided and/or mitigated.
Stronger and Constant High Altitude Wind Isn’t the Original Enabling Factor
Text quoted from page 2 paragraph 10:
“[Developers] They currently rely on oversimplified approximations such as the logarithmic
wind profile (Optiset al., 2016) or coarsely resolved reanalysis data sets (Archer and Caldeira,
2009) as the applicability of conventional spectral wind models (Burton, 2011) have not been
verified for these altitudes.”
This statement is also not true and, again, potentially undermines the integrity of, and
professional work accomplished, by KiteGen. We have already observed such an attitude in
other publications where the authors try to gain some additional credibility, attempting to criticize
the proceeding developments, their motive not clear [6].
At KiteGen, we prefer to be asked timely questions about our technical opinions or doubts about
our assertions rather than be surprised after-the-fact. This is an open invitation to meet the
team. In any case, it is a great opportunity to continue the discussion of this unprecedented
opportunity.
KiteGen relies on two features/achievements regarding wind availability, which are precise and
certainly not an oversimplification or approximation:
1) Tethered airfoils can generate far more power than wind turbines simply because they
can sweep a greater area for an equivalent or reduced expenditure of resources, since they
would not incur the cost of the tower or be limited to the blade sizes that towers must
accommodate. It is easy to compute such an increase in performance through Betz laws. In
particular, the flying wings expose a lower Betz efficiency, compensated for by the larger area
swept, which allows it to outperform the energy-harnessing potential of the wind turbine blades
by a factor of three, assuming equal conditions of wind speed and aerodynamic surface.
2) In 2003, KiteGen, in collaboration with Dutch astronaut Wubbo Ockels [1], gained insight
into the potential of high, or tropospheric, winds; stronger and more constant than biosphere
winds; then, in 2009, sought and obtained a study from an Italian research centre [5], providing
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 8
great amounts of data gained in Italy using Sodars, that made us fully aware of the greatly
multiplied advantages at previously unforeseen and unexpected altitudes, creating a definitive
and satisfactory solution to the wind issue.
Multiplying the threefold increase of performance due the “Betz” advantage, with an eightfold
minimum increase of wind power at altitude, we obtain an astonishing exploitable natural
resource that is at least 24 times
the typical wind turbine’s harnessable power. This fact
suggested that it was better to focus all efforts on the challenge of industrial-scale harnessing
technology.
Finally Some Positive Remarks Regarding the Technology
Text quoted from page 16 paragraph 5:
“Therefore, AWES need to be able to operate in a wide range of wind speeds or be controlled in
a way that they avoid extreme conditions. The 12 months NoOBS simulation shows lower wind
speeds than the 6 months simulations as the included summer months generally have lower
wind speeds due to higher probability of unstable stratification. The Weibull fit of this simulation
tends to overestimate higher wind speeds and underestimate low wind speeds at all altitudes.”
Text quoted from page 24 paragraph 10:
“Using a simplified AWES model, assuming a constant tether length of 1500 m and neglecting
drag and weight all data sets suggested an optimal operating altitude between 150 and 400 m.
However, since stratification leads to a vast range of wind speed profiles AWES greatly benefit
from dynamically adapting their operating altitude to maximize power production and minimize
losses”
Disregarding the fallacy of the over-simplification of the tropospheric wind generation model,
those observations are certainly true, and finally desirable and quite easy to obtain. The wing’s
directional freedom effectively deals with extreme conditions and provides an effective
adaptation opportunity. Stronger winds will not be exploited by regulating the operative altitude
and/or the wing flying position compared to the wind direction (exiting the power spot by not
flying crosswind). That being said, there are a lot of automatic controls and engineering
solutions to ensure safety and to manage modulation, transient conditions and all the possible
issues that may arise when dealing with this natural resource.
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 9
Optimal Operating Altitude and Power Production: Is It Really Required?
Text quoted from page 22 paragraph 5:
“Figure 13 summarizes the probability distribution of optimal operating altitude and optimal
power with the white solid line showing the cumulative frequency of optimal operating altitude.
Both simulations for this particular location and time period show similar trends with the most
probable optimal altitude between approximately 200 and 400 m. Times of very high traction
power are fairly rare and likely associated with low level jets. Lower power at higher altitudes is
caused by the misalignment losses. Here we assume a constant tether length of 1500 m.”
This article is addressing a wind resource assessment totally outside of the KiteGen dynamic,
unfortunately risking to be useless to both developers and researchers in general, which again
falls into the error of inappropriate exaggeration. Although theoretically correct, the proposed
wind environments for deployment are technologically unreachable. In fact, our 100 m2 wing,
according to the authors, would reach a peak of 900MW. In short, a single wing would generate
power almost equivalent to that from a nuclear power plant
!
The out-of-scale wing 8-9MW/m2 must be compared with the desired trend in wind turbine to
reduce the specific power addressed, and the requirement of our giant wing that is even lower:
30kW/m2 of wing surface or 300W/m2 of specific power of the wind front
Subject article figure 13 here modified to highlight the scale mismatching
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 10
The plausibility of the project needs to preserved by correcting such inaccuracies, arguing the
uselessness of this approach and introduce and make it clear that the most valuable feature of
KiteGen is its baseload behavior, which is achieved without forcing it into optimization. It is
better to avoid exploiting intense wind and address development toward obtaining nominal
power with weak or very weak winds. Losing wind power when it is excessive, on the other
hand, can be quite easily addressed, even though this was the biggest obstacle during the
operation of our research prototypes, regularly leading to damaging some components of the
equipment.
The KiteGen Carousel is superior to the best baseload power plants, including coal, gas and
nuclear. The data are coming from several available data and reanalyses. The pink area depicts
wind speeds available in the temperate zones of the planet, actually better with respect to the
global average. This means that the KiteGen Carousel needs a very low wind speed (about 7
m/s on average) to work at high capacity for more than 8300 hours per year, even at altitudes
less than 3000 m, especially in energy intensive areas of the world (yellow balloon “A”). The
pumping kites need more power density to work at a capacity factor greater than 6000 hours per
year at even lower altitudes (about 10 m/s on average - yellow balloon “B”). Wind turbines work
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 11
for 2000 equivalent hours per year, requiring a minimum wind speed of 12-14 m/s or 1100-1646
W/m2 to provide nominal power and is also reported the recent announced prototype of GE
Haliade-X (yellow balloon “D”) that is claimed to have a potential capacity factor of 63% or
5500h in very lucky sites. The Haliade-X abnormal data is in fact a merely and different
commercial strategy, if compared to competitors, the turbine is geometrically and economically a
36 MW wind machine with the nameplate derated to 12 MW, this adjust the denominator of the
CF formula (MWh/MW), unfortunately the expected manufacturing batch cost per unit is close to
150M€ while the prototype including the industrial tooling was announced at 400M€,
skyrocketing the LCOE of the envisageable batch produced units to over €300/MWh, two order
of magnitude higher compared to the LCOE of the “dematerialised” KiteGen Carousel.
3
The extreme optimization issue is a common thread to practically all the (pseudo) scientific
articles generated by third parties which ignores grid requirements and energy quality, then is
easily ridiculed, consequently leading to the potentially damaging underestimation of the value
of the project, thus sharing the same errant promotion of photovoltaic and conventional wind
turbines, when KiteGen is obviously the long-awaited solution to such issues.
3 Dematerialization refers to the absolute or relative reduction in the quantity of materials used and/or the quantity of
waste generated in the production of a unit of economic output.
INTERACTIVE COMMENT to Sommerfeld M. et al. (2019) 12
revie
References
[1] Ippolito, M. Ockels, W. (2003).“Kite Wind Generator, smart control of power kites for
renewable energy production” submitted in PRIORITY 6.1 “Sustainable Energy
Systems” Call FP6-2003 -TREN-2
Retrieved from http://energykitesystems.net/KiteGen/2003meeting56pages.pdf
[2] Cherubini, A., Papini, A., Vertechy, R., and Fontana, M. (2015). Airborne Wind Energy
Systems: A review of the technologies, Renewable and Sustainable Energy Reviews
, 51,
1461–1476, doi:10.1016/j.rser.2015.07.053,
Retrieved from http://linkinghub.elsevier.com/retrieve/pii/S1364032115007005
[3] Archer, C. L. and Caldeira, K. (2009). Global Assessment of High-Altitude Wind Power,
Energies
, 2, 307–319, doi:10.3390/en20200307,
Retrieved from http://www.mdpi.com/1996-1073/2/2/307/
[4] Ippolito, M Saraceno, E. (2019) KiteGen Research high altitude wind generation tropospheric
wind exploitation under structural and technological constraints. Research Gate
doi:
10.13140/RG.2.2.12701.97766
[5] Casale C., Silvano Viani S., Marcacci P. (2009) Valutazioni sui sistemi “kite wind generator”
CESI RICERCA
(in Italian) Retrieved from
https://docplayer.it/13336123-Valutazioni-sui-sistemi-kite-wind-generator.html
[6] Ippolito M. (2019) Reaction Paper to the Recent Ecorys Study KI0118188ENN.en.pdf
Challenges for the commercialization of Airborne Wind Energy Systems
DOI: 10.13140/RG.2.2.17236.24966 Retrieved from
https://www.researchgate.net/publication/331715736_Reaction_Paper_to_the_Recent_Ecorys_St
udy_KI0118188ENNenpdf_Challenges_for_the_commercialization_of_Airborne_Wind_Energy
_Systems
ResearchGate has not been able to resolve any citations for this publication.
Preprint
Full-text available
This a reaction paper issued after some unsuccessful attempts to invite the Ecorys author in KiteGen in order to provide them with fresh and consistent information. KiteGen considers the document published by Ecorys "Challenges for the commercialization of Airborne Wind Energy Systems" as repetitious and delays progress by at least 10 years due to not comprehensively understanding all aspects of the technology, which has created misleading information as well as the support of erroneous claims that contradict most already-published results and state of the technology already in place.
Method
Full-text available
Evaluation of tropospheric wind energy systems. The math needed to understand the two KiteGen architectures is straightforward, making it incredibly simple to plan a fully-specified design for independent evaluation and finally begin to recognize, with absolute clarity, the distinct advantages over all other means of producing electrical energy.
Article
Full-text available
Abstract Among novel technologies for producing electricity from renewable resources, a new class of wind energy converters has been conceived under the name of Airborne Wind Energy Systems (AWESs). This new generation of systems employs flying tethered wings or aircraft in order to reach winds blowing at atmosphere layers that are inaccessible by traditional wind turbines. Research on AWESs started in the mid seventies, with a rapid acceleration in the last decade. A number of systems based on radically different concepts have been analyzed and tested. Several prototypes have been developed all over the world and the results from early experiments are becoming available. This paper provides a review of the different technologies that have been conceived to harvest the energy of high-altitude winds, specifically including prototypes developed by universities and companies. A classification of such systems is proposed on the basis of their general layout and architecture. The focus is set on the hardware architecture of systems that have been demonstrated and tested in real scenarios. Promising solutions that are likely to be implemented in the close future are also considered.
Article
Full-text available
The available wind power resource worldwide at altitudes between 500 and 12,000 m above ground is assessed for the first time. Twenty-eight years of wind data from the reanalyses by the National Centers for Environmental Prediction and the Department of Energy are analyzed and interpolated to study geographical distributions and persistency of winds at all altitudes. Furthermore, intermittency issues and global climate effects of large-scale extraction of energy from high-altitude winds are investigated.
Kite Wind Generator, smart control of power kites for renewable energy production
  • M Ippolito
  • W Ockels
Ippolito, M. Ockels, W. (2003)."Kite Wind Generator, smart control of power kites for renewable energy production" submitted in PRIORITY 6.1 "Sustainable Energy Systems" Call FP6-2003 -TREN-2
Airborne Wind Energy Systems: A review of the technologies, ​ Renewable and Sustainable Energy Reviews​
  • A Cherubini
  • A Papini
  • R Vertechy
  • M Fontana
Cherubini, A., Papini, A., Vertechy, R., and Fontana, M. (2015). Airborne Wind Energy Systems: A review of the technologies, ​ Renewable and Sustainable Energy Reviews​, 51, 1461-1476, doi:10.1016/j.rser.2015.07.053, Retrieved from ​ http://linkinghub.elsevier.com/retrieve/pii/S1364032115007005
Global Assessment of High-Altitude Wind Power, Energies​
  • C L Archer
  • K Caldeira
Archer, C. L. and Caldeira, K. (2009). Global Assessment of High-Altitude Wind Power, Energies​, 2, 307-319, doi:10.3390/en20200307, Retrieved from ​ http://www.mdpi.com/1996
Valutazioni sui sistemi "kite wind generator" CESI RICERCA
  • C Casale
  • Silvano Viani
  • S Marcacci
Casale C., Silvano Viani S., Marcacci P. (2009) Valutazioni sui sistemi "kite wind generator" CESI RICERCA (in Italian) Retrieved from https://docplayer.it/13336123-Valutazioni-sui-sistemi-kite-wind-generator.html