Airborne Wind Energy

Implemented concepts

Roland Schmehl

20 September 2024

CC BY 4.0

Outline

Max Dereta

Learning objectives

The commercial development of airborne wind energy is still in an exploration state and characterized by many different concepts. The aim of this lecture is

  • to classify the various concepts that are pursued, and
  • to present and discuss representative prototypes in more detail.

Representative companies and their technology choices are outlined with an overview table, the system concept and operation illustrated by schematics and photos.

Complementary illustrated portfolios are given by Schmehl and Tulloch (2019) and Nelson (2019).

Classification

AWE systems can be classified in many different ways.

  • Energy conversion concept
  • Kite design
  • Launching and landing concept
  • Kite control
  • Rated power
  • …

Classification criteria are generally correlated.

Criterion 1: Energy conversion location

Lorenzo Fagiano | Dylan Eijkelhof

Criterion 2: Kite type

Antonello Cherubini

Criterion 3: Launching and landing concept

Enerkíte

Currently developed commercial prototypes















  • The classification is based on 14 currently developed commercial prototypes

  • Several other implemented prototypes, not pursued commercially anymore, are included in the subsequent discussion

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Skysails SKN-PN-14 ground soft wing static mast 15.6–22a 90b, 180c 170d 200-400 200

a projected wing span
b projected wing surface area
c flat (laid-out) wing surface area

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Kitepower Falcon ground soft wing winch 13.3a 47b, 60c 73d 70-400 100

a projected wing span
b projected wing surface area
c flat (laid-out) wing surface area

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Kitenergy KE60 Mark II ground soft wing winch 12.5a 42b, 50c 100-400 60

a projected wing span
b projected wing surface area
c flat (laid-out) wing surface area

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Toyoya Mothership v11 ground soft wing winch 8 8 5.2 300-600 1 
Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
CPECC Airpower ground parachute pilot parachute 40a 1256b 1480 500-3000 2400e

a projected parachute diameter
b projected parachute surface area
e rated generator power

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Wind Fisher MAG1 ground Magnus rotor winch 1.7 0.32f 1.0 0-50 0

f rotor diameter × width

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
EnerKíte EK30/Enerwing ground hybrid wing HTOL rotating arm 8-14 4-8 22.7 50-300 30 
Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Mozaerog AP3 ground hard wing HTOL catapult 12 12 475 200-450 150

g formerly Ampyx Power

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Kitemill KM1 ground hard wing VTOL quad-plane 7.4 3 54 200-500 20 
Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
TwingTec Twing (T29) ground hard wing VTOL tri-plane 5.5 2 25 up to 300 10 
Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Windswept Kite Turbine ground rotary pilot kite 6×1h 6×0.2 10 1

h rotor diameter 4.48 m

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
someAWE MAR3 ground rotary pilot kite 4×1i 4×0.15 0.5

i rotor diameter 3.5 m

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Kitekraft SN9 onboard box wing VTOL tailsitter 2.4 1.08 32 100j 12

j tether length

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Windlift C1 onboard hard wing VTOL tailsitter 3.8 0.95 11.3 30-100 2 

Applying classification criteria 1-3

Developer Prototype name Electricity generation location Kite type Launching & landing concept Wing span (m) Wing surface area (m2) Kite mass (kg) Min.–max. operation height (m) Rated power (kW)
Skysails SKN-PN-14 ground soft wing static mast 15.6–22a 90b, 180c 170d 200-400 200
Kitepower Falcon ground soft wing winch 13.3a 47b, 60c 73d 70-400 100
Kitenergy KE60 Mark II ground soft wing winch 12.5a 42b, 50c 100-400 60
Toyoya Mothership v11 ground soft wing winch 8 8 5.2 300-600 1
CPECC Airpower ground parachute pilot parachute 40a 1256b 1480 500-3000 2400e
Wind Fisher MAG1 ground Magnus rotor winch 1.7 0.32f 1.0 0-50 0
EnerKíte EK30/Enerwing ground hybrid wing HTOL rotating arm 8-14 4-8 22.7 50-300 30
Mozaerog AP3 ground hard wing HTOL catapult 12 12 475 200-450 150
Kitemill KM1 ground hard wing VTOL quad-plane 7.4 3 54 200-500 20
TwingTec Twing (T29) ground hard wing VTOL tri-plane 5.5 2 25 up to 300 10
Windswept Kite Turbine ground rotary pilot kite 6×1h 6×0.2 10 1
someAWE MAR3 ground rotary pilot kite 4×1i 4×0.15 0.5
Kitekraft SN9 onboard box wing VTOL tailsitter 2.4 1.08 32 100j 12
Windlift C1 onboard hard wing VTOL tailsitter 3.8 0.95 11.3 30-100 2

a projected wing span
b projected wing surface area
c flat (laid-out) wing surface area
d excluding tether, but including suspended kite control unit and bridle line system
e rated generator power

f rotor diameter × width
g formerly Ampyx Power
h rotor diameter 4.48 m
i rotor diameter 3.5 m
j tether length



Classification scheme



awesco.eu/awe-explained/

SkySails

skysails-power.com

Years active 2001-
Headquarters Hamburg, Germany
Type Company
Conversion concept Pumping cycle
Kite design Ram air kite
Kite control Suspended kite control unit
Ground connection Single tether
Launching & landing Static, from mast

Photo SKN-PN-14

Photo SKN-PN-14 operation sequence

Skysails demo flight

Skysails steering (2013): roll control

Paulig et al. (2013)

Power Curve SKN-PN-14, released March 22th 2024

TU Delft

github.com/awegroup
@Laddermill

Years active 2004-
Headquarters Delft, Netherlands
Type University research group
Conversion concept Pumping cycle
Kite design Leading edge inflatable tube kite
Kite control Suspended kite control unit
Ground connection Single tether
Launching & landing Winch & upswing from hanging position

System components




Vlugt et al. (2019)

Pumping kite concept


Vlugt et al. (2013)

Dynamic Simulation

Fechner et al. (2015)

Pumping cycle operation - simulation

Fechner (2016)

Power curve - simulation



Fechner (2016) p. 166 & 181

V3 kite






Oehler and Schmehl (2019)

Control bridle layout in flight


Left actuation loopRight actuation loop

Max Dereta

Kite control unit

Features:

Shock- and water-proof casing (shown without extra foam padding)
Two separate micro winches for depowering and steering
Depower winch includes piston brake
Onboard computer and wifi antenna
Rechargeable batteries for >2h flight
Angular encoders to measure tape actuations

V3 kite bridle line system

Poland and Schmehl (2023)

V3 kite control


Left: Poland and Schmehl (2023), right: Oehler and Schmehl (2019)

V3 kite control during launching and landing

End point of depower tape is marked.


Powered


Depowered


Depowered & steering

Oehler and Schmehl (2019)

Mast-based launching and landing

TU Delft V3 kite on 25 October 2012.

Pulley mechanism

Pulley mechanism to retain the tether at the circular rail (left), gradual release of the retaining pulley (center and right)

V3 kite launching and landing

doi:10.5446/48640, doi:10.5446/48647

Ground station

Tether path

Kitepower

thekitepower.com

Years active 2015-
Headquarters Delft, Netherlands
Type Registered trademark of TU Delft spin-off
company Enevate B.V.
Conversion concept Pumping cycle
Kite design Leading edge inflatable tube kite
Kite control Suspended kite control unit
Ground connection Single tether
Launching & landing Winch, upswing from hanging position

Daytime

Courtesy of Kitepower B.V. (2018)

Nighttime

Courtesy of Kitepower B.V. (2018)

Kitepower on Aruba (2021)

Kitepower on Aruba (2021)

System operation

System operation

Courtesy of Kitepower B.V. (2019)

System operation

Courtesy of Kitepower B.V. (2019)

Operational zones

Salma et al. (2019)

Kite park layout

Faggiani and Schmehl (2018)

Kite park power output

Faggiani and Schmehl (2018)

Ground station

Diehl et al. (2017)

Onboard wind turbine

Diehl et al. (2017)

Zeeland, May 2021

Demo event May 2021, Melissant, the Netherlands (courtesy of Kitepower BV)

Fagiano et al. (2022)

Aruba, October 2021

Operation of the 100 kW system on Aruba in an exercise with the Dutch engineering corps.

Fagiano et al. (2022)

Offgrid charging

Dirksland, July 2023

Walter Hueber

Ireland, September 2023

Maiden flight on 22 September 2023 on the RWE test site at Bangor Erris, County Mayo.

Kitenergy

kitenrg.com

Years active 2010-
Headquarters Turin, Italy
Type Company
Conversion concept Pumping cycle
Kite design Ram-air kite
Kite control Multiple winches on ground station
Ground connection Multiple tethers
Launching & landing Winch

KE60 Mark II

Toyota

global.toyota/en/

Years active 2018-
Headquarters Japan, USA
Type Company
Conversion concept Pumping cycle
Kite design Leading edge inflatable kite
Kite control Aerodynamic control surfaces
Ground connection Single tether
Launching & landing Winch

Mothership v11

CPECC

www.cpecc.ceec.net.cn

Years active 2024-
Headquarters Beijing, China
Type Company
Conversion concept Pumping cycle
Kite design Parachute
Kite control Power/depower mode
Ground connection Single tether
Launching & landing Pilot parachute

Airpower

Parachute-based prototype during take-off.

Wind Fisher

www.wind-fisher.com

Years active 2021-
Headquarters Les Adrets, France
Type Company
Conversion concept Pumping cycle
Kite design Magnus rotor
Kite control Control tethers and cylinder rotation
Ground connection Two tethers
Launching & landing Winch

MAG1 kite

MAG1 tow test

MAG1 control

View from kite to towing vehicle.

EnerKíte

enerkite.de

Years active 2010-
Headquarters Berlin, Germany
Type Spin-off company of TU Berlin
Conversion concept Pumping cycle
Kite design Hybrid swept wing without fuselage
Kite control Multiple winches on ground station
Ground connection Three separate tethers & bridle line system
Launching & landing Rotational HTOL with mast

EnerKíte

Enerkite swept wing

Ampyx Power

ampyxpower.com

Years active 2008-2022 (continued as Mozaero / Fuchszeug B.V.)
Headquarters The Hague, Netherlands
Type Spin-off company of TU Delft
Conversion concept Pumping cycle
Kite design Fixed wing with double fuselage & tailplane
Kite control Aerodynamic control surfaces
Ground connection Single tether
Launching & landing Linear HTOL with catapult

AP-1B1

Launch on 29 September 2012 (Schmehl 2015)

AP-2

AP-2

AP-2

AP-2

AP-2

AP-2

ampyxpower.com/

AP-2

AP-3

nlr.org/news/sustainability-by-a-crossover-technology/

AP-3

Diehl et al. (2017)

AP-3

Two prototypes in the workshop in May 2021

AP-4

Comparison of a 2 MW AWE system with a HAWT

Kruijff and Ruiterkamp (2018)

AP-4 floating windpark

AP-4 floating windpark

Mozaero

mozaero.com

Years active 2022- (continued from Ampyx Power B.V.)
Headquarters Breda, Netherlands
Type Project of Fuchszeug B.V.
Conversion concept Pumping cycle
Kite design Fixed wing with double fuselage & tailplane
Kite control Aerodynamic control surfaces
Ground connection Single tether
Launching & landing Linear HTOL with catapult

AP-3

Breda International Airport in May 2021

AP-3

Breda International Airport in May 2021

AP-3

Breda International Airport in May 2021

AP-3

Breda International Airport in May 2021

AP-3 untethered flight

Oostwold Airport in November 2023

AP-3 untethered flight

Oostwold Airport in November 2023

AP-3 untethered flight

Oostwold Airport in November 2023

Mozaero

Kitemill

kitemill.com

Years active 2008-
Headquarters Voss, Norway
Type Company (absorbed E-Kite and KPS)
Conversion concept Pumping cycle
Kite design Fixed wing with single fuselage & tailplane
Kite control Aerodynamic control surfaces
Ground connection Single tether
Launching & landing VTOL

Kite producing up to 20 kW

Kitemill’s KM1 prototype during testing, Lista, Norway.

TwingTec

twingtec.ch

Years active 2013-
Headquarters Dübendorf, Switzerland
Type Spin-off company of EMPA
Conversion concept Pumping cycle
Kite design Fixed wing with single fuselage & tailplane
Kite control Aerodynamic control surfaces
Ground connection Single tether
Launching & landing VTOL

Comparison

TwingTec pilot next to wind turbine of comparable power (Schmehl and Tulloch 2019)

TwingTec

Windswept

windswept.energy

Years active 2012-
Headquarters Lerwick, Shetland, United Kingdom
Type Company, affiliated to University of Strathclyde
Conversion concept Tensile torque transfer to ground generator
Kite design Rotating autogyro kite with fixed wings
Kite control Yaw stall via lift bearing on rotor top-side
Ground connection 5x networked rotary tethers & backline anchor
Launching & landing Pilot kite and backline anchor

Kite Turbine

Windswept (left) | Tulloch et al. (2022) (right)

Kite Turbine sideview

Windswept

Windswept

Windswept

someAWE

someawe.org

Years active 2017-
Headquarters Alicante, Spain
Type Company
Conversion concept Tensile torque transfer to ground generator
Kite design Rotating kite with fixed wings
Kite control Passive with pilot kite or cyclic pitch control
Ground connection Networked tethers
Launching & landing Pilot kite

MAR3

someAWE

Windlift

windlift.com

Years active 2006-
Headquarters Morrisville, NC, USA
Type Company
Conversion concept Onboard wind turbines
Kite design Fixed wing with single fuselage & tailplane
Kite control Aerodynamic control surfaces & onboard turbines
Ground connection Single tether
Launching & landing VTOL

Windlift C1

CoastalReview

Windlift C1

CoastalReview

Windlift video

Windlift vision

Windlift

kiteKRAFT

kitekraft.de
@Kitekraft

Years active 2019-
Headquarters Munich, Germany
Type Spin-off company of TU Munich
Conversion concept Onboard wind turbines
Kite design Box wing with double fuselage & tailplane
Kite control Aerodynamic control surfaces & onboard turbines
Ground connection Single tether
Launching & landing VTOL

Kitekraft

Kitekraft

Wind tunnel

KK3Plus V1 for 5-15 kW, testing multi-element airfoils (Courtesy kiteKraft GmbH)

Fully automatic flight

Nighttime flight in 2024

Kitekraft

Kitekraft’s flying wind turbine illuminated by the Anti-Collision-Lights.

Makani

x.company/projects/makani

Years active 2006-2020
Headquarters Alameda, CA, USA
Type Subsidiary company of Google (2013-2020)
Conversion concept Onboard wind turbines
Kite design Fixed wing with single fuselage & tailplane
Kite control Aerodynamic control surfaces & onboard turbines
Ground connection Single tether with two-line bridle
Launching & landing VTOL

M600

x.company/projects/makani/

M600







x.company/projects/makani/

Flight modes

Hardham (2012)

FAA testing

Echeverri (2020)

M600 test site on Mauii

Still visible on Google Maps satellite footage.

M600 testing on Mauii

M600 testing on Mauii

Comparison wind turbine

Offshore testing

Karmøy, Norway (2019)

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Offshore testing

Simulation

Oktoberkite

Homsy (2020)

Oktoberkite

Homsy (2020)

Oktoberkite

Homsy (2020)

Makani’s legacy

References

Diehl, M., Leuthold, R., Schmehl, R. eds: The 7th International Airborne Wind Energy Conference 2017: Book of Abstracts. University of Freiburg | Delft University of Technology, Freiburg, Germany (2017. doi:10.6094/UNIFR/12994
Echeverri, P.: Makani’s flight testing approach. In: Echeverri, P., Fricke, T., Homsy, G., and Tucker, N. (eds.) The energy kite: Selected results from the design, development, and testing of Makani’s airborne wind turbines, Part I of III. Makani Technologies LLC (2020)
Faggiani, P., Schmehl, R.: Design and economics of a pumping kite wind park. In: Schmehl, R. (ed.) Airborne wind energy – advances in technology development and research. pp. 391–411. Springer, Singapore (2018). doi:10.1007/978-981-10-1947-0_16
Fagiano, L., Croce, A., Schmehl, R., Thoms, S. eds: The 9th International Airborne Wind Energy Conference 2021: Book of Abstracts. Delft University of Technology, Milan, Italy (2022. doi:10.4233/uuid:696eb599-ab9a-4593-aedc-738eb14a90b3
Fechner, U.: A methodology for the design of kite-power control systems. Delft University of Technology (2016). doi:10.4233/uuid:85efaf4c-9dce-4111-bc91-7171b9da4b77
Fechner, U., Vlugt, R. van der, Schreuder, E., Schmehl, R.: Dynamic model of a pumping kite power system. Renewable Energy. 83, 705–716 (2015). doi:10.1016/j.renene.2015.04.028
Hardham, C.: Response to the federal aviation authority: Docket no.: FAA-2011-1279; notice no. 11-07; notification for airborne wind energy systems (AWES). Makani Power (2012)
Homsy, G.: Oktoberkite and the MX2: Toward best practices in energy kite design. In: Echeverri, P., Fricke, T., Homsy, G., and Tucker, N. (eds.) The energy kite: Selected results from the design, development, and testing of Makani’s airborne wind turbines, Part I of III. Makani Technologies LLC (2020)
Kruijff, M., Ruiterkamp, R.: A roadmap towards airborne wind energy in the utility sector. In: Schmehl, R. (ed.) Airborne wind energy – advances in technology development and research. pp. 643–662. Springer, Singapore (2018). doi:10.1007/978-981-10-1947-0_26
Nelson, V.: Innovative wind turbines: An illustrated guidebook. CRC Press, Boca Raton, FL (2019). doi:10.1201/9781003010883
Oehler, J., Schmehl, R.: Aerodynamic characterization of a soft kite by in situ flow measurement. Wind Energy Science. 4, 1–21 (2019). doi:10.5194/wes-4-1-2019
Paulig, X., Bungart, M., Specht, B.: Conceptual design of textile kites considering overall system performance. In: Ahrens, U., Diehl, M., and Schmehl, R. (eds.) Airborne wind energy. pp. 547–562. Springer, Berlin Heidelberg (2013). doi:10.1007/978-3-642-39965-7_32
Poland, J.A.W., Schmehl, R.: Modelling aeroelastic deformation of flexible membrane kites. Energies. 16, 5264 (2023). doi:10.3390/en16145264
Salma, V., Friedl, F., Schmehl, R.: Improving reliability and safety of airborne wind energy systems. Wind Energy. 23, 340–356 (2019). doi:10.1002/we.2433
Schmehl, R. ed: The 7th International Airborne Wind Energy Conference 2015: Book of Abstracts. Delft University of Technology, Delft, The Netherlands (2015. doi:10.4233/uuid:7df59b79-2c6b-4e30-bd58-8454f493bb09
Schmehl, R., Tulloch, O. eds: The 9th International Airborne Wind Energy Conference 2019: Book of Abstracts. University of Strathclyde | Delft University of Technology, Glasgow, United Kingdom (2019. doi:10.4233/uuid:57fd203c-e069-11e9-9fcb-441ea15f7c9c
Tulloch, O., Yue, H., Kazemi, A., Read, R.: Design analysis of a rotary airborne wind energy system. In: Fagiano, L., Croce, A., Schmehl, R., and Thoms, S. (eds.) The 9th International Airborne Wind Energy Conference (AWEC 2021): Book of Abstracts. pp. 142–143, Milan, Italy (2022
Vlugt, R. van der, Bley, A., Schmehl, R., Noom, M.: Quasi-steady model of a pumping kite power system. Renewable Energy. 131, 83–99 (2019). doi:10.1016/j.renene.2018.07.023
Vlugt, R. van der, Peschel, J., Schmehl, R.: Design and experimental characterization of a pumping kite power system. In: Ahrens, U., Diehl, M., and Schmehl, R. (eds.) Airborne wind energy. pp. 403–425. Springer, Berlin Heidelberg (2013). doi:10.1007/978-3-642-39965-7_23

Questions?





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