Welcome to Airborne Wind Energy
Welcome to the forum - a call to all pioneers, researchers, and enthusiasts!
We started this forum as a meeting place to explore and develop the field of Airborne Wind Energy (AWE). We welcome you to join, share your knowledge, ask your questions, and take part in the discussion.
Unlike conventional wind energy that is limited by the height and mass of a tower, AWE uses rigid or soft kites to access the stronger and more consistent winds found at higher altitudes.
AWES kites and tethers are made using lightweight, high-strength materials. This can reduce the carbon cost of construction and can enable rapid and remote deployments at scale.
This post will cover only the basics.
Dive into the forum for more detail.
A Historical Perspective
Early Pioneers and Foundational Concepts
Airborne wind energy isnât new. In the 1930s, German engineer, Aloys van Gries, filed patents for using kites to elevate wind turbines to higher altitudes. He proposed using large lifter kites with emerging wind turbine technology.
Hermann Oberth revived the concept of airborne wind energy during the 1970s energy crisis. Bryan Roberts developed his Gyromill starting in 1979.
Crosswind flight AWE began with Miles L. Loydâs 1980 paper Crosswind Kite Power which provided the first quantitative analysis and laid the theoretical foundation for crosswind flight AWE systems.
In 2004, former astronaut Wubbo Ockels established an AWES research group at TU Delft. Ampyx Power spun off from this group in 2008 and Kitepower in 2016.
Makani Technologies was founded in 2006 and was acquired by Google in 2013, boosting its profile and capital. In 2020 Alphabet shut down Makani. Makani said âDespite strong technical progress, the road to commercialization is longer and riskier than hoped.â[14]
Other companies have made progress toward market entry. SkySails Power announced the launch of what it described as the âworldâs first fully autonomous commercial âairborne wind energyâ (AWE) systemâ in Mauritius in late 2021. This system has been consistently[2] delivering close to its target of 100 kilowatts[3]. This achievement could be a first step toward moving beyond research and development to concrete, albeit small-scale, commercial operations.
A 2021 report[5] by the U.S. Department of Energy to Congress recognized AWEâs âsignificant potential,â[8] noting its capacity to generate energy on par with traditional wind systems[6], though acknowledging the technologyâs need for further development for large-scale deployment[9]. Similarly, a 2018 EU-commissioned study[7] asserted a âstrongâ industrial leadership case for AWE, despite its early stage of maturity[8]. Needs sources and updated info.
The Corporate and Academic Landscape
Globally, about 70 research entities contributed to AWE development[3].
Europeâs AWE sector benefits from a collaborative ecosystem of companies and research institutions. Airborne Wind Europe is the industry association. Key industry players include Kitemill (Norway), Kitekraft (Germany), Enerkite (Germany), Kitepower (Netherlands), Wind Fisher (USA), SkySails (Germany), Windswept (UK), SomeAWE (Spain) Kite Dynamics (Germany) and KiteNRG (Italy)
Academic research plays a vital role, with significant contributions from institutions like the TU Delft Wind Energy Institute, Carlos III University of Madrid (UC3M), and the University of Freiburg, DTU, Strathclyde and more. This network of universities, research labs, and startups as well as the AWEC[2] conference series[2] and various AWES seminars[2] and involvement in mainstream Wind Energy conferences[2] is a catalyst for innovation within the AWE sector.
Deconstructing the Technology: A Guide to AWES Typology
Fundamental Principles
A core advantage for AWES is access to a better wind resource. At higher altitudes, wind speeds are generally greater and more consistent due to the absence of ground-level impediments and friction.
The power available in the wind is not a linear function of wind speed; it scales with the cube of the wind velocity (Pâv^3). This means that even a twofold increase in wind speed results in an eightfold increase in potential power.
Crosswind flight is the primary method for harnessing wind power. The lift force (Fl) of an airfoil is proportional to the square of its apparent airspeed (Va). By flying in patterns like a figure-eight or circle, a tethered wing significantly increases its speed relative to the ambient wind (Vw). This dramatically increases tether tension and power. For instance, a wing flying at five times the ambient wind speed generates twenty five times more tether tension than a stationary wing in the same wind. This dynamic flight is a crucial innovation, enabling a small, lightweight wing to sweep a large area and harvest substantial energy. Consequently, a single square meter of an AWE wing can generate over 150 times more power than a square meter of solar cells at peak irradiation[4].
A conventional wind turbine needs to resist the weight from the nacelle and the rotor and the considerable wind force on the tower and rotor trying to tip it over. In AWE this force from the wind is aligned with the tether so that the tether is only working in tension, eliminating this cantilever effect and allowing it to be enormously lighter.
In a conventional wind turbine the fast-moving outer 20 percent of the rotor generates around 80 percent of the power. The rest of the rotor needs to still be there and be very strong to resist the very strong cantilever force from the wind and the cyclic loading on the long blades. In AWE the inner 80 percent of the blade is missing and only the fast-moving outer 20 percent of the blade is used. Most of the mass of the blade therefore is removed. Kite bridling can further reduce the weight of the kite.
AWES still need ground stations. Often shipping containers are used as enclosures for the ground-based equipment.
Some disadvantages of AWES are:âŚ
The kites in an AWES operate in constant tethered flight. Most designs require sophisticated, autonomous control software to takeoff, stay airborne and maintain efficient flight, and land. This is a significant challenge.
Tether wearâŚ
DurabilityâŚ
Some AWES Taxonomy
The majority of research so far has focused on two categories of AWE systemsâGround-Generation Pumping/Yo-Yo/Bounding (where the generator is on the ground and the kite cyclically pulls the tether from around the drum) and Fly-Generation (where small wind turbines are placed on the kite and driven by the high apparent wind speed they experience).
In conventional wind energy three-bladed started to be developed starting in the 1950s[222] and have now become standard, in AWE there is still no equivalent. There are still a large variety of concepts being explored. More study and development is still needed to find and develop competitive products.
The following is a more detailed breakdown of AWE system types that have been discussed in the broader research community and also on this forum.
Ground-Generation (Pumping/Yo-Yo/Bounding)
This common design positions the generator on the ground. A tethered flying device, either a soft kite or a rigid wing, generates a strong pulling force on its tether by flying in a crosswind pattern. This force unwinds the tether from a drum, which is connected to a generator to produce electricity; this is known as the âtraction phaseâ or âreel-out.â Because the tether is of finite length, the system must periodically stop generating power to retract the wing. This is the ârecovery phase,â during which the wing changes its flight pattern to produce less lift, and the drum is motored to reel the tether back in. Due to this intermittent, cyclical process, these systems are often called âpumpingâ or âYo-Yoâ generators.
- Examples & Discussion: This category is widely explored by companies like SkySails Power, Kitepower, Enerkite and Kitemill
Fly-Generation
An alternative method places power conversion equipment directly on the airborne device. A rigid-winged aircraft, similar to a large drone, generates electricity from high apparent wind speeds by flying in a crosswind pattern and utilizing onboard rotors. The generated power is then sent to the ground via a conductive tether. Key benefits of this âfly-generationâ approach are easier control through launch and landing maneuvers and its potential for a more continuous power output, as it avoids a cyclical recovery phase. However, challenges exist regarding the weight of the onboard generators and the intricate nature of the conductive tether.
- Examples & Discussion: KiteKraft and WindLift are the main developers still active in Fly-Gen. Makani Technologies, acquired by Google, was a prominent fly-gen system. KiteX and KiwiGen were also working on this design.
Underwater Systems
Minesto.
Multi-kite airborne wind energy systems (MAWES)
Ground-Generation (Rotary)
Ground-gen rotary systems generate power from a continuous rotation of multiple kites. These kites are often networked together as a rotor. The kite tethers are connected to a rotary ground station. As the kites rotate, the motion is transmitted through the kite tethers to the ground station generator through tensile rotary power transmission (TRPT)
Early examples of this approach were the âCarouselâ system, proposed by KiteGen. The Superturbine tested by Doug Selsam used multiple small rotors connected to a semi-rigid shaft.
Active research is being done by AlphAnemo, SomeAWE, Windswept and Interesting ltd, and Tallak Tveide.
Ship Propulsion
Some concepts directly or indirectly harness the force of wind for propulsion. For instance, SkySails pioneered the use of large kites for traction to propel cargo ships, aiming to reduce their reliance on diesel fuel.
Lighter-Than-Air (LTA) Systems
Buoyant aerostats or hybrid kytoons (kite balloons) are employed in this category of AWE systems to maintain airborne device elevation, even during periods of low or no wind. The LTA component functions as a lifter for airborne turbines or other energy-harvesting equipment. Examples include the Magenn Air Rotor System (MARS), which proposed a vertical-axis wind turbine supported by an inflated helium-filled aerostat, and Altaeros Energies, which utilized a helium-filled balloon shroud to elevate a wind turbine and transfer power via a tether.
One of our most prolific contributors Pierre Benheim has proposed several AWES variants in this category (as well as others)
Debate in this category often centers on the practical challenges of maintaining buoyancy, such as helium leakage, environmental and legal challenges and the validity of scaling materials and cost.
Novel Concepts & Non-Generation Systems
Other ideas remain experimental, such as spiral airfoils.
This forum provides a platform for startups, universities, open-source projects and independent researchers to disseminate and discuss their work.
The Economics of AWE: A New Equation for Wind Power
The Material Advantage
Airborne Wind Energy can drastically cut material use compared to conventional wind energy as it replaces the tall and rigid tower with lightweight, force-aligned tethers and the long blades with shorter wingspan kites. It still needs a ground station. Claims of up to a 90 percent material reduction have been made. This can result in lower costs and a smaller environmental footprint.
AWEâs material efficiency also offers portability. Systems are designed to fit into a shipping container and to be deployed in a short time. Niche markets envisioned include supplying power to remote areas, serving as emergency power, or enabling offshore installations where traditional turbines are impractical.
The Levelized Cost of Energy (LCOE)
The Levelized Cost of Energy (LCOE) compares energy technology competitiveness, representing the average cost of electricity production over a systemâs lifespan. For Airborne Wind Energy, one goal is to achieve an LCOE comparable to or lower than that of conventional wind energy to ensure competitiveness.
AWE systems have the potential to achieve this for two reasons. Firstly, their significantly lower mass and material requirements can result in a reduced Initial Capital Cost (ICC). Secondly, by accessing higher, more consistent winds, AWE systems have the potential for a higher capacity factorâthe ratio of actual energy produced over a given period to the theoretical maximum.
LCOE figures for AWE are still based on projections. A 2023 design study for a 1 MW fly-gen system on a floating offshore foundation estimated an LCOE of 49.5 to 69 âŹ/MWh. This figure is competitive, falling within the unsubsidized LCOE range for conventional onshore wind, which typically ranges from $27 to $75/MWh. This suggests that the fundamental economic case for AWE is sound.
The following table synthesizes the available LCOE and cost driver data to provide a comparative overview of AWE and conventional wind technologies.
Table 1: Comparative LCOE and Key Cost Drivers
| Technology | Estimated LCOE ($/MWh or âŹ/MWh) | Relative Material Use by Mass | Typical Capacity Factor (%) | Primary Application |
|---|---|---|---|---|
| Airborne Wind Energy (AWES) @ Early Stage | 49.5 - 69 âŹ/MWh (Projected) | 10-30% of conventional | High, due to access to high-altitude winds | Remote, off-grid, and deep offshore sites |
| Conventional Onshore Wind | $27 - $75/MWh | 100% (Baseline) | 18-48% | Established utility-scale grid sites |
| Conventional Offshore Wind | $67 - $146/MWh | Very high | 29-52% | Offshore sites, often in shallower water |
| Solar PV | $40/MWh (Global Weighted Average) | N/A | 12-30% | Distributed and utility-scale solar farms |
Economic Hurdles and Commercialization Challenges
Despite promising economics, Airborne Wind Energy (AWE) faces significant hurdles to commercialization, exemplified by Googleâs Makani project. Makani, a Fly-Gen pioneer, was shuttered in 2020 due to uneconomical design choices rather than fundamental AWE flaws. Its rigid-winged, high-speed approach led to an overly complex, heavy, and costly design. Makaniâs openly documented failure underscores the need for reliable, manufacturable, and economically feasible designs beyond mere proof-of-concept. A broader challenge is the âchicken and eggâ problem of investment and regulation, hindering commercial deployment.
IV. Navigating the Human and Regulatory Landscape
Public Perception and Societal Integration
Public acceptance of airborne wind energy (AWE) is crucial, initial studies have been performed at TU Delft. Early literature was optimistic but is becoming more scientific backing.
Key concerns include:
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Safety: Unlike stationary turbines, AWE systems fly, raising crash concerns. Reliability âclose to civil airplanesâ is needed.
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Visibility/Aesthetics: While proponents claim reduced visual impact, invisible tethers pose a safety risk to other airspace users. Ground stations remain visible.
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Acoustic/Ecological Impacts: Noise from generators, winches, and kites is a concern. The impact on birds and bats is ânot yet very well studied,â which is critical given AWEâs operation in migratory bird airspace.
Regulations: Airspace, Certification, and Safety
The regulatory environment is a significant non-technical challenge when commercialising and deploying AWES. Some of the main concerns being addressed by the industry and researchers are
Conspicuity of the Tether
Airspace Volume & Safety
Certification & Standards
Interference with National Air Space Facilities
Airborne Wind Europe publish guidance on Safe operation and Airspace integration
Potential Applications and Future Outlook
AWE shows promise in niche markets due to its portability, ideal for remote power, humanitarian, or high-cost diesel areas. Offshore, floating AWE systems can exploit deep-water winds where conventional turbines are unfeasible. AWE also complements other renewables, offering consistent power at night and in low-wind conditions to supplement solar farms.
V. Concluding Remarks: A Call to Community
Airborne wind energy (AWE) is a distinct, potentially disruptive renewable energy technology. AWE leverages high-altitude winds with less material than conventional turbines, promising versatile, portable, and cost-effective wind power. However, challenges remain, including economic scaling, regulatory frameworks, and public perception issues. The Makani case highlights that commercial viability requires robust engineering, reliability, and a pragmatic development approach.
This forum, at awesystems.info, is the ideal venue for these discussions. We invite you to explore the rich history, delve into the technical nuances of ground-gen versus fly-gen, and debate the economic and regulatory realities that will define the industryâs trajectory. Share your ideas, ask your questions, and engage with others who are passionate about the future of energy.
We welcome considerate contributions to this vibrant community.
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