High-altitude wind energy is a prospective resource for the long-term generation of electrical energy. Airborne Wind Energy Systems (AWESs) are important and trending renewable energy technology. This is because of the wide availability of winds blowing between 300 and 10000 meters above ground and their high power capacity. In the recent decade, some of the leading players in the worldwide airborne wind turbine industry including, Vestas Wind Systems, KiteGen Research, Kitenergy, SkySails Power, TwingTec, TU Delft, Ampyx Power, Enerkite, and Windlift, have joined the AWES sector, patenting various ideas and technical solutions for their application.

What is Airborne Wind Energy (AWE)?

High-altitude Wind energy, also known as Airborne Wind Energy (AWE), is a renewable energy technology that generates electricity using airborne equipment. AWE, as opposed to traditional wind power, uses free-floating devices such as balloons, kites, and tethered wings held high in the air. Many well-established technologies in conventional ground-based wind energy turbines, such as generators, gearboxes, and grid-tied power converters, are also utilized in the AWE system.

The way these aerial wind turbines gather energy from the wind distinguishes them from their land-based or ocean-based counterparts. A tether line or a cable attaches the AWE device to the ground instead of a huge steel tower construction, and instead of long rotating turbine blades, specially designed aerofoil kites and wings sweep an area across the sky to capture wind energy. Further, these devices, such as a tethered wing or an aerofoil kite, are electromechanical systems that harness the kinetic energy of the winds circulating in the sky. Most airborne wind power devices are designed to fly in a crosswind or transverse direction, concentrating the wind's enormous power supply at medium to high altitudes of more than 200 meters. This is because the wind speed is often higher and steadier at altitudes above 200 meters than at lower altitudes, thus allowing the harnessing of these high winds as an energy source and creating electricity.

Furthermore, the lift and forces created by the wind at these heights are adequate to both sustain and power the flying apparatus. Because these airborne wind devices operate at a higher altitude and at higher wind speeds, more power can possibly be generated more consistently. Thus, with such high elevations and levels of power generation, these AWE devices can possibly be preferred over the typical wind turbine towers.

Working Principle of AWE

AWE is a wind energy system that uses flying blades or wings tethered to the ground. There are two primary concepts for converting wind energy into electricity are as follows:

1. Small propeller turbines with generators installed on the flying wing (Figure A) or
2. By having the wing or kite pull on the tether and the rope unwind from a ground drum, which drives the generator. This ground production approach necessitates reeling in the winch tether, resulting in a pumping or yoyo action (Figure B).

In the diagram, the onboard and off-board power generation has been showcased, where the kite (Airborne device) flies constantly across the wind, such that the onboard/off-board generators are responsible for power generation. In one case, the generated power is transmitted from the kite to the ground station via a tether (transmission lines) and extracted at the ground level. However, in another case, the electricity is generated at the ground station based on the in/out action of the tether connected with the kite.

Classification of AWE

Ground Gen: In this type of AWE classification, the electrical energy is created on the ground in a Ground-Gen AWES (GG-AWES) through mechanical work done by traction force. This force is carried from an airplane to the ground system by one or more ropes/cables. Further, this causes an electrical generator's motion, resulting in electricity production. Additionally, the GG-AWESs are subdivided into two types, i.e., fixed-ground station devices and moving-ground-station systems. Significantly, the ground station is fixed to the ground in the fixed-ground station devices. In the case of moving-ground-station systems, the ground station is not stationary but a moving vehicle.

Fly Gen: In this type of AWE classification, the electrical energy is generated onboard the aircraft during flight and delivered to the ground through a customized rope that incorporates electric wires in Fly-Gen AWESs. Further, the Fly-Gen AWESs convert this electrical energy using one or more specifically constructed wind turbines and store it in battery storage or transmit it to the required connections. Furthermore, the FG-AWESs are subdivided into two types, i.e., crosswind and non-crosswind flights. Significantly, these types of flights differ based on wind direction, i.e., wind perpendicular to the flight or non-perpendicular to the flight.

Present Deployments in Process

Ground Gen (Fixed Ground)

Ground Gen (Moving Ground)

Fly Gen

Advantages of AWE

• Less material means less environmental effect: CO2 footprint, aesthetic impact, and resource consumption.
• Additional wind resources: harnessing greater global renewable potential
• High full load hours imply more consistent power generation.
• Low Levelized Cost of Energy: the possibility for decreased energy production costs.
• Flexibility: simpler logistics, faster set-up
• Scalability ranges from a few kW to many MW.
• Mobile applications, repowering, and floating offshore are all new markets.

Disadvantages of AWE

• As airborne gadgets and power connections fall to the earth, they may become separated or damaged, posing a safety risk.
• If the gadget is retracted during inclement weather, no electricity is generated, and thus, the power balance will be affected.
• Electrical energy losses, given the lengthy conducting wire that connects the aerial producing equipment to the ground, is a major issue. With the increase in altitude, the transmission losses increase significantly.
• Acceptance of these big floating airborne devices over land and residential areas by the general public is a significant concern.
• These autonomous devices face design and control issues in all wind and weather situations.
• To fly in high altitude winds, kites and wings must be light and robust.
• Thunder and lightning strikes (Bad weather) represent a significant threat to the destruction of any aerial item, specifically AWE.

Seminal Patent

Title: Wind installation comprising a wind turbine and an airborne wind energy system

Patent: US11002252B2

Grant Date: 2021-05-11

Current Assignee: Vestas Wind Systems AS

The patent discloses a wind turbine system for harvesting and utilizing maximum wind energy and an airborne wind energy system for increasing the total power production.

As per the analysis, a conventional wind energy system is installed on a wind turbine site that includes electrical and mechanical components like rotors, blades, towers, etc. At the top of the tower, a nacelle (housing or a structure) is mounted, with each nacelle a rotor being rotatable about an axis of rotation is coupled. Further, this rotor is connected to the generator to convert the rotating rotor's energy into electrical energy for a power grid. The rotor, the generator, and the connections with the power grid are done via a power transmission line. Furthermore, an airborne wind energy system is connected at the top of the nacelle such as to increase the power production level of the installed system. Further, this airborne wind energy system is coupled to the wind turbine via a cable (tether) and comprises a separate generator that is electrically connected via the power transmission lines. Thus, such a system with the coupling of multiple wind energy sources allows for the harvesting of maximum power.

Conclusions and Future Scope

High-altitude wind energy is a prospective resource for the long-term generation of electrical energy. Airborne Wind Energy Systems (AWESs) are important and trending renewable energy technology. This is because of the wide availability of winds blowing between 300 and 10000 meters above ground and their high power capacity. In the recent decade, some of the leading players in the worldwide airborne wind turbine industry including, Vestas Wind Systems, KiteGen Research, Kitenergy, SkySails Power, TwingTec, TU Delft, Ampyx Power, Enerkite, and Windlift, have joined the AWES sector, patenting various ideas and technical solutions for their application. In the future, Airborne wind energy research and development is predicted to accelerate rapidly. Several prototypes that are currently being researched will be finished and tested on the basis of the key affecting parameters that include - flying mass, landing/takeoff, cables, altitude, movement curvature, cable electrostatic behavior, etc.

The compound annual growth rate (CAGR) of the airborne wind energy (AWE) market is estimated to be 9.4% from 2023 to 2030. This means that the AWE market is expected to grow by 9.4% every year on average over the next seven years. The ever-increasing need for power, particularly in rising economies such as China, Brazil, India, and Russia, has increased the demand for alternative energy sources.

References

1. https://www.alternative-energy-tutorials.com/wind-energy/airborne-wind-energy.html
2. https://www.mordorintelligence.com/industry-reports/airborne-wind-turbines
3. https://www.sciencedirect.com/science/article/pii/S1364032115007005?via%3Dihub
4. https://airbornewindeurope.org/about-airborne-wind-energy/
5. https://e360.yale.edu/features/after-a-shaky-start-airborne-wind-energy-is-slowly-taking-off
6. https://www.nrel.gov/docs/fy21osti/79992.pdf