Airborne Wind Energy Systems

💨Airborne Wind Energy Systems Unit 9 – Modeling Airborne Wind Energy Systems

Airborne Wind Energy Systems (AWES) are innovative technologies that harness wind energy at higher altitudes using tethered flying devices. These systems access stronger, more consistent winds than traditional turbines, potentially reducing costs and expanding wind power's geographical range. AWES consist of flying devices, tethers, and ground stations, utilizing aerodynamic lift and tether tension to generate power. They operate in pumping or drag power cycles, employing crosswind flight patterns to maximize energy capture. Understanding aerodynamics, flight dynamics, and control systems is crucial for optimizing AWES performance.

Key Concepts and Principles

  • Airborne Wind Energy Systems (AWES) harness wind energy at higher altitudes using tethered flying devices
  • AWES can access stronger and more consistent winds compared to traditional wind turbines
  • Two main types of AWES: ground-gen systems generate electricity on the ground, while fly-gen systems generate electricity onboard the flying device
  • AWES have the potential to reduce the cost of wind energy and expand the geographical range of wind power deployment
  • Key principles of AWES include aerodynamic lift, tether tension, and power generation through the periodic motion of the flying device
    • Aerodynamic lift is generated by the flying device's interaction with the wind, similar to an airplane wing or kite
    • Tether tension is maintained to transmit forces and power between the flying device and the ground station
  • AWES can operate in pumping or drag power cycles, alternating between generation and retraction phases
  • Crosswind flight patterns are employed to maximize the apparent wind speed and energy capture

System Components and Configuration

  • AWES consist of three main subsystems: the flying device, the tether, and the ground station
  • The flying device can be a rigid wing, a soft kite, or a hybrid design, each with its own advantages and challenges
    • Rigid wings offer high aerodynamic efficiency and controllability but are heavier and more complex
    • Soft kites are lightweight and easy to launch but have lower efficiency and control accuracy
  • The tether connects the flying device to the ground station and serves multiple functions:
    • Transmits mechanical forces and power between the flying device and the ground station
    • Provides electrical conductors for power transmission in fly-gen systems
    • Enables communication and control signals between the flying device and the ground station
  • The ground station includes the winch system, generator, power electronics, and control equipment
  • AWES can be deployed in various configurations, such as single-kite systems, multi-kite arrays, or stacked kite systems, to increase power output and reliability

Aerodynamics and Flight Dynamics

  • Understanding the aerodynamics and flight dynamics of AWES is crucial for their design, control, and performance optimization
  • AWES rely on the principles of aerodynamic lift and drag to generate forces and power
    • Lift is the upward force generated by the flying device's interaction with the wind, perpendicular to the wind direction
    • Drag is the force acting opposite to the flying device's motion, parallel to the wind direction
  • The lift-to-drag ratio (L/D) is a key performance metric, indicating the efficiency of the flying device in generating lift relative to the drag it experiences
  • The apparent wind speed and angle of attack are critical factors affecting the aerodynamic forces and power generation
    • Apparent wind speed is the relative wind speed experienced by the flying device, which is higher than the true wind speed due to the flying device's motion
    • Angle of attack is the angle between the flying device's chord line and the apparent wind direction, influencing lift and drag coefficients
  • Crosswind flight patterns, such as figure-eight or circular trajectories, are employed to maximize the apparent wind speed and energy capture
  • Tether dynamics, including tension, drag, and elasticity, significantly influence the flight dynamics and control of AWES
  • Aeroelastic effects, such as wing deformation and flutter, need to be considered in the design and operation of AWES

Power Generation and Transmission

  • AWES generate power through the periodic motion of the flying device, which drives a generator either on the ground or onboard
  • In ground-gen systems, power is generated by the winch system on the ground as the tether is reeled out under tension
    • The tether's mechanical power is converted into electrical power by the generator
    • During the retraction phase, the winch motor consumes a fraction of the generated power to reel the tether back in
  • In fly-gen systems, power is generated by onboard turbines or generators mounted on the flying device
    • The generated electrical power is transmitted to the ground station through conductive tethers
    • Fly-gen systems eliminate the need for mechanical power transmission and can potentially achieve higher efficiency
  • Power electronic converters, such as rectifiers and inverters, are used to condition and regulate the generated power for grid integration or energy storage
  • The power output of AWES depends on factors such as wind speed, flying device size, tether length, and system efficiency
  • Advanced power transmission techniques, such as high-voltage direct current (HVDC) or superconducting tethers, are being explored to minimize losses and enable longer tether lengths

Control Systems and Automation

  • Robust and reliable control systems are essential for the autonomous operation and optimization of AWES
  • Control objectives include maximizing power generation, ensuring flight stability, and maintaining safe operating conditions
  • Sensors, such as GPS, inertial measurement units (IMUs), and load cells, provide real-time data for feedback control
    • GPS receivers track the position and velocity of the flying device
    • IMUs measure the orientation, acceleration, and angular rates of the flying device
    • Load cells monitor the tether tension and detect anomalies
  • Control algorithms, such as proportional-integral-derivative (PID) controllers or model predictive control (MPC), are used to regulate the flying device's trajectory and power output
    • PID controllers provide simple and robust control based on error feedback
    • MPC optimizes the control actions over a future time horizon, considering system constraints and predictions
  • Supervisory control and data acquisition (SCADA) systems enable remote monitoring, control, and data logging of AWES
  • Fault detection and diagnosis (FDD) techniques are employed to identify and mitigate potential failures or anomalies in the system
  • Collision avoidance and airspace integration strategies are crucial for the safe operation of AWES in shared airspace with other aircraft

Modeling Techniques and Tools

  • Accurate modeling of AWES is essential for design, simulation, control, and optimization purposes
  • Multiphysics modeling approaches are employed to capture the complex interactions between aerodynamics, structural dynamics, and electrical systems
  • Computational fluid dynamics (CFD) simulations are used to analyze the aerodynamic performance of the flying device and tether
    • CFD models solve the Navier-Stokes equations to predict the flow field, pressure distribution, and forces acting on the system
    • Turbulence models, such as Reynolds-averaged Navier-Stokes (RANS) or large eddy simulation (LES), are used to capture the effects of turbulent flow
  • Finite element analysis (FEA) is employed to model the structural dynamics and aeroelasticity of the flying device and tether
    • FEA models discretize the structure into elements and solve the equations of motion to predict deformations, stresses, and vibrations
  • Multibody dynamics (MBD) simulations are used to model the coupled motion of the flying device, tether, and ground station
    • MBD models consider the rigid body dynamics, joint constraints, and external forces acting on the system
  • Electrical system modeling, including generator, power electronics, and grid integration, is performed using circuit simulation tools
  • Integrated simulation environments, such as MATLAB/Simulink or OpenFAST, enable the co-simulation of multiple domains and the development of control algorithms

Performance Analysis and Optimization

  • Performance analysis and optimization are critical for maximizing the energy capture, efficiency, and cost-effectiveness of AWES
  • Key performance indicators (KPIs) are used to evaluate and compare the performance of different AWES designs and configurations
    • Power output, capacity factor, and annual energy production (AEP) quantify the energy generation potential
    • Levelized cost of energy (LCOE) assesses the economic viability and competitiveness of AWES
  • Parametric studies and sensitivity analyses are conducted to identify the most influential design variables and optimize the system performance
    • Design variables such as wing size, aspect ratio, tether length, and operating altitude are systematically varied to study their impact on performance
    • Sensitivity analyses determine the robustness of the system performance to uncertainties in input parameters or operating conditions
  • Optimization techniques, such as gradient-based methods or evolutionary algorithms, are employed to find the optimal design and control parameters
    • Objective functions, such as maximizing power output or minimizing LCOE, are defined to guide the optimization process
    • Constraints, such as structural limits, safety margins, or airspace regulations, are incorporated to ensure feasible and realistic solutions
  • Techno-economic analyses are performed to assess the economic viability and potential market penetration of AWES
    • Cost models, considering capital expenditures (CAPEX) and operational expenditures (OPEX), are developed to estimate the total system costs
    • Market studies and demand forecasts are conducted to evaluate the potential adoption and competitiveness of AWES in different regions and applications

Challenges and Future Developments

  • AWES face several technical, regulatory, and social challenges that need to be addressed for their successful commercialization and widespread deployment
  • Scaling up AWES to larger sizes and higher altitudes poses engineering challenges related to materials, structures, and power transmission
    • Lightweight and durable materials, such as carbon fiber composites or advanced textiles, are being developed to enable larger and more efficient flying devices
    • Novel tether designs, such as multi-layer or tapered tethers, are being explored to optimize the trade-off between strength, drag, and power transmission capacity
  • Ensuring the reliability and robustness of AWES in various weather conditions and failure scenarios is crucial for their long-term operation and maintenance
    • Fault-tolerant control strategies and redundant systems are being developed to mitigate the impact of component failures or extreme events
    • Prognostic and health management (PHM) techniques are being applied to monitor the system health, predict potential failures, and schedule proactive maintenance
  • Airspace integration and regulatory frameworks are essential for the safe and harmonized operation of AWES in shared airspace
    • Collaborative efforts between AWES developers, aviation authorities, and other stakeholders are ongoing to establish standards, guidelines, and best practices
    • Detect and avoid (DAA) systems and protocols are being developed to ensure the safe coexistence of AWES with other aircraft and obstacles
  • Social acceptance and environmental impact assessments are important considerations for the public perception and sustainable deployment of AWES
    • Engaging with local communities, conducting public outreach, and addressing concerns related to visual impact, noise, or wildlife are crucial for gaining social acceptance
    • Life cycle assessments (LCA) and environmental impact studies are being conducted to quantify the carbon footprint, resource consumption, and end-of-life management of AWES
  • Future developments in AWES include the integration of advanced technologies, such as artificial intelligence (AI), machine learning (ML), and sensor fusion, to enhance the system performance and autonomy
    • AI and ML techniques can be applied for wind field estimation, flight path optimization, and predictive control
    • Sensor fusion algorithms can combine data from multiple sources, such as lidars, radars, or cameras, to improve the situational awareness and decision-making of AWES


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© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.