Airborne wind energy is a promising newly emerging wind energy harvesting technology. Due to low material use and high potential harvesting density it aspires to be competitor to the conventional wind turbines we see today. Kitepower bv, a company in the Netherlands, is developing a airborne wind energy system based on a flexible kite. To be able to get a share in the energy market, reliability, safety and long term operation are aspects that are still challenging. The kite is controlled by a robot, called a kite control unit(KCU), that is suspended under the wing and steers the wing inside the wind window to create a traction force. This research focuses on improving long term operation by improving the power supply of this KCU. A wind turbine attached to the KCU is used as a power supply, but the electronic power conversion has not been optimized yet. A maximum power point tracker is optimised for this system, in which a new control model is used. Here the rotational speed is taken as a controlled variable. In addition, a method to protect the battery and the electrical system is implemented when abundant energy is available. This research shows how a converter is designed and how it can be controlled to provide the demanded functionalities.

As airborne wind energy is a relatively new field, much of the current research is rapidly progressing towards the development of larger commercial systems with larger airborne components. Farms of airborne wind energy systems can provide higher power generation than a single kite system and offer a potential solution to issues that single kite systems exhibit with continuous power production. An in depth analysis of small scale kite farm systems will be conducted based on Kitepower’s single kite flight path model. This model has been further developed for improved performance, and has been verified with experimental data from the Kitepower system. From this single kite model, a kite farm simulation was developed to evaluate the effects of varied flight paths for several kite farm layout configurations, providing results for power density, power stability, and spatial requirements of the systems.

With growing energy demands and a need to switch to a sustainable source of energy key stakeholders are considering the use of high altitude wind energy systems. TU Delft and its start up company kitepower are key stakeholders investigating the commercial viability of this technology. With this goal the research group has developed several kite systems capable of accessing high altitude winds. It is believed that the low investment cost and high performance of kites could lead to a lower cost of energy. Concepts currently being considered involve a leading edge inflatable (LEI) kite that is controlled by an on-board control unit and is connected to a ground-based generator. Once the kite is deployed to the required altitude it enters a power generation stage where it is flown in a figure eight routine. This routine is controlled by the on-board control unit that pulls on tethers that are connected to the tip of the kite. This process is followed by a retraction phase where the kite is pulled back in. The goal of the system is to maximize energy production in the generation phase while limiting the energy consumed in the retraction phase. It is critical to assess and improve the kite design and its performance at all stages of operation such that the net power production can be maximized. While significant advancements have been made into the performance for normal flight there is a lack of research on the aerodynamic performance when there is control input to initiate a turn. The shape of the kite and the high angle of attack at which the kite is flown results in complex flow behavior involving separation, flow vortices, flow reattachment etc. This poses several challenges to maintain accuracy. A computational approach involving a steady-state Reynolds-averaged Navier Stoke (RANS) simulation is believed to be a computationally viable mode of analysis to capture the flow behavior. This thesis details the approach used to improve results attained using this method and understand the influence of deformations associated with control inputs on the aerodynamic performance of the kite. A control input is simulated using a finite element model (FEM) with the Abaqus software by reducing the length of the right steering and increasing the length of the left steering line by 0.5 m. This results in the right side reducing its curvature and being pulled towards the kite control unit (KCU). Whilst on the left side the bridle lines are less tensed, leading to an increase in curvature. The turning performance is governed by the offset and variations in magnitudes of forces. Meshes are generated that attempts to minimize geometry alterations whilst still maintaining high quality. The influence of boundary layer parameters are investigated. A trade-off is made where the influence of key parameters on accuracy and computational time is evaluated; where applicable improvements are made. Both the global as well as the local parameters of the kite in normal as well as turning orientation are analyzed. The results show that control induced deformations lead to a percentage reduction in the lift, whilst the effect on the drag is minimal. It is further seen that the kite initiates stall at an angle of approximately 40 degrees. The stall behavior is initiated at the mid-span of the kite and gradually moves to the tip. The turning performance is measured by looking at the yaw moment. The magnitude of this parameter is linked to the offset and magnitude in force vectors at the tip. Due to the delayed stall at the tips, it is observed that the yaw moment increases beyond 40 degrees. Accuracy issues using this method were seen when performing a validation study on a profile similar to that of the kite. These issues could be due to limitations of the method or potential errors in the reference study. It is recommended to reevaluate the validation study before using this method for detailed flow analysis. It is concluded, that in order to fully trust the relevance of the results, one would have to have to conduct a validation study. However the method’s ability to address non-linear flow effects within a limited time frame makes it a viable option for design optimization/system modelling.

Airborne wind energy (AWE) is a new generation of wind energy technology which uses tethered kites to reach the stronger and steadier high altitude wind resource. Research and development of AWE has been accelerated in the last two decades. Around 40 institutions around the world are working on their own concepts and architectures of the technology. This research has been collaborated with Ampyx Power B.V, a Dutch company involved in development of one of the concepts of AWE. No company has yet been able to prove the commercial viability of their technology. A successful market diffusion is possible when there is a perfect product market fit i.e. the technology development should be aligned with the market requirements. Economies of scale and maturing of technology is continuously reducing the cost of utility scale variable renewable energy sources (VRES) like wind and solar PV. Anticipating a subsidy free future, utility scale VRES will be dependent on the day-ahead electricity market (DAM) for their revenue generation. The electricity prices from the market are dynamic and are dependent on the supply and demand characteristics of the country. Higher influx of VRES in the grid depress the DAM prices, this effect is known as the merit-order effect of VRES. Therefore, the value of electricity depends on the time at which it is produced. This indicates to investigate if there is a need to shift from cost driven system design to value driven system design for VRES. Energy production and revenue generation of AWE at a certain time, depends on the wind speed and the energy price at that particular time. A data driven statistical model has been developed in MATLAB environment to identify and quantify the merit order effect of wind power by estimating the correlation of DAM prices and wind speeds. A decision support tool for the system design of AWE is developed by integrating the correlation model with a revenue model and the existing cost model of Ampyx Power. Correlation model results for different locations in Europe confirms that there exists a negative correlation between the DAM prices and wind speeds. Among the tested locations, the German DAM prices drop by around 1.2€/MWh, the Danish by around 0.9€/MWh, and the Dutch by around 0.6€/MWh per 1m/s increase in wind speed. Different locations in different European markets have different strengths of the correlation depending on their wind climate and their energy mix. A case study based on three different locations in Germany has been analyzed using the developed tool to understand the influence of the merit order effect on the system design of AWE. The results show that in a DAM based revenue generation scenario, value driven optimization leads to a different system configuration than cost driven optimization. It leads to systems which perform better at lower wind speeds.

The human eye has turned itself back to the sky with the commercialisation of the space industry, and a new goal has been set. Setting foot on the Red Planet is the next stage of the human exploration of the universe. The travel to Mars is very lengthy and costly, nonetheless the planet still shows great potential for sustaining human life. To make this a possibility, there is a need for locally sourced energy. The presence of (re-)usable resources on Mars could pave the way to further expand the exploration to an interplanetary scale, and successfully maintain a human presence outside the Earth's atmosphere. The availability of energy will be a key indicator for the success of the human race in the colonisation of Mars. To answer this call for the need to generate locally sourced energy, the design of a renewable energy system was started by a team of students and staff from the faculty of Aerospace Engineering at Delft University of Technology: The Arcadian Renewable Energy System (ARES). The energy system will power the construction and operations of a Mars habitat, to support the livability of humans. The system will use complementary renewable energy sources integrated into a microgrid, to sustainably harvest energy from local Martian environment and resources. To ensure the design will be able to fulfil its purpose, a mission need statement and a project objective statement are generated: Mission Need Statement: To provide renewable energy supply of 10 kW to a Mars habitat. Project Objective Statement: Design a renewable energy supply system, primarily focusing on wind energy, which provides 10kW to a Mars habitat, by 10 students in 10 weeks. Synthesis Exercise (DSE) will last a total of 10 weeks, beginning on the 20th of April, ending on the 2nd of July, with a poster session and symposium. The DSE is in collaboration with the Architectural faculty, where a separate team of students is working on a rhizomatic Mars habitat project as part of an ESA competition, which has an ESA-ESTEC feasibility study proposal incorporated. Due to the multi-disciplinary nature of this project, it is important that the DSE team produces a complete and verified design as the outcome. The Design The design the DSE has come up with consists of two energy production systems, namely the primary and secondary energy system providing wind and solar energy, respectively. In addition the system also consists of a power management and energy storage system.

Power output during flight operation of multi-megawatt airborne wind energy systems is substantially affected by the mass of the airborne subsystem, resulting in power fluctuations. In this paper, an approach to control the tether force using the airborne subsystem is presented that improves the quality of the power output. This kite tether force control concept is implemented on the 3DOF dynamic simulation of the MegAWES reference model. First, the winch of MegAWES is resized because an analysis of winch inertia and radius shows its effect on power output and tether force overshoot. Second, the power consuming sections during the traction phase are eliminated by using a feedforward winch controller. Finally, the peak power is substantially reduced by implementing the kite tether force controller which uses a measurement of the tether force, angle of attack, and airspeed to keep the tether force constant when the system is at its power limit. This reduces the range between minimum and maximum power output by 75%.

In recent years, development of a concept from the mid- 1970's has led to the emergence of Airborne Wind Energy Systems (AWES). Currently the AWES sector encompasses dozens of companies that are developing a range of concepts of, more or less automated, flying wings attached to a tether which convert wind energy to electricity. At the time of this writing however, AWE as a technology discipline is still in early stages of development; not a single company has been capable of producing a commercially ready system. This phase, where the primary goal is to commercialise technology, is described as the 'valley of death' as here the risk of failure is high. In literature this phase has gathered attention from a policy perspective, however the perspective of the entrepreneur is scarcely researched. This research will attempt to find an answer to the problems that entrepreneurs encounter in the valley of death. The valley of death is defined as: A phase that occurs during commercialisation of technology where a combination of long and costly development and a lack of resources cause an environment where the risk of failure is high for organisations to introduce the first commercial product.This definition, combined with a literature review on challenges that are likely to occur in this phase, forms the context that defines the strategies.In four expert interviews with private sector investors and experienced entrepreneurs, this context is discussed. The findings from these interviews are combined with insights from literature to identify three likely challenges: 1) technology uncertainty, which is caused by the inherent complexity of hardware development and production, which result in long and costly development. 2) market uncertainty, which is caused by difficulties in matching technology characteristics to market needs, hesitance by other stakeholders or competing against an incumbent regime and 3) lack of financial resources, which is the result of high costs during the commercialisation of hardware technology and a tendency to under invest by the private sector. In order to identify a possible way to deal with these answers findings from a separate literature review and from the four expert interviews are combined. From this, eight strategies emerge.The findings in this analysis show that activities belonging to all seven functions are found in the AWES TIS. Possible barriers are found in functions five and six. There is little to no market formation, only through technology push by the entrepreneurs. Resources are considered scarce for development and AWES technology development is costly and long. These barriers are similar to the challenges and characteristics of the valley of death. Concluding on the main research question the valley of death was redefined from the perspective of the technology developer, including multiple perspectives. It is characterised by a low availability of resources and organisations that develop hardware based technology are at risk of failing to commercialise. By identifying and testing common strategies for their applicability this research was able to provide a way to reduce the risk of failure in this phase. Start-ups that develop new technologies must prioritise commercialisation of their technology by focusing on minimum development towards specific needs in order to generate revenue. However, for hardware based innovation external resources are needed to fund development. By demonstrating the ability to find value these start-ups increase the chance to appeal to investors in the private sector and secure the necessary funding.

Airborne Wind Energy is a promising technology that is becoming the point of interest for many applications. One market in which the AWE systems can open a path as a renewable distributed generator is in offgrid communities or camps. Nowadays, this market is dominated by fossil fuel energy like diesel generators. Even though the diesel is cheap, in some cases the complexity to transport the diesel can increase its price considerably. A military camp is an example of this cases. AWE systems designed by the start-up Kitepower can offer a solution to this type of application. Nevertheless, there are some points in the AWE mechanism that should be improved. The most important of these aspects is the cyclic power production that generates a power gap. This thesis compares solutions as 2 KP systems, other distributed generators (DG) and storage systems (SS) to find the best option to mitigate the power gap. For the integration of the components with the KP system, microgrids designs and layouts were studied. This led to one of the most important things in a microgrid that is the SS sizing. Here, also a method to size the SS to fill the power gap is proposed based on the distribution of power generated by the KP system each cycle. To test the sizing and the operating of the system, a model was built in Simulink. The results show that the method finds a power balance between the power produced and the power generated. Finally, an efficient integrated system is proposed to mitigate the power gap of the KP system. Additionally, a method is developed to start the design and size additional DERs for future offgrid microgrid projects.

A method is introduced to measure the in flight flow field and geometric shape of an energy producing kite. The method is applied on beach tests during controlled flight maneuvers as well as equilibrium positions. The measurements of different sensors are validated by use of independent coherence of the found results. After this the deformations and performance as a result of altering power setting and steering inputs are analyzed and compared with current theory describing the behavior. It is concluded that the theory is correct in qualitatively describing the phenomena driving the steering behavior of the kite. It is also concluded that the proposed system can contribute to a more streamlined design process for energy producing kites.

Airborne Wind Energy (AWE) is a field of engineering that utilizes tethered aircraft for the generation of electrical power. The potential for the application of AWE in deep-water offshore environments on top of floating foundations is enormous. Where conventional wind turbines would require a very stable platform to reduce motions at the nacelle, AWE requires just enough stability to survive extreme conditions, take-off and land horizontally, and not negatively affect cross-wind performance. The requirements scale well with increasing capacity of AWE systems, which mostly influences the mooring configuration instead of the steel structure. That is why Ampyx Power started an investigative study into the floating offshore application of AWE in collaboration with Mocean Offshore, MARIN and ECN. A driving factor in the design of the floating foundations is the maximum allowed motions in different sea states. The objective of this research is to determine the relative magnitude of the effect of platform motions on the landing performance. This will result in more clearly defined design requirements for both the floating platform and the aircraft. The method used in this research can be extended to more advanced numerical models at a later stage of the design to obtain quantified motion constraints or operational limits. It is assumed that standard deviations of several parameters at the end of the landing approach serve as good indicators of successful landings. A numerical model of a tethered aircraft (RPA) making a horizontal landing in time domain is developed to determine these parameters in a multitude of wind conditions. By performing a Monte-Carlo analysis, the standard deviations of these parameters can be acquired. Especially symmetric motions (X, Z and RY) are expected to affect landing performance, which is why a 3DOF model is used. Then harmonic platform motions are included in the model in order to investigate what type of platform motions are most critical. Finally, the platform designed by Mocean Offshore is examined. By combining the motion response of this platform with metocean data at a reference location, the standard deviation of critical parameters is obtained in comparison to an onshore application. The motion response of the platform is determined using a numerical model that combines potential theory with semi-empirical drag formulations. This model is validated with basin tests at MARIN. Simulations with harmonic platform motions indicate that both frequency and amplitude of platform motions are critical for the landing performance. The landing performance appear to be mainly related to the platform motion velocities. Therefore, increasing damping and added mass of the platform will both have a positive effect on the landing of the RPA. When looking further at the results of the simulations with platform motions based on metocean data and the hydrodynamic, numerical model, it was found that the current design of the floating platform by Mocean Offshore leads to an expected decrease in landing performance compared to the onshore application. The performance decrease is not insurmountable, and multiple methods of reducing the negative effects on landing performance are presented.

Wind farm layouts in industry show a range of patterns with an overall trend from regular to irregular patterns over time. Wind farm layout optimisation studies in literature generally result in irregular wind turbine patterns. Review of existing literature shows that the performance of irregular and regular wind farm layouts has not been compared in a consistent way. Although there are indications that irregular layouts outperform regular layouts, it is yet to be determined if this is the case for the overall performance and if so, to what degree. In this research the effect of regular and irregular wind farm layouts on selected performance indicators is quantified. This quantification is performed through means of a comparative case study. The performance of both regular and irregular wind farm layouts is assessed on the basis of three performance indicator groups: (1) power performance; (2) wake-induced tower fatigue; and (3) inter-array cabling system. The performance indicators in these groups are affected by a change in wind farm layout, feasible, site independent, and technical as concluded from a multi-criteria decision analysis. The irregular wind farm layout has a higher annual energy production and a higher persistence to wind direction. The net present value of this increase in cash flow over the lifetime of the wind farm is estimated at 10 million Euros. A higher persistence to wind direction means that the power output is less sensitive to fluctuations in wind direction. This characteristic increases the predictability of the wind farm power, which can indirectly lead to a decrease in imbalance cost on the electricity market. The wake induced tower fatigue is found to be negatively impacted by an irregular wind farm layout. Implementation of the Frandsen model shows that the maximum effective turbulence of the irregular wind farm is 23.8% higher than that of the regular wind farm layout. For fatigue-driven tower design, this leads to an increase in tower wall thickness, which in turn results in an increase in tower material consumption. The increase in tower cost in the wind farm is estimated at 4 million Euros. Application of a minimum inter-turbine spacing to ameliorate the negative effect on effective turbulence is can lead to a decrease of 20 % (as compared to the case study). The inter-array cable design results show a marginal increase in cable cost of 1.15 % for the irregular wind farm. The analysis reveals that this performance indicator is strongly dependent on site-specific input data. Due to this marginal change and dependency on site specific input data, this performance indicator is omitted from further conclusions. Comparing the negative effect of the tower cost and the increase in revenue due to the higher AEP, the net present value is computed. With a discount rate of 5 %, the net present value of the AEP reduced by the increase in tower cost results in an increase of 6 million Euros. For improved performance in future wind farm layouts, the implementation of irregular wind turbine patterns is advisable. That is, with the proviso that the minimum inter-turbine spacing is taken into consideration with respect to wake-added turbulence levels.

A method to help renewables flourish is mitigating the variability that is inherent in natural resources. To do so, we explore the intricacies of the relationship between airborne wind (AWE) and solar energy to uncover the possibilities of future energy-generating hybrid power plants (HPP). Which leads to steering away from fossil fuel reliance, while increasing the dependability of renewable technologies. The resources were investigated at one primary test site, where anomalies and trends were uncovered. By tracking the solar radiation and wind speed over time, the complementarity of the two is studied. When the Pearson correlation coefficients are negative, a non-variable energy generation capacity can be found leading to less intermittency in energy stock. These results are expanded to evaluate other locations in Europe, identifying the main contributing factors of a successful hybrid set-up. The case study location was Marseille based on pre-analysis of solar and wind availability. Using resource correlation, energy output, and location data, the model developed to assess the location feasibility of HPPs found that most areas are not suited for annual generation situations, but are more successful on a quarterly basis. The HPP setup would allow the dependency on fossil fuels and storage options to decrease while having a flexible implementation option meaning it is a viable option for off-grid / remote locations and urban areas to help lighten the grid load. The model created can be further developed into an HPP site map, to help further identify areas that would benefit from more renewable options without as many drawbacks. Overall, this research leads to a method for reaching 2050 climate goals by identifying HPP potential on a variable time basis.

Wind turbine noise is one of the grand challenges in the public acceptance of onshore wind farm projects. The field of psychoacoustics identifies the auralisation of wind turbine noise as a link between technical design and annoyance estimation. There is currently limited work on the auralisation of wind turbine noise, and none targets an application in psychoacoustic research. This work investigates the auralisation of the aeroacoustics output of DTU's HAWC2 for use in annoyance estimation. A Gaussian beam tracing approach propagates the frequency domain output to observer locations. The resulting spectrograms are converted into sound signals by applying random phase and the inverse short-time Fourier transform. This work includes a binaural rendering module to enable future VR applications. The methodology's implementation results in the Wind Turbine Auralisation tool, WinTAur. The noise signal output of WinTAur is validated using the HAWC2 model of a stall-controlled NTK 500/41 wind turbine and corresponding acoustic field measurements. Psychoacoustic sound quality metrics show significant differences between the auralised and measured noise. In the overall psychoacoustic annoyance metric, these differences mainly depend on the observer's position around the turbine. All metrics show this directionality dependence, while the loudness, sharpness and tonality metrics also indicate a dependence on wind speed. Differences in fluctuation strength show a minor dependence on the simulation case but are difficult to relate to a specific simulation parameter. Spectral analysis of the simulation output samples reflects the limitations of HAWC2, demonstrating that it is the primary source of discrepancy. The analysis especially highlights the inaccurate prediction of the directionality and stall noise of the HAWC2 code. The choice of ground type is another probable source of discrepancy, as it does not accurately represent the measurement setup. A subjective listening experiment demonstrates the significance of these discrepancies in human perception with generally high difference ratings between the simulated and recorded noise. The results illustrate a dependence on wind speed and the position around the turbine. These dependencies match well with the findings from the numerical validation.\ Future work should focus on a sensitivity analysis of WinTAur since the case-independent parameters may be additional sources of discrepancy. Another recommendation is to investigate the unveiled errors in the underlying methodology. Lastly, better propagation modelling concerning the wind turbine wake and turbulence should be part of future wind turbine noise modelling. Overall, using modelled wind turbine noise for the auralisation in psychoacoustic research has shown promising results. Validation with sound quality metrics provides good insights into the discrepancies found in subjective listening experiments. Eliminating the existing discrepancies through modelling improvements will allow this work to be applied in a fully modelled approach to estimate wind turbine noise annoyance.

Airborne Wind Energy (AWE) is an emerging renewable energy technology that aims to replace the use of fossil fuels for energy production on an economical basis. A characteristic feature of the various AWE concepts is the use of tethered flying devices to access wind energy at higher altitudes where the wind is more consistent. Over the past decade the AWE scientific and industrial community has grown considerably. The largest AWE demonstrator system to date is a 600kW system; many other demonstrator systems exist in the electricity output range up to 80 kW. The 8th Airborne Wind Energy Conference (AWEC 2019) will be held on 15-16 October 2019 at the University of Strathclyde, Glasgow, United Kingdom. Previous international Airborne Wind Energy Conferences have been held in Chico, CA, USA in 2009, in Stanford, CA, USA in 2010, in Leuven, Belgium in 2011, in Hampton, VA, USA in 2012, in Berlin, Germany in 2013, in Delft, The Netherlands in 2015 and in Freiburg, Germany in 2017.@en

Airborne Wind Energy (AWE) is an emerging renewable energy technology that aims to replace the use of fossil fuels for energy production on an economical basis. A characteristic feature of the various AWE concepts is the use of tethered flying devices to access wind energy at higher altitudes where the wind is more consistent. Over the past decade the AWE scientific and industrial community has grown considerably. The largest AWE demonstrator system to date is a 600kW system; many other demonstrator systems exist in the electricity output range up to 80 kW. The 8th Airborne Wind Energy Conference (AWEC 2019) will be held on 15-16 October 2019 at the University of Strathclyde, Glasgow, United Kingdom. Previous international Airborne Wind Energy Conferences have been held in Chico, CA, USA in 2009, in Stanford, CA, USA in 2010, in Leuven, Belgium in 2011, in Hampton, VA, USA in 2012, in Berlin, Germany in 2013, in Delft, The Netherlands in 2015 and in Freiburg, Germany in 2017.@en

Airborne Wind Energy (AWE) is an emerging renewable energy technology that aims to replace the use of fossil fuels for energy production on an economical basis. A characteristic feature of the various AWE concepts is the use of tethered flying devices to access wind energy at higher altitudes where the wind is more consistent. Over the past decade the AWE scientific and industrial community has grown considerably. The largest AWE demonstrator system to date is a 600kW system; many other demonstrator systems exist in the electricity output range up to 80 kW. The 8th Airborne Wind Energy Conference (AWEC 2019) will be held on 15-16 October 2019 at the University of Strathclyde, Glasgow, United Kingdom. Previous international Airborne Wind Energy Conferences have been held in Chico, CA, USA in 2009, in Stanford, CA, USA in 2010, in Leuven, Belgium in 2011, in Hampton, VA, USA in 2012, in Berlin, Germany in 2013, in Delft, The Netherlands in 2015 and in Freiburg, Germany in 2017.@en

Airborne wind energy (AWE) is an emerging renewable energy technology that harnesses wind energy using tethered flying systems. The extra degrees of freedom allow these systems to harvest wind resources at altitudes currently unrealisable by conventional turbines. These flying devices, often resembling kites or drones, are typically divided into two classes. The first converts kinetic energy into electricity using onboard generators and transmits it to the ground via a conductive tether. The second class transfers aerodynamic forces via the tether to the ground, where the mechanical energy is converted into electrical energy using an electrical machine.As the tether’s length constrains the system, once the flying device reaches this tether length limit, some energy must be used to retract it back to its initial position. This cycle of traction and retraction is known as a pumping cycle. Therefore, AWE systems must be designed to maximise the harvesting or traction phase while minimising the retraction phase to ensure a net positive power output. From the AWE system landscape, this thesis is based on tethered aircraft-style fixed-wing systems. Typically, such systems utilise composite structures owing to their high stiffness-toweight ratios. Designing these composite structures demands special attention due to their anisotropic nature, which results in complex load-deflection couplings. Here, a multi-disciplinary simulation framework for tethered composite aircraft wings is developed. The research focuses on methods used during the iterative phases of initial (conceptual and preliminary) design that are commonly employed in a spiral system engineering approach. The proposed framework integrates computational methods for the design of the aerodynamic A, bridle B, and structural S domains. The bridle is a system of segments of tether and pulleys that distribute the tether forces into the wing structure. The aerodynamic and structural domains are divided into 2D and 1D models, which are then integrated to determine the 3D response of the wing. A nonlinear vortex-lattice method (VLM) is utilised for the aerodynamic domain. For the structural domain, an anisotropic 1D finite element (FE) model is developed that is coupled with a 2D FE sectional solver. In addition, methods are proposed that enable detailed topology optimisation. For tailless swept-wings, like those used by EnerKíte, the aero-structural-bridle interactions are crucial. The developed framework is used to investigate the impacts of different wing and bridle configurations to determine the sufficient level of fidelity required at the initial design phases. Typically, such aeroelastic phenomena are captured during detailed design stages wherein full 3D structural and aerodynamic simulations are employed. However, this mandates design knowledge typically unknown at the initial design stages. This motivates a multi-fidelity modelling approach to include these coupling effects while abstracting the composite ply level details during the design exploration. This is achieved by combining geometric discretisation approaches with lamination parameters. Thus, the framework aims to provide viable design options during the initial stages while considering aero-structural-bridle couplings.@en

The airborne wind energy (AWE) technology aims to utilise tethered wings to harvest wind energy at altitudes conventional wind turbines cannot reach. There are two distinct methods to harvest airborne wind energy: onboard and ground-based generation. The onboard generation is achieved through flying fast manoeuvres driving propellers attached to the tethered wing, while the generated electricity is conducted through the tether. On the other hand, the ground-based generation utilises the tether tension of the kite to unwind it from a drum, driving a generator. When the tether is fully extended, it is reeled in by the generator, which consumes energy. Since the traction phase is a lot longer and produces a lot more electricity than electricity needed in the reel-in phase the net energy of such a cycle is positive. SkySails Power is one of the leading companies developing a ground-based AWE generator driven by a large ram-air kite. This thesis describes the development of a methodology for simulating their wing.@en

The potential of utility-scale airborne wind energy (AWE) systems to contribute significantly to the energy transition hinges on their large-scale deployment, which depends on the cost-competitiveness and complementarity with conventional wind turbines. Central to the assessment of these metrics is understanding long-term energy production, which is influenced by the variability of wind profiles. This thesis investigates the significance of wind profile variability on annual energy production estimation for AWE systems. The study establishes the climatology of vertical wind profiles and expands flight operation models of AWE systems. By synthesising these aspects, a new energy production estimation framework is developed to incorporate variations in the wind profile shape. This framework is utilised to assess the impact of different wind profile shapes on the energy production estimation. The research underlines the need to move away from conventional wind energy calculation methods and offers a more suitable alternative for AWE systems. The framework offers a valuable tool for increasing the understanding of the viability of large-scale deployment of AWE systems.@en