Airborne wind energy (AWE) is an emerging technology that differs in operating principles from horizontal axis wind turbines (HAWTs). It uses tethered flying devices to harness higher-altitude wind resources. The primary motivation for AWE development lies in its potential to deliver similar energy output at lower costs and reduced carbon emissions compared to wind turbines of equivalent power ratings. AWE is in its early development stage, with commercial prototypes reaching power outputs of up to several hundred kilowatts. At this early stage of technology development, the AWE industry can significantly benefit from a systems-level understanding of the technology. To this end, the work reported here developed a multi-disciplinary design, analysis and optimisation (MDAO) tool for the conceptual system design of an AWE device and applied it to identify key design drivers, trade-offs and the scaling potential of a chosen AWE concept.

The MDAO tool is a framework that integrates models, including wind resources, power production, energy production and costs. As part of this research, new models were developed to enable the framework’s functionality. This study focused on the fixed-wing ground-generation (GG) concept of AWE. Still, the proposed methodology can be applied to any AWE concept depending on the availability of individual models tailored to the particular concept. In most markets, performance is measured using a metric known as the levelised cost of energy (LCoE). This metric relates the system's total costs to the energy it can produce over its lifetime. This metric is used here as the objective for system design, evaluating trade-offs and scaling analysis.

In order to decarbonize the industry, green hydrogen production will need to be increased. An option for green hydrogen production is to use electrolysers and wind energy in an offshore location. This thesis aims to improve the design of offshore wind based hydrogen production by optimizing the design with the use of Multidisciplinary Design Optimization. The question is answered with the use of a modular design including desalination, hydrogen production, hydrogen compression and transportation with a hydrogen pipeline. The main conclusion from this thesis is that the design problem included non-linearities. The complex optimization problem could be solved by using a sequential differential evolution algorithm. The resulting optimized design showed that optimizing the pressure of the electrolyser could result in lower work requirements for the compressor and desalination and increasing hydrogen production.

Wind energy is a crucial component of the ongoing energy transition. Over the past decade, technologies in this field have advanced significantly. Currently, the industry is following a trend of increasing the size of wind turbines, both onshore and offshore units. However, this trend brings about complexities in design, maintenance, and operation. Wind turbines are highly dynamic structures, and accurate prediction of dynamic loads is crucial for future design and, consequently, installation costs and lifetime expectancy. Dynamic stall is a highly dependent process influenced by various parameters such as Reynolds number and airfoil geometry. It involves significant changes in pressure in the flow field around the airfoil due to the development and shedding of vortex structures from the leading or trailing edge. Another characteristic is flow reversal from the trailing edge, leading to a delay in boundary layer attachment and the formation of significant hysteresis in lift force, pitching moment, and drag force values. Due to the constant rotation of the rotor, this process is cyclic, necessitating accurate modeling for proper assessment of fatigue damage, instability levels, and turbine noise. This study aims to compare the results of dynamic stall models for the FFA-W3-211 airfoil, with a maximum thickness of 21.1% of the chord length. Previously unavailable dynamic data for the considered airfoil is obtained through experiments in a Low-Speed Low-Turbulence Wind Tunnel located at TU Delft. Static and dynamic polars are obtained for various Reynolds numbers, amplitudes, mean angles, and oscillation frequencies. Measurements are conducted using pressure taps located on the airfoil model, and static data is validated against existing data and RFOIL results. The study considers two semi-empirical models. The first is the Beddoes-Leishman model, one of the most popular at the time of writing. Its optimization and comparison with the default version revealed that optimized shape-based coefficients are crucial for obtaining correct results. It is found that the optimized model significantly outperforms the default version in almost all cases. Additionally, it is established that the model lacks the leading edge vortex effect in modeling negative stall. The second model chosen is the first-order Snel model. Optimization of this model also led to significant improvements in the results obtained. A significant improvement in modeling both hysteresis size and reattachment area with increasing Reynolds number is identified. However, a significant drawback of the model in modeling negative stall is revealed. During uppstroke motion, the model predicts trailing edge vortex effects instead of leading edge, which negatively affects the overall model performance. Comparison of the two models identified their strengths and weaknesses. The Beddoes-Leishman model appears more stable for all cases considered, while the Snel model is sensitive to changes in Reynolds number. It is also noted that both models have difficulties in correctly determining dynamic stall onset angle of attack and the slope of the normal force coefficient. Additionally, both models tend to overpredict values in a greater number of cases. When comparing negative stall, the optimized Beddoes-Leishman model performs significantly better than the Snel model. It accurately predicts the overall form and severity of hysteresis as well as the reattachment area. The Snel model requires additional modifications for correct modeling of negative stall.

Many wind turbines experience leading-edge erosion on their blades due to rain and hail impacting at speeds of up to 100 m/s. The impact speed is driven predominantly by the blade tip-speed, which is expected to grow in future turbine generations as they become larger. Erosion can remove substantial amounts of material from the blades. Eventually, the damage can reach deep into the structural layers of the blade, where it then starts to jeopardize its structural integrity. The associated roughening of the blade is accompanied by losses in the annual energy production (AEP). These are estimated to be up to several percent, depending on the severity of the erosion damage. While some leading-edge protection systems have been developed, no satisfying solution has been found, and the mechanisms that lead to erosion have yet to be fully understood. The aim of this thesis is to enhance the understanding of the physical mechanisms that promote erosion, understand which site conditions contribute to erosion and apply the gained insight in the erosion-safe mode.

This thesis starts in Chapter 2 by analyzing the impact of erosion on the AEP loss by using reduced-order modeling and subsequently compares it with the erosion-safe mode (ESM). The ESM is an alternative operational erosion mitigation strategy that aims to mitigate erosion by reducing the tip-speed of the turbine during precipitation events. It is shown that, depending on the mean wind speed and frequency of damaging rain at the site, the erosion-safe mode can lead to a lower AEP loss in comparison to a mildly eroded blade or a blade that was fitted with a leading-edge protection solution that leads to similar flow disturbance. However, it still needs to be sufficiently understood what rain is damaging and what other site conditions might promote erosion.

A step toward resolving this knowledge gap is taken in Chapter 3 by investigating the behavior of rain droplets before impact with the blade. Contrary to prior state-of-the-art, it is shown that droplets deform and break up near an incoming wind turbine blade. This finding contradicts the current approach in erosion research of modeling rain droplets as circular. It is shown that deformation reduces the impact velocity of rain droplets with the blade. This effect depends on the diameter of the rain droplets and can be in the order of 10 m/s. Small droplets experience significantly more slowdown than larger rain droplets. This reduction highly influences the formation of erosion damage since the main driver for erosion is the impact velocity. As droplet deformation and slowdown depend on the rain droplet diameter, the described effect can be termed drop-size-dependent effect.

Chapter 4 continues the investigation of drop-size-dependent effects in leading-edge erosion. An advanced erosion damage model is built that includes several drop-size-dependent effects. It is shown that the significant drop-size-effects all suggest that the erosiveness of rain droplets increases with increasing droplet diameter. This is found to be true on a per-drop basis but also when normalizing for droplet size. Therefore, selecting an appropriate droplet diameter for experiments and numerical studies is essential since not all droplet diameters contribute equally toward forming erosion damage. Drop-size effects have substantial implications for the ESM, as increasing rain intensities shift the composition of precipitation from primarily small droplets to a composition dominated by larger ones. For an equal rain column, high-intensity precipitation events are, hence, more erosive. It is found that, for a coastal site in the Netherlands, 50 % of the erosion damage is produced by the 10 % highest-rain intensity events. Thus, in ESM operation, it is advantageous to reduce the tip-speed mainly during high-intensity precipitation events to maximize lifetime and minimize AEP loss. However, a precise relation between precipitation intensity and tip-speed that optimizes this objective is not yet known in leading-edge erosion research. A novel semi-analytical approach is devised to bridge this gap, taking into account site conditions, turbine type, and drop-size effects. With this approach, it is possible to extend the erosion lifetime of a contemporary blade by a factor of 13 for a moderate AEP loss of 1 %.

A critical component for the successful utilization of the ESM is the accurate forecasting of precipitation events minutes to hours ahead. However, the best approach for obtaining this information is still debated. For the first time, Chapter 5 benchmarks a state-of-the-art weather-radar-based probabilistic rainfall nowcast product by the Royal Netherlands Meteorological Institute (KNMI). The performance of the nowcast is assessed for various lead times for three sample sites in the Netherlands and for two distinct ESM strategies. The results show that the quality of the nowcast degrades with increasing lead times. The 5- and 15-minute lead times exhibit sufficiently good accuracy and response time for the successful utilization of the ESM. Across the sites, for a large 15 MW turbine, a lifetime extension of factor five can be achieved for an AEP loss of about 1 %.

To summarize, this thesis introduced the highly significant effect of droplet slowdown and deformation occurring in the vicinity of wind turbine blades. It investigated drop-size-dependent effects and established their significance for ESM operation. It provided new theoretical insights into the ESM and used these to devise a method for finding optimal ESM strategies that exploit drop-size effects. Finally, it benchmarked the devised strategies using a state-of-the-art (operational) nowcasting product and showed that the ESM could already be a viable erosion-mitigation strategy.

Hydrogen is emerging as a promising energy carrier that can potentially solve the challenges like long-term storage and intermittent power supply associated with a 100%-renewable economy. Moreover, hydrogen can be used in industry sectors such as steel manufacturing and aviation, which struggle with carbon abatement. To increase the supply of green hydrogen, the European Union aims to have at least 40 GW of renewable energy sources connected to electrolysis by 2030. In light of this ambition, the Dutch government recently issued an offshore wind tender that should incorporate 500 MW of offshore electrolysis capacity.

A hybrid farm with offshore electrolysis contains both a hydrogen pipeline and an electricity cable as the export connection to shore. Appropriately sizing these connections to ensure financial feasibility becomes a design challenge for wind farm developers as the technology is still maturing.

This study considers a case study of an offshore hybrid wind farm situated in the European North Sea, connected to the Dutch energy infrastructure. A Python model was developed to simulate the sales and production of hydrogen and electricity on an hourly time scale. The simulation was executed by using historical data for electricity pricing and assuming a perfect forecast from a developer’s perspective. The objective function was to determine the optimal ratio between electrolyzer and electricity cable capacity (EC ratio) to maximize the net present value (NPV) of such a project. A sensitivity analysis on various system parameters was performed, and multiple scenarios reflecting potential future circumstances were simulated.

The study revealed that both oversizing and downsizing the total export capacity was not beneficial. Instead, the optimal EC ratio followed a linear trend, where the sum of connection capacities equaled the total farm capacity. The hydrogen price, electricity price, and nominal efficiency of the electrolyzer were identified as key factors influencing the optimal EC ratio.

This research establishes optimal EC ratios for a range of hydrogen prices spanning from €3/kg to €8/kg based on different scenarios. For each scenario, different electricity prices and electrolyzer specifications were defined. The findings indicate that including an electrolyzer in the design is not economically viable for hydrogen prices below €4.00/kg. Conversely, an electrolyzer-dominated system becomes favorable in each scenario when the hydrogen price
exceeds €7.50/kg. For prices in between, optimal EC ratios resembling hybrid systems were identified depending on the other key parameters defined by the scenarios.

Operating in real-world conditions, modern large capacity wind turbines often experience off-design situations, enduring dynamic loads characterized by complex unsteady aerodynamics. Key among the challenges in predicting these dynamic loads is understanding the effects of wind shear and turbulence, both individually and in their complex interplay. This research aims to shed light on these phenomena, with an emphasis on their impacts on wind turbine fatigue loads and power production.

The research first provides an in-depth analysis of the influence of atmospheric stability on wind shear profile, aiming to extend the wind shear profile beyond the range of LiDAR measurements. Recognizing the limitations of existing power law and logarithmic law extrapolation methods, the study validates the use of multiple stability correction functions for accurate wind speed extrapolation. Subsequently, the research delves into the intricate effects of wind shear and turbulence on fatigue loads at the blade root of wind turbines, leveraging aeroelastic simulations. This research addresses the challenge of assessing wind turbine suitability for sites where one or several wind climate parameters surpass their design class values. It investigates the potential of the Response Surface Methodology (RSM) to estimate site-specific fatigue loads, a process that conventionally requires extensive aeroelastic simulations. This research also extends the scope to include the assessment of site-specific wind turbine power curves, validating the use of the Rotor Equivalent Wind Speed (REWS) and turbulence renormalization methods. Both methods show promise in estimating site-specific wind turbine power curves using a power curve measured under varying wind conditions.

In essence, this study emphasizes the significant impact of wind shear and turbulence on the performance and longevity of wind turbines. By shedding the light on potential improvements, this study hopes to contribute towards accurate power output and fatigue load assessments.

With an increased demand for renewable energy wind farms, their efficiency receives growing attention from both the industry and academics. Mitigating wake interaction effects in wind farms is one of the ways wind farms could increase their efficiency. Control techniques to increase wake reenergizing are currently under development, however, are being held back by a lack of available medium-fidelity wake modeling methods. To sufficiently support developments in the wind industry, the wake model should yield an axial wind profile that can be used for load calculations for the downstream wind turbine and assess its energy production. Moreover, for the model to be useful in the research effort the method must either show an increase in accuracy or a decrease in time-cost. Finally, the model is desired to include the effects of wake control techniques in later iterations outside the scope of this research. This thesis investigates medium-fidelity models for wind turbine wake control techniques, with an exploratory study into applying a semi-infinite spectral method with an adjusted Laguerre basis to wind turbine wake modeling. The wake model used in this research is an altered version of the Ainslie wake model. To model the wake model a spectral method with Laguerre functions for the basis is employed in the radial direction and a marching scheme with a piecewise linear basis for the basis in the downstream direction. The potential benefits of spectral methods are lower rank systems and spectral convergence. The adjusted Laguerre functions used for this research naturally fit the boundary conditions for the wake model. At the start of the domain, a Dirichlet boundary condition is applied with fitted Laguerre functions to the result of a blade element simulation. The results did not account for wake expansion and diffused the wake much sooner than physical. The implementation of the explicit formulation for the triple product integral hindered higher-order simulations, disabling research into simulations for domains much higher than 11 radial modes. The errors for the different conservated quantities are significantly higher than they should be. From the verification efforts, a relation can be observed between the number of radial modes in the domain with respect to the number of radial modes used for the inflow, which suggests that the model should use much higher numbers of radial modes than this implementation allowed. i

The energy transition towards carbon neutrality requires a rapid electrification of all energy sectors by 2050. In the EU-27, the REPowerEU strategy, initiated in March 2022, is pursuing this target even more ambitiously. However, in order to achieve the aforementioned goals, the increasing demand for green hydrogen will cause an increase of the renewable energy needs as early as 2030. In this way, offshore wind can be a solid supplier of the renewable energy for green hydrogen production. However, since nearly 80% of the worldwide wind energy potential is situated in deep waters, floating offshore wind turbines (FOWT) can be used to cover those energy needs. In addition, the literature review showed that when green hydrogen production via FOWT is considered, the most economically and energy efficient layout is the in situ topology, where hydrogen is locally produced on the FOWT. Although FOWT and green hydrogen production via FOWT have been lately examined in literature, a literature gap was found. More specifically, no attention was given on the performance change of a turbine when it is adapted from a bottom fixed (BF) application to a FOWT. Also, the effect of the in situ hydrogen plant to the FOWT performance was not considered. Thus, the aim of this project is to highlight if FOWT for in situ hydrogen production should be aerodynamically redesigned to improve their performance or to tackle possible energy losses. In this direction, several sub-questions should be answered, including the selection of turbine, floater type and site to be investigated, the effect of the floater design on the FOWT performance, the performance change of a turbine due to its adaptation as FOWT and the effect of the added mass of the hydrogen plant on the FOWT performance. Lastly, in case of a proven FOWT performance deterioration, solutions should be provided so as to regain performance.  Aligned with the previous goals, the IEA 15MW reference wind turbine on top on the UMaine Volturn US-S semi-submersible floater is simulated in OpenFAST under steady and turbulent wind fields, according to wind & wave conditions of a typical US East Coast site. In addition, the in situ hydrogen plant is incorporated in the model using a simplified approach. The results suggest that in the whole partial load region, the FOWT experiences power losses due to the static floater pitch angle, which reduces the inflow wind speed seen by the rotor. However, between 9 and 12 m/s, a peak shaving routine is incorporated in the FOWT controller, which results in early power shedding and contributes, together with the static floater pitch, to considerable power losses. Furthermore, the simulations conducted using the OpenFAST FOWT model, which incorporated the hydrogen plant, suggest that it has a negligible effect on the FOWT performance and can be omitted from the model.  Finally, the comparison of the FOWT and of the BF turbine under turbulence, highlights the fact that the FOWT exhibits a spanwise aerodynamic torque reduction and a spanwise airfoil aerodynamic inefficiency in terms of angle of attack, that can be solved via an aerodynamic redesign. As a result, a variety of blade twist angle and airfoil chord length profiles are developed, tested and evaluated using the FOWT annual energy production (AEP) as an indicator. The results point out that all solutions result in a slight FOWT AEP gain, compared to the original FOWT design, at the expense of increased rotor loading, which effectively increases the static floater pitch. Thus, the aerodynamic redesign approach requires a more cautious approach.

The objective of the thesis was to evaluate the cost reductions and tower design when production costs are included in the design process of an offshore wind turbine tower. First, a tower cost model had to be developed. Then, based on the findings, a cost optimization model was built with the tower design software from Siemens Gamesa Renewable Energy (SGRE). Three scenarios were developed
to mimic different supply chains. The results show that the production costs can be reduced by [0.2, 2%]. Moreover, in each scenario, a different optimum tower design was found. Another study into the optimum number of shells per section showed wind turbine manufacturers could reduce production costs up to 20%.

Renewable energy sources have become a cost-competitive and green option for supplying power to the grid in recent years. Nonetheless, their variable nature poses a problem to the regular operation of the electrical grid by introducing severe fluctuations of large magnitudes and/or short-duration known as ramps. There is a lack of research in the literature on characterizing ramp events induced by wind-based hybrid power plants. The main research question of this study is how to characterize the ramping behaviour of wind-based hybrid power plants and what impact they have on the system. The application of the different methods to detect and assess the implications of ramps were presented in this thesis using wind and solar power based on the reference location.

Due to dependence on threshold values that vary across the literature and the limitations associated with calculating thresholds as a percentage of installed capacity, it was demonstrated that binary ramp definitions are not ideal and result in under-reporting. On the other hand, the wavelet approach extracts ramp events from the generation using statistically determined threshold values. As a result, the problem of under-detection of ramp events is mitigated. The proposed approach of "significant ramps" allows the evaluation of which ramp events are important and which are far less disruptive and may be ignored.

It was demonstrated that anti-correlation between wind and solar resources alone is not adequate to promise a smoother output as it does not provide sufficient information about ramp events. Anti-correlations at shorter time resolutions, such as 15 minutes or an hour, could be preferable. While seasonal anti-correlation may benefit national system adequacy, it does not benefit daily ramping events.

The optimal wind-PV capacity size for decreasing the total number of ramps was such that wind turbines filled the grid capacity, as solar power would result in extra ramps. It was observed that solar over-planting leads to a significantly increased number of ramp events, whereas wind over-planting results in a minimal change in ramp events. A penalty price was proposed to internalize the severity of ramp events, which could influence the choice between wind and solar over-planting. A solution was presented to mitigate ramp incidents in a hybrid power plant using a battery which was found to be more effective and/or more economical in minimizing ramps compared to over-planting.

The proposed "significant wavelet ramp approach" is shown to be a useful metric for characterizing wind-based hybrid power plant ramp occurrences. For a future in which variable renewable energy sources account for a substantial portion of the energy mix, it is proposed that demand information be considered when defining ramp events. More attention must be paid to power ramp occurrences, either by penalizing ramps or enforcing tougher grid codes. The ramp events must be considered at the sizing and development stage, with the possibility of including a ramp-mitigating battery strategy. A thorough examination of ramp events in hybrid power plants demonstrates the importance of minimizing and managing ramp events for both the system operator and the producer.

The idea behind Power-to-Gas (P2G) is to help provide flexibility to renewable energy sources such as wind farms with intermittent nature. Additionally, hydrogen shows a great potential to help decarbonize several industries and its demand is expected to rise massively. Several studies for the technical and economic feasibility of P2G show possibilities of positive business cases far offshore. Platforms, owing to their minimal construction time and lower environmental impact provide an interesting choice of hub structure to equip electrolyser systems. However, gaps exist in the understanding of the costs of such a P2G offshore platform, driving factors, equipment involved, capacity limit and the feasible substructures to support such a facility. The main goal of this thesis is to increase the knowledge of system integration of offshore wind and electrolysers, estimate the scale and size of such a platform involving stacks, balance of plant, power electronics, auxiliary systems and the substructure supporting the topsides. In line with this goal, the study details the system design and parameters, estimates costs of each of the components involved and finally builds a cost model to understand the driving factors for an economical design of such a facility offshore.

In the current world, fossil fuels and non-renewable energy sources are being phased out and renewable energies are taking their place. Electrical energy from these renewable energies are more difficult to store than fossil fuels. Transportation and feedstock for industries can also not always be supplied through electricity. Here, hydrogen has the potential to be a good alternative, clean energy source. However, hydrogen is currently either not produced in a renewable manner (grey hydrogen), or renewable but too expensive (green hydrogen). Grey hydrogen is less expensive at a cost of around 1.50 €/kg, while green hydrogen has a cost of 2.50 - 5.00 €/kg. A new method to produce green hydrogen at a lower cost is the hydrogen turbine developed by HYGRO. This method uses an integrated electrolyser system in an existing wind turbine to produce green hydrogen and has the potential to drop the cost of green hydrogen to a more competitive level. Since this new method changes design questions of the wind turbine, a potential increase in specific power, along with a decrease in cost of hydrogen (expressed in levelised cost of hydrogen, or LCoH) is expected. In order to research these effects, this thesis investigated the effects of an increased specific power on the cost of the components of the turbine and its design, as well as the amount of hydrogen it was able to produce. This investigation was done through a model along with a case study to determine the results for a specific case. The increase in specific power was achieved by increasing the power rating of the turbine, but maintaining a constant rotor radius and maximal rotor speed. The case study performed investigates the effects based on a 15 MW reference turbine, which has a specific power of 331 W/m2. Its power rating was increased from 15 MW up to 35 MW and the resulting costs and production amount were compared to determine an optimal point were the resulting LCoH would be lowest. The result of the case study suggests that if the 15 MW reference turbine was converted to a hydrogen turbine, the optimal power rating would be in the range of 25-30 MW, where an LCoH of around 1.69 €/kg was achieved. These power ratings are equal to a specific power range of 553 - 663 W/m2 or 66 - 100 % higher than the reference. Through an error analysis, the results were validated and determined to have a reasonable degree of certainty. The main component of the model that could be improved upon to increase its robustness is the wake loss model, which was not precisely modelled but does have a significant effect on the results.
The increase in specific power suggests that hydrogen turbines have the potential to perform at higher power ratings than the wind turbine it is based on. This would allow the green hydrogen cost to drop significantly, down to a value were it is nearly competitive with grey hydrogen.

The largescale installation of wind energy will provide challenges, such as maintaining a stable grid, security of supply, and profitability of renewables. The unpredictable nature of wind energy will cause more imbalances between generation and consumption to occur, consequently increasing the demand for the balancing energy reserves that ensure the grid’s stability. The intermittent nature of wind energy necessitates the ability to time shift energy production from high to low periods of wind energy availability to retain the security of supply. Furthermore, generators can face imbalance costs due to errors in wind energy generation forecasts. They are already being confronted with the declining value of wind energy in energy systems with a high share of renewables. Storage capacity is widely perceived as a technologically possible solution to alleviate these issues. Additionally, storage capacity can be a carbon neutral alternative to the traditional power plants that currently provide the required flexible generation and balancing energy. However, the lack of economic benefits is the missing link between the technical benefits and mass implementation of storage capacity.

This study explores whether operating storage, collocated with a utility scale wind power plant, can solve these challenges while improving the bottom line for operators. Spot market arbitrage, providing balancing energy through the automatic frequency restoration reserve, and generator imbalance cost reduction are identified as possible strategies for operating storage that can add value whilst also alleviating the identified issues. Furthermore, this study explores if arguments for co locating storage with wind energy to form hybrid wind and storage power plants exist or if the business case for operating storage is independent of being collocated.

It was found that an 8-hour battery performs best when undertaking spot market arbitrage. Still, even with a perfect market forecast and no storage degradation costs, it will need at least a 65% decrease from current Li-ion storage costs to become profitable. The 8-hour battery outperforms the higher power batteries because the low volatility of the spot market doesn’t warrant the higher costs of 1 and 4-hour batteries. Additionally, it was found that providing non-contracted balancing energy to the grid with a 1-hour battery provides a potential 5-fold increase in profitability compared to having no co-located storage. However, the sensitivity analysis to storage degradation costs ultimately makes the case less profitable compared to having no co-located storage. The lower sensitivity to degradation costs of the 8-hour battery cause it to outperform the 1 and 4-hour batteries. Providing contracted balancing energy showed less potential than non-contracted balancing energy before the sensitivity analysis. However, the contracted balancing energy scenario is less sensitive to storage degradation costs. It was found that a 4-hour battery providing contracted balancing energy performed best. However, this strategy was ultimately 20% less profitable compared to not operating co-located storage. Furthermore, the results of the proposed strategies turned out to be independent of the storage being co-located. Therefore, no strong arguments for collocating storage could be made here.

The business case for storage, as put forth in this project, might not exist today. However, strong clues exist that it will in the future. The predicted drop in costs of storage and the increased volatility in electricity markets will provide opportunities for the profitable operation of storage systems. When that time comes WPP operators should also be interested to operate these storage systems to further their goal of competing with traditional fossil-fuel-fired power plants.

The rapid growth in world population and increasing demands have led to the lack of fresh water, taking a toll on several of earths reserves, mainly the fresh water supply reserves. Water stress deters economic growth, leads to conflicts and has a direct impact on the health of humans. Studies show the trends in the
increase of water consumption per capita due to increase in higher standards of living over the last years, resulting in the decrease of usable high purity water. 97% of the world’s water supply is locked in the salted, often unusable oceans. In recent times, water stressed countries are using the saline water from the oceans and desalinating it to produce fresh water for domestic, industrial or agricultural use. The state-of-the art method for desalinating saltwater is by Reverse Osmosis (RO). The biggest drawback of this technology is its high energy consumption mostly provided by conventional sources like fossil fuels. Therefore, for a sustainable future, a renewable energy source must be integrated to power the RO system.
Delft Offshore Turbine (DOT) is currently developing and testing a new hydraulic drive train solution for fluid power transmission in offshore wind turbines using seawater as the medium. A hydraulic positive displacement pump is driven by the DOT wind turbine creating a flow of sea water under high pressure. This high-pressure flow can be either directed to a RO unit to desalinate seawater or converted into electricity using a spear valve and pelton turbine generator. A major challenge while using wind as an energy source is its intermittency. Reverse osmosis plants are designed to operate at a fixed flow and pressure while due to the uncontrolled, varying nature of the wind, the pump output experiences fluctuations in both pressures and flows.
The aim of this thesis is to analyze the steady-state behavior of the integrated system for wind speeds up to the turbine rated wind speed under different operating conditions. This is achieved by simulating the behavior of the DOT500 hydraulic drive train wind turbine coupled to a RO system with pressure exchanger energy recovery device and a nozzle with a pelton turbine generator. The main objective of this research is to build a numerical model in Python using algorithms to solve the system of steady-state equations and optimize the integrated system for maximum water and maximum electricity production at specified locations.
The numerical model is simulated for all combinations of wind speeds and nozzle positions and the behavior of the high-pressure pump, RO system, pelton turbine and various system parameters are shown. A sensitivity study is performed for important desalination parameters and their effect on system performance is analyzed.
This research has yielded three main conclusions / deliverables:
1. Behavior of the wind powered integrated system to produce freshwater and electricity at different operating conditions.
2. Steady state control of DOT500 turbine and behavior of the pelton turbine to produce either maximum electricity or maximum water.
3. Sensitivity of important desalination system parameters on overall system behavior for future optimization of RO membranes.

The global issue on global warming leads nations to reduce their carbon emission, and one way to do it is by decarbonising the power system and employing higher penetration of renewable energy technology. However, due to the variable nature of renewable energy, their integration to the power system poses challenges to the utilities and system operators. Hybrid power system, due to its feature of complementary generations, serves as one of the option to answer the integration issues. This research studies the optimisation of a hybrid power system, consisting of a wind turbine and solar PV, by designing the wind turbine that operates in such systems. The design approach of the wind turbine design emphasises the complementary generation feature of the hybrid power system, which is conducted by optimising the wind generation for times when the output power from the solar PV are low. Thus, the wind turbine design considers the diurnal and seasonal variation. The diurnal turbine design is optimised for the night-time, and the seasonal turbine design is optimised for the low solar irradiance season. The wind turbine design is focused on the conceptual design phase with the objective of rotor diameter optimisation that generates electricity with the lowest cost. The cost function employed is taken from the NREL mass and cost model with additional adjustment, due to the different scaling approach. The data for the design process is obtained from a case study to represent real generation data, and the chosen location is Muppandal, India. The research aims to identify the impact of the specific operational conditions on the design parameters and the design result. Subsequently, the impact on the system performance is observed by modelling the hybrid power system in different topologies that include zero-curtailment, grid-constrained and demand load-supplying topology. The result on the site condition indicates that the affected important design parameters include wind speed distribution, wind shear profile and turbulence intensity. The research limits the analysis only on the wind speed distribution and the wind shear profile. The site condition analysis of the case study indicates that the diurnal variation of the wind speed distribution is similar to the full-year wind speed distribution and the seasonal variation that consider the season with low solar irradiance coincide with the low wind speed season. In zero-curtailment topology, higher wind speed distribution leads to smaller optimum rotor diameter and vice versa. In the grid-constrained and demand load supplying topology, larger rotor diameter suffers from curtailment due to the limited grid capacity and low demand load level. This condition leads to the shifts of optimum rotor diameter to the smaller rotor. The level of curtailment is higher in the demand load-supplying topology due to the overall lower evacuation capacity. When the night-time design and low-wind speed period design is fully operated in a year, the wind turbines are not operating at its optimum, and higher cost of electricity is expected. This result implies the higher cost for designs that correspond to the diurnal and seasonal variation. The storage system is applied to save the curtailment of wind energy. The result of this analysis suggests that the relationship between the amount of saved curtailment and the capacity of the storage is linear for higher storage capacity (<10%) and non-linear at lower storage capacity. It is found that the first few additions of storage yield the most cost-efficient of curtailment saving. The cost and benefit analysis of the storage system also indicates that the current cost of the storage technology is not compensated by the benefit of evacuating the curtailment.

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.