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Interest in small-scale wind turbines as energy sources in the built environment has increased due to the desire of consumers in urban areas to reduce their carbon footprint. Vertical axis wind turbines (VAWTs) have shown to be potentially well suited within the urban landscape. However, there is a large gap in the fundamental understanding of VAWT operation in turbulent, unsteady wind that is typical of the built environment. This dissertation investigates the aerodynamics and performance of VAWTs in fluctuating wind through experiments and numerical simulations. All experimental investigations utilise a low-speed open section wind tunnel. The use of a shutter mechanism that generates unsteady wind in the wind tunnel is detailed. Performance measurements for turbine power use a validated method previously developed in the same laboratory with slight modification for unsteady wind performance. Both steady and unsteady power performance tests results are presented. Near–blade flow physics during steady wind operation is scrutinised using Particle Image Velocimetry (PIV). Complementing the findings in experiments, numerical simulations using Unsteady Reynolds Averaged Navier–Stokes Computational Fluid Dynamics (URANS CFD) are employed. The numerical model is validated using experimental data. Blade force measurements that are not available from experiments are extracted from the numerical models to provide additional insight for performance analysis. A survey of varying unsteady wind parameters is conducted to examine the effects of various unsteady wind conditions on the performance of the VAWT. The aerodynamics is inspected through vorticity visualisations alongside blade force metrics to link performance to blade stall. Results show marginal improvement on VAWT performance (CP) with small wind speed fluctuations versus steady wind CP. Operating the VAWT at tip speed ratios (λ) higher than steady wind peak CP λ also improve performance. Conditions other than the stated above reduce VAWT CP.

In Chapters 2 and 3 of the thesis we propose a self-scheduled control method for a doublyfed induction generator driven by a wind turbine (DFIGWT), whose rotor is connected to the power grid via two back-to-back PWM power converters. We design a controller for this system using the linear matrix inequality based approach to linear parameter varying (LPV) systems, which takes into account the nonlinear dynamics of the system. We propose a two-loop hierarchical control structure. The inner-loop current controller, which considers the synchronous speed and the generator rotor speed as a parameter vector, achieves robust tracking of the rotor current reference signals. The outer-loop electrical torque controller aims for wind energy capture maximization, grid frequency support and generates the reference rotor current. We perform a controller reduction for the inner-loop LPV controller, which is not doable by conventional model-reduction techniques, because the controller is parameter-dependent. In simulation, the reduced order controller has been tested on a nonlinear 4th order DFIG model with a two-mass model for the drive-train. Stability and high performances have been achieved over the entire operating range of the DFIGWT. More importantly, simulation results have demonstrated the capability and contribution of the proposed two-loop control systems to grid frequency support. In Chapter 4 we investigate the integral input-to-state stability (iISS) property for passive nonlinear systems. We show that under mild assumptions, a passive nonlinear system which is globally asymptotically stable is also iISS. Moreover, the integral term from the definition of the iISS property has a very simple form (like an L1 norm). These theoretical results will be useful for our stability analysis of wind turbine systems in Chapter 5. In Chapter 5 we investigate the stability of a variable-speed wind turbine operating under low to medium wind speed. The turbine is controlled to capture as much wind energy as possible. We concentrate on the mechanical level of the turbine system, more precisely on the drive-train with the standard quadratic generator torque controller. We consider both the one-mass and the two-mass models for the drive-train, with the inputs being the deviation of the active torque from an arbitrary positive nominal value and the tracking error of the generator torque. We show that the turbine system is input-to-state stable for the one-mass model and iISS for the two-mass model. Using our abstract results from Chapter 4, we identify the iISS gain of this system. We also propose an adaptive search algorithm for the optimal gain of the quadratic torque controller.

In recent years the energy sector has looked to renewables as a means to reduce emissions. Wind power is able to provide large amounts of energy at a reasonable cost from presently available products. Thus the amount of wind generation has risen steeply in recent years, notably in the countries of northern Europe. However, this rise in wind power has lead to issues regarding the variability of the wind power output. Wind power is related to the wind speed, which varies greatly. This variability can cause issues with wind operators' ability to participate in electricity markets and can also lead to a rise in balancing costs. The system proposed in this thesis aims to reduce the variation of wind farm output seen in the minute to minute time-scale and provide controllability in longer time-scales. To do this the system uses short-term wind speed predictions and the inertial energy storage of the wind turbines themselves and does so in a co-ordinated fashion across the whole farm. Using short term wind speed predictions, the amount of energy in the wind is calculated for the next short period. This energy can be exported in a controlled manner using the inertial energy to cover short-term wind energy shortfall or excess. The rotor speed must vary for the storage effect to be achieved and this requires extra control systems to prevent over-speed or turbine stalling. The system was tested and found to be effective at smoothing the output power in a range of different wind scenarios. Tests were performed to assess the effects of using co-ordinated control on the frequency of an example grid and on the use patterns of portfolio generators. Both tests show that the use of a co-ordination controller at wind farm level reduces the balancing burden on the remainder of the system in comparison with the common maximum power form of control.

In terms of future power generation in UK and Germany, offshore wind is the next big player with 40GW and 32GW capacity planned for installation in both countries respectively by 2030. The latest Round 3 of sites owned by the Crown Estate explore deeper water depths of up to 78m in the Irish Sea. Foundations for offshore wind structures consume around 25% of the total project cost therefore the design of support structures is the subject of this thesis. The current state-of-the-art support structure options available for offshore wind turbines have been outlined in this thesis with an evaluation of the preliminary design of monopile and jacket solutions. This assessment resulted in further studies into the loading acting on a monopile foundation along with research into the fatigue design of multiplanar tubular joints for jacket structures. Mathematical modelling of linear and nonlinear waves combined with the Morison equation was completed to check the effects of breaking waves on a monopile foundation. Results indicated that measured forces were up to a factor of 2.5 times greater than calculated values, which suggests that loads could be under predicted if the effects of breaking are not considered. The theoretical maximum wave height before breaking was then linked to wind speed and a comparison of overturning moments from the two loads was made. Wave loads dominated at water depths of around 30m for lower wind speeds but this depth decreased to around 12m as wind speeds approached cut-out of 25m/s. For deeper water depths and larger capacity turbines, jackets are the preferred design solution. Joint design in FLS is the critical aspect of jacket design with castings often required to provide adequate capacity. A review of stress concentration factors (SCF) for tubular joints indicated that the coded approach, which uses SCF equations for uniplanar joints, could be missing the multiplanar effects. Finite element (FE) modelling of multiplanar tubular joints was completed using ANSYS Workbench to examine the effects of loading in out-of plane braces. Carry-over of stress from the loaded brace of the joint to unloaded neighbouring braces was observed which implies the importance of modelling joints as multiplanar geometries. A parameter study in ANSYS Workbench covering 1806 different geometrical configurations and loads was carried out with a regression of the data to give new sets of SCF equations for multiplanar tubular joints. SCFs from these equations were improved compared to Efthymiou but difficulties were encountered when superimposing the output (including Efthymiou). Further work on the superposition of individual load cases was therefore recommended for future work.

The UK has committed to sourcing 15% of its energy from renewable sources by 2020 and wind turbines have the potential to contribute towards this target. Due to the Feed-In-Tariffs introduced by the UK Government in 2010, the potential uptake of micro-generation methods such as small wind is likely to increase. However, many barriers exist which prevent widespread implementation, such as noise concerns. There is little work available in the open literature quantifying the problem because much of the existing research focuses on large scale turbines. The need for an increase in interdisciplinary research in this area has also been called for. This research fills the gap in the literature by seeking to better understand the noise levels generated by small wind systems, the characteristics of the noise and people’s reactions to this noise. The research is interdisciplinary, incorporating engineering, to measure, characterise and model the noise from small wind systems and psychology, to identify the type of people who are most likely to perceive the noise. Environmental noise measurements have been taken at small wind system installations to quantify and characterise the noise levels. This work included an assessment of the attenuation of the noise. Studies have been carried out on individuals living close to small wind system installations, as well as individuals being played recordings of wind turbine noise to investigate the level and type of noise they perceive and to link this to an individual’s attitude towards wind turbines, personality traits and symptom reporting. CFD has been used to model the flow fields around 2D blade sections to identify the likely noise mechanisms associated with small wind systems by observing the turbulent regions near the aerofoil wall. Finally, a comparison of the three methods has been carried out to identify that the overall level of small wind system noise is low but it is the nature of the sounds that increase the likely perception of the noise.

This thesis investigates the potential of using wind turbine to offset electricity demand for dwellings or public building. This work involves onshore small and large wind turbine implementation considering the suitability of the location to machine size, starting with wind resource assessment of a candidate site depending on reliable wind data. The present research can be divided into three main parts: modelling and monitoring of small wind turbine performance in built environment using detailed data which was measured on site, measuring longterm hourly data for the design of wind energy systems, and then comparing that annual energy output against four-second and minute by minute data. The third 'part presents a novel statistical tool developed to evaluate relative performance and overall accuracy of wind speed frequency distribution functions. An exploration of the potential for using hourly- as opposed to minute-by-minute data for the utilization of large wind turbines was undertaken as the former set is much more widely available for a larger number of locations within the developing world. It was found that the difference between the annual energy outputs from the latter two data sets was in close agreement with only small differences. The results thus obtained can have significant effect. on the capital cost related to purchase of data, since minute by minute data may be up to 60 times more expensive than hourly data. Actual power curve was experimentally obtained for Zephyr Dolphin micro wind turbine, which was then compared to manufacturer's reported performance; this was done by using four-second data for two complete years. Significant differences were found between the two curves. On-site measured performance of mentioned wind turbine was found to be similar for other reported urban locations. In each case the measured output was only a sixth of the acclaimed output of 2 MWh/annum.Urban wind energy potential for Merchiston site in Edinburgh was investigated. The results are presented in the form of average wind speed, wind roses, and density distribution functions. The effect of sampling interval on wind energy production was also analysed. Finally local spatial variations of wind speed were also studied for the City of Edinburgh.

Fossil fuel will eventually become exhausted. Also, fossil fuels produce large amounts of carbon dioxide, which cannot only bring environment pollution, but can also cause global warming. Therefore, clean and renewable energy sources should be investigated. In this project, renewable wind power was considered. Wind energy is free, clean and available in large quantities, although it is difficult to use due to its stochastic variability. Energy storage can reduce this variability allowing energy production to match energy demand. In this study, different kinds of energy storage approaches were introduced, compared, and simulated by using half hourly wind data from the Met Office, UK, and half hourly load data from the University of Bath, UK. Hydrogen has higher mass energy density than all other energy storage methods. It is seen as a versatile energy carrier of the future, complementary to electricity and with the potential to replace fossil fuels due to its zero carbon emissions and abundance in nature. On the other hand, because hydrogen is the lightest element under normal conditions; the same amount of hydrogen must occupy a huge volume compared to other elements. The mature technology for converting hydrogen into electricity has high cost and low efficiency. These are big issues that limit the usage of hydrogen energy storage methods. Using wind and load data, a new algorithm was developed and used for sizing the wind turbine, and energy storage requirements. The traditional way to supply energy is distributing electricity, but in this PhD research, there are some discussions about a new method, hydrogen transport-hydrogen pipeline. From the results of the comparison and algorithm, a practical hydrogen energy storage system for the University of Bath network was proposed and designed. In the proposed design the energy from a wind turbine was directed to the load and the remaining excess power was used to produce hydrogen by water electrolysis. The hydrogen was stored in a high pressure compressed tank, and finally a hydrogen fuelled combined cycle gas turbine was used to convert the hydrogen to electricity. In this thesis, the dynamics of the complete hydrogen cycle energy storage and recovery mechanism are discussed, identifying potential applications such as power smoothing, peak lopping and extending power system controller ranges. The results of calculations of the payback time and revenue verify the feasibility of the designed hydrogen energy storage system. The main objective of the PhD was to design a practical hydrogen energy storage system for micro-grid applications. During this research, hydrogen energy storage was investigated to show that it does solve the problems arising from renewable energy.

The work presented here is a research thesis of the Ph. D programme in The School of Computing, Science & Engineering at The University of Salford UK. The work presents the evaluation of using explicit finite element techniques for structural non-linear dynamic analysis of a floating offshore wind turbine used for harnessing wind kinetic energy and converting it to electricity. The LS-DYNA3D explicit finite element analysis programme is used in performing the evaluation of the analysis and in creating a full scale model typical to the one evaluated. The developed model (case study) is a 1.4MW power rated floating 3 blades turbine elevated at 46.5 m above main sea level a top a tripod lattice steel tower firmly resting on a moored floating concrete hull buoy, positioned on a concrete circular disk. The mooring cables supporting the floating units in the multi unit farm are designed to share seabed anchoring piles for economic reasons. The model is intended for use in moderately deep waters of up to 500m. The State-of-the-art report is presented concerning wind energy technology, floating offshore wind structures and important features of the LS-DYNA3D code. The theoretical basics for service loads experienced by the floating wind turbine are explored and the loads are quantified. The Verification and validation work on developed small models is presented to ensure confidence in the developed full scale model and the evaluation of the finite element techniques which may be applied to such structures. Development of full scale model, material properties, loads and boundary conditions are presented. Recommendations both for this model and future development are accordingly made.