In modem electrical power systems there is trend towards an increase of renewable generation being present on the main electrical grid and energy transmission is generally operated under a deregulated environment where electricity is bought and sold in a market. This thesis investigates the effects of renewable generation intermittency and electricity market operations on optimal placement of FACTS devices. Two techniques based on the MC simulation associated with an evolutionary optimization technique are proposed for determination of the optimal placement of the FACTS device considering uncertainty of demand and renewable generation output. These techniques can be useful to support practical industrial and research activities on FACTS planning for future networks where there is a significant presence of intermittent renewables as there is no sufficient planning with respect to FACTS deployment in its current form. These methods, established in this thesis, collectively are called Renewable Uncertainty based optimal FACTS Allocation (RUF A) techniques. This is a key outcome of the research reported in this thesis. This thesis considers the operation under Power Exchange (PX) and a simplified mixed power pool with bilateral transactions as they are commonly used models and as such they provide good domain coverage in terms of their applicability. Under the PX only model, the influence of changes in price elasticity of demand on the optimal F ACTS allocation is determined. It is found that there is no strong influence on the optimal placement and only a little influence on the operational rate.

This thesis presents several aspects of the control and operation of a DC micro grid with variable generation and energy storage. These aspects mainly concern the dynamic performance improvement of energy storage interface converters, a standardized autonomous control strategy for a DC microgrid, and its stability and dynamics assessment method. Several predictive average current control schemes are proposed for a bi-directional DC- DC converter which is used to interface the energy storage device to the DC microgrid. By properly arranging the sampling and duty cycle updating points, optimal control laws are derived for enhanced dynamic performance. Robustness and static error correction are also analyzed. An autonomous 3-level hierarchical control strategy is proposed for DC microgrids with selective slack terminal(s) assigned to each operation level. The system operational status is acknowledged via the common DC voltage and the transitions between different operational levels are triggered by its variation. A 4-terminal DC micro grid system is established and specific control scheme is outlined to demonstrate the proposed strategy during various operating conditions. During grid-connected condition, a voltage droop based power sharing and coordination strategy among the slack terminals is proposed for power smoothing. A simulation study is carried out to preliminarily verify the effectiveness of the proposed control strategy. A stability and dynamic assessment method is proposed for converter interfaced DC networks. Based on the virtual impedance modelling method, a case study concerning DC voltage variation suppression in a multi-terminal DC network is performed using root locus and open-loop margin analysis. The accuracy of the modeling method and its effectiveness for assessing system stability and dynamic performance is validated using circuit simulation in time domain. A prototype DC micro grid is also established to validate the effectiveness of the control proposals and analytical method.

Global economic and social development has lead to the growth in demand for electrical power. The amount of greenhouse gases emitted into the atmosphere, which leads to climate change, is increasing considerably. It is therefore expected of people to reduce their energy consumption to reduce the amount of fossil fuels as a source of energy and also the search is on for improving efficiency of conventional power generation and for renewable and sustainable energy sources which are environmentally friendly. One of the new renewable energy sources of great interest is geothermal energy which can be considered as the most clean and sustainable energy that can be exploited in a wide variety of locations. The urgent need for reducing global warming and the recent increase in the cost and uncertainty of future conventional energy supplies are making low-temperature geothermal resources very attractive as an alternative energy source. These resources are starting to attract significant interest, as lower temperature water resources are common in many countries and new technologies are beginning to appear that allow theses resources to be developed commercially. Currently, the main worldwide direct uses for low-temperature geothermal resources are in the domestic sphere for space heating, bathing, in agriculture for heating greenhouses, and numerous industrial applications. The absorption refrigerator, such as the single/half effect lithium bromide water mixture (LiBr/HzO) absorption refrigeration has been developed as a new method for capturing significantly more heat from low-temperature geothermal resources. This holds promise for producing virtually pollution-free cooling effects. Organic Rankin cycles (ORC) have also been considered for generating electrical power from these energy sources. Remote communities, in arid zones, such as Waddan city in Libya, which have close by four readily available high potential low-grade temperature geothermal resources could greatly benefit from the development of this technology. Such resources located in desert areas are very attractive energy sources for absorption cooling and ORC electrical power generation. The utilization of these resources would solve numerous local social and economic problems, raise living standards and also share the worlds concerns about global warming (by producing green energy even on a small-scale basis). The work described in this thesis is an attempt at developing a thermodynamic and economic model of the geothermal resource at Waddan city based on the local climate conditions and social and economic factors. The presence of natural gas fields near Waddan City close to the geothermal resources also allows the development of integrated energy systems using all the natural resources available to be considered. Five models have been evaluated and simulated using the commercially available software package IPSEpro. The first three models were designed to provide cooling from the geothermal resource and evaluated the choice of absorption refrigerator for this duty. The chillers considered in turn were a water-cooled single effect chiller, an air-cooled single effect chiller and a water-cooled half effect LiBr-HzO absorption chiller. The fourth model was based upon a standalone organic Rankine cycle (ORC), also driven by the geothermal resource to produce electricity. The fifth model utilised the natural gas and geothermal resources combining a simple gas turbine to generate electrical power, a water-cooled half effect chiller for inlet air cooling of the gas turbine and an organic Rankin cycle using R-245fa refrigerant. This was designed to produce electricity and also district heating. The absorption models were validated thermodynamically using a relevant Duhring chart, empirical equations and similar results available in the literature. The organic Rankine cycle models were successfully plotted on relevant thermodynamic T-S diagrams and approved by a leading European manufacturer of ORC units, Tuboden®. The results from the simulation have revealed that the low-temperature geothermal resources at Waddan city could be successfully utilized to power three different stand- alone absorption cycles. The highest cooling capacity of the chilled water that could be supplied to the community was from the water-cooled half effect absorption chiller at 5°C and 4516 kW refrigeration capacity. This capacity was approximately double that of the single effect chillers because the half effect chillier absorbs more heat than the single effect cycles. In addition the stand-alone half effect chillier was found to be directly economically viable, while stand-alone single effect chillers were not economically viable unless they were heavily subsidised or combined with the district hot water supply at least in the winter. The parametric study has shown that the most important independent parameter that could have the greatest effect on the performance of other dependent parameters of the chillier cycles was the coolant temperature. The results obtained of the stand-alone organic Rankine cycle model have shown that this geothermal resource could also used to power an ORC unit using refrigerant R-245fa to produce 350 kW of electrical power at an efficiency of 4.0%. This is useful to meet some of the power demands of the community. This model was found not to be viable economically to produce electricity all year round when the selling price of the electricity is fixed and in line with the subsidized Libyan government selling price of 0.02 £/kWhr. However if the model is used to generate electricity only during spring, summer and autumn and to produce district heating energy in the winter, this model is then economically feasible. The developed combined system could provide Waddan city and surrounded villages with their full electrical demand of 100 MW in an uninterrupted and stable way and also supply district heating and hot water if required. The simulated results show that the output power and thermal efficiency of the combined cycles were improved by 5% and 1.5% respectively compared to the stand alone gas turbine with a reduction in the carbon emissions of 55.7% (291 g/kWh instead of 649 g/kWh). Adding district heating to the electrical energy raised the Energy Utilization Factor to 55.1 %.

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This study focuses on an actual cogeneration power and MSF desalination plant and models it, analyses it, and proposes enhancements to MSF desalination at different, real operating scenarios. Based on actual data gathered from the plant for a full operating year, the study has identified the major operating scenarios of this cogeneration plant due to seasonal change to provide a real basis for assessing thermal, economic and environmental performance. It is difficult to standardize thermal evaluation of such systems because the net products, electrical power and water, are different in quality. Exergy analysis has achieved worldwide acceptance for thermal system assessment but no study was found in the literature that addressed the evaluation of power and MSF desalination together using exergy analysis. This thesis, therefore, makes an original contribution to this issue in three areas. Firstly, as simulation is the only practical approach to investigate enhancements to complex plants, the simulation models developed for the power and water desalination plant have been validated against actual operating data to substantiate the credibility of this approach. For the power plant model, validation against actual plant data at the three operating scenarios gave differences between the model and actual data varying from 1.0% to 3.7%. The MSF desalination system was modelled and validated against vendor testing data with the highest difference of 3.9%. Secondly, while previously both power production and desalination have been evaluated separately using the exergy approach, this study has applied it in a standardized approach to a specific cogeneration power and water desalination plant, including exergy analysis of the MSF desalination in detail that has not been found in the literature. It has been shown that the specific coupling of MSF desalination with a combined power plant is not a preferable option for thermal performance, which is contrary to the previous studies using Heat Utilization Factor as a performance indicator. The simulation was used to carry out a pioneer attempt of detailed energy and exergy analysis using the latest published thermodynamics properties, assuming that seawater solution is not an ideal solution (assumed in previous studies). Extraction of the hot distillate water from MSF up to stage 8 could enhance exergy efficiency to 14%. Extraction of hot distillate water from MSF stages was found to increase the unit water production up to 2%. Further, utilizing the hot water to heat up the make-up seawater flow through an Internal Heating (IH) caused an increase of brine recirculation temperature and reduced the powering steam by 5% and therefore reduces natural gas consumption and CO2 emissions by 57000 tonnes. Implementation of this modification has a one-year payback period. Thirdly, this study has, for the first time, studied the recovery of low-grade heat from MSF hot distillate water to enhance power or water production through the Absorption Chiller (AC), the Organic Rankine Cycle (ORC), and the Single Effect Desalination (SED). There appears to be no literature exploring MSF hot distillates to power AC to cool the gas turbine inlet by AC or dedicated SED (though previous studies have investigated steam powered MED). The temperature of these hot distillate stages was between 65ºC and 100ºC, suitable for low-grade heat recovery technologies and it was confirmed that utilizing part of the heat up to 10ºC temperature difference in the AC, ORC, and SED and reconnected back to IH had no adverse impact on the original MSF performance. Utilizing the heat to produce cooling from a single effect H2O/LiBr AC, the produced cooling load could be used to cool down the gas turbine inlet temperature to augment the electrical power generation. The AC was modelled and validated against manufacturer data. Reducing the GT inlet temperature by AC cooling increased the cogeneration plant electrical power production by 3.8% for every 5ºC reduction, with CO2 emissions reduced by 29000 tonnes and a 2.4 year payback period to implement such a modification. An ORC unit was modelled and validated against an existing plant. From both energy and exergy aspects, it was found that R245fa performs better as a working fluid than R134a in this application. Annually this option could increase plant power generation by 9000 MWh and reduce CO2 emissions by 13000 tonne. The economic assessment of this option showed the payback period was the highest at 5.2 years. Powering of hot water SED from hot MSF distillate water was the fourth heat recovery option studied (for the first time). The SED was modelled and validated against manufacturer published data with a 3.2% difference. The SED was able to produce 240000 tonne/year of water. This hybridization saved 11000 tonnes/year in CO2 emissions. The implementation of the modification has a 1.8 years payback period.

With the rapid development of electronic technology, the power consumption of electronic devices has decreased significantly. Consequently, there is substantial interest in harvesting energy from ambient sources, such as vibration, in order to power small-scale wireless devices. To design optimal vibration harvesting systems it is important to determine the maximum power obtainable from a given vibration source. Initially, white noise base excitation of a general nonlinear energy harvester model is considered. The power input from white noise is known to be proportional both to the total oscillating mass of the system and the magnitude of the noise spectral density, regardless of the internal mechanics of the system. This power is split between undesirable mechanical damping and useful electrical dissipation, where the form of the stiffness profile and device parameters determine the relative proportion of energy dissipated by each mechanism. An upper bound on the electrical power is derived and used to guide towards optimal harvesting devices, revealing that low stiffness systems exhibit maximum performance. Many engineering applications will exhibit more complicated spectra than the flat spectrum of white noise. Expanding upon the white noise analysis, a method to investigate the power dissipation of nonlinear oscillators under non-white excitation is developed by extending the Wiener series. The relatively simple first term of the series, together with the excitation spectrum, is found to completely define the power dissipated. An important property of this first term, namely that the integral over its frequency domain representation is proportional to the oscillating mass, is derived and validated both numerically and experimentally, using a base excited cantilever beam with a nonlinear restoring force produced by magnets. Another form of excitation prevalent in many mechanical systems is a combination of deterministic and broadband random vibration. Lastly, the Duffing oscillator is used to illustrate the behaviour of a nonlinear system under this form of excitation, where the response is observed to spread around the attractor that would be seen if purely deterministic excitation was present. The ability of global weighted residual methods to produce the complex responses typical of nonlinear oscillators is assessed and found to be accurate for systems with weak nonlinearity.

The exploitation of renewable energy sources is currently at the top of the agenda of many governments that are required to face the problem of the rising energy demand. In particular photovoltaics is considered one of the most promising technologies to meet the energy needs in the long term. However the effective exploitation of this source has always been hindered in many northern countries (like the UK) due to the weather conditions which are detrimental for the efficiency of photovoltaic generators. As a possible solution to this problem, this research presents the preliminary concept evaluation of an innovative power generator based on photovoltaic and lighter than air technologies (Aerostat for Electric Power Generation – AEPG). The generator consists of a helium filled platform tethered to the ground that would be used to locate a photovoltaic array at high altitude, ideally above the cloud coverage, in order to reduce the negative effect of the atmosphere and optimize the power production. The power produced at high altitude would then be transmitted to the ground via the mooring tether. First of all, the potential of this technology is evaluated in terms of the solar energy that can be collected at high altitude. The results obtained demonstrate that a generator located at an altitude between 6 km and 12 km could collect between 3.3 and 4.9 times the solar radiation that would fall on a ground based photovoltaic array. Furthermore the environmental conditions in which the system is due to operate are evaluated, employing standard atmospheric models and experimental wind speed datasets. An overview of the main parameters involved in the design is then provided and general considerations are discussed in order to narrow the range of values these different parameters can take. A simplified mathematical model is introduced to assess the performance of the system in steady state conditions and a set of design parameters is chosen to define a baseline configuration for the concept design. Moreover, a transient 3D analysis of the whole system is performed in order to check if the dynamic behaviour can constitute a show stopper. Finally the concept design of the AEPG is addressed and the most critical technical issues are identified. The location of the different subsystems is briefly discussed and a possible solution for the system layout is proposed. The study is completed with an initial sizing of the main components (structural in particular) in order to evaluate the different mass contributions and provide a preliminary assessment of the technical feasibility of the AEPG.

This thesis explores the effect that the unsteady hydrodynamics of the marine climate has on the load generation and subsequent durability of horizontal axis tidal stream turbines (TSTs). This is achieved through several campaigns of numerical modelling where the methodologies adopted were chosen on the principle of maximising the computational efficiency, allowing for time-domain durability calculations to be performed. The inflow was modelled by a variety of engineering wave models coupled with the underlying current profi€les and the rotor loads were resolved using blade element momentum theory (BEMT). The rotor loads were then fed to a six degree of freedom drive train model to analyse the stresses and the fatigue damage in the system. In order to inform on the input-output relationships of a turbine’s operating conditions and the generated loads, a sensitivity analysis was performed on the BEMT model to show each input parameter’s influence on the loading. The results showed that the rotor radius, blade pitch, signifi€cant wave height, inflow velocity and shear current steepness were the dominant factors in regards to the loading. Furthermore,an investigation on the internal contact stresses in the turbine’s main bearing found that simplifying the turbine loading problem down to a one-dimensional phenomenon gave a signi€ficant underestimation in the internal loads. It is concluded that to accurately model the internal loads on a TST, the full spatial range of the rotor loads including the o‚-axis components, must be incorporated in the structural modelling to avoid under prediction of the stresses and the related over predictions of the resulting fatigue life. The standard fatigue analysis techniques used in this work were also identifi€ed as possibly being unsuitable for the highly dynamic marine climate and suggestions on how to address this issue are provided.

Computerised systems have been developed to simulate the dynamic thermal performance of a building over a period of time, against a given weather pattern, with the aim of predicting the environmental and energy performance of the building. The usage of these systems has been limited, however due to the difficulty in describing the problem to be simulated to the system, and in interacting with the system. In particular the geometrical form of a building can be very tedious to input. This thesis considers the graphical creation of a building model for environmental analysis, such that the necessary geometrical data can be automatically derived and input into the analysis. Current geometrical modelling techniques and the use of CAD in building design are considered. The geometrical and topological modelling requirements for the building model are established, and a data structure is derived and checked for sufficiency. A possible modelling method is described for simple 21/2 dimensional buildings, and uses the property that the floor plan of a building can be represented by a planar graph. The necessary extensions to the modelling method are considered to allow more complex 3 dimensional forms to be created. The assignment of attributes to the model, necessary for the thermal analysis, is also included. Details arc given of the functionality of a user interface, using an implementation of this modelling method. This includes a description of the interaction to create the model, and the graphical displays that are generated. This modelling method has also been used in the development of an interface to an architectural CAD system, such that the necessary building data can be transferred for analysis.

The overall aim of this research is to investigate the underpinning science behind constructing a practical travelling-wave thermoacoustic refrigerator. At the outset, this was defined as a demonstrator that could be further developed into a means of thermal management of various enclosures – for example weather proof enclosures containing heat generating electronics, popular across the process industries. The practical requirements were set as 400 to 500 W of cooling power at 25 K temperature difference between the inside of the enclosure and the ambient. The initial research addressed issues of coupling the linear motors to such a refrigerator. This included analytical solutions of equations governing the electrodynamic behaviour of the motors, which lead to obtaining preferred acoustic conditions for their optimum performance. Meanwhile, a series of DeltaEC simulations was conducted to investigate possible configurations of the acoustic network that provide the required acoustic impedance matching. The project had the practical limitations of using two existing Q-drive linear motors. As a result, a refrigerator network has been developed which required a compliance and inertance matching a twin-alternator excitation and a two-stage looped-tube travelling-wave refrigerator. The second part of the research was concerned with engineering a practical demonstrator of the above refrigerator concept. DeltaEC simulations have been used to design a practical build and predict its performance characteristics. A prototype, based on helium pressurised at 40 bar and operating frequency of 60 Hz, has been subsequently built and commissioned. A number of experiments have been conducted to evaluate its performance “as built” followed by improvements including, in particular, the use of elastic membranes to supress Gedeon streaming. The prototype achieved a maximum temperature difference of 40ºC, minimum cold temperature of -7.5ºC, maximum COP of 2.05, highest COPR of 21.72% and total cooling power of 283W. Good overall agreement was found between modelling and experiments.