The publications listed in date order in this document are offered for the Degree of Doctor of Science in Durham University and have been selected from the author’s full publication list. The papers in this thesis constitute a continuum of original work in fundamental and applied electrical science, spanning 30 years, deployed on real industrial problems, making a significant contribution to conventional and renewable energy power generation. This is the basis of a claim of high distinction, constituting an original and substantial contribution to engineering science.

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The zinc-cerium redox flow battery (RFB) offers a higher open circuit cell potential than all vanadium and zinc-bromine systems and competes in the emerging market of utility-scale storage of renewable energy. Previous work on the Zn-Ce RFB has investigated electrolyte composition, the inhibition of hydrogen evolution at the negative electrode, electrode materials and operational conditions of both divided and undivided laboratory cells. After applying 3D- printing to the development of flow cells and porous electrodes, the present work advances the development of the system by introducing new high surface area porous, platinised titanium (Pt/Ti) electrodes for the cerium positive reaction and by performing electrochemical mass transport studies and surface area determination on these materials, along with the measurement of their hydraulic properties. The reaction environment in the critical positive half-cell of the Zn-Ce battery, which governs the cell potential at increasing operational current densities, is considered from the perspective of electrochemical engineering, in contrast to previous literature. Additionally, the cell potential vs. current density relationship for an ideal Zn-Ce unit cell with planar electrodes was simulated, taking into account the Ohmic and kinetic components of cell potential assuming charge transfer regime. Pt/Ti felt and Pt/Ti micromesh electrodes for cerium conversion were electroplated in a flowing alkaline solution. The morphology and distribution of platinum were studied by SEM, EDS and X-ray computed tomography. The volumetric mass transport coefficient of these porous electrodes was determined by the limiting current method and compared to expanded metal and flat plate electrodes. This volumetric mass transport coefficient was found to be more than two orders of magnitude higher with a Pt/Ti felt compared to the planar electrode, yielding a limiting current up to 160 times higher. The pressure drop at the Pt/Ti porous electrodes was higher in those materials with larger surface areas and smaller pore sizes. A pathway for future research and scale-up is discussed.

Wave energy has become one of the most promising energy resources and hence has attracted more attention from the governments and energy companies. In order to meet the growing demands on global energy, the next generation of energy extracting device needs to be more efficient with less operation cost, and as an offshore structure, the survivability also needs to be taken into consideration. Therefore, it is vital that the hydrodynamic behaviour of the energy device can be predicted accurately at the initial design stage. In this research, the wave structure interaction with application to wave energy device is studied numerically through an open source CFD library: OpenFOAM. The computational fluid dynamic (CFD) analysis based on the Reynolds Average Navier Stokes (RANS) equations is used to investigate the interaction between wave and structure, and array effects among devices. The numerical method with a reasonable computational cost can be an alternative to physical experimental test in offshore engineering. The background to this research is firstly introduced, including methodologies adopted in this study, followed by a series of case study to demonstrate the applicability of the numerical model. These include wave generation validation, hydrodynamic behaviour determination, and the predication of the performance of wave point absorber and wave point absorbers array. It has been shown that the numerical model is capable of modelling wave propagation and interaction with structure including nonlinear effect with a reasonable degree of accuracy. The wave point absorber energy device has been chosen as the object to study. The RANS approach in time domain improves the accuracy when compared with the potential theory based method. The influence of wave point absorber devices array on their performance is then investigated under the irregular wave conditions in order to improve the overall performance. The influence factors include array configuration, separation distance and wave direction. The study yields an improved understanding of wave-structure problem and has extended the range of RANS model used in wave energy research.

Rural electrification has been a priority for many governmental and international donor organisations. Grid extension and various renewable energy technology (RET) options are recognised as viable means of providing enhanced energy and water services to isolated rural communities, and these have been successfully deployed in many regions across the world. In Nigeria, decentralized energy generation systems based on solar PV systems are often used to meet the low energy demands of rural areas and they have also been widely adopted for water pumping purposes in these places. However, the failure or underperformance of many of these installations is in stark contrast to their theoretical viabilities as asserted in many academic papers; this suggests deep underlying problems. Such failures have discouraged government and policy makers from supporting solar PV and, as an extension, other forms of RE projects as viable options for isolated rural locations, even when grid extensions to these places often remain economically and practically challenging. Hence, whereas a number solar PV projects have been implemented in rural communities in the country, appraisal of their success and failures has moved at a much slower pace. Evidence is needed, not only about the factors that contribute to the deployment of these RE installations, but also on issues that took place after such installations have been completed: if the technology fulfils people’s needs and priorities, if the equipment remained in working order and for how long, and the particular and general decisions and actions that may have contributed to the success or failure of the installations. The aim of this study is therefore two-fold. Firstly, to reveal and understand the fundamental issues and factors that mitigate against the proper deployment, diffusion and performance of solar PV installations in isolated rural locations in Nigeria and, secondly, to develop a framework and set of recommendations that could lead to improved deployment processes and better performance of such installations. In order to understand and address these fundamental issues, a systematic analysis of relevant literatures on renewable energy technologies and technology diffusion is initially undertaken. In addition, multiple methods including site visits, observation and physical evaluation of installations, interviews and discussions with stakeholders and key players, and seven exploratory studies of rural communities are utilised to collect primary data on the performance and effectiveness of solar PV installations. Thirty-Eight indicators across five core sustainability dimensions of Technical, Economical/Financial, Environmental Impact, Social-Ethical Development, and Institutional Development and Government Policies are used to assess and evaluate the study cases, revealing diverse and interconnected pre- and post-installation factors that contribute to both successful and failed installations. A main finding of the study is that involvement of private energy providers in the deployment and running of solar PV installations in rural communities in the country is more effective than the sole use of government agencies or contractors. It was also revealed that a number of factors including weak or absence of post-installation maintenance arrangements, non-existence of local representative authorities, failure to enlighten local residents on limitations of the installation and to train them on basic maintenance practices, weak implementation and low success of government policies, weak institutions and overlapping functions of government agencies impacted negatively on the performance of the installations. In addition, the study provides insights into the interrelationships between the factors; how the presence or absence of some can strengthen or weaken others. Finally, a framework and set of recommendations are generated that could support improved deployment procedures and enhanced performance of solar PV installations in rural communities. Although the study deals with the Nigerian situation, some of the findings can be readily extended to other developing countries with similar challenges in the provision of energy and water services to isolated rural communities.

Heat-driven energy system attracts ever increasing attentions to improve the efficiency of overall energy utilisation by recovering the heat energy such as solar thermal energy, wasted heat from industry and geothermal energy. Adsorption technology is recognised as one of the promising solutions to convert low-grade heat to refrigeration or be used as heat pump. Based on the working principle of this technology, it can promisingly be developed into combined refrigeration and power generation system by integrating an expander in to the system. However, due to the limited research efforts on the system investigation, refrigeration generation by adsorption technology is still immature. The investigation on the working conditions of the system, the selection of proper expansion machine for power generation part of the cogeneration and overall system evaluation are important to be conducted. This study aims to explore the feasibility of integration the adsorption technology with expansion machine for refrigeration and power generation. The proposed cogeneration combines resorption system, which has potentially twice of the cooling capacity compared with conventional adsorption system, integrated with expansion machine to continuously produce refrigeration and power. The design and optimisation methods of the proposed system were studied in order to select the proper resorption working pairs under different heat source conditions. Furthermore, the system performance with and without the optimisation methods were evaluated by the first and second law analysis. Results indicated attractive performance and MnCl2-SrCl2 was stood out as the optimal resorption working pair for the purpose of high refrigeration generation under low grade heat source, when ammonia is the working fluid in the system. Scroll expander was selected as the expander to be explored in this study because of its highest average isentropic efficiency, low cost, low vibration noise, high availability and easy modification from compressor to expander for our special application demand. A lab scale scroll expander test rig was designed, constructed and tested to obtain the performance such as isentropic efficiency and electrical efficiency of a selected scroll machine under various working conditions. An assessment of a case study of the resorption cogeneration system was conducted to evaluate the variation of the power and refrigeration performance with the time. Results indicated that a resorption cogeneration with 25.2 kg MnCl2 and 18.9 kg SrCl2 could potentially produce 1 kW power and 2.5 kW cooling capacity when the cycle time is around 25 minutes.

To date, most offshore wind farms are deployed in coastal regions including both well-mixed regions and other areas where water-column stratification plays an important role such as regions of freshwater influence and seasonally stratified shelf seas. In the UK for example, a number of offshore wind farms have been commissioned and approved in Liverpool Bay, which is a key region of freshwater influence, and approved in regions of the North Sea where the water column can stratify seasonally. While there has been significant work on determining the local environmental impacts of offshore wind farms, in particular when they relate to the structural integrity of the turbines (e.g. scour), there has been far fewer studies focusing on the water column dynamics in complex regions such as regions of freshwater influence, even though they have a significant control on the ecosystem. This project addresses both issues: assessment of the modelling techniques; and impact of offshore wind farms on the dynamics of regions of freshwater influence. This is achieved via a numerical modelling study in which a new module was developed to simulate the impacts of offshore structures in the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS). The overall model was then applied to a case study in Liverpool Bay, which is a salinity driven, hyper-tidal region of freshwater influence with complex dynamics in the North West of the UK and where an increasing number of offshore windfarms have been deployed since 2003. This new module is based on a modified drag force approach, which takes both momentum and turbulence effects into account by introducing impact equations and additional terms to the governing equations of the momentum solver in POLCOMS and of the k-e turbulence model (General Ocean Turbulence Model, GOTM). The updated coupled model is then implemented for Liverpool Bay with numerical simulations covering the full year 2008 and with 55 turbines represented in the model. It is validated using mooring data over the same period at selected locations in Liverpool Bay. A yearly time series of temperature, salinity, velocity and density shows that the model predicts the hydrodynamics well, and that inclusion of the wind farms in the model results in a slight improvement of numerical predictions based on skill values. A number of sensitivity tests address the influence of the modelling techniques used on the numerical results. These include a model-model comparisons considered the relative effect of taking into account changes to momentum and turbulence equations. The results demonstrate that using only one equation change (either momentum or turbulence) overestimates the effects of a structure in the water column and that both momentum and turbulence should be considered when assessing the impacts of structures in a 3D model. Finally, numerical results from the best simulation are analysed to determine the impact of the offshore wind farms on the region of freshwater dynamics. The position of the wind farms controls the level of impacts in the region of freshwater influence. When the wind farm is positioned in an area where the ambient velocity is high, the velocity is affected. In contrast, where the velocity is lower, the salinity and temperature is more affected. The main conclusions are: even a small number of structures do have a discernible impact on the dynamics of a region of freshwater influence; the representation of offshore wind farms in the model, considering momentum and turbulence modifications to governing equations, is critical for predictions of the total impact on the water column in a 3D model.

In this thesis, we study the theoretical approach on energy-efficient scheduling problems arising in demand response management in the modern electrical smart grid. Consumers send in power requests with flexible feasible timeslots during which their requests can be served. The grid controller, upon receiving power requests, schedules each request within the specified interval. The electricity cost is measured by a convex function of the load in each timeslot. The objective is to schedule all requests with the minimum total electricity cost. We study the smart grid scheduling problem in different models. For the offline model, we prove the problem is NP-hard for the general case. We propose a polynomial time algorithm for special input where jobs have unit power request and unit time duration. By adapting the polynomial time algorithm for unit-size jobs, we propose an approximation algorithm for more general input. On the other hand, we also present an exact algorithm to find the optimal schedule for the problem with general input. For the online model, we propose an online algorithm for jobs with jobs with arbitrary power request, arbitrary time duration, and arbitrary contiguous feasible intervals. We also show a lower bound of the competitive ratio for the smart grid scheduling problem with unit height and arbitrary width. For special cases, we design different online algorithms with better competitive ratios. Finally, we look at other optimization problems and show how to solve them by adapting our techniques. We prove that our online algorithm can solve the machine minimization problem with an asymptotically optimal competitive ratio. We also show that our exact algorithm can be adapted to solve other demand response management problems.