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Power loss due to photovoltaic (PV) module mismatch is a well-known problem for PV systems. The ability to recuperate the power lost has increased the popularity of distributed maximum power point tracking (DMPPT) systems using per-module ‘power optimisers’; DC-DC converters that track the maximum power point (MPP) of each module. There are concerns over systems with multiple maximum power point trackers (MPPTs) incurring unwanted interactions between MPPT controllers. A method for electrical engineers to analyse such systems is required. A lack of in-depth evaluation in literature has been addressed in this work through practical testing and development of a computer model for simulating various DMPPT systems. To achieve acceptably accurate models of DMPPT power conditioning devices (PCDs) practical testing systems were employed: a solar emulator with real PV module, a real outdoor DMPPT test system and a PV emulator (PVE) developed during this work. A fast and dynamically stable PV module emulator (PVME) was developed for testing a power optimiser. The PVME consists of a linear regulator and an analogue computation circuit for speed and flexibility. The steady-state operation of the power optimiser was tested with the PVME whereas the solar emulator obtained the true dynamic response. The extension of the PVME into a PV array emulator (PVAE) through the addition of a switched-mode controllable DC voltage source and a digital lookup table was considered. PSpice ‘block models’ of PCDs were created for ease of reconfiguration using averaged equations of the switching power electronics and an equation for inverter ripple derived in this work. An MPPT model was developed in Simulink for co-simulation with the PSpice electrical models using SLPS. The overall DMPPT model showed similar behaviour to the outdoor test system. A number of proposed scenarios for investigating DMPPT system interactions have been suggested for further work.

One of the most important operational requirements for any electrical power network for both distribution and transmission level is voltage control. Many studies have been carried out to improve or develop new voltage control techniques to facilitate safe connection of distributed generation. In Saudi Arabia, due to environmental, economic and development perspectives a wide integration of photovoltaic (PV) generation is expected in the near future. This development in the networks may cause voltage regulation problems due to the interface with the existing conventional control system. Therefore, this work determines the impact of linking PV directly with the grid to find the level of penetration that can be achieved without any technical changes in the distribution network. Then, the effect of Grid-Connected Photovoltaic (GCPV) systems on the voltage regulation in residential networks has been investigated. This thesis introduces a new voltage control scheme for residential area networks in Saudi Arabia based on Fuzzy Logic concept (FL). The structure of two implementations of FL control to regulate the voltage by setting the on-load tap changing transformer in the primary substation is proposed. Finally, another approach for solving the feeder voltage regulation problem at a local level is presented with the goal of fulfilling the plug-and-play feature desired by manufacturers and regulatory bodies. Also, this technique use the FL concept to set up the operating power factor for the inverter used to connect the PV generator. In order to confirm the validity of the proposed methods, simulations using PVSYST, ETAP and MATLAB/Simulink softwares have been carried out for a realistic distribution network with real data for load and solar radiation. Results showing the performance of each scheme are presented in detail, and demonstrate that each scheme is capable of keeping the voltage levels within statutory limits, both in steady-state and under dynamic condition.

This thesis examined solar thermal collectors for use in alternative hybrid solar-biomass power plant applications in Gujarat, India. Following a preliminary review, the cost-effective selection and design of the solar thermal field were identified as critical factors underlying the success of hybrid plants. Consequently, the existing solar thermal technologies were reviewed and ranked for use in India by means of a multi-criteria decision-making method, the Analytical Hierarchy Process (AHP). Informed by the outcome of the AHP, the thesis went on to pursue the Linear Fresnel Reflector (LFR), the design of which was optimised with the help of ray-tracing. To further enhance collector performance, LFR concepts incorporating novel mirror spacing and drive mechanisms were evaluated. Subsequently, a new variant, termed the Elevation Linear Fresnel Reflector (ELFR) was designed, constructed and tested at Aston University, UK, therefore allowing theoretical models for the performance of a solar thermal field to be verified. Based on the resulting characteristics of the LFR, and data gathered for the other hybrid system components, models of hybrid LFR- and ELFR-biomass power plants were developed and analysed in TRNSYS®. The techno-economic and environmental consequences of varying the size of the solar field in relation to the total plant capacity were modelled for a series of case studies to evaluate different applications: tri-generation (electricity, ice and heat), electricity-only generation, and process heat. The case studies also encompassed varying site locations, capacities, operational conditions and financial situations. In the case of a hybrid tri-generation plant in Gujarat, it was recommended to use an LFR solar thermal field of 14,000 m2 aperture with a 3 tonne biomass boiler, generating 815 MWh per annum of electricity for nearby villages and 12,450 tonnes of ice per annum for local fisheries and food industries. However, at the expense of a 0.3 ¢/kWh increase in levelised energy costs, the ELFR increased saving of biomass (100 t/a) and land (9 ha/a). For solar thermal applications in areas with high land cost, the ELFR reduced levelised energy costs. It was determined that off-grid hybrid plants for tri-generation were the most feasible application in India. Whereas biomass-only plants were found to be more economically viable, it was concluded that hybrid systems will soon become cost competitive and can considerably improve current energy security and biomass supply chain issues in India.

This work details the synthesis of a functionalised all-donor polymer, poly(3- hexylthioacetate thiophene) (P3HTT) [42] along with four new donor-acceptor (D-A) copolymers. Two of the four copolymers are based on fluorene (F) and carbazole (C) as electron donors copolymerised with DEBT to give, PFDEBT [62] and PCDEBT [63] respectively, while the other two are based on the same electron donors, but copolymerised with DES to give PFDES [64] and PCDES [65] respectively. All the polymers exhibited good solubility in common organic solvents and good thermal stability. The spectrophotometry analysis of polymer [42] in chloroform showed that it emits in the green region with 26% photoluminescence quantum yield (PL <I». The optical response of copolymers [62] and [63] in chloroform solution and thin films are similar; both have two broad absorption bands with peaks at short and long wavelengths which are within comparable range. In addition, both emit in the deep red region of the emission spectrum and have similar PL <I> values, 28 % and 27 % respectively. In contrast, copolymers [64] and [65] have single broad absorption band and emit in the green region with PL <I> values of 55 % and 51 % respectively. The electrochemical responses of the polymers were measured using cyclic voltammetry. The results obtained for polymer [42] were different from what was expected; its band-gap was similar to that of P3HT and its energy levels were elevated. In contrast, the band-gaps of the copolymers were tuned in the range of 1.47 to 1.65 eV The results showed that the acceptor units have exhibited the same effect of band-gap lowering in the two sets of the copolymers, for instance, the LUMO energy level of copolymers [62] and [63] is - 3.32 eV and those of copolymers [64] and [65] is - 3.57 eV Conversely, different effect was observed in the values of the HOMO energy levels, for example, the values for [62] and [64] which contain the same donor (fluorene) are - 4.86 and - 5.07 eV respectively; while those of copolymers [63] and [65] composed of carbazole are - 4.97 and - 5.04 eV respectively. This may suggest that the acceptor unit reduced the band-gap by lowering the LUMO energy level but at the same time elevated the HOMO energy level probably due to the presence of EDOT.

Dye-sensitized Solar Cells (DSCs) and Solid State Dye-sensitized Solar Cells (ssDSCs) are photovoltaic devices with short energy payback times compared to existing technologies. DSCs and ssDSCs have the potential to become cheap flexible devices with new building integrated and portable applications.

For photovoltaics to achieve wide-scale implementation it is essential that their cost is reduced while maintaining or exceeding the present level of solar to electrical conversion performance. Concentrating solar energy onto a photovoltaic cell allows a reduction in the output electricity cost, if the cost of the concentrator is less than that of the displaced photovoltaic materials. Photovoltaic cell efficiency is shown to decrease with increasing temperature, causing the photovoltaic cells to exhibit both short-term (efficiency loss) and long term (irreversible damage) degradation due to excessive temperatures. Hence the analysis of thermal management is an important issue in photovoltaic power generating systems for both one-sun (lx) and concentrated applications. This thesis presents an experimental and numerical study of solar cell temperature in a midconcentration silicon photovoltaic concentrator (CPV), with a geometric concentration ratio of 42X. Experimental and computational fluid dynamic (CFO) modelling of heat transfer in six designs of CPV device is carried out. A detailed experimental study was designed and carried out in order to investigate the temperature and initial boundary conditions of the two initial CPV prototypes, with a without passive cooling arrangements, operating under standard test conditions (STC) in conjunction with the effect of environmental variables, namely the irradiance incident on the plane-of-array of the CPV module, the local wind speed and the ambient temperature on the operating temperatures of the CPV prototypes. The operating temperature is shown to depend strongly on the irradiance, less so on the wind speed and is found to be insensitive to short term fluctuations in ambient temperature. Temperature profiles of the CPV prototypes were measured experimentally with thermocouples placed both internally and externally along the enclosure and walls aJong the length of each CPV module. To investigate the performance of the CPV devices under a fixed set of repeatable environmental conditions, a solar simulator was designed and built to facilitate indoor testing at a range of illumination levels (0 to 1000W 1m2) and environmental conditions. Reviewing the results it was found that the spectrum and uniformity of irradiance source incident the plane of a single module (1 x 0.lm) is of great importance. The solar simulator was also found to artificially increase the module operating temperature, with greater temperatures recorded during indoor testing. Wind speed and direction measurements were taken in order to establish the module convective heat transfer coefficient (CHTC) which was determined to relatively insensitive to wind direction and to be a power law function of the mean wind speed. In the second phase of the work, three dimensional numerical studies of the photovoltaic concentrator prototypes were developed using ANSYS Fluent Computational Fluid Dynamic (CFD) software to solve the mass, momentum and energy transfer governing equations. The simulations provided thermal and dynamic maps of the fluid flow and the heat transfer between the cell and the passive cooling systems. The results show that a maximum of seven radial fins (CPV design 3) of 27mm height, 3.3mm thickness with a 4 degree taper can be effectively used to reduce the solar cell temperature, from 97.8"C with no cooling fins to 67.7"C with seven fins, measured at nominal operating cell temperature (NOCT) conditions. In addition. to validate the model. experimental measurements of temperature and flow characteristics are compared with experimental data. Numerical results of the CPV operating temperature are shown to have a strong correlation with experimental data with a maximum 0.3% deviation from experimental data for prototype one and a maximum 1.5% deviation from experimental data for prototype two. Simulation models are shown to be important design tools for predicting a photovoltaic concentrator's experimental and real world performance. Informed design decision making and optimisation is a significant goal of this work.

This thesis discusses a number of approaches which increase the efficiency of photovoltaic (PV) cells. PV cells generate electricity they become inefficient at high temperatures. Contemporary heat dissipation approaches are reviewed to maintain PV cells at their optimal temperature. Exploiting this excess heat through a novel technology termed solar photovoltaic-thermal (PVT) system which enables both electricity and heat to be generated from a single system is the focus of the research presented in this thesis. In order to maintain an optimal PV cell temperature a number of phase change materials (PCMs) have been used in the PVT panel assembly which absorb heat whilst charging and release heat whilst discharging. A number of PCMs were tested within the PVT panels such as RT27, OM35, OM46 and OM56. PVT simulation showed that electrical output can be increased by 9% coupled with an average water temperature rise of 20°e. Four types of PVTs have been developed by modifying the standard thermal collector and standard PV panel which constitute the PVT collector and PVT panel respectively. It was observed that modification of the standard thermal collectors for PVT purpose is not feasible due to brittleness of the PV cell and the ambient high temperature in the collector. However, modification of the PV panel is feasible with the integration of a heat carrying fluid at the rear of the panel. A significant part of the research is an innovative design where a polycarbonate {PC} channel type PVT panel was developed. It was observed that the PC is a good PV base with the channels suitable for both water and PCM heat transfer. It was concluded this offered the best solution. The feasibility of a PV panel using PC and other polymers was tested for optical properties, electrical insulation, physical insulation, physical protection and climatic impact. The PV panel fabrication, testing and installation were undertaken in India. It was demonstrated that the polymer PV panels are cost effective and feasible to be fabricated locally even in a rural undeveloped environment.

Large area sprayed or silk screen printed CdS/Cu (_2) S solar cells are potentially cheap and efficient devices for the direct conversion of sunlight into electrical energy. They do not require the expenditure of large amounts of energy during fabrication as do silicon cells. There are, however, various degradation processes associated with the operation of the cells and the major mechanism is thought to be associated with a gradual oxidation of the copper sulphide. It is clear therefore that the degradation of single crystal and evaporated thin film cells must be better understood before the more difficult problems associated with the fabrication and operation of sprayed or printed layer cells can be solved. This thesis describes an investigation into the photovoltaic properties of CdS/Cu (_2) S heterojunctions. The cells were prepared by forming layers of CU (_2) S on single crystals and thin films of CdS. Undoped crystals with both high and low resistivity have been used as have low resistivity samples containing grown-in copper, indium and chlorine impurities. A study of the spectral dependence of the open circuit voltage and of the current-voltage characteristics, after baking in air at 200 C, shows that the maximum spectral sensitivity of the cells in the range 0.6 to 0.7 nm is associated with a photo- conductive region in the cadmium sulphide caused by a diffusion of copper into the cadmium sulphide. The effects of forming the cuprous sulphide layers on basal planes of opposite polarity have also been investigated. It was shown that the conversion of cadmium sulphide to cuprous sulphide proceeds 1.5 times faster on sulphur than on cadmium planes and the photovoltages of unbaked cells with the cuprous sulphide formed on sulphur faces are some 20% Larger than the photo- voltages from cells in which the cuprous sulphide is formed on cadmium faces. It was further shown that the plating temperature must be carefully controlled at 90 C to ensure production of stoichiometric Cu (_2) S.

No description available.