The semiconducting sulphosalt Wittichenite has been identified as a possible absorber material for thin film photovoltaic devices. It has the chemical formula Cu3BiS3 and its component elements are those of low toxicity and high abundance making it a very attractive prospect for photovoltaic devices. The copper bismuth sulphur material system is not very well understood and information on it limited to a few small regions. To aid understanding of this system a pseudo-binary phase diagram along the CuS-Bi join of the Cu-Bi-S ternary phase diagram was constructed by making bulk samples of various compositions along the join and analysing them using X-ray diffraction and differential scanning calorimetry. This join was chosen because is crosses the point at which Cu3BiS3 would be expected to occur due to its stoichiometry. The CuS-Bi phase diagram shows Cu3BiS3 forms across a wide compositional range but is mixed with either bismuth metal or copper sulphides depending on composition. Films of Cu3BiS3 were made using sputtered copper and bismuth films annealed in a sulphur atmosphere and thermal co- evaporation of copper sulphide and bismuth.

This research applies a recently developed dynamic state-estimation based protection scheme, the settingless protection, to the photovoltaic (PV) industry for the first time. At this time, the proposed protection algorithm has been implemented on traditional protection zones for individual power system devices, but this research extends this protection to a microgrid, specifically, a system of PV network composed of several PV modules. Several illustrative examples on various anomalies such as high impedance faults and shorted-out PV modules have been provided to demonstrate the effectiveness of this protection scheme. The detection of these anomalies has been demonstrated in the presence of changing atmospheric conditions, and with the operation of maximum power point tracking (MPPT) equipped dc-dc converters. This protection scheme requires an accurate model of the PV module, therefore, a two-diode PV model has been developed using quadratic integration modeling. In this PV model development, a scaling factor is applied to the Taylor series expansion of the exponential terms of the model of the PV module. Then the higher order terms of the Taylor series expansion are reduced to at most second order terms using the quadratization technique. Furthermore, a novel approach for extracting the PV parameters, namely, the ideality constants, leakage currents, PV module internal current, shunt and series resistances, has been presented. A comparison was performed between numerically generated data using the determined PV module parameters and data measurements from a physical PV module. It was shown that the maximum error from this comparison was below 0.12A, and less than 0.05A around the maximum power point region of the PV modules used for this research. The residual data from the PV array protection scheme has been used to develop a method for identifying the location of faulted PV modules. Also, condition-based monitoring of the PV array system has also been presented with examples. From the PV array system monitoring, the shading and underperformance of a PV module have been identified. From the contributions of this research, an accurate module of the PV array has been developed in a form that can be integrated with other power system devices. This accurate module can be used for state estimation of the PV array, load flow analysis, short circuit analysis, and other power system analytical studies. Also, by determining the location of the faulted PV module, the time to identify this faulted PV module in a large PV installation is drastically reduced. Lastly, by identifying shading conditions and underperforming PV modules, the PV system operator can quickly bring the underperforming module or modules to optimal performance, thereby, maximizing the power yield of the PV array, and maximizing the revenue of the PV system owner.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The solar photovoltaic industry has many barriers to overcome before it can become a technically and economically competitive generation source including (1) lowering true generation costs, (2) decreasing reliance from government subsidies, and (3) developing a suitable energy storage solution. Current unsubsidized costs of electricity from solar photovoltaic sources range from 24.0 to 58.3¢/kWh. Subsidies bring the generation costs down to as low as 11¢/kWh, competitive with the average retail price of electricity in certain parts of the country. Current subsidy policies used to encourage technology development may generate more profits rather than research and innovation. The most optimistic predictions for solar photovoltaics include a convergence of a steep and prolonged rise in the cost of fossil-fuel based generation with a deep and prolonged decrease in the cost of photovoltaic generation by 2019. Deviation from optimal conditions will prolong the delay the crossover until at least 2021 and possibly beyond 2030. The development of a solution to store excess electricity when the sun is available during the day for use at night is necessary for photovoltaic electricity to become a dominant generation source. / text

Les sources d'énergie renouvelable connaissent un essor grandissant. Parmi celles-ci se trouvent les cellules photovoltaïques. Elles ont pour objet la transformation de la lumière en électricité. Les dispositifs actuels, basés sur le silicium, nécessitent des matériaux de très grande pureté et de hautes températures de mise en œuvre, les empêchant de concurrencer les principales sources d’énergie actuelles (fossile, nucléaire). Une alternative pourrait provenir des matériaux semi-conducteurs organiques. En effet, l’utilisation de méthodes de mise en œuvre à partir de solutions pourrait permettre la fabrication de dispositifs flexibles et bon marché. Des résultats encourageants ont été obtenus avec des polymères conjugués et de petites molécules organiques. Les cristaux liquides discotiques CLDs forment une catégorie particulièrement intéressante de matériaux. Ils ont en effet la capacité de s’organiser spontanément en colonnes de molécules, formant des semi-conducteurs à une dimension. Leurs propriétés intéressantes en tant que semi-conducteurs, combinées à une mise en œuvre facile, en font de bons candidats pour de futures applications. Dans ce travail, deux familles complémentaires de matériaux discotiques ont été développées, formant une paire de semi-conducteurs de type n et p. Leurs structures chimiques ont été étudiées en vue d'obtenir des matériaux possédant un ensemble de propriétés choisies afin d’optimiser les paramètres clefs du processus de photo-génération de charges. Ces propriétés sont les suivantes: forte absorption de la lumière dans le visible, fort caractère semi-conducteur de type n ou p, pas de phase cristalline à température ambiante, présence d'une phase cristal liquide colonne, phase isotrope en dessous de 200°C. De plus, les matériaux doivent être accessibles en un nombre minimum d’étapes d’une synthèse efficace, et ce avec un haut niveau de pureté. Ils doivent également être fortement solubles dans les solvants organiques usuels. Cette étude comporte, pour chacune des deux familles de matériaux, le design de leur structure chimique, leur synthèse et la caractérisation de leurs propriétés physiques (thermotropes, optoélectroniques, électrochimiques). Comme possible semi-conducteur de type p, cinq dérivés tétrasubstitués de la phthalocyanine non-métallée ont été synthétisés, donnant un matériau possédant l’ensemble des propriétés recherchées. Comme possible semi-conducteur de type n, six dérivés hexasubstitués de l’hexaazatrinaphthylène ont été étudiés. L’un d’eux possède les propriétés requises. Finalement, les propriétés optoélectroniques et photovoltaïques de mélanges des deux matériaux les plus prometteurs, ensemble ou avec d’autres matériaux, ont été étudiées. Des cellules solaires de rendement maximum de 1 % ont été obtenues pour deux dispositifs de compositions différentes. Ces rendements, bien qu’inférieurs à ceux obtenus précédemment par d’autres groupes (jusqu’à 34 % à ce jour), sont néanmoins révélateurs des potentialités des matériaux organiques, et plus particulièrement des cristaux liquides discotiques, pour de futures applications dans le domaine des dispositifs électroniques.

Energy plays a pivotal role in human development. Not only is it sine qua non for national economic development, but it also provides services that enhance social development including, health and sanitation, education, potable water, cooking. In spite of this, at present, there are about two billion people without access to modern sources of energy, most of them in the rural areas of the developing world. Consequentially, the social and economic development of these two billion people hangs in the balance. In recent times, however, considerable advocacy has taken place in the academic and policy studies, environmental fora, and national agenda about solar PV energy technology serving as a panacea to the energy problems of rural populations in developing countries, especially Sub-Sahara Africa, whilst also helping to reduce greenhouse gas emissions. Notwithstanding this great advocacy, the literature on the dissemination of this technology has been incomplete in fostering understanding on the discourses surrounding its low dissemination rates in rural Ghana compared to countries such as Kenya and Zimbabwe; the sustainability of installed solar PV systems; and the usefulness of solar PV in serving the needs of the rural poor. In resorting to an interdisciplinary approach (methodology and theoretical foundation), this study has explored the energy perspectives of Ghana, the dynamics of rural electrification and energy needs, and the interplay of processes and forces underpinning the adoption and non-adoption of solar PV in rural Ghana. Results of this study show that, Ghana has abundant renewable energy resources, especially solar radiation. However, the study further reveals that the resource base alone of solar PV technology is not the panacea to its successful dissemination and the energy needs of all in rural Ghana. Significantly, this study has shown that the adoption and non-adoption perspectives of solar PV in rural Ghana and the sustainability of installed solar PV systems, as well as the disparate levels of solar PV dissemination in Ghana, Kenya and Zimbabwe, are contingent on multi-dimensional circumstances. This stands in contrast to the majority of literature that often emphasise cost as the sole determining factor of the non-adoption of solar PV in most developing countries. Results of this study therefore have implications for rural energy supply policy approaches and other institutional arrangements on solar PV issues in Ghana.

PV/Thermal technology is the combination of solar thermal and photovoltaics - two mature and widely understood technologies. Combining the two technologies complicates existing standardized rating procedures and performance modeling methods. Currently a standardized performance test method does not exist for PV/Thermal (PV/T) panels. Existing and developing PV/T panels are commonly tested using separate standardized solar thermal and photovoltaic test procedures. Solar thermal performance is rated in terms of temperature difference whereas photovoltaic performance is dependent on absolute temperature level. The thermal and electrical performance of a PV/T panel is, however, coupled so performance equations derived using traditional test methods may not accurately reflect the performance of a combined PV/T panel over a wide range of conditions. The purpose of this work was to develop an efficiency equation for a PV/T panel which can be derived from a minimal amount of empirical test data and still accurately predict its thermal and electrical performance over a wide range of conditions. To accomplish this, a quasi- 3-dimensional steady-state model of a sheet-and-tube PV/T collector was developed and used to generate a broad data set from which a simplified PV/T performance equation was developed. Using this numerically generated data set, and introducing additional coefficients into the traditional solar thermal performance characteristic, a modified PV/T efficiency equation was derived which expressed the electrical and thermal efficiency in terms of ambient temperature, incident solar irradiation and the temperature difference between the inlet fluid and the ambient. It was also shown, for the case studied, that the efficiency equation can be produced from as few as 6 data points and still accurately predicts the performance at a wide range of operating conditions. A TRNSYS [1] model was developed to demonstrate how the performance equation can be used to simulate the annual performance of a PV/T collector in a domestic hot water system. It was shown that a performance equation, derived from 6 data points, performed as well as a performance map which used over 1000 data points. The annual thermal and electrical production predicted by both models was within 1.5% of each other. The PV/T efficiency equations were also shown to perform well for a range of electrical parameters, thermal properties and substrate thermal conductivity values. Future work is recommended to validate the PV/T performance equation using real empirically derived data for a range of collector designs. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-01-22 15:40:03.337

M. Tech. (Engineering, Electrical, Department Electronic Engineering, Faculty of Engineering and Technology), Vaal University of Technology / In order to facilitate sustainable development, it is necessary to further improve and increase the energy efficiency and use of renewable energy and its related technologies. The main limiting factors to the extensive use of photovoltaic (PV) modules include the high initial investment cost and the relatively low conversion efficiency. However, other factors, such as an increase in ambient temperature, exert a considerable negative influence on PV modules, with cell efficiencies decreasing as the cell’s operating temperature increases. Higher PV module surface temperatures mean lower output voltages and subsequent lower output power. Therefore, this dissertation focuses on optimizing the available output power from a PV module by investigating and controlling the effect that the PV module’s surface temperature exerts on the amount of electrical energy produced. A pilot study was conducted by using a PV module set to three different tilt angles with an orientation angle and temperature sensors placed at different points. This was done to determine temperature distribution on the PV module surfaces as well as identify which tilt angle produces the highest PV module surface temperature. The main study was designed to investigate the electrical performance of a PV module with different cooling systems (water and forced air) as against a referenced measurement (no cooling). The cooling systems will be switched on and off at specific time intervals with the help of an electronic timer circuit incorporating a PIC microcontroller. The pilot study was conducted for a 50 week period where the results indicated a direct correlation between temperature rise and voltage decrease. The PV module’s temperature is highest at a tilt angle of 16° during the day and lowest at night time. It further reveals that the PV module’s front and back surface temperature can be distinctly different, with the highest recorded values occurring at the back of the PV module. The main study was conducted for a period of 15 weeks with results indicating that the water cooling system resulted in an average higher output power of 49.6% when compared to the reference system (no cooling system). Recommendations are made that sufficient space should be included between the module frames and mounting structure to reduce high operating temperatures owing to poor air circulation.