Thesis (M.E.E.)--University of Delaware, 2008. / Principal faculty advisor: Allen Barnett, Dept. of Electrical & Computer Engineering. Includes bibliographical references.

Thesis (M.S.)--Humboldt State University, 2009. / Includes bibliographical references (leaves 69-70). Also available via Humboldt Digital Scholar.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Mary E. Galvin-Donoghue, Dept. of Materials Science & Engineering. Includes bibliographical references.

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Science, 2006. / "May, 2006." Title from electronic dissertation title page (viewed 10/11/2006) Advisor, Frank W. Harris; Committee members, Stephen Z. D. Cheng, David A. Modarelli, Judit Puskas, William J. Brittain; Department Chair, Mark D. Foster; Dean of the College, Frank N. Kelley; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Prepared under contract no. EX-76-A-01-2295-037.

The purpose of this investigation is to compare high frequency to low frequency (50Hz) technologies. To accomplish this, two highly optimized candidate converters are built to champion each of the inverter classes. Both candidates are constrained to produce the same quasi-sinusoidal output waveforms in identical operating conditions. The low frequency inverter is designed with optimization of its output power quality and accurate loss characterization taken in mind. A new iron core design procedure is proposed that may predict core losses when using non-sinusoidal excitation. Experimental results indicate that it has a promising degree of accuracy. The high frequency candidate is designed using planar integration technology. A topology selection determines that a critical-conduction mode flyback is the most suitable option. Components are added the topology to allow resonant switching for reduced switching losses. Common-mode current arising from good capacitive coupling between windings in the planar coupled inductor is reduced using charge balancing technology. The novelty of the converter lies is in the fact that all passive components, barring the bulk of the input capacitance and the output capacitance, are incorporated into the single planar structure. Finally, a comparison of the inverters is made in the categories of power quality, regulation, efficiency, robustness and applicability to the application. The high frequency inverter is found to promise substantial advantages over the low frequency variety in most of these elements. / Dr. I.W. Hofsajer

Low concentrator photovoltaic systems are capable of increasing the power produced by conventional silicon photovoltaic cells, thus effectively lowering the cost per kWh. However, power losses associated with resistance and temperature have limited the large scale implementation of this technology. In this study, the optical-,electrical- and thermal sub-systems of a low concentrator photovoltaic system are theoretically and experimentally evaluated with the aim of minimizing the power losses associated with series resistance and temperature. A 7-facet reflector system, with an effective concentration ratio of 4.7, is used to focus irradiance along a string of series connected poly-crystalline photovoltaic cells. I-V characteristics of 4-, 6- and 8-cell photovoltaic receivers are measured under 1-sun and 4.83-sun conditions. Under concentration, the 8-cell photovoltaic receiver produced 23 percent more power than the 4-cell photovoltaic receiver, which suggests that the effect of series resistance can be minimized if smaller, lower current photovoltaic cells are used. A thermal model, which may be used to predict operating temperatures of a low concentrator photovoltaic system, is experimentally evaluated within a thermally insulated enclosure. The temperatures predicted by the thermal model are generally within 5 percent of the experimental temperatures. The high operating temperatures associated with the low concentrator photovoltaic system are significantly reduced by the addition of aluminium heat sink. In addition, the results of a thermal stress test indicated that these high operating temperatures do not degrade the photovoltaic cells used in this study. The results of this study suggest that the power output of low concentrator photovoltaic systems can be maximized by decreasing the size of the photovoltaic cells and including an appropriate heat sink to aid convective cooling.

Semiconductor materials used for making photovoltaic (PV) cells have defects and impurities due to constraints of keeping production costs low. Electrically active defects that are distributed over the bulk material lead to reduced overall performance of a photovoltaic (PV) cell. In this study an adaptable Light Beam Induced Current (LBIC) system was designed in order to characterize the local performance of PV cells. The system uses a laser source and objective lens mounted vertically above the sample on the X-Y stage. Two current pre-amplifiers are used for converting the photo-generated current from the PV cell and the signal from the reflection detector cell into a voltage that can be measured by the data acquisition board. Two configurations for measuring the photo-current maps of either bare cells or encapsulated PV mini-modules can be used. To add flexibility it was envisaged that the system would be built in such a way that it allows easy integration of carrier lifetime mapping capabilities while keeping costs to a minimum. The carrier lifetime measurement technique integrated into the LBIC system is based on the optical Open-Circuit Voltage-Decay (OCVD) method. In a single-crystalline silicon PV cell that was tested, photo-current and opencircuit voltage LBIC scans revealed shunting behaviour due to scratch marks on the front surface. The marks are believed to have been caused by poor handling during manufacturing process. Reduced photo-current due to edge shunting was observed towards the edges of the PV cell. In another sample of single crystalline silicon cell an edge shunt resulted in a 30 percent drop in photo-current measured. LBIC measurements performed on multi-crystalline cells revealed nonuniformities such as enhanced photo-current on one side of grain boundaries. These asymmetric enhancements of local photo-current are attributed to the incline of the grain boundary into the bulk of the material. LBIC results obtained from mini modules showed a high degree of mismatching from cell to cell. It is well known that mismatching can degrade the performance of a PV module with series connected cells. The LBIC measurements presented also illustrated the negative effects of delamination on the photo-current of PV modules. The LBIC measurements performed on mini PV modules highlight some of the benefits of using an LBIC technique as a tool for investigating PV cell’s local photo-current response. The effective lifetime maps obtained highlight the importance of optical OCVD method as a tool that can be used in conjunction with conventional LBIC technique. Effective minority carrier lifetimes around 40 ms were measured on a single crystalline silicon cell of 2.5 x 2.5 cm2. Local features such as cracks and lifetime degrading defects were revealed by LBIC maps and were also confirmed on effective lifetime maps. The results presented demonstrate the importance of using effective carrier lifetime maps to complement photocurrent maps of PV cells and identification of areas where defects are located.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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.