3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Analysis of the dynamic power requirements for controllable energy storage on photovoltaic microgrid(2016) Horonga, NyashaStandalone microgrid studies are being done because an expansion of the existing utility grids to supply power to remote communities is not feasible. Standalone microgrids can be considered as one of the solutions for remote communities because power can be generated close to these communities and it minimizes cost related to power transmission. Renewable energy sources with large uctuations are frequently the source of power for these standalone microgrids. The uctuating nature of these renewable sources can often lead to frequent blackouts. This research is aimed at minimizing power uctuations using controllable energy storage systems. This MSc focuses on the analysis of the ramp rate and delay time requirements for controllable energy storage system used in standalone PV microgrids. Measured insolation data and recorded load demand data for typical domestic appliances are used in this study to analyze ramp rates present. The ramp rates are then used to determine the range of energy storage ramp rate and delay time required to maintain the microgrid voltage within the standardized range of 1pu 5%. From the recorded data it has been observed that PV power can be sampled from at least 1-second intervals without losing important information. The 1 second averaged ramp rates obtained from the insolation data measurements have been found to have the highest value of 0.12pu/sec. However, this ramp rate increases to 0.3pu/sec when the allowable microgrid voltage band is narrow (1pu 5%). These insolation ramp rates are very low compared to the ramp rates of typical loads that can be connected to a microgrid. This means that, if the energy storage system is speci ed to meet the load ramp rate requirements, it will be able to respond to the uctuating PV power. The results obtained from the simulations con rm that energy storage system ramp rate plays an important role in the stability of a standalone microgrid. The minimum allowable energy storage ramp rate was found to be 8.15pu/sec for load transients with a ramp time of 20ms. This value is 28 times the energy storage ramp rate required to cancel out insolation uctuations. This further con rms that energy storage system ramp rates must be speci ed using the load demand data. The maximum allowable delay time was also found to be 0.53s to maintain the microgrid voltage within the standardized range of 1pu 5%. This delay time is applicable when canceling out only the insolation uctuations. To cancel out load transient power uctuations, there should be no delay time.Item Double-layer capacitance from the charged surface(2016) Malaza, NkosinathiEnergy storage has become an important issue for society, there is a need for affordable and efficient devices that can store energy optimally. Supercapacitors are energy storage devices that can solve society’s energy storage problem. They can store the energy generated by renewable energy systems. In this work approaches will be studied that may be used to estimate capacitance of materials that can be used as the electrode of these devices. These materials must have high energy density, which will address one of the limitations of supercapacitors. To estimate the capacitance of the double layer, the double layer theory and ab initio numerical tools based on density functional theory (DFT) are used. The ab initio tools work with periodic systems, when charging the system one violates the periodicity of the system. This is overcome by using the effective screening medium method, which prevents energy divergent of the system. In this work different configurations of the water molecules are used to average the different orientations of water molecules in the electrolyte. The Pt(111) electrode is used, and electrolyte of sodium ion and water. In different configurations the sodium ion in the electrolyte is located at different positions. The capacitances calculated using two different approaches that we developed in this work are comparable to previously estimated capacitance. This is achieved by using minimal computational efforts. We obtained capacitance within that range. Double layer capacitance can be estimated to a good accuracy with the methods developed in this work. Though there are improvements that can be made on the methods that have been developed in this work to better estimate the double layer capacitance. And also more research has to be done in this field to come up with a theory that will accurately estimate capacitance. At the moment calculating the double layer capacitance is not trivial due to the lack of theory that describe the processes taking place at the surface of the electrode where the capacitance is calculated.