Estimating the dynamic power requirements for controllable energy storage on PV microgrid
Declaration I, Nyasha Horonga, declare that this dissertation titled, ANALYSIS OF THE DY-NAMIC POWER REQUIREMENTS FOR CONTROLLABLE ENERGY STOR-AGE ON PHOTOVOLTAIC MICROGRID and the work presented in it are my own. I confirm that: • This work was done wholly or mainly while in candidature for a research degree at this University. • Where any part of this dissertation has previously been submitted for a degree or any other qualification at this University or any other institution, this has been
... early stated. • Where I have consulted the published work of others, this is always clearly attributed. • Where I have quoted from the work of others, the source is always given. With the exception of such quotations, this dissertation is entirely my own work. • I have acknowledged all main sources of help. • Where the dissertation is based on work done by myself jointly with others, I have made clear exactly what was done by others and what I have contributed myself. Signed: Date: i I would like to dedicate this dissertation to my loving parents, my fiancee Zanele Njazi and my siblings Simbarashe, Tapiwanashe, Cynthia and Tonderai Our premise is that many of the circumstances that seem to block us in our daily lives may only appear to do so based on a framework of assumption we carry with us. Draw a different frame around the same set of circumstances and new pathways come into view The Art of Possibility -R.S. Zander iii Acknowledgements The author would like to thank the ALSTOM chair for clean energy system technology for funding the research. Most of all the Author would like to thank the Supervisor Prof W.A. Cronje and the University of the Witwatersrand Energy group for their continued support during the course of the research. Special thanks to W. Doorsamy and Dr M. Shuma-iwisi for their valuable inputs. Abstract Standalone 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 fluctuations are frequently the source of power for these standalone microgrids. The fluctuating nature of these renewable sources can often lead to frequent blackouts. This research is aimed at minimizing power fluctuations 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 specified to meet the load ramp rate requirements, it will be able to respond to the fluctuating PV power. The results obtained from the simulations confirm 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 fluctuations. This further confirms that energy storage system ramp rates must be specified 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 fluctuations. To cancel out load transient power fluctuations, there should be no delay time.