Mohamed, Mohamed Tarek Mohamed Hussein (2019-12). Modeling, Simulation, and Monitoring of a Photovoltaic Application Powering a Flywheel Energy Storage System. Master's Thesis. Thesis uri icon

abstract

  • One of the current technologies widely used to extract the earth's renewable energy is a solar module, which harnesses energy from the sun; however, its operating conditions and energy harnessing capacities vary greatly under different weather conditions. Flywheel Energy Storage Systems (FESS) present an environment-friendly solution for storing and utilizing solar energy, yet, frequent fluctuations of solar module voltage and current limit the efficiency of the FESS in photovoltaic (PV) applications. Existing literature investigates various FESS solutions for on- and off-grid PV applications; however, reported low FESS efficiency values up to 40%. Moreover, there is no commercially available FESS for off-grid or residential PV systems. In this paper, a novel bi-directional converter is proposed to regulate the power output of the PV system to the FESS while maintaining the harnessed solar energy. A typical bidirectional converter has a fixed duty cycle that is determined based on a constant input voltage source; which is not the case with the voltage of a solar module. Hence, the proposed bi-directional converter imposes a varying duty cycle that changes based on the solar module voltage and current operating point. A fully integrated FESS, with a PV system, is modeled to simulate the overall energy harvesting capabilities. The solar module is modeled using the one-diode solar cell model technique to predict the overall system efficiency and determine the most efficient time of day for switching between the FESS's charging (morning time) and discharging mode (night time). To validate the developed solar module model experimentally, four 250-Watt Ankara Solar PV modules are installed and field-tested. The solar insolation (solar power per square meter), wind speed, cell temperature, solar module power output, and FESS power output are logged during the system's operation. The theoretical model predicts that the total energy output for a five-day test is 27.3 kWh, while the experimental analysis shows that the solar modules produce 24.2 kWh (12% percentage difference). The average efficiency of the solar module model is determined to be 15.2%, which matches the solar module manufacturer's efficiency value of 15.4%. The theoretical power curve follows the experimental one throughout the day, which assures that the model can accurately predict the daily energy output of the solar module. The solar module simulation serves as a repeatable replication of the actual solar module source, which enables convenient, lowcost estimation of the solar module system under different environmental conditions. The proposed bi-directional converter is modeled and integrated in the developed FESS model to determine the modified FESS power output, efficiency, and flywheel rotational speed. The FESS model is constructed based on parameters from the actual FESS being built in College Station. The daily solar energy model input is 6.75 kWh while the daily energy stored in the FESS model is 5.39 kWh, giving the proposed FESS model efficiency of 79.8%. This efficiency value is higher than both the efficiency of available lead-acid batteries (60%) and FESS (40%) in off-grid PV systems. The maximum rotational speed of the flywheel model is 300 krpm which matches the maximum rotational speed reported in the manufacturer's datasheet. After the completion of the FESS experimental setup, the integrated solar module-FESS model will be validated further against the overall experimental power output and efficiency.

publication date

  • December 2019
  • December 2019
  • December 2019