Solar Domestic Hot Water (SDHW) systems collect energy from the sun to heat the household water. In the context of a system energy balance, numerical simulations were conducted using the commercial software “TRNSYS-17” to study the SDHW system performance (solar fraction) influenced by the critical parameters in various sizes of the thermal storage tank (TES) tank. The key parameters were the magnitude of the collector mass flow rate, degree of thermal stratification within the TES tank, and the duration of the mass flows through the collector. An empirical correlation was obtained to determine the operating collector mass flow rate and TES volume to deliver the peak system performance. The correlation was preliminarily verified with different weather data. The studies showed that the optimal collector mass flow rate occurred when the same amount of total daily household demand passed through the collector. Furthermore, when the twofold amount of the household demand passed through the collector, the optimal dimensionless tank volume became insensitive to the change of collector flow rate and remained constant at 0.84. Researchers discovered that promoting thermal stratification within the TES tank would enhance system performance. Thermal stratification within a TES improves the system performance by sending colder water to the solar collector and hotter water to the household. This research challenges the research community’s focus on thermal stratification by showing that solar fraction is directly related to the solar collector heat losses. As such, the role of the TES tank is to supply cold fluid to the collector to minimize collector losses. Thermal stratification in the top portion of the tank is thus unimportant in influencing solar fraction. In this research, the pump is turned on/off by monitoring the temperature difference between the collector inlet and outlet. Different pump control strategies at different collector mass flow rates were implemented to adjust the pump-on time. The studies showed the system performance was negligibly affected (~0.5%) by employing different pump control strategies while the collector mass flow rate was held constant. / Thesis / Master of Applied Science (MASc)