The growth of intermittent solar power has developed a need for energy storage systems in order to decouple generation and supply of energy. Microgrid (MG) systems comprising of solar arrays with battery energy storage studied in this paper desire high levels of autonomy, seeking to meet desired demand at all times. Large energy storage capacity is required for high levels of autonomy, but much of this expensive capacity goes unused for a majority of the year due to seasonal fluctuations of solar generation. In this paper, a model-based study of MGs comprised of solar generation and battery storage shows the relationship between system autonomy and battery utilization applied to multiple demand cases using a single particle battery model (SPM). The SPM allows for more accurate state-of-charge and utilization estimation of the battery than previous studies of renewably powered systems that have used empirical models. The increased accuracy of battery state estimation produces a better assessment of system performance. Battery utilization will depend on the amount of variation in solar insolation as well as the type of demand required by the MG. Consumers must balance autonomy and desired battery utilization of a system within the needs of their grid.