To ensure high performance, reliability, and economic profitability of a PV-battery system, the sizing of key components, such as PV panels and battery, are important during the design stage. Sizing procedures with low complexity and minimum input data requirement have become a more appealing solution than complex optimization methods. However, accuracy of such simplified sizing principles, e.g., compared to comprehensive models, should be investigated for different installation site conditions. Hence, in this paper, a robustness evaluation of currently available simplified sizing principle is performed where various mission profiles are considered. The analysis results have shown that using a simplified sizing principle results in less than 5% error in economic profitability compared to ones from the comprehensive model which includes advanced performance, lifetime and economic aspects.