Solar water heating system has a vital potential for low and medium thermal applications. This study proposes a metaheuristic optimization technique, namely Search Group Algorithm (SGA), for energetic optimization of solar water heating system using flat plate collector (SWH-FPC). For this purpose, the following parameters are considered as design variables: mass flow rate, fluid inlet temperature, absorber plate thickness, riser tube outer diameter, tube spacing, and insulation thickness. In this study, SGA is applied to find optimal values of such parameters for maximum energy efficiency of flat plate solar collector. Moreover, the impact of each design variable on energy efficiency is also analyzed. The simulation results show that energy efficiency is improved by 4.904 compared to the base case, which emphasizes the effectiveness and robustness of SGA to achieve high performance of solar thermal collector. © 2019 PENERBIT AKADEMIA BARU.