This paper proposes a flat-plate solar collector system (FPSCs) with antifreeze characteristics which uses the phase change material (PCM) to store up a moderate amount of thermal energy during the daytime and release the energy during the night to prevent the FPSCs from freezing damage. Previous studies about the FPSCs exploiting the PCM are mainly focus on the purpose of balancing the tank water temperature between the daytime and night. In the present work, the study on the characteristics of the PCM-FPSCs for the purpose of antifreeze has been conducted. A mathematical model with high precision for the daytime working and night freezing of the system is present. The daytime working and night antifreeze performance of the system are evaluated. The results show that the conventional FPSC system will get frozen when the daily average temperature is less than 5 degrees C. The PA-FPSC system can work when the daily average temperature is in the range of 0-5 degrees C. (C) 2018 Elsevier Ltd. All rights reserved.