In the desalination field, the membrane distillation (MD) is a new process of producing distilled water that has been developed and tested in recent years. In this paper, the integrated single cassette air-gap membrane distillation (AGMD) module in the solar thermal desalination system is validated and numerically simulated with the TRNSYS program. This model is studied to be ideal for obtaining a distilled water flow rate of 5.5 kg/h at different times under changing climatic conditions throughout the year in Ain-Temouchent weather, Algeria. The auxiliary heater is added to ensure the thermal energy continuity in the cold climatic conditions, where the photovoltaic system is used to power electrically the auxiliary heater. Therefore, the energy needed is calculated for the auxiliary heater and is replaced by 10 photovoltaic panels, each one has an area of 1.6 m² using seven of the energy storage batteries (12V, 200Ah) with 1.5 KW via TRNSYS and PVGIS help programs. Simulated results showed excellent compatibility with experimental results in previous studies. Additionally, it was found that when the inlet temperature of AGMD reaches 85 °C, the distilled water flow from the distillation membrane reaches 5.5 kg /h and that remains stable on different days throughout the year by relying solely on solar energy.