Extension of the operational time of a solar water heating system is essential for overnight industrial and domestic use. One technique is by integrating the solar water heater with thermal energy storage. In the present study, an outdoor experimental investigation of Integrated Phase Change Material (PCM)-flat plate solar collector was carried out with paraffin wax. The absorber plate was modified by installing extended surfaces into the PCM reservoir to increase the heat transfer area. Paraffin wax is used to store heat during the day time. Water is the heating medium and was circulated between a 120 L water tank and the solar collector by pumping. Two cases have been investigated that is with and without PCM. It was found that on the average, 0.5 kg min-1 10 to 20° inclination angles with PCM can provide promising 38°C hot water temperature for daytime demand with 52±2.2 efficiency. PCM case gives the highest performance when considering the day and night time efficiency compared to the case of without PCM. © 2012 Asian Network for Scientific Information.