One of the most promising solar heaters is the evacuated tube solar collector (ETSC). Enhancing the performance of ETSCs using latent heat energy storage system has been widely investigated. Accordingly, paraffin wax as phase changing material (PCM) has taken a large portion of research work. Although paraffin wax has a significant disadvantage of having low thermal conductivity, using fins to enhance the overall heat transfer coefficient has been studied to overcome such drawback. The present work compares experimentally the performance of two
evacuated tubes systems having two novel fins systems. Namely; an ETSC with copper helical fins of 20 mm pitch and an ETSC with copper helical fins of 40 mm pitch. The experimental work was done under four different flow rates to investigate the effect of the thermal load on the systems performance. These flow rates are; 0.165 L/min, 0.335 L/min, 0.5 L/min and 0.665 L/min with normal water as the heat transfer fluid (HTF). In addition, the PCM temperature inside the evacuated tubes are measured along the tube axis to investigate the fins effect on PCM temperature homogeneity and thermal storage. The systems performances and daily efficiencies are also compared to emphasis the effect of fins configurations. The experimental results have shown that both systems provided a proper PCM temperature homogeneity ant peak temperatures. However, both systems have shown different trends for PCM temperature distribution along the tubes axis. A peak HTF temperature of 53 ˚C was achieved in the system with 40 mm helical pitch fins. Both systems have successfully supplied hot HTF throughout the night for the four different flow rates. However, regarding daily efficiency, the 20 mm pitch system provide an enhancement of 11.85% with maximum efficiency of 68.66% at 0.665 L/min flow rate.