Performance evaluation of an enhanced self-storing evacuated tube solar collector in residential water heating application

Phase change materials (PCMs) offer higher levels energy storage density than conventional hot water tanks commonly used with solar hot water systems. The present study aims at investigating the integration of a selected PCM within the structure of an evacuated tube solar hot water system to create some compact thermal storage capacity. Then conventional solar water heater is compared with this novel PCM-based self-storing design. The results show that the proposed self-storing design can maintain the collector output temperature at around 63 °C after 15 h of not receiving any sunlight. That is whilst the output temperature of the normal collector drops down to ambient temperature in the same period. The obtained energy storage efficiency is 57 % and 75 %, and overall thermal efficiency is 49 % and 72 %, for the normal and the self-storing collectors, respectively. For the small-scale system used in this study, the proposed design helps reduce the size of the hot water storage tank required to supply the hot water demand by 55 %. The study also shows that the same design can even yield better performance at larger scales used in practical applications. •Normal evacuated tube collector is compared with a novel self-storing collector.•Collectors are compared in a residential hot water delivery application.•Direct hot water storage is compared with energy storage in an enhanced PCM.•The self-storing design has higher energy storage and overall thermal efficiencies.•The need for hot water storage is significantly reduced by the self-storing design.