Comparative thermal performance: An experimental study of self-stored U-pipe vacuum tube collectors operated in closed mode

Hot water production using solar collectors is the utmost comprehensive application of solar energy. Solar water heaters are still incapable of operating in night/off-weather conditions and lacking in thermal performance. Researchers can see heat storage (thermal battery backup) as a potential solution. The novelty of this study is the fabrication and testing of newly designed U-pipe-based vacuum tube collectors (VTCs) integrated with thermal energy storage. Furthermore, Stearic acid and PEG6000 were selected as phase change materials in this study, and collectors were operated in closed mode for specially designed cases. Also, a cost analysis was evaluated for these collectors to show their economic viability. The thermal performance and economic outcomes of storage-based collectors were compared with conventional collector. Measured experimental data encompassed instantaneous inlet and outlet water temperatures, solar radiation and ambient temperature. The empirical findings showed that the maximum daily thermal performances were 69. 81, 68. 34%, and 61. 33% obtained by stearic acid-filled collector-2, followed by PEG-filled collector-3 and conventional collector-1 at. 334 LPM for case-III, respectively. Moreover, the maximum energy enhancement ratio was 6. 28% for collector-2 and 6. 21% for collector-3 at. 5 LPM for case-II, respectively. From the economic analysis results, it was observed that the modified solar water heaters (collector-2 and collector-3) have an average levelized water heating cost of. 06885 /kWh and. 06818 /kWh, respectively, with a payback time of 5. 37 and 5. 15 years, which makes the modified collectors economically viable. Finally, the results indicate that the storage-based collectors can be used for applications with specific temperatures of hot water.