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ABSTRACT
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.
Nomenclature
| Acollector | = | Collector aperture area (m2) |
| AES | = | Annual energy saving (INR) |
| mwater | = | Mass of water (kg) |
| mPCM | = | PCM mass (kg) |
| L | = | Latent heat of fusion (kJ/kg) |
| CPCM | = | PCM specific heat (J/g.K) |
| Cpwater | = | Water specific heat (J/g.K) |
| Qgain | = | Useful heat gain (MJ) |
| Qinput solar | = | Incident input solar energy (MJ) |
| To,water | = | Inlet water temperature (°C) |
| Ti,water | = | Inlet water temperature (°C) |
| Ak | = | Annual cash flow (INR) |
| TIC0 | = | Total initial cost (INR) |
| IC0 | = | Initial cost (INR) |
| dR | = | Discount rate (%) |
| DR | = | Depreciation rate (%) |
| n | = | Life spam of system (years) |
| GEa | = | Annual energy generation (kWh) |
| L | = | Tube length (mm) |
| D | = | Tube diameter (mm) |
| IT | = | Incident solar radiation (W/m2) |
| QER1 | = | Enhancement ratio for collector-2 |
| QER2 | = | Enhancement ratio for collector-3 |
| ηDTP | = | Daily thermal performance |
| Abbreviations | = | |
| LPM | = | Liter per minute |
| LPH | = | Liter per hour |
| PCM | = | Phase change material |
| VTC | = | Vacuum tube collector |
| LWHC | = | Levelized water heating cost |
| NPV | = | Net present value |
| PBP | = | Payback period |
| RTD | = | Resistance temperature detector |
Highlights
The fabrication and testing of PCMs filled U-pipe-based vacuum tube collectors performed in this study.
A cost analysis was evaluated for these collectors to show their economic viability.
The maximum efficiency was 69.81 and 68.34% for storage-based collectors (2 and 3) at .334 LPM.
The energy enhancement ratio was 6.28% for collector-2 and 6.21% for collector-3 at .5 LPM
The collectors have LWHC of .06885 and .06818 $/kWh with a payback time of 5.37 and 5.15 years
Disclosure statement
No potential conflict of interest was reported by the author(s).
Correction Statement
This article has been corrected with minor changes. These changes do not impact the academic content of the article.
Additional information
Notes on contributors
Sudhir Kumar Pathak
Sudhir Kumar Pathak graduated with an M.Tech degree in Thermal Engineering from Rajasthan Technical University, Kota in 2016 with distinction and earned his B.Tech. degree from same university in 2011. He is currently pursuing his doctoral degree in Energy Management from Shri Mata Vaishno Devi University, Katra. His research interests are solar thermal systems, thermal energy storage, phase change materials, solar energy etc.
V.V. Tyagi
V. V. Tyagi is an Assistant Professor in Shri Mata Vaishno Devi University (SMVDU). He received his Ph.D. degree from School of Energy & Environmental Studies, Devi Ahilya University, Indore India, 2007. He has more than 10 years of research and teaching experience. His research interests are solar thermal energy storage with phase change materials, solar energy-based wastewater treatment technology, energy policy, PV & PV/thermal systems and applications.