Energy matrices, techno-economic and environmental assessment of fin-integrated HP-ETSC systems with thermal battery backup: Machine learning insights from experimental data

The evacuated tube solar collectors (ETSCs) represent a promising advancement in water heating technology, with ongoing research aimed at enhancing its performance through the integration of phase change materials (PCM). This study compares two innovative solar water heaters (SWHs): (a) the porous aluminium fin based HP-ETSC-A with PCM and (b) the HP-ETSC-B featuring plane fins without PCM. Comprehensive thermal performance, sustainability, and environmental analyses were conducted for both systems across various flow rates under full-day operation (FDO) and mid-day operation (MDO). Results demonstrate that HP-ETSC-A significantly outperforms HP-ETSC-B in heat transfer efficiency, achieving a maximum energy enhancement ratio of 24.07 % under FDO and 21.16 % under MDO at a flow rate of 0.134 LPM. The peak daily energy output reached 81.16 % for HP-ETSC-A during FDO and 79.7 % during MDO at a flow rate of 0.34 LPM, exceeding the performance of HP-ETSC-B. Additionally, HP-ETSC-A achieved maximum daily exergy efficiencies of 13.33 % and 12.58 % under MDO and FDO at a low flow rate of 0.067 LPH, respectively, compared to 11.28 % for HP-ETSC-B. Economically, HP-ETSC-A demonstrated optimal values of net present value (NPV) at $402.62 and levelized water heating cost (LWHC) at $0.053/kWh, with a payback time of 4.10 years, indicating more economic viability than the reference system. Environmentally, HP-ETSC-A achieved a maximum net CO₂ mitigation of 22.93 tons/lifetime under FDO and an exergy-based mitigation of 1.66 tons/lifetime under MDO, along with potential carbon credit earnings of $332/lifetime for energy perspective and $24/lifetime for exergy perspective. The artificial neural network (ANN) model effectively aligned experimental results with predictions.