Solar thermal potential of phase change material based U-pipe ETSCs for different climatic zones: Evaluating energy matrices and economic viability

Utilizing evacuated tubes as solar collectors grips significant hot water needs in domestic and commercial buildings. This study focuses on designing and developing U-pipe-evacuated tube solar collectors (U-ETSC-A and U-ETSC-B). The collector-A is filled with PEG6000 as phase change material (PCM), whereas the other one collector-B remains unfilled. Here, collector-A operated under simultaneous charging mode (SCM) and midday charging mode (MCM) at five mass flow rates within the cold climatic region of Jammu, India. The main objective of this study is to examine the energetic, exergetic, economic and solar thermal potential of U-ETSCs with and without heat storage. The results demonstrate that the maximum energy output of collector-A was 86.71% (for SCM) and 84.34% (for MCM) at 0.50 LPM. Collector-B's maximum daily energy efficiency was 72.96% at the same flow rate. Collector-A's maximum daily exergy output was 24.01% (for MCM) and 22.18% (for SCM) at 0.17 LPM. In contrast, collector-B achieved a maximum daily exergy output of 20.22% at the same flow rate. From the economic and solar thermal potential assessment, it was overserved that the optimum levelized cost of water heating, net present value, and payback period values for PCM-filled U-ETSC-A are 3.57 INR/ kWh for Region -V, 292109 INR for Region-III and 4.06 years for Region-II. Also, the minimum number of evacuated tubes required for rated power is 30 for PCM-integrated collector-A. Moreover, to promote the solar water heaters (SWHs) in India, various practical implications are discussed in this study. Hence, for improved thermal performance, it is recommended to utilize PEG6000 as energy storage material with SWHs in on-demand operation.