Evaluating the impact of recycled ceramic-PCM compound and absorber tube positioning on the efficiency of flat-plate solar collector

• Evaluating thermal performance of solar collector with thermal storage materials. • Utilizing RC-PCM compound to enhance thermal energy storage. • Heat exchanger positioning impacts efficiency more than storage capacity. • Lower-bound heat exchanger raises system efficiency to a peak of 38 % • Upper-bound design reduced efficiency by about 3 % The demand for hot water remains heavily reliant on fossil fuels, leading to environmental degradation. Solar energy offers a sustainable and reliable alternative, particularly through flat plate solar water heaters (FPSWHs). This study investigates the performance enhancement of FPSWHs by integrating thermal energy storage (TES) materials. A novel hybrid material composed of phase change material (PCM, RT31) and recycled ceramic (RC) was developed to improve the thermal diffusivity of the storage medium, serving a faster thermal absorption. Two TES configurations, including pure PCM and RC-PCM composite, were experimentally tested for irradiation in an indoor setup. The impact of the heat exchanger position (inside or outside the TES layer) was evaluated. The study employed a combination of experimental testing and theoretical analysis to evaluate the performance of the different TES configurations. Results showed that immersing the heat exchanger within the TES material (lower-bound configuration) significantly improved the mean system efficiency by about 8% compared to the conventional flat plate collector, and increased the cumulative energy gain by approximately 12 %. In contrast, the heat exchanger position above the TES layer (upper-bound configurations) reduced the mean efficiency by about 3 % compared to the conventional collector. The findings indicate that the performance of a flat plate solar water heating collector integrated with a back-filled thermal energy storage module (TESM) is strongly influenced by the positioning of the heat exchanger tube. Specifically, the location of the tube plays a more critical role in enhancing system efficiency than simply increasing the thermal storage capacity. This research introduces a reassuringly cost-effective, eco-friendly RC-PCM composite and highlights the optimal placement of the heat exchanger tube for an enhanced flat plate solar collector.