In this work, a comparative experimental analysis of a conventional flat plate solar collector (FPSC) and an identical prototype with thermal storage system by PCM is presented. Thermal performance of the devices was studied from experimental and mathematical approaches. For experimental approach, both collectors were operated and analyzed simultaneously under the same real outdoor conditions. An experimental set-up monitored solar radiation, water inlet and outlet temperature, ambient temperature, wind speed, and temperatures of main components as glass cover, absorber plate and PCM. Heat transfer rates losses, internal PCM behavior as liquid fraction of PCM and accumulated energy were estimated and discussed using a mathematical approach. In this method, experimental results were evaluated to assess the performance of both collectors under the same operating conditions. In addition, different experimental cases were considered in order to improve the thermal performance of the prototype. Two different PCMs, a contact thermal conduction enhancement, and inclination of the collectors were analyzed. Experimental and analytical results indicate that the contact conduction between the absorber and PCM, and the selection of the PCM itself are key factors to increase the collector performance respect to conventional FPSC, while tilting the collector presented no significant improvement in latitude of the experimental tests. The prototype with PCM increased the night outlet temperature in 2 °C and maximum accumulated energy increased 630 Wh respect to the collector without PCM. The proposed improvements for collector with PCM rose the maximum liquid fraction of PCM from 0.3 to 0.9.
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