The development of modern photovoltaic thermal systems (PV/T) is one of the most important steps in the application of using solar energy to produce both electricity and heat. Studies have shown that a system consisting of a heat-collecting tank the is most efficient system, in which the phase change materials (PCMs) are mixed with nanoparticles inside the system that are cooled by a cooling fluid (preferably a nanofluid). The PCMs have a high capacity to store energy in the form of latent heat. Nanoparticles are added to PCMs to treat and improve the low thermal conductivity of these materials. In this experimental study, nano-iron oxide III (Fe2O3) was added to paraffin wax in multiple mass fractions to evaluate the thermophysical changes that can be occur on the wax properties. Four samples of paraffin–nano-Fe2O3 were prepared with mass fractions of 0.5%, 1%, 2% and 3%, and their thermophysical properties were compared with pure paraffin (without nano additives). The results from this study showed that adding nano-Fe2O3 at any mass fraction increases the viscosity and density of the product. Thermal conductivity is improved by adding nano-Fe2O3 to paraffin wax by 10.04%, 57.14%, 76.19%, and 78.57% when adding mass fractions of 0.5%, 1%, 2%, and 3%, respectively. Stability tests showed that the prepared samples have excellent thermal stability (especially for 0.5% and 1% added nano-Fe2O3) to acceptable level of stability when adding 3% of nano-Fe2O3. The nano-Fe2O3 paraffin PV/T system was tested outdoors to ensure its ability to operate in the harshest weather conditions of Baghdad city. The current experimental results indicated clear evidence of the success of the examined nano-PCM.
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