Thermal management of photovoltaic panels using phase change materials and hierarchical ZnO/expanded graphite nanofillers

Although PV panels are widely used to generate electricity from solar energy, their most important defect is the reduction of electrical efficiency with the increase of their temperature. The aims of this research is thermal management of a PV panel using phase change materials (PCM) and hierarchical ZnO/expanded graphite (EG) nanofillers to increase its production capacity. Two types of ZnO nanoparticles (rod- and flower-shaped) are synthesized using sonochemical method, and doped on EG particles to improve the thermal conductivity of the PCMs. A new bio-PCM consisting of oleic acid and beeswax is prepared and its performance is compared with paraffin and beeswax. The effect of PCM thickness (h=10-30 mm) and weight fraction of nanoparticles (ϕ = 1–5%wt) on temperature (Ts,ave), open-circuit voltage, current, and electrical performance of the PV panel is investigated. Results show that Ts,ave for pure paraffin, beeswax and bio-PCM has decreased from 64.23oC (without cooling) to 54.11oC, 57.15oC and 51.41oC, respectively. For all PCMs, adding flower-shaped ZnO/EG particles shows better results compared to rod-shaped one. The composite of bio-PCM with ZnO/EG has a higher positive effect on Ts,ave reduction and in generating voltage compared to paraffin and beeswax. PCMs composed of ZnO/EG particles with ϕ=5 wt% exhibited the minimum values of electrical efficiency. In addition, Ts,ave decreased intensively from h=10 mm to h=25 mm, but no significant difference is observed between h=25 mm and h=30 mm. The bio-PCM has proper melting point and heat storage capacity to cool down PV panel, which led to high power production. The maximum electrical efficiency is achieved using composite of bio-PCM and flower-shaped ZnO/EG particles at h=25 mm, which is circa 12.88 %.