Passive Thermal Management of Photovoltaic Modules in Qatar by Utilizing PCMMatrix Absorbers
Authors: Hassabou Abdelhakim 
Published: June 2019

Performance and reliability is essential factor for deploying the solar Photovoltaic (PV) technology in desert environment due to the high ambient temperature and high humidity. During daytime, the PV conversion efficiency decreases considerably due to high temperature and weak natural cooling effects on PV modules. During night, sky radiation cooling promotes atmospheric water vapor condensation on PV modules surface, where dust accumulates and consequently, leading to cementation of dust that necessitates manual or mechanical cleaning in absence of rainfall. Therefore, thermal management in hot climates is crucial for reliable application of PV systems to prevent the efficiency drop due to high temperature rise during day time and to keep the module temperature above the dew point during night time to avoid mud formation on PV modules surface. Thermal management of PV modules in hot climates can be achieved by either active or passive cooling. Active cooling includes air-cooling, through natural or forced air flow, and water cooling. In hot summer, air-cooling would be less effective as the ambient temperature reaches up to 50°C, hence water cooling or passive thermal management of PV cells become a necessity. The present research focuses on utilization of Phase Change Materials (PCM) for passive thermal management of solar PV systems. The main focus is to explore the effect of utilization of PCM-based cooling elements on the thermal behavior of solar PV modules. By attaching PCM-Absorbers to the back side of PV modules, the modules temperature can be regulated by the virtue of PCM to extract and accumulate heat at high density, as PCM have a high specific heat density capacity due to latent heat of fusion during melting and solidification. Moreover, the PCM absorber can help reducing atmospheric water vapor condensation during night on the surface of PV module by releasing the absorbed thermal energy during the daytime to keep the PV module on a temperature above the dew point. Some of the important advantages of the proposed solution include, simplicity, no moving parts such as coolant circulation pumps or air blowers are needed, low tech and can be manufactured locally from aluminum waste and oil waste, zero self-energy consumption, involves no hazards such as chemical toxicity, flammability or explosivity, and has a longer life time than the life span of top quality PV modules available in the international market. The PV module and PCM material have been modelled using Finite Element method in COMSOL Multiphysics software. A macro scale transient model has been developed to capture the underlying physics related to energy and heat transfer balances. The setup contains six main sections; transparent top glass cover, PV cells, aluminum back sheet, heat conduction film, PCM matrix absorber and aluminum heat fins. The effect of PCM thickness, i.e. heat storage capacity, PCM melting temperature, fiber porosity and thermal conductivity of matrix absorber with/without heat fins has been extensively studied. The numerical simulation results showed that there are optimum thermos-physical properties for PCM Absorbers for cooling of PV modules under Qatar weather conditions. It has been concluded that the ideal PCM-Absorber should have a melting temperatures of 53–54 °C, 30 mm PCM thickness, and 85 % fiber porosity of metallic aluminum fiber structure and with aluminum heat fins. With the optimum design of PCM-Absorber, the PV module's peak temperature can be reduced by 16 °C during daytime and at night it can be maintained at 3-5 °C higher than conventional modules, which reduces water vapor condensation tendency. Furthermore, depending on the temperature coefficient of a PV module, the power production can be increased by up to 6–8% for mono and poly crystalline cells respectively, and up to 5% for thin film technology. The module's instantaneous efficiency can be increased by 1–2%. In addition, study of the effect of passive thermal management on PV modules lifetime is ongoing and preliminary results revealed that a significant increase in lifetime would be expected. A techno-economic analysis for commercial scale application of the proposed thermal management solution has also revealed promising results, especially under local manufacturing in Qatar utilizing oil waste, which makes it economically viable.