Passive cooling of photovoltaic modules in Qatar by utilizing PCM-matrix absorbers
Operation of solar PV systems under extremely high temperatures and high humidity in hot climates represents one of the major challenges to guarantee higher system's reliability. Therefore, thermal management in hot climates is crucial for reliable application of PV systems, as it has a potential to increase the efficiency and life expectancy and to stabilize the output power characteristics. On the other side, dust accumulation on PV module together with atmospheric water vapor condensation may cause a thick layer of mud that is difficult to be removed. The present research focuses on utilization of Phase Change Materials (PCM) for passive thermal management of solar systems. Passive cooling uses the high temperature differences between day and night in arid desert regions, due to sky radiation in the night. The high thermal capacity of PCM accumulates coolness during night to keep the PV cells at a moderate temperature during the day. This also can help maintaining the PV panel temperature well above the dew point to prevent condensation during day and night, thereby avoiding mud formation on the panel surface, which reduces water consumption and mechanical efforts in cleaning. Initially the passive cooling concept has been examined with one type of solar PV panels; Monocrystalline, with two thicknesses of PCM Absorber; 30 mm and 50 mm, melting point of 54°C and another arrangement with heat fins in place of the PCM layer, where both arrangements are compared with a reference PV module with no cooling devices attached to it. The experimental campaign has been conducted at the outdoor testing facility under weather conditions in Qatar for nine months from April to December 2018. The experimental analysis showed that the PV module's peak temperature was shaved by 10 °C with the PCM effect compared to reference PV modules without PCM. The experimental analysis confirmed the results of the numerical optimization, which revealed that there is an optimum thickness for PCM layer ~ 20-30 mm at 54 °C melting point. The analysis has revealed that cooling mechanism with heat fins alone (without PCM) achieved a temperature shaving of 5-8 °C. Moreover, the module peak temperature can be shaved at a constant temperature for a longer time with higher PCM thickness during noontime and remains at the same as the PCM melting temperature for five hours. Although the magnitude of peak shaving effect decreases with the higher thickness, stabilized temperature for longer time around the noontime can have a positive impact on stabilized power supply that is important for grid operation when installing large capacities of solar PV. It is worth mentioning that a numerical simulation model has been developed in parallel, and validated against measurements under real operation conditions of PV modules in Qatar, to examine the effect of the PCM-Matrix Absorber (PCMMA) on solar PV systems and optimize its properties for Qatar. For the optimized PCM-MA, which has been arrived at later after manufacturing the pilot plant, the PV module temperature is reduced by 23 °C, the energy yield can increase by 9-11% for mono and polycrystalline PV modules and 6-8% for thin film modules depending on the temperature coefficient of the high quality modules available in the international market. Presentation of the numerical simulation model and results will be elaborately discussed in a following publication.