Numerical Study On Photovoltaic/Thermal Hybrid Systems For Different Glazing Methods And Combined With Phase Change Materials

Solar energy is one of the most trustable and environmentally beneficial renewable sources.Solar energy can be harnessed by two different methods:solar photovoltaic system(PV)which transforms solar energy to electrical power directly,and solar thermal unit that transforms solar irradiation directly to heat.These two systems are usually employed separately in the solar thermal systems with an external electrical power to circulate the coolant.The PV installed capacity has been expanded widely in the last 10 years representing the highest share percentage among the renewable energy installations globally.Therefore,the recent intensified installation of PV modules is a motivation to give a considerable attention for further efficiency enhancement.The substantial surface temperature increase under the solar radiation is a key contributor for the PV module power output reduction.Currently,it is only around 10 to 25%of the solar radiation reaching the PV unit surface is transformed into electricity with the remainder dissipated by heat.The heat accumulation on the photovoltaic modules affects the electricity conversion efficiency.Therefore,the photovoltaic/thermal(PV/T)system is considered to be one of the most promising technologies,which is proficient in producing both electrical and thermal energies.Despite different researches have theoretically investigated the PV/T performance by using several assessment approaches,the selection of the appropriate glazing method,working fluid and phase change material have not been paid a great attention simultaneously.The current thesis mainly focusses on the hybrid PV/T module numerically by considering different cooling fluids,glazing techniques and PCMs at distinct positions by utilizing the energy and exergy approaches,along with assessing the performance in the turbulence and laminar regions at different climatic conditions.By considering different coolant passages and glazing methods,six PV/T-air based configurations are designed and numerically investigated firstly.The performance for a typical day in August under the climatic data of Beijing,China,is evaluated from the energetic and exergetic points of view.The results reveal that the overall energetic and exergetic efficiencies are significantly higher for the double pass configurations than those of single pass configurations either with or without an air gap.Among the proposed layouts,the double pass with single glass glazing PV/T module offers the highest average daily overall energy and exergetic efficiencies giving values of 85.15 and 13.92%,respectively.Additionally,the electrical efficiency and output for the single pass configurations without an air gap are found to be dramatically higher than those achieved by the other suggested structures.The effect of the thermophysical properties of PCM on the performance of PV/TPCM hybrid structure are also examined by adopting water as a cooling fluid.The PV/TPCM and traditional PV/T structures are theoretically compared at different ambient data and coolant flow rates.A merit function is adopted to measure the thermophysical properties of PCM influence on the proposed modules.The results show that the mean PV surface temperature is apparently lower for the PV/T-PCM structure than that of PV/T layout,although the coolant discharge temperature is slightly enhanced.The thermal and overall energetic efficiencies are reduced from 60.8 to 49.2%and 72.6 to 61%,respectively,for PV/T-PCM structure when the latent heat of PCM is boosted from 80 to 240 kJ/kg.The heat to electricity ratio and the merit function value are substantially improved for the PV/T-PCM design with the increase of the melting temperature and the thermal conductivity of the PCM.For further enhancement of the PV/T module performance,different PV/T-PCM structures are designed through burying the water pipes within the PCM and positioning an additional PCM layer with different melting temperature from the upper one.Six glazed and unglazed PV/T or PV/T-PCM configurations are evaluated and compared from the energy and exergy aspects.The impact of varying the coolant flow rate is also evaluated in both the laminar and turbulent regions along with assessing the environmental impact of the proposed modules to analyze the daily CO2 reduction.It is shown that burying the water pipes inside the PCM beneath the PV/T module yields a significant enhancement of the overall performance.Also,the electrical energy generated from unglazed modules is somewhat higher than that generated from the glazed modules.The daily thermal energy output for the glazed modules is marginally higher than that generated from unglazed layouts having the same layer arrangement.Among the proposed structures,the glazed and unglazed PV/T modules integrated with dual PCMs achieve the highest daily average energetic and exergetic efficiencies,respectively.