Performance Study On PV/T System Featured By A Nanofluid-based Spectrum-splitting Top Channel And An S-shaped Bottom Channel

Nanofluids with good optical performance act as liquid spectrum filters above PV cells to absorb solar radiation which cannot be used by PV cells.This PV/T system with a top channel not only reduces the working temperature of PV cells,but also improves the thermal efficiency of PV/T system,which becomes one of the research hotspots in the comprehensive utilization of solar energy.With a view to temperature uniformity of PV cells,this paper combined the spectrum-splitting technique with structural innovation of PV/T system,and firstly proposed a novel dual-channel PV/T system featured by a nanofluid-based spectrum-splitting top channel and an S-shaped bottom channel（called Model A）.To quantitatively reflect the temperature uniformity of PV panel,two evaluation criteria were presented.A 3-D numerical model was established,and the effects of the cooling channel thickness e_n,nanofluid mass flow rate m,inlet temperature T_i,wind velocity V_wind and solar radiation concentration ratio C on PV panel’s temperature uniformity and system’s efficiency were analyzed.Simultaneously,a comprehensive performance analysis assessing the superiority of Model A in temperature uniformity and efficiency was compared with the dual-channel PV/T system featured by two rectangular channels above/below PV panel（called Model B）and the single-channel PV/T system only with an S-shaped channel below the PV panel（called Model C）,which provides theoritical guidance for engineering.The results indicate that,for Model A,the temperature distribution of PV panel is more uniform at relatively larger e_n and m,or relatively lower C.Among them,m and C have the greatest influence on temperature uniformity,while T_i and V_wind have very limited influence.The optimal value of e_n is 10 mm,at which the total energy efficiencyη_total of Model A reaches its maximum of 86.97%.Larger m and C can promoteη_total of PV/T system,but larger T_i and V_wind have negative influence onη_total.The increase of e_nis not conducive to the improvement of the overall exergy efficiencyη_ex of Model A,while the increase of T_i and C is beneficial toη_ex.Moreover,η_ex is insensitive to the change of V_wind and at m of 0.008 kg/s,the overall exergy efficiencyη_ex attains a maximum of 13.80%.However,considering all factors（temperature uniformity,energy efficiency and exergy efficiency）,the recommended mass flow rate is 0.02 kg/s.From the perspective of temperature uniformity,Model A is featured by a top channel and an S-shaped bottom channel,so its temperature distribution is always the most uniform,and the worst is Model C.From the perspective of energy efficiency,the total energy efficiencyη_total of Model A is always higher than that of Model B,and only when m=0.006～0.01 kg/s,η_total of Model A is lower than that of Model C.From the perspective of exergy efficiency,because of high electrical exergy efficiency of Model C,its overall exergy efficiencyη_ex is always the highest,and the second is Model A.If the user’s demand is the quantity of energy or the supply of thermal energy,Model A is preferred.If the user’s demand is the grade of energy or the output of electrical energy,Model C is recommended,but the temperature uniformity of PV panel should be taken into full consideration.In addition,under the condition of high solar radiation concentration ratio,Model A is recommended as the preferred choice comprehensively considering the temperature uniformity,energy efficiency and exergy efficiency.