Theoretical Modulation And Experimental Study Of Nanofluid Based On Integrated Photovoltaic And Thermal Utilization

The PV/T system combines two energy conversion technologies,photovoltaic conversion,and photothermal conversion,which greatly improves the comprehensive utilization efficiency of the incident light,but there are still problems such as the PV cell cannot operate at the optimal working condition and the temperature coupling between the cell and the thermal output.The SBS-PV/T system utilizes spectral beam splitting technology to segment the solar irradiation,effectively reducing the heating of PV cells,and ensuring the cells operate at high efficiency while achieving flexible regulation of energy distribution in the system.The optical nanofluid,as a good carrier to regulate the spectrum division effect and enhance the photothermal conversion,its selective absorption property achieves the effect of projecting the spectral response band of the PV cell to the cell surface and absorbing the rest of the band as much as possible,which improves the thermal output grade of the nanofluid spectrum splitting photovoltaic/thermal(NSS-PV/T)system and solves the cell over-temperature problem.The output of the NSS-PV/T system is influenced by the combination of nanofluid performance and system operation parameters,but so far,the mechanism and optimization of multiparameter effects on the output of the NSS-PV/T system have not been fully investigated,the selection of nanofluid parameters has rarely been discussed,and the improvement of NSS-PV/T system performance needs to be further discussed.The optical properties of the nanofluid directly affect the energy distribution and thermoelectric output in NSS-PV/T.In this paper,the extinction coefficient of Ag/water nanofluid is calculated and discussed in conjunction with Mie theory,and the optical property curves are calculated around the changes of particle type,size,concentration,base fluid type,and the optical path of the nanofluid,respectively,while the Ag/water nanofluid is prepared,and using the optical test platform and particle size test instrument,the reliability and accuracy of the optical calculations were experimentally verified.The results show that the Ag/water nanofluid has good spectral tunability between 400 nm and 500 nm,while the experimentally measured spectral curves are in good agreement with the theoretical calculation in the strong absorption band.A theoretical calculation model of the double-pass NSS-PV/T system was established with full consideration of the optical properties of the nanofluid.Using this model,the effects of several parameters on the system outputs were analyzed,mainly including the effects of nanofluid parameters(particle size,concentration,and channel thickness)and system operation parameters(flow rate and concentration ratio)on the system outlet temperature,electrical efficiency,and the exergy efficiency.To ensure the reliability of the model,experimental data were measured in real time using an outdoor photovoltaic thermal platform when the working fluid was water and nanofluid,and the reasons for the causes of errors were analyzed through the comparative verification of experiments and calculations.In addition,the parameter selection of nanofluid was optimized by combining genetic algorithm to constrain the nanofluid outlet temperature under different concentration ratios with the goal of achieving the maximum exergy efficiency of the NSS-PV/T system.The results show that the NSSPV/T system under low concentrated conditions tends to require smaller particle size and higher particle concentration compared to the non-concentrated case,and the optimization results of the algorithm at low concentration ratio(concentration ratios from 2 to 7)show that particle sizes between 30 and 60 nm,concentrations between 50 and 150 ppm,and thicknesses between 0.005 and 0.01 m can provide the system with better overall performance.