Performance Study Of Photovoltaic/Thermal System Based On Ag/CoSO₄ Nanofluid Spectral Filtration

Energy is the material basis for human survival and social development.Solar energy as a renewable energy has great potential for solving energy crises and air pollution.In recent years,solar photovoltaic/thermal（PV/T）utilization technology has attracted much attention due to its ability to provide electrical energy and thermal energy simultaneously.The application of nanofluid spectral splitting technology to PV/T system essentially solves the problem of temperature rise of photovoltaic modules,and also obtains higher grade thermal energy than traditional PV/T system,achieving solar full spectrum efficient utilization and the improvement of solar energy total utilization efficiency.But so far,the traditional nanofluids still can not achieve the ideal filtration matching the spectral response of solar cells,and the overall efficiency of PV/T system need to be further improved.Therefore,water based and propylene glycol based Ag/CoSO₄ nanofluids were proposed as new spectral filters for the PV/T system using silicon concentrator solar cells.The splitting performance of Ag/CoSO₄ nanofluids were analyzed theoretically and experimentally,and the performance of the PV/T system using the nanofluid filters were evaluated.（1）Firstly,different concentrations and uniformly dispersed water based and propylene glycol based Ag/CoSO₄ nanofluids were prepared.The relatively accurate optical transmittance of each nanofluid was obtained by spectrophotometer using a double pathlength transmittance method,and the long-term stability of each nanofluid was also investigated.The results show that the Ag/CoSO₄ nanofluids with different base fluids have strong absorption at the wavelength range of 380-555 nm,but maintain a high transmittance at the wavelength range of 675-940 nm,which are close to the ideal spectral splitting curve of silicon concentrator solar cells.And the propylene glycol based Ag/CoSO₄ nanofluid exhibit excellent long-term stability.（2）An experimental platform of photovoltaic/thermal conversion performance was built,and experimental studies on the effects of Ag/CoSO₄ nanfluid filters on the performance of PV/T receiver were carried out.The results show that the PV/T receiver achieve the best performance with Ag/CoSO₄ nanofluid filter at the highest concentration of 84.7 mg/L,with the total efficiency up to 84%and MF value of 1.97,approximately twice that of the alone photovoltaic system.（3）The optical transmittance model and photovoltaic/thermal performance model of Ag/CoSO₄ nanofluid were established respectively to explore the influence of nanoparticle mass fraction,optical pathlength,concentration ratio and thermoelectric conversion ratio on the performance of spectral splitting PV/T receiver.The results show that the total efficiency of PV/T receiver increases with the increase of the mass fraction of silver nanoparticles and the optical pathlength.However,with the increase of the concentration ratio,the total efficiency of the receiver increases first and then decreases,with the maximum total efficiency at the concentration ratio of 3.And for the propylene glycol based Ag/CoSO₄ nanofluid filter,the thermoelectric conversion ratio w=3 is the turning point of the PV/T receiver thermoelectric proportional distribution.（4）The physical model and radiation transfer model of the spectral splitting heat pipe type CPV/T system were established respectively,and MATLAB software was used to simulate and calculate the influence of ambient temperature,wind speed,water quantity of storage tank,water quantity of collector,concentration ratio and mass flow rate of splitting liquid on the all-day performance of the CPV/T system.The results show that the ambient temperature has a great influence on the maximum water temperature of the storage tank and the average electrical efficiency of the system,while the wind speed has a significant influence on the average thermal efficiency of the system.Increasing the amount of water in the storage tank and the amount of water in the collector are both helpful to improve the performance of the system,but at the same time,the lower the grade of heat energy obtained.In addition,increasing the concentration ratio can obviously improve the temperature of water in the storage tank,but at the same time,the system performance will be significantly reduced.