| The proposal of carbon peaking and carbon neutrality goals ushered in an excellent opportunity for the development of renewable energy.Solar energy is hailed as the future energy with the greatest development potential due to its wide distribution,clean and efficient.Therefore,vigorously developing and making full use of solar energy resources will be an important measure to reduce global carbon emissions and achieve sustainable development in the future.At present,the mainstream way to collect solar energy is to use related equipment to absorb and convert solar radiation energy to obtain electrical and thermal energy,so photovoltaic modules and heat collection devices to maintain efficient operation is a key factor to increase the proportion of clean energy.However,the flat plate solar collector(FPSC)in practical application was affected by the working environment,circulation flow,operation strategy and other parameters,so there is room for further improvement of the thermal performance.On the other hand,photovoltaic/thermal(PV/T)system,which collects electrical and thermal energy at the same time,and can improve the functional simplicity of FPSC.Due to the limited by shielding effect of surface PV modules,the thermal efficiency of PV/T device is often low,which is difficult to meet the expected water temperature conditions,and the thermal energy quality will also decline.Based on the above problems,this paper carried out a study on the efficiency improvement and application optimization of the solar photoelectric-photothermal system through the established experimental platform,and combined with the simulation data and experimental conditions to provide reference ideas and optimization suggestions for the efficient,economical and practical operation of FPSC and PV/T systems.To this end,the full text has done the following preparation and research work:Firstly,this paper introduces the basic situation of energy utilization at home and abroad,and the current consumption proportion of fossil fuels.After focusing on the importance of global development and application of solar energy at this era,and then introduces the research of domestic and foreign scholars in the field of solar photovoltaic/thermal utilization.The paper describes the structure and operation mode of FPSC and PV/T modules in detail,lists the specifications and parameters of the experimental platform and instruments,improves the evaluation method of the photoelectric-photothermal system based on the thermodynamic theory,conducts experimental data processing from the aspects of heat transfer characteristics,heat collection loss,electrical and thermal efficiencies,etc.,takes into account the entropy production of the system,and calculates the error of the experimental results,so as to evaluate the system performance more comprehensively and reasonably.Secondly,CFD technology was used to establish the three-dimensional model of FPSC module,and the solution method,calculation model and discrete equation in the simulation process are compared and selected,and the relevant boundary conditions are set up to carry out the numerical simulation of the operating conditions of FPSC in winter.The influence of circulating flow rate on the thermal efficiency of FPSC under low temperature conditions was analyzed through the temperature distribution nephogram of absorbing plate and heat exchange pipeline,which provided a theoretical basis for the subsequent large-scale flow operation experiment of FPSC system in winter.The simulation results show that,with the increase of circulation flow(0.02 kg/s to 0.15 kg/s),the thermal efficiency of the system gradually increases from 67.13% to 72.84%,but the improvement trend of efficiency gradually slows down,indicating that the heat collection capacity of the system is close to saturation.There are certain intervals and ranges in the selection of the flow rate of the working medium.Thirdly,the paper carried out the working performance test and operation strategy optimization experiment of the FPSC system in winter,analyzed and compared the corresponding heat transfer characteristics of the single,series and parallel heating modes in the operation of the system under large flow conditions,and further explored the parallel system with excellent thermal performance to verify the feasibility of large flow operation of the FPSC system.The economic and environmental benefits of the FPSC system are analyzed by using relevant formulas,and the recycling life and carbon emission of the system are calculated.It is concluded that,the thermal efficiency of single FPSC model is obviously higher than that of series and parallel system,and the lower temperature of heat absorbing plate and heat loss coefficient show better thermal performance,but the temperature of water tank is relatively low.The thermal performance parameters of the parallel system are better than those of the series system.Under the condition of 0.15 kg/s of the flow rate and 160 L of the water tank volume,the parallel system has the maximum heat collection and can save 8.68 k Wh of the electric energy.Meanwhile,increasing the heat collection area of the system can shorten the payback period of investment costs.Fourthly,based on the FPSC experimental platform,the paper made improvements,proposed PV/T-FPSC system and carried out relevant experimental tests,in order to improve the thermal performance of PV/T system with the help of FPSC.In the process,under the premise of large flow operation,the influence of different circulating water volume on electrical and thermal performance of the system was explored.As for the performance evaluation of the system,the first law of thermodynamics and the second law of thermodynamics were combined to carry out in-depth analysis.The energy equilibrium equation of enthalpy-entropy-exergy was used to calculate the entropy production of the system,which provided experimental support for the operation and optimization of the new system PV/T-FPSC.The research shows that,there are differences in the temperature of absorbing plate of different components in PV/T-FPSC system,and the thermal energy contribution of FPSC module is much larger than that of PV/T module.With the gradual increase of the tank capacity,the thermal efficiency and electrical efficiency of the system are gradually improved.The maximum thermal efficiency can reach 51.91%,and the electrical efficiency is stable at 13.40%.In addition,it was not a reasonable choice whether the water volume of the tank was too low or too high.Data show that,the tank volume of160-180 L is the optimal water distribution range for the system,while the overall exergic efficiency reached the 19.13%.Because of the PV/T module also has an electrical output,the cost recovery life of the system is further reduced.In this paper,some deficiencies existing in the process of solar energy utilization at the present stage are taken as the problem-oriented research,and relevant operating parameter assumptions are made to improve the working efficiency of the system,and corresponding experimental plans and operation schemes are formulated.Through the combination of numerical simulation and experimental testing,the hypothesis conditions are verified,and experimental conclusions based on the operation optimization conditions are obtained.The research results provide application guidance for the practical operation of FPSC and PV/T-FPSC systems,and provide research ideas and practical reference for the new utilization mode of efficient combined operation of solar the photovoltaic and photothermal system under the background of carbon peaking and carbon neutrality goals.Figure [42] table [23] reference [76]... |
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