| Energy has become an important strategic factor restricting national development in today’s society.Energy issues are related to the global response to climate change,national security,and the overall situation of economic development,with far-reaching implication and great significant.Solar energy has been vigorously promoted by the country for its abundant resources and eco-friendly advantages.There are two main methods to utilize solar energy: photo-thermal utilization and photovoltaic utilization.For photovoltaic utilization of solar energy,as photovoltaic cells are greatly affected by temperature,the maximum temperature of photovoltaic cells can reach 70～80℃ when solar radiation is strong,and the photovoltaic efficiency drops significantly.The capacity of soil heat storage is large,and the stratum temperature is relatively stable throughout the year.This characteristic of the soil makes it an excellent source of cold and heat.This project proposes to combine soil heat storage technology with PV/T technology to establish a coupling system of soil heat storage and PV/T.Through circulating working fluid circulating between the PV/T collector and the ground heat exchanger,the photovoltaic cells can be cooled and the solar waste heat can be recovered,which way greatly improves the photovoltaic efficiency.At the same time,the recovered heat stored underground can be used for ground source heat pump heating in winter,which solves the problem of winter and summer heat imbalance of ground source heat pump application in cold areas.The project serves multiple purposes and greatly improves the rationality of energy utilization.This paper focuses on the simulation study of summer operating characteristics of the system,the main work is as follows:The structure and heat transfer mechanism of PV/T collector and ground heat are analyzed.Theoretical models of PV/T and ground heat exchanger were established based on the structure and heat transfer mechanism.The heat storage of PV/T is negligible compared to the soil heat storage,so the steady-state model is used for PV/T and the transiently finite-line heat source model is used for soil heat transfer.For the variable heat flow conditions caused by changes in environmental conditions,the superposition method is used to calculate.Based on the establishment of the theoretical model,a calculation program was written to solve the thermoelectric parameters of the PV/T collector and the three-dimensional transient temperature field of the ground heat exchanger.The accuracy of the models were verified by comparing with experimental data from literature.Two operating modes of the circulating pump shutdown mode and soil cooling mode are designed for the system.According to the climate characteristics of Jilin,a total of 740 h meteorological data from July 3rd to August 3rd were selected to simulate the summer operating characteristics of the coupling system,including the seasonal variation characteristics of parameters such as thermal efficiency,electrical efficiency,thermal power,electrical power,overall efficiency,temperature field around drilling,water temperature at inlet and outlet of the ground heat exchanger.Based on the study of seasonal characteristics and typical meteorological conditions,the effects of different solar collector area and circulating water flow rate on the thermoelectric characteristics of PV/T,the axial temperature field of the soil and the water temperature at the inlet and outlet of the ground heat exchanger were studied.The results show that the water temperature at the outlet of the ground heat exchanger is generally lower than the ambient temperature during the summer operation period.During the period when the cooling channel is open,the average photovoltaic efficiency of the system is 15.1%,which exceeds the photovoltaic efficiency under the standard state by 15%,indicating that the soil can be better cooling photovoltaic.In the soil cooling mode,the maximum thermal efficiency is 67.7%,the maximum photovoltaic efficiency is16.1%,and the maximum total efficiency is 81.3%.The system greatly improves the comprehensive utilization efficiency of solar energy.The research provides theoretical support for the application of the integrated system of PV/T and ground source heat pumps. |
