| The heating demand in North China is large and solar energy resources are in abundance,and solar seasonal storage technology is preferred by the market as a renewable energy utilization technology for efficient utilization of solar energy resources.To solve the problems of large consumption of municipal electricity and complicated control of start-stop temperature difference in the existing system,this paper proposes a solar seasonal storage system with direct photovoltaic drive,and applies the direct photovoltaic drive technology to the solar seasonal storage system.A solar seasonal storage test system direct-driven by photovoltaic was built to test and analyze the electrical and thermal performance of the system on sunny and cloudy days,and to explore the effect of the collection/storage flow ratio on the system performance.The test results showed that the DC water pump used in the test was directly driven by 2.45 m2PV cells,started at an irradiance of 420 W/m2and operated stably at over 750 W/m2,and the overall thermal performance of the system was better on sunny days,and the heat collection efficiency,heat storage efficiency and solar heat storage rate were 19.59%,2.13%and 22.01%higher than those on cloudy days,and the variation of the heat collection/storage flow ratio has a small effect on the thermal performance of the system.The system simulation model was established based on the joint simulation platform of TRNSYS and MATLAB,and the accuracy of the model was verified.The results show that the root mean square coefficient of variation of the established simulation model is within 15%,which can reflect the actual operational state of the system more accurately.The orthogonal method was used to simulate the system and obtain the degree of influence of the total collector area,collector tilt angle,system circulation flow rate and PV cell capacity on the thermal and electrical performance of the system and the combination of optimal parameters.The highest solar energy storage rate was obtained for the above parameter combinations of 30.00 m2,40°,1.00 m3/h and 560 Wp.In addition,simulations determined that the 10 Ah battery is the most suited for this system application,which allows the system to work 6.63%longer in one storage season.The collection efficiency and solar heat storage rate of the system with the battery increased by 3.83%and 3.77%,respectively,compared with the system without the battery,and the average PV utilization efficiency increased by 15.17%.The annual heat storage increased by 1,329.33 k W·h or 11.12%.After adding the battery,the demand for the total collector area is reduced to a limited extent.Using the storage capacity of the system without batteries as the basis,the required collector area was calculated to be 2.26 m2for the system with batteries and 2.51 m2for the system without batteries for every 1 MW·h of heat stored to the soil,reducing the requirement by 10%.Based on a solar seasonal storage system with a collector area of 280.00 m2,the structural and performance differences between the direct-drive PV scheme and the traditional control scheme,as well as their economics and environmental friendliness,were compared and analyzed,and the results showed that the direct-drive PV scheme has a simpler structure and better heat storage capacity than the traditional control scheme.According to the simulated data comparison,the total heat storage of the PV direct-drive scheme with and without battery increased by 5.93%and 2.51%,respectively,compared with the conventional control scheme during the operating life.During the 20-year lifetime of system,the unit heat storage cost of the direct-drive PV system with and without battery is reduced by￥216.58/MW·h and￥215.64/MW·h,respectively,compared with the conventional control system,which reduces the capital investment by 37.82%and 37.66%.Within 20 years of operation,the direct-drive PV solution with and without battery saves about 941.48 MW·h and 942.62 MW·h of electricity,and reduces 938.61 t and 939.75 t of CO2emissions,respectively.In summarizing,the solar seasonal storage system with direct photovoltaic drive presented in this paper has a high capacity of thermal storage and is more cost-effective and environmentally friendly.Among them,the direct-drive PV scheme with battery is more suitable for promotion and application The research work in this paper provides a useful reference for the wider application of the solar seasonal storage system with direct photovoltaic drive. |
