A Study On The Performance And Optimization Of Inclined North-south Axis Three-positions Sun Tracking Photovoltaic Water Pump System

In recent years,with the widespread popularization of photovoltaic power generation technology and the significant reduction of power generation cost,photovoltaic water pump system(PVWPS)has become one of the effective ways to solve the local water shortage in remote rural areas.PVWPS can be divided into direct-coupled system and indirect drive system.The structure and control system of indirect drive photovoltaic water pump system is complex,which is suitable for large water supply projects and photovoltaic power generation system with pumped storage.Direct-coupled photovoltaic water pump system(DC-PVWPS)uses the electric energy of solar cells to directly drive the water pump.Because of its simple structure,little maintenance and no need for special personnel on duty,it depends on the storage tank to adjust the water supply needs of agricultural production and daily life,so it is very suitable for remote and local water shortage in rural areas.However,due to the instability and periodic variation of solar radiation,the mismatch between power supply and demand of DC-PVWPS leads to low solar energy utilization,and the pumping cost is much higher than that of conventional electric-driven pump systems.Therefore,how to improve the solar energy utilization of DC-PVWPS and reduce the pumping cost is an important direction of future DC-PVWPS research.The core of improving the solar energy utilization of DC-PVWPS is to make the photovoltaic output of the solar cell stable to meet the stable demand of the water pump for electric energy,and then to make the current and voltage output of the solar cell match the current and voltage required for the efficient operation of the DC-PVWPS under specific operating conditions.The mechanical and control system of conventional single-axis and dual-axis continuous tracking system is complex and prone to failure,and the tracking system cost is high,so it is difficult to meet the simple and practical technical requirements of remote villages.Therefore,this study constructed a inclined north-south axis three-positions solar tracker for DC-PVWPS(INSA-3P-PVWPS),and carried out in-depth theoretical and experimental research on the influence factors of the system and the causal relationship of the influence;The system optimization design theory was established to maximize the solar energy utilization of the system,combined with the optical characteristics of the INSA-3P tracking system and the photovoltaic output characteristic curve of the solar cell,and in-depth theoretical research was carried out on the optimal design of the system under different operating conditions.The specific research contents and results are as follows:1.A mathematical model describing the optical and photovoltaic performance of PV modules in fixed and different tracking modes is established based on the law of sun-earth motion,vector algebra and solar radiation theory;The annual output of PV modules under different tracking modes was studied;The influence of design and installation parameters on optical and photovoltaic performance was analyzed;The optimum tilt andq_a of INSA-MP are explored to maximize the annual power generation;According to the average solar radiation data of 34 meteorological stations in China for many years,the optimum installation tilt of tracking axis with the maximum annual amount of solar radiation received and the empirical correlation ofq_a are obtained.The results show that with the increase of azimuth adjustment times(M)per day,the annual PV output of photovoltaic(PV)modules gradually increases,but the increase gradually decreases.After optimized design,the annual power generation of INSA-3P,INSA-5P and INSA-7P reach 96%,97%and more than 98%of the dual-axis tracking,respectively.For small PVWPS,INSA-3P is preferred because it can be operated manually.2.A DC-PVWPS performance test platform was built,and the performance of INSA-3P-PVWPS were compared with FIX-PVWPS and 2A-PVWPS respectively for a year.The experimental results show that compared with FIX-PVWPS,the increase of daily water volume of INSA-3P-PVWPS in sunny days is much higher than the increase of daily collected irradiation(accumulated value from sunrise to sunset),which is due to the early start time,late stop time and stable photovoltaic output of INSA-3P-PVWPS.The experimental contents and test results include:Under typical sunny irradiation conditions,the daily collected irradiation,power generation and water volume of INSA-3P-PVWPS were 1.56,1.50 and 1.56 times of FIX-PVWPS in daily operation period in winter,1.51,1.57 and 1.61 times in spring,and 1.68,1.65 and 1.75 times in summer.Even on occasional cloudy days in autumn,the daily water volume can reach 1.4times.The performance percentage of INSA-3P-PVWPS was 97%compared with2A-PVWPS under typical sunny conditions in all seasons of the year.3.A month-long comparison test showed that compared with FIX-PVWPS,the monthly water volume of INSA-3P-PVWPS in January was 1.46 times.The theoretical calculation results show that compared with FIX-PVWPS,the benefit ratio of monthly collected irradiation is 1.15～1.27,and the benefit ratio of monthly water volume is 1.27～1.43.Overcast and cloudy weather adversely affects the system.In cloudy weather,INSA-3P tracker can improve the energy utilization efficiency of PVWPS and its subsystems compared with FIX-PVWPS.4.In this paper,based on the operation characteristics of pump(I_L-V_L),photovoltaic characteristics of solar cell(I-V)and optical characteristics of INSA-3P tracking solar cell,the system is optimized and matched with the goal of the highest solar energy utilization of the system.In this method,the optimal matching interval of solar radiation is determined by calculating the maximum power output utilization factor,and the optimal matching between water pump and PV module is realized by combining the matching factor method.The results showed that the energy utilization efficiency of FIX-PVWPS and INSA-3P-PVWPS without optimization matching were 1.7%and 2.3%,and the matching factor was 54%and 68%;The energy utilization efficiency of the two systems is 2.2%and 2.8%,and the matching factor is 66%and 83%.Both tracking and optimization matching can improve the energy efficiency and matching factor of PVWPS,and the combination of tracking and optimization matching is the most effective for improving the energy efficiency and matching factor of PVWPS.