| Photovoltaic irrigation equipment is highly efficient,clean,flexible,and not subject to grid power supply constraints,and is suitable for the needs of Chinese agricultural development.In order to speed up the promotion of agricultural photovoltaic irrigation equipment and improve the utilization rate of equipment,the same equipment may need to meet the requirements of different regions,seasons,and daily working hours.Therefore,it is necessary to carry out research on the output power of agricultural photovoltaic equipment and the length of daily power supply.The initial design of the power supply system provides a reference.In view of the fact that the farmland operation and the urban industrial life use electricity,the requirements for the power supply guarantee rate are relatively low,the economic input is less,the farmers use level is low,and the on-site monitoring is inconvenient,this paper starts from the practical application of the agricultural photovoltaic power supply system.Establish a nationwide small-scale photovoltaic power supply system time-of-day output power prediction model,and further obtain theoretical calculations of quarterly power supply durations in different regions,so that users can reasonably arrange work tasks,improve equipment utilization,and accelerate the application and promotion of photovoltaic power supply equipment.The main research contents and conclusions of this paper are as follows:(1)The time-dependent output power model of the national small-scale agricultural photovoltaic power supply system was constructed.In 2016～2018,the photovoltaic power generation data of Shaanxi Yangling was monitored and tested.The Polynomial function was used to quadraze the peak power and irradiance of the PV module per unit area and the ambient temperature(R~2=0.987).The influence of illuminance and ambient temperature on the power generation of PV modules,based on the analysis results,further linearly fits the peak power and irradiance per unit area of PV modules(R~2=0.968),from the perspective of simplicity and accuracy requirements.The latter uses a linear model of the latter.(2)Through the theoretical derivation,a time-based irradiance prediction model based on peak sunshine hours and sunshine duration is established.Based on the sunshine distribution function model of the sunny days built by the predecessors,a time-based irradiance model based on peak sunshine hours and sunshine duration is established by theoretical derivation.This model can reduce the disadvantages of“shaving peaks and valleys”to some extent.It is applied to the prediction of time-lapse irradiance under the type of sunny and rainy weather.The irradiance measured data of Yangling,Shaanxi Province was used to verify that the irradiance intensity of sunny days was generally higher than that of rainy days.The theoretical and measured values of time-lapse irradiance were very close,and the prediction model had the highest agreement(R~2=0.92～0.98).The prediction accuracy of the rain irradiance model is lower than that of sunny days(R~2=0.84～0.93);the cloudy irradiance prediction model is the worst(R~2=0.64～0.80).Further,we downloaded and compiled the China Meteorological Data Network from 1958 to 2017 for a total of 60 years,and the radiation data of 106 stations nationwide,and collected peak sunshine hours database in different regions of the country(see Appendix).(3)The relation between the output power reduction rate of photovoltaic modules and the change of ash density and dust equivalent particle size is established.The influence of dust particle size,ash density and light intensity on the output power of photovoltaic module was studied by using the laboratory test method of artificial cloth ash and the solar energy automatic simulation tracking device.The prediction model of output power reduction rate was established and the model was verified under outdoor natural light.The results show that the reduction rate of PV module output power increases with the increase of ash density,but the growth rate gradually slows down.When the dust deposit density is the same,the output power reduction rate of the photovoltaic module decreases as the dust particle size increases.The results of two-factor anova show that the dust particle size,ash density and their interaction have significant influence on the output power reduction rate,while the light intensity has no significant influence on the output power reduction rate.Through theoretical analysis,the concept and calculation formula of the equivalent particle size of dust with different particle gradations with the same shielding effect were proposed,and a calculation model(R~2=0.986)for the change of the output power reduction rate of photovoltaic modules with ash density and equivalent particle size was established by polynomial fitting.The calculation model was verified by the solar fertilizer applicator,and the absolute errors were all less than 1.5%,indicating that the model could provide design basis for the optimal configuration of power supply system in photovoltaic agricultural equipment.(4)A calculation model for the power supply duration of PV modules based on peak hours of sunshine and duration of sunshine is established.Based on the relationship between the output power and the load power per unit area of photovoltaic modules,the calculation model of the power supply duration based on the peak sunshine hours and the sunshine duration in different regions was established,and the results of the Yangling 2016～2018 test were used to determine the power supply duration.The model was verified and evaluated,and the calculation formula of the power supply duration of the photovoltaic module per unit area in spring,summer,autumn and winter with the load power was obtained.It was found that the summer power supply time was the longest under the same configuration,followed by spring,autumn and winter. |
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