The stand-alone type is a system that is not connected to the power company’s public grid. The photoelectric conversion efficiency of a solar cell is affected by the temperature of the cell itself, the intensity of the sun and the fluctuation of the battery voltage, and these three will change within a day. The spectrum and intensity of the radiant light from the sun on the ground are affected by the thickness of the atmosphere (that is, the quality of the atmosphere), the geographical location, the climate and meteorology of the location, and the topography and features. Its energy varies greatly in one day, one month, and one year, and even the total annual radiation amount varies greatly from year to year. The cycle of solar radiation and radiant energy changes in various regions on the earth is 24h a day, and the power generation of solar cells in a certain area also has a 24h periodic change, which is the same as the law of the sun’s radiation in the area. In addition, changes in the weather will affect the power generation of solar cell modules. If there are continuous cloudy and rainy days for several days, the solar cell modules can hardly generate power, so the power generation of solar cells is variable.
The battery pack works in a floating charge state, and its voltage changes with the power generation of the square array and the power consumption of the load. The energy provided by the battery is also affected by the ambient temperature. The solar cell battery charge and discharge controller is made of electronic components, and it also needs energy consumption. The performance and quality of the components used are also related to the amount of energy consumption, which affects the efficiency of charging. The power consumption of the load also depends on the purpose. There are fixed power consumption of equipment, such as communication relay stations, unmanned weather stations, etc., and some equipment such as lighthouses, navigation lights, civil lighting, and domestic electricity, the power consumption is often changed.
For independent photovoltaic systems, photovoltaic power generation is the power system with the only source of electricity. In this case, it can be divided into three types of loads: daytime, nighttime, and daytime and nighttime. For the loads that are only used during the day, most of the loads can be directly supplied by the photovoltaic system, which reduces the consumption caused by the charging and discharging of the battery. The capacity of the photovoltaic system can be appropriately reduced. The capacity of the volt system will increase accordingly. The capacity required by the load used overnight is somewhere in between. In addition, it can be divided into balanced load, seasonal load and random load to distinguish it from the time of use throughout the year. There are many factors that affect the operation of the photovoltaic system, and the relationship is very complicated. In actual situations, it must be dealt with according to the on-site conditions and operating conditions.
Due to the random nature of solar radiation, it is impossible to determine the exact amount of solar radiation at each time period on the front of the photovoltaic system after installation, and can only be used as a reference based on the calendar data recorded by the weather station. However, usually the meteorological station provides the solar radiation on the horizontal plane, which needs to be converted into the radiation on the inclined square front. For the general photovoltaic system, it is enough to calculate the monthly average solar radiation on the inclined surface, without considering the instantaneous solar radiation flux. The task of the designer is to design the solar battery application system under the environmental conditions where the solar battery is located (ie, the location of the site, solar radiation energy, climate, weather, topography and features, etc.), not only pay attention to economic benefits, but also ensure the high reliability of the system.