Designing a complete solar distributed photovoltaic power generation system needs to consider many factors and carry out various designs, such as electrical performance design, lightning protection grounding design, electrostatic shielding design, mechanical structure design, etc., for independent distributed photovoltaic power generation systems applied on the ground. Said that the most important thing is to determine the capacity of the solar cell array and the storage battery according to the requirements of use, so as to meet the needs of normal work. The general design principle of the distributed photovoltaic power generation system is to determine the minimum solar cell components and battery capacity on the premise of ensuring that the load needs to be met, so as to minimize investment, that is, to consider reliability and economy at the same time.
The design idea of an independent solar photovoltaic system is to first determine the power of the solar cell module according to the power consumption of the electric load, and then calculate the capacity of the storage battery. However, the grid-connected solar distributed photovoltaic power generation system has its particularity. It is necessary to ensure the stability and reliability of the operation of the distributed photovoltaic power generation system, so the following items need to be paid attention to during design:
1) The spectrum and light intensity of the radiated light from the sun shining on the square array of solar cells on the ground are affected by the thickness of the atmosphere (that is, the quality of the atmosphere), the geographical location, the climate and weather of the location, the topography and features, etc. There are large variations both within a month and within a year, and there are even large differences in total annual radiation between years. The area where the solar distributed photovoltaic power generation system is used, the solar radiation of the area, the longitude and latitude of the place where the solar cells are used. Understand and master the meteorological resources of the place of use, such as monthly (annual) average solar radiation, average temperature, wind and rain, etc. According to these conditions, the local solar standard peak hours (h) and the inclination angle and azimuth.
2) Due to different uses, power consumption, power consumption time, and requirements for power supply reliability are different. Some electrical equipment has a fixed power consumption pattern, while some loads have irregular power consumption patterns. The output power (W) of the solar photovoltaic system directly affects the parameters of the entire system. The photoelectric conversion efficiency of the solar cell array is affected by the temperature of the solar cell itself, the intensity of sunlight and the floating charge voltage of the battery, and these three will change within a day, so the photoelectric conversion efficiency of the solar cell array is also variable. Therefore, the output power of the solar cell phalanx also fluctuates with the changes of these factors.
3) The working time (h) of the solar photovoltaic system is the core parameter that determines the size of the solar cell components in the solar photovoltaic system. By determining the working time, the daily power consumption of the load and the corresponding charging current of the solar cell components can be initially calculated .
4) The parameter of the number of consecutive rainy days (d) in the place where the solar photovoltaic system is used determines the size of the battery capacity and the power of the solar cell components required to restore the battery capacity after the rainy day. Determining the number of days D between two consecutive rainy days is to determine the battery component power required by the system to fully charge the battery after a continuous rainy day.
5) The battery pack is working in the state of floating charge, and its voltage changes with the power generation of the solar cell array and the power consumption of the load. The energy provided by the battery is also affected by the ambient temperature.
6) Solar battery charge and discharge controllers and inverters are composed of electronic components. When they are running, they have energy consumption that affects their working efficiency. The performance and quality of components selected by controllers and inverters are also related to power consumption. The size of the energy, thus affecting the efficiency of the distributed photovoltaic power generation system.
These factors are quite complicated. In principle, each power generation system needs to be calculated separately. For some influencing factors whose quantities cannot be determined, only some coefficients can be used to estimate them. Due to the different factors considered and their complexity, the methods adopted are also different.
The task of designing a solar distributed photovoltaic power generation system is to select the solar cell square array under the environmental conditions of the solar cell square , battery, controller, and inverter constitute a power supply system that not only has high economic benefits, but also ensures high reliability of the system.
The change cycle of sunlight and radiation in various regions on the earth is 24 hours a day, and the power generation of solar cell arrays in a certain region also changes periodically within 24 hours. The rules are the same. But changes in the weather will affect the amount of power generated by the solar array. If there are several days of continuous rainy days, the solar cell phalanx can hardly generate electricity, and can only be powered by the battery, and the battery needs to be replenished as soon as possible after it is deeply discharged. In the design, the total daily radiant energy of the sun or the average value of the annual sunshine hours provided by the meteorological station should be used as the main data of the design. Since the data in a region varies from year to year, the minimum data in the past ten years should be taken for reliability. According to the power consumption of the load, the battery needs to be powered both under sunshine and without sunshine, so the total solar radiation or total sunshine hours provided by the meteorological station are indispensable data for determining the capacity of the battery.
For solar cell arrays, the load should include the consumption of all power consuming devices in the system (except electrical appliances, batteries and lines, controllers, inverters, etc.). The output power of the solar cell array is related to the number of modules connected in series and parallel. The series connection is to obtain the required operating voltage, and the parallel connection is to obtain the required operating current. According to the power consumed by the load, for an appropriate number of solar cell modules, After series-parallel connection, the required output power of the solar cell array is formed.