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First, Introduction to off-grid photovoltaic system
The off-grid photovoltaic system is a system that can directly supply the electrical energy generated by the photovoltaic cell to the load or energy storage device. It can provide both direct current and alternating current. The difference from the grid-connected photovoltaic system is that it is not connected to the public power grid. Its application range is very wide.
Second, off-grid photovoltaic system classification
Off-grid PV systems include: household systems, off-grid photovoltaic power plants, and wind-solar complementary off-grid systems.
Third, off-grid photovoltaic system design mainly involves factors
1. Understand and master the data of the place of use
The information we need to know includes: location of the installation location: including location, longitude, latitude, topography, altitude, etc.; meteorological conditions at the installation site: including annual average (month) average solar total radiation in recent years, direct radiation The amount of exposure or sunshine. Annual average temperature, wind speed, rainfall, and the longest rainy days. Based on these conditions, local solar standard peak hours (H) and the tilt and azimuth angles of the solar modules can be determined and the basis for battery capacity selection.
2, understand the user load situation
The capacity of the solar cell array and the battery is determined according to the user load condition and the use requirements. The overall design principle of the off-grid power generation system is to select the minimum solar module and battery capacity to ensure the reliability and economy while considering the need to meet the power requirements of the load.
3. Determine off-grid PV system configuration
Based on the information we have learned, we can determine solar module capacity, battery capacity, inverter, and controller parameters.
3.1 Firstly, according to the power consumption of the user load, the local climatic conditions and the working time of the solar photovoltaic system, the power level of the solar cell module is determined. By determining the working time, the daily power consumption of the load and the corresponding solar cell module can be preliminarily calculated. recharging current. Thereby determining the solar charge controller parameters.
3.2 Then calculate the battery capacity based on the user's load power consumption and the number of local continuous rainy days. In addition, in the floating state of the battery operation, the voltage varies with the solar cell array power generation and the load power consumption. The energy supplied by the battery is also affected by the ambient temperature. Therefore, the choice of the battery should be combined with the above various factors to make appropriate selection.
3.3 The selection of the inverter is determined by the power of the electrical equipment. In the design process of the household system, the load nature and the load starting current should be fully considered. Therefore, the selected inverter should meet the normal working condition of the normal load. Under the same time, the inductive load start condition is satisfied. In addition, because of the solar cell charge and discharge controller. The inverter is composed of electronic components. When it runs, it has energy consumption, which affects the efficiency of its work. The performance and quality of the components selected by the controller and inverter are also related to the energy consumption, which affects the photovoltaic. The efficiency of the power generation system. System efficiency factors should also be fully considered in the design selection process.
4, system structure design
First confirm the number of series connection of solar photovoltaic modules, the DC bus voltage should be suitable for the battery voltage, the number of series is too small, the series voltage is lower than the battery float voltage, and the square array cannot charge the battery. If the number of series is too large and the output voltage is much higher than the float voltage, the charging current will not increase significantly. Therefore, the best state of charge can be achieved only when the series voltage of the solar cell module is equal to the proper float voltage. The number of series connection and the number of parallel connection of the PV modules are determined, and the component layout design can be carried out by integrating the site and other factors. At the same time, the basic scheme of the photovoltaic system and the structure of the support structure should be determined according to the project conditions. There are also the location of electrical equipment placement, the layout of energy storage batteries, and the layout of power distribution rooms.
5, electrical design
Including control inverter unit selection, PV combiner box, DC power distribution cabinet selection, energy storage battery selection, security, monitoring system design, other electrical equipment selection, equipment electrical safety design. All electrical specifications in the design process should comply with relevant national standards.
6. Environment and safety protection
The design process should comply with the relevant provisions of the environmental and noise standards of the base city and the safety standards for engineering construction and installation of electrical installations.
7. Packaging, transportation, installation and commissioning operation design
Give a reasonable design according to different project requirements
8, lightning protection grounding design
The design should comply with the lightning protection design standards of the building according to local weather, geographical environment and power plant specifications.
9, maintenance and testing design
10. Economic cost accounting and economic and social benefit analysis.
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