1. The working principle of solar photovoltaic power generation system
Solar photovoltaic power generation systems can be divided into two categories: off-grid (independent) photovoltaic power generation systems and grid-connected photovoltaic power generation systems.
Figure 1 is a schematic diagram of the working principle of an off-grid photovoltaic power generation system. The core component of solar photovoltaic power generation is the solar cell module, which directly converts the light energy of sunlight into electric energy, and stores the electric energy generated by the cell module in the storage battery through the photovoltaic controller. When the load uses electricity, the electric energy in the storage battery is reasonably distributed to each load through the photovoltaic controller. The current generated by the battery assembly is direct current, which can be directly applied in the form of direct current, or it can be converted into alternating current with an alternating current inverter for use by an alternating load. The electricity generated by solar energy can be used as soon as it is generated, or it can be stored with energy storage devices such as batteries and used when needed.
The off-grid photovoltaic power generation system is suitable for the following situations and occasions: ①The power supply of the equipment that needs to be moved; ②The remote areas, agriculture, forestry and pastoral areas, mountainous areas, and islands far away from the power grid; ③The occasions that do not need to be connected to the grid; ④The occasions that do not require backup power, etc. .
Generally speaking, it is more economical and environmentally friendly to use off-grid photovoltaic power generation systems in places far away from the grid and where power supply is necessary, such as diesel power generation, where transportation fuel is required and the cost of power generation is high, and it can be given priority. In some occasions, in order to ensure the stability, continuity and reliability of off-grid power supply, it is often necessary to use diesel generators, wind generators, etc. and photovoltaic power generation systems to form a wind and diesel power generation system.
Figure 2 is a schematic diagram of the working principle of the grid-connected photovoltaic power generation system. The grid-connected photovoltaic power generation system converts light energy into electric energy from a square array of battery components, and enters the grid-connected inverter through the DC combiner box and DC distribution cabinet. Some types of grid-connected photovoltaic power generation systems also need to be equipped with energy storage systems to store electrical energy. . The grid-connected photovoltaic inverter is composed of power regulation, AC inverter, and grid-connected protection switching. The AC power output by the inverter passes through the AC power distribution cabinet and then is used by users or loads. The excess power can be fed back into the public grid through power transformers and other equipment (it can be called electricity selling). When the grid-connected photovoltaic power generation system is due to climate reasons When the power generation is insufficient or its own electricity consumption is too large, the public grid can supplement the power supply to the user’s load (referred to as buying electricity). The system is also equipped with a monitoring, testing and display system, which is used for monitoring, testing and generating statistics of various data such as the working status of the entire system. It can also use the computer network system to remotely control and display the data.
The grid-connected photovoltaic power generation system can provide countercurrent power supply to the public grid, and its power generation characteristics of “day and night” can be used to adjust the peak and valley of the public grid, which is very beneficial to strengthen the stability and reliability of power supply. Compared with off-grid photovoltaic power generation systems, energy storage equipment can be eliminated (except for special occasions), which expands the scope and flexibility of use and greatly reduces the cost of the power generation system.
For grid-connected photovoltaic power generation systems with energy storage systems, the photovoltaic inverter will contain charge and discharge control functions, which are responsible for regulating, controlling and protecting the normal operation of the energy storage system.
2. Classification of solar photovoltaic power generation systems
Solar photovoltaic power generation systems can be divided into two categories: off-grid (independent) photovoltaic power generation systems and grid-connected photovoltaic power generation systems. Among them, off-grid photovoltaic power generation systems can be divided into DC photovoltaic power generation systems, AC photovoltaic power generation systems, and AC and DC hybrid photovoltaic power generation systems. The DC photovoltaic power generation system can be divided into a system with a battery and a system without a battery.
Grid-connected photovoltaic power generation systems can be divided into countercurrent photovoltaic power generation systems and non-countercurrent photovoltaic power generation systems, and can also be divided into energy storage systems and non-energy storage systems according to their uses.
Off-grid photovoltaic power generation system mainly refers to a distributed independent power generation and power supply system, which has two main operating modes: ①The system operates independently to supply power to nearby users; ②The system operates independently, but there is a guarantee between the photovoltaic power generation system and the local grid Automatic switching device for power supply.
Grid-connected photovoltaic power generation systems can be further divided into three types according to the operation mode: ①The system runs in parallel with the grid system, but the photovoltaic power generation system has no power output to the local grid (no reverse current); ②The system runs in parallel with the grid system and can be connected to the local The grid outputs electric energy (with reverse current); ③The system runs in parallel with the grid system and has an energy storage device, which can be switched to an independent power supply system for local users as needed, or it can form a local area or user’s “microgrid” operation mode.
According to the different access points, it can be divided into two modes: user-side grid-connected and grid-side grid-connected. Among them, the user-side grid-connected is divided into two modes: reversible current to the grid and irreversible current to the grid.
According to different forms of power generation and utilization, it can be divided into three modes: completely spontaneous and self-use, spontaneous and self-use + surplus electricity to go online, and full amount to go online.
According to the installed capacity, it can be divided into small photovoltaic power generation system (≤1MW); medium photovoltaic power generation system 1MW to 30MW, including 30MW and large photovoltaic power generation system (≥30MW).
According to the grid-connected voltage level, it can be divided into small photovoltaic power plants: the connection voltage level is 0.4kV low-voltage power grid; medium-sized photovoltaic power plants: the connection voltage level is 10~35kV high-voltage power grid; large photovoltaic power plants: the connection voltage level is 66kV and above High-voltage power grid.