⑴Power generation principle of photovoltaic power station
The working principle of an independent photovoltaic power station: photovoltaic modules convert solar energy into electrical energy when there is light, and the load is powered by the solar charge and discharge controller, and the battery pack is charged at the same time; when there is no light, the battery is charged by the solar charge and discharge controller The group supplies power to the DC load. At the same time, the battery also directly supplies power to the off-grid inverter, which is inverted into AC power through the off-grid inverter, and supplies power to the AC load. The independent photovoltaic power station system composition is shown in Figure 1.
The working principle of the grid-connected photovoltaic power station: the grid-connected solar photovoltaic power generation system is mainly composed of photovoltaic components and grid-connected inverters. Without battery storage, the grid-connected inverter directly inputs electric energy into the public grid. Grid-connected photovoltaic power generation system Compared with the independent photovoltaic power generation system, it saves the process of battery energy storage and release, reduces the energy consumption, saves the space, and reduces the configuration cost. The grid-connected photovoltaic power station system composition is shown in Figure 2.
⑵Several common photovoltaic power generation systems
Generally, we divide photovoltaic power generation systems into three categories: independent systems, grid-connected systems, and hybrid systems. According to the application form, application scale and load type of solar photovoltaic power generation system, the photovoltaic power generation system can be divided into the following seven types: Small DCO power supply system ), simple DC power supply system (Simple DC power supply system), large solar power supply system (Large DC power supply system), AC/DC power supply system (AC/DC power supply system), grid-connected PV power supply system, oil Machine solar hybrid power supply system (Hybrid power supply system) and grid-connected hybrid system.
The working principle and characteristics of each system are explained below.
①Small solar power supply system (Small DC power supply system)
The characteristic of this system is that there is only DC load in the system and the load power is relatively small. The whole system has a simple structure and easy operation. It is mainly used in general household systems, various civilian DC products and related entertainment equipment.
②Simple DC power supply system (Simple DC power supply system)
The characteristic of the system is that the load in the system is a DC load and there is no special requirement for the use time of the load. The load is mainly used during the day, so there is no battery in the system and no controller is needed. The system has a simple structure and directly uses photovoltaic components to supply power to the load, eliminating the need for energy storage and release in the battery, as well as energy loss in the controller, and improving energy utilization efficiency. The system is often used in some temporary equipment during the day and some tourist facilities. The solar DC PV (Photovoltaic) pump system shown in Figure 4 is a simple DC power supply system. This system has been widely used in developing countries where there is no pure tap water for drinking, and has produced good social benefits.
③Large solar power supply system (Large DC power supply system)
Compared with the above two photovoltaic power generation systems, this photovoltaic power generation system is still suitable for DC power supply systems, but this kind of solar photovoltaic power generation system usually has a larger load power. In order to ensure a reliable supply of stable power to the load, its corresponding system The scale is also larger, requiring a larger photovoltaic array and a larger battery pack. Its common application forms are communication,
Power supply for telemetering and monitoring equipment, centralized power supply in rural areas, navigation beacon, street lights, etc.
④AC/DC power supply system (AC/DC power supply system)
Different from the above three solar photovoltaic power generation systems, this photovoltaic power generation system can provide power for both DC and AC loads at the same time. In terms of system structure, it has more inverters than the above three systems to convert DC power to AC power. To meet the demand of AC load. Generally, the load power consumption of this kind of system is relatively large, so the scale of the system is also relatively large. It is mainly used in some communication base stations with both AC and DC loads and other photovoltaic power stations with AC and DC loads.
⑤ Grid-connected PV power supply system
The biggest feature of this solar photovoltaic power generation system is that the DC power generated by the photovoltaic array is converted into AC power that meets the requirements of the grid through the grid-connected inverter and then directly connected to the grid network. The power generated by the PV array in the grid-connected system is not only supplied to the AC load. In addition, the excess power is fed back to the grid. In rainy days or at night, when the photovoltaic array does not generate electricity or the generated electricity cannot meet the load demand, it will be powered by the grid. Because the electrical energy is directly input to the grid, the battery is not required, and the process of energy storage and release of the battery can be omitted. The electricity generated by the photovoltaic module can be fully utilized, thereby reducing energy loss and reducing the cost of the system. However, a dedicated grid-connected inverter is required in the system to ensure that the output power meets the requirements of the grid power for voltage, frequency and other indicators. Because of the inverter efficiency, there will still be some energy loss. This kind of system can usually use city electricity and solar photovoltaic module arrays in parallel as the power source of the local AC load, reducing the load shortage rate of the entire system, and the grid-connected system can play a role in peak regulation of the public grid. However, this system, as a decentralized power generation system, will have some undesirable effects on the grid of the traditional centralized power supply system, such as harmonic pollution and islanding effects.
⑥Oil engine and solar hybrid power supply system (Hybrid power supply system)
In addition to solar photovoltaic arrays, this type of solar photovoltaic power generation system also uses diesel generators as a backup power source. The purpose of using a hybrid power supply system is to comprehensively utilize the advantages of various power generation technologies and avoid their respective shortcomings. For example, the above-mentioned independent photovoltaic power generation systems have the advantage of less maintenance, but the disadvantage is that the energy output depends on the weather and is unstable. Compared with a single-energy independent system, a hybrid power supply system using diesel generators and photovoltaic arrays has the advantages of providing energy independent of weather and flexible load matching. However, the hybrid power supply system has disadvantages such as complicated control, large initial engineering, high pollution and noise