Photovoltaic system

Photovoltaic systems are generally divided into independent systems, grid-connected systems and hybrid systems. According to the application form, application scale and load type of the solar photovoltaic system, it can be divided into six types.

system introduction

According to the application form, application scale and load type of the solar photovoltaic system, the photovoltaic power supply system should be divided into more detail. Photovoltaic systems can also be subdivided into the following six types: small solar power supply system (Small DC); simple DC system (Simple DC); large solar power supply system (Large DC); AC and DC power supply system (AC/DC); Grid-connected system (Utility Grid Connect); hybrid power supply system (Hybrid); grid-connected hybrid system. The working principle and characteristics of each system are described below.

power supply system

The characteristics of the small solar power supply system are that there is only a DC load in the system and the load power is relatively small, the whole system has a simple structure and is easy to operate. Its main uses are general household systems, various civilian DC products and related entertainment equipment. For example, in the western region of my country, this type of photovoltaic system has been widely used, and the load is DC lamp, which is used to solve the problem of household lighting in areas without electricity.

DC system

The characteristic of this 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 no battery is used in the system, and no controller is required. The system has a simple structure and can be used directly. The photovoltaic module supplies power to the load, eliminating the storage and release process of energy in the battery, as well as the energy loss in the controller, and improving the energy utilization efficiency. It is commonly used in PV water pump systems, some temporary equipment power during the day and some tourist facilities. Figure 1 shows a simple DC PV pump 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.

Large-scale solar power system

Compared with the above two photovoltaic systems, the large-scale solar-powered photovoltaic system is still suitable for the DC power system, but this kind of solar photovoltaic system usually has a large load power. In order to ensure a stable power supply to the load, its corresponding The scale of the system is also large, and it needs to be equipped with a larger array of photovoltaic modules and a larger battery pack. Its common application forms include communication, telemetry, monitoring equipment power supply, centralized power supply in rural areas, beacon lighthouses, street lights, etc. This form is used in some rural photovoltaic power stations built in some areas without electricity in the west of my country, and the communication base stations built by China Mobile and China Unicom in remote areas without power grids also use this photovoltaic system for power supply. Such as the communication base station project in Wanjiazhai, Shanxi.

AC and DC power supply system

Different from the above three solar photovoltaic systems, this photovoltaic system can provide power for both DC and AC loads at the same time, and has more inverters than the above three systems in terms of system structure, which is used to convert DC power to AC power to meet the needs of AC load requirements. Usually, the load power consumption of such a system is also relatively large, so the scale of the system is also relatively large. It is used in some communication base stations with both AC and DC loads and other photovoltaic power plants with AC and DC loads.

Grid-connected system

The biggest feature of this solar photovoltaic system is that the direct current generated by the photovoltaic array is converted into alternating current that meets the requirements of the mains grid through the grid-connected inverter and then directly connected to the mains network. Outside the load, 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 is powered by the grid. Because the electric energy is directly input into the power grid, the configuration of the battery is omitted, and the process of storing and releasing the battery is saved. 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 problem, there will still be some energy loss. Such systems are often able to use utility power and an array of solar PV modules in parallel as power sources for local AC loads. The load power shortage rate of the entire system is reduced. Moreover, the grid-connected PV system can play a role in peak regulation for the public power grid. According to the characteristics of the grid-connected system, Soying Electric has successfully developed a solar grid-connected inverter several years ago, which is specially designed for the recycling of electric energy with various gains and losses. Great progress has been made, and a series of technical difficulties have been overcome on the grid-connected system.

Mixed supply system

In addition to the solar photovoltaic module array used in this solar photovoltaic system, an oil generator is also used 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 advantages of the above-mentioned independent photovoltaic systems are less maintenance, and the disadvantage is that the energy output is weather-dependent and unstable.

A hybrid power supply system that uses a combination of diesel generators and photovoltaic arrays can provide weather-independent energy compared to a single-energy stand-alone system.

Grid-connected mixed supply system

With the development of the solar optoelectronics industry, a grid-connected hybrid power supply system that can comprehensively utilize solar photovoltaic module arrays, utility power and backup oil generators has emerged. This kind of system usually integrates the controller and the inverter, using a computer chip to fully control the operation of the entire system, comprehensively using various energy sources to achieve the best working state, and can also use batteries to further improve the system’s load power supply guarantee rate , such as AES’s SMD inverter system. The system can provide qualified power for local loads and can work as an online UPS (Uninterruptible Power Supply). Power may also be supplied to or obtained from the grid. The working mode of the system is usually to work in parallel with the commercial power and the solar power. For the local load, if the power generated by the photovoltaic modules is sufficient for the load to use, it will directly use the power generated by the photovoltaic modules to supply the needs of the load. If the power generated by the photovoltaic modules exceeds the demand of the immediate load, the excess power can also be returned to the grid; if the power generated by the photovoltaic modules is insufficient, the utility power will be automatically enabled, and the utility power will be used to supply the demand of the local load. When the power consumption of the load is less than 60% of the rated mains capacity of the SMD inverter, the mains will automatically charge the battery to ensure that the battery is in a floating state for a long time; if the mains fails, that is, the mains power failure or the mains If the quality is not up to standard, the system will automatically disconnect the mains power and switch to independent working mode, and the AC power required by the load will be provided by the battery and the inverter. Once the mains returns to normal, that is, the voltage and frequency return to the above-mentioned normal state, the system will disconnect the battery, change to grid-connected mode, and supply power from the mains. In some grid-connected hybrid power supply systems, system monitoring, control and data acquisition functions can also be integrated into the control chip. The core components of such a system are the controller and the inverter.

Off-Grid Photovoltaic System

The off-grid photovoltaic power generation system is a new type of power source that generates electricity from photovoltaic modules, manages the charge and discharge of the battery through the controller, and provides electrical energy to the DC load or to the AC load through the inverter. It is widely used in plateaus, islands, remote mountainous areas and field operations with harsh environments. It can also be used as a power supply for communication base stations, advertising light boxes, street lights, etc. Photovoltaic power generation system utilizes inexhaustible natural energy, which can effectively alleviate the conflict of demand in areas with power shortages and solve the problems of life and communication in remote areas. Improve the global ecological environment and promote sustainable human development.

System functions

Photovoltaic panels are power-generating components. The photovoltaic controller adjusts and controls the generated electric energy. On the one hand, the adjusted energy is sent to the DC load or the AC load, and on the other hand, the excess energy is sent to the battery pack for storage. When the generated electricity cannot meet the load needs When the controller sends the power of the battery to the load. After the battery is fully charged, the controller should control the battery not to be overcharged. When the electric energy stored in the battery is discharged, the controller should control the battery not to be over-discharged to protect the battery. When the performance of the controller is not good, it will greatly affect the service life of the battery and ultimately affect the reliability of the system. The task of the battery is to store energy so that the load can be powered at night or in rainy days. The inverter is responsible for converting DC power to AC power for use by AC loads.