Classification of photovoltaic systems

Generally, battery energy storage system manufacturers divide photovoltaic systems into independent systems, grid-connected systems and hybrid systems. If the photovoltaic power supply system is divided more carefully according to the application form, application scale and load type of the photovoltaic system, the photovoltaic system can be divided 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/DC power supply system (AC/DC); grid-connected system (Utility Grid Connect); hybrid power supply system (Hybrid); grid-connected hybrid system.

Photovoltaic power generation is an electronic component technology that directly converts light energy into electrical energy using the photovoltaic effect of semiconductor interfaces. The key component of this technology is solar cells. After being connected in series and packaged for protection, solar cells can form large-area solar cell elements, and then combined with power controllers and other components to form photovoltaic power generation devices. The advantage of photovoltaic power generation is that it is less restricted by geographical location because the sun shines on the earth; photovoltaic systems also have the advantages of being safe and reliable, noise-free, low-pollution, and can generate and supply electricity locally without consuming fuel and setting up transmission lines, and the construction period is short.

Photovoltaic systems are generally divided into independent systems, grid-connected systems and hybrid systems. If the photovoltaic power supply system is divided more carefully according to the application form, application scale and load type of the photovoltaic system, the photovoltaic system can be divided 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/DC power supply system (AC/DC); grid-connected system (Utility Grid Connect); hybrid power supply system (Hybrid); grid-connected hybrid system.

Photovoltaic power generation is an electronic component technology that uses the photovoltaic effect of semiconductor interfaces to directly convert light energy into electrical energy. The key component of this technology is solar cells. After being connected in series and packaged for protection, solar cells can form large-area solar cell elements, and then combined with power controllers and other components to form photovoltaic power generation devices. The advantage of photovoltaic power generation is that it is less restricted by geographical location because the sun shines on the earth; photovoltaic systems are also safe and reliable, noise-free, low-pollution, can generate electricity and supply power on-site without consuming fuel and setting up transmission lines, and have the advantages of short construction period.

Photovoltaic power generation is based on the principle of photovoltaic effect, using solar cells to directly convert sunlight energy into electrical energy. Whether it is used independently or connected to the grid, the photovoltaic power generation system is mainly composed of three parts: solar panels (components), controllers and inverters. They are mainly composed of electronic components and do not involve mechanical parts. Therefore, photovoltaic power generation equipment is extremely refined, reliable, stable, long-lasting, and easy to install and maintain. In theory, photovoltaic power generation technology can be used in any occasion where power is needed, from spacecraft to household power, from megawatt-level power stations to toys, photovoltaic power sources are everywhere. The most basic element of solar photovoltaic power generation is solar cells (sheets), including single crystal silicon, polycrystalline silicon, amorphous silicon and thin film batteries. At present, single crystal and polycrystalline batteries are used the most, and amorphous batteries are used for some small systems and computer auxiliary power supplies.

Solar photovoltaic systems are composed of the following three parts: solar cell modules; power electronic equipment such as charge and discharge controllers, inverters, test instruments and computer monitoring, and batteries or other energy storage and auxiliary power generation equipment.

Solar photovoltaic systems have the following characteristics:

- No rotating parts, no noise;

- No air pollution, no wastewater discharge;

- No combustion process, no fuel required;

- Simple maintenance, low maintenance cost;

- Good operational reliability and stability;

- Long service life of solar cells as key components, crystalline silicon solar cells can last for more than 25 years;

It is easy to expand the scale of power generation according to needs.

Photovoltaic systems are widely used, and the basic forms of photovoltaic system applications can be divided into two categories: independent power generation systems and grid-connected power generation systems. The main application areas are mainly in space aircraft, communication systems, microwave relay stations, TV differential stations, photovoltaic water pumps and household power supply in areas without electricity. With the development of technology and the need for sustainable development of the world economy, developed countries have begun to promote urban photovoltaic grid-connected power generation in a planned manner, mainly by building household rooftop photovoltaic power generation systems and MW-level centralized large-scale grid-connected power generation systems, and at the same time vigorously promote the application of solar photovoltaic systems in transportation and urban lighting.

Solar photovoltaic system consists of the following three parts: solar cell module; power electronic equipment such as charge and discharge controller, inverter, test instrument and computer monitoring and storage battery or other energy storage and auxiliary power generation equipment.

Solar photovoltaic system has the following characteristics:

- No rotating parts, no noise;

- No air pollution, no wastewater discharge;

- No combustion process, no fuel required;

- Simple maintenance, low maintenance cost;

- Good operation reliability and stability;

- As a key component, solar cells have a long service life, and the life of crystalline silicon solar cells can reach more than 25 years;

It is easy to expand the scale of power generation according to needs.

Photovoltaic system is widely used, and the basic forms of photovoltaic system application can be divided into two categories: independent power generation system and grid-connected power generation system. The main application areas are mainly in space aircraft, communication systems, microwave relay stations, TV differential stations, photovoltaic water pumps and household power supply in areas without electricity or power shortage. With the development of technology and the need for sustainable development of the world economy, developed countries have begun to promote urban photovoltaic grid-connected power generation in a planned manner, mainly by building household rooftop photovoltaic power generation systems and MW-level centralized large-scale grid-connected power generation systems, and vigorously promoting the application of solar photovoltaic systems in transportation and urban lighting.

The scale and application forms of photovoltaic systems vary. For example, the scale of the system spans a large range, from 0.3 to 2W solar garden lights to MW-level solar photovoltaic power stations, such as 3.75kWp household rooftop power generation equipment and Dunhuang 10MW project. Its application forms are also diverse, and it can be widely used in many fields such as household, transportation, communication, and space applications. Although the scale of photovoltaic systems varies, their composition structure and working principle are basically the same. Figure 4-1 is a typical schematic diagram of a photovoltaic system supplying DC loads. It contains several main components in the photovoltaic system:

Photovoltaic module array: It is composed of solar cell elements (also called photovoltaic cell modules) connected in series and parallel according to system requirements. It converts solar energy into electrical energy output under sunlight. It is the core component of the solar photovoltaic system.

Battery: It stores the electric energy generated by solar cell elements. When there is insufficient sunlight or at night, or when the load demand is greater than the amount of electricity generated by the solar cell elements, the stored electric energy is released to meet the energy demand of the load. It is the energy storage component of the solar photovoltaic system. At present, lead-acid batteries are commonly used in solar photovoltaic systems. For systems with higher requirements, deep discharge valve-controlled sealed lead-acid batteries and deep discharge liquid-absorbing lead-acid batteries are usually used.

Controller: It regulates and controls the charging and discharging conditions of the battery, and controls the electric energy output of the solar cell elements and the battery to the load according to the power supply requirements of the load. It is the core control part of the entire system. With the development of the solar photovoltaic industry, the functions of the controller are becoming more and more powerful, and there is a trend to integrate the traditional control part, inverter and monitoring system. For example, the SPP and SMD series controllers of AES integrate the above three functions.

Inverter: In the solar photovoltaic power supply system, if there is an AC load, an inverter device must be used to convert the DC generated by the solar cell elements or the DC released by the battery into the AC required by the load.

The basic working principle of the solar photovoltaic power supply system is that under the irradiation of sunlight, the electric energy generated by the solar cell elements is controlled by the controller to charge the battery or directly supply power to the load when the load demand is met. If the sunlight is insufficient or at night, the battery supplies power to the DC load under the control of the controller. For photovoltaic systems with AC loads, an inverter is also required to convert DC power into AC power. The application of photovoltaic systems has many forms, but their basic principles are similar. For other types of photovoltaic systems, they only differ in control mechanisms and system components according to actual needs. The following will describe different types of photovoltaic systems in detail.