1. The composition and principle of solar photovoltaic system
The solar photovoltaic system consists of the following three parts: solar cell modules; charge and discharge controllers, inverters, test instruments, and computer monitoring and other power electronic equipment 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 discharge of wastewater;
- No combustion process, no fuel;
- Simple maintenance and low maintenance costs;
- Operational reliability and stability;
- Long service life of solar cells as key components, crystal silicon solar cells can reach 25 years of life;
It is easy to expand the scale of power generation as needed.
Photovoltaic systems are widely used. The basic forms of photovoltaic system applications can be divided into two major categories: independent power generation systems and grid-connected power generation systems. The main areas of application are mainly household power supply in space aircraft, communications systems, microwave relay stations, television differential transmissions, photovoltaic pumps, and areas with no electricity or electricity. With the development of technology and the need for sustainable development of the world economy, developed countries have begun to systematically promote urban photovoltaic grid-connected power generation, mainly by constructing household rooftop photovoltaic power generation systems and MW-level centralized large-scale grid-connected power generation systems, etc. The use of solar photovoltaic systems is strongly promoted in such areas as transportation and urban lighting.
Photovoltaic systems vary in scale and application. For example, the scale of the system ranges from solar garden lights with 0.3 to 2 W in size to solar photovoltaic power plants in the MW class, such as 3.75 kWp home-type rooftop power generation equipment and the Dunhuang 10 MW project. Its application forms are also varied and can be widely used in many fields such as home, transportation, communications, and space applications. Although the PV system is of different sizes, its composition and working principle are basically the same. Figure 4-1 is a schematic diagram of a typical photovoltaic system that supplies DC loads. It contains several major components in the photovoltaic system:
Photovoltaic module: It is made up of solar modules (also called photovoltaic modules) that are connected in series and in parallel according to the system requirements. It converts solar energy into electricity output under the sunlight. It is the core component of the solar photovoltaic system.
Batteries: Store the electrical energy generated by the solar cell module. When the light is insufficient or at night, or when the load demand is greater than the amount of electricity generated by the solar cell module, the stored electrical energy is released to meet the energy demand of the load. It is a storage system of the solar photovoltaic system. Can parts. At present, the solar photovoltaic system is commonly used lead-acid batteries, for the higher requirements of the system, usually used deep-discharge valve-regulated sealed lead-acid batteries, deep-discharge liquid-absorbing lead-acid batteries.
Controller: It regulates and controls the charging and discharging conditions of the battery, and controls the solar module and battery power output to the load according to the power demand of the load. It is the core control part of the entire system. With the development of the solar photovoltaic industry, controllers have become more and more powerful. There is a trend to integrate traditional control parts, inverters, and monitoring systems. For example, the AES SPP and SMD series controllers integrate the above three. Functionality.
Inverter: In a solar photovoltaic power supply system, if an AC load is included, inverter equipment is used to convert the DC power generated by the solar cell module or the DC power discharged by the battery into AC power required by the load.
The basic working principle of the solar photovoltaic power supply system is that under the irradiation of sunlight, the power generated by the solar cell module is charged by the controller to charge the battery or directly to the load when the load demand is met, if the sunshine is insufficient or at night Then, the battery supplies the DC load under the control of the controller. For the photovoltaic system containing the AC load, an inverter needs to be added to convert the DC power into AC power. Photovoltaic systems have many applications, but their basic principles are similar. For other types of photovoltaic systems, the control mechanism and system components are different depending on the actual needs. The different types of photovoltaic systems will be described in detail below.
2. Classification and introduction of photovoltaic systems
PV systems are generally divided into independent systems, grid-connected systems and hybrid systems. According to the application form, application scale and type of the PV system, the photovoltaic power supply system can be divided into six types as follows: small solar power system (Small DC) and simple DC system (Simple) DC); Large-scale solar power 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 utilizes the photovoltaic effect of the semiconductor interface to convert light energy directly into electrical energy. The key element of this technology is solar cells. After the solar cells are connected in series, they can be packaged to form a large-area solar cell module, and then a photovoltaic device can be formed by combining the power controller and other components. Photovoltaic power generation has the advantage of being less subject to geographic restrictions because it is sunny; the photovoltaic system also has the advantages of being safe, reliable, noise-free, low-pollution, energy-efficient, and without the need to consume fuel and erection of transmission lines to generate electricity on-site and for short construction periods. Photovoltaic power generation is based on the principle of photovoltaic effect, using solar cells to convert solar energy directly into electrical energy. Regardless of whether it is used independently or connected to the grid, the photovoltaic system is mainly composed of solar panels (components), controllers and inverters. They are mainly composed of electronic components and do not involve mechanical components. Therefore, photovoltaic power generation equipment Extremely refined, reliable and stable, long life, easy installation and maintenance. In theory, photovoltaic technology can be used in any application where power is needed, from spacecraft, down to home power, up to megawatts of power stations, to toys, and photovoltaic power is everywhere. The basic components of solar photovoltaic power generation are solar cells (sheets), monocrystalline silicon, polysilicon, amorphous silicon, and thin-film batteries. At present, the single crystal and polycrystalline batteries are the most used, and amorphous batteries are used in some small systems and calculators as auxiliary power sources.
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