Composition and principle of photovoltaic system

Composition and principle of photovoltaic system 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. Photovoltaic system has the following characteristics:

No rotating parts, no noise;

No air pollution, no wastewater discharge;

No combustion process, no need for fuel;

Simple maintenance, low maintenance cost;

Good operation reliability and stability;

As a key component, solar cells have a long service life, and the service 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 at the same time vigorously promoting the application of solar photovoltaic systems in transportation and urban lighting.

The scale and application form of photovoltaic systems vary. For example, the system scale spans a large range, from 0.3~2W solar garden lights to MW-level solar photovoltaic power stations. Its application forms are also diverse, and it can be widely used in many fields such as home, transportation, communication, and space applications. Although the scale of photovoltaic systems varies, their composition structure and working principle are basically the same. Figure 1-1 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 modules (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 the solar cell module. When there is insufficient sunlight or at night, or the load demand is greater than the amount of electricity generated by the solar cell module, 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 module and the battery to the load according to the power supply demand 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, then an inverter device must be used to convert the DC generated by the solar cell module 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 module 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 will supply power to the DC load under the control of the controller. For photovoltaic systems with AC loads, an inverter is 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, the control mechanism and system components are different according to actual needs.

Figure 1-1 Solar photovoltaic system with DC load