Photovoltaic system has the following characteristics:
-No rotating parts, no noise;
-No air pollution and no waste water discharge;
-No combustion process, no fuel is needed;
-Simple maintenance and low maintenance cost;
-Good operation reliability and stability;
As a key component, solar cells have 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 as needed.
Photovoltaic system is widely used, and the basic forms of photovoltaic system application can be divided into independent power generation system and grid-connected power generation system. The main application fields are spacecraft, communication system, microwave relay station, TV differential turntable, photovoltaic water pump and household power supply in areas without electricity and power shortage. With the development of technology and the sustainable development of the world economy, developed countries have begun to promote urban photovoltaic grid-connected power generation in a planned way, mainly building household rooftop photovoltaic power generation systems and megawatt 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 form of photovoltaic system are different, for example, the scale of the system spans a lot, from 0.3 ~ 2 W solar garden lights to megawatt solar photovoltaic power stations. Its application forms are also varied, which can be widely used in many fields such as home, transportation, communication, space application and so on. Although the scale of photovoltaic system is different, its composition structure and working principle are basically the same. Figure 4- 1 is a schematic diagram of a typical photovoltaic system that supplies power to DC loads. It contains several main components in the photovoltaic system:
Photovoltaic module phalanx: It consists of solar cell modules (also called photovoltaic modules) connected in series and in parallel according to the system requirements, and converts solar energy into electric energy for output under the irradiation of sunlight. It is the core component of solar photovoltaic system.
Battery: Store the electric energy generated by solar cell module, and release the stored electric energy to meet the energy demand of the load when the light is insufficient or at night, or when the load demand is greater than the electric energy generated by solar cell module. It is the energy storage element of solar photovoltaic system. At present, lead-acid batteries are widely used in solar photovoltaic systems. For demanding systems, deep discharge valve-controlled sealed lead-acid batteries and deep discharge liquid-absorbing lead-acid batteries are usually used.
Controller: it is the core control part of the whole system to adjust and control the charging and discharging conditions of the battery and control the power output of the solar cell module and the battery to the load according to the power demand of the load. With the development of solar photovoltaic industry, the function of controller is becoming more and more powerful, and there is a trend to integrate traditional control components, inverters and monitoring systems. For example, the SPP and SMD series controllers of AES company integrate the above three functions.
Inverter: In the solar photovoltaic power supply system, if there is an AC load, then the DC generated by the solar cell module or the DC released by the battery will be converted into the AC required by the load by inverter equipment.
The basic working principle of the solar photovoltaic power supply system is to charge the storage battery with the electric energy generated by the solar cell module under the control of the controller or directly supply power to the load under the condition of meeting the load demand. If the sunshine is insufficient or at night, the battery will supply power to the DC load under the control of the controller. For photovoltaic system with AC load, it is necessary to add an inverter to convert DC into AC. The application of photovoltaic system has many forms, but the basic principles are similar. For other types of photovoltaic systems, according to actual needs, the control mechanism and system composition are different, and different types of photovoltaic systems will be described in detail below.