1. Composition and principle of solar photovoltaic system
A solar photovoltaic system consists of the following three parts: solar cell components; 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 and no waste water discharge;
- No combustion process, no fuel required;
- Simple maintenance and low maintenance costs;
- Good operational 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;
Power generation can easily be scaled up as needed.
Photovoltaic systems are widely used. 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 fields are mainly in space aircraft, communication systems, microwave relay stations, TV differential turntables, photovoltaic water pumps and household power supply in areas without electricity. With the development of technology and the needs of 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 MW-level centralized large-scale grid-connected power generation systems. At the same time, in The application of solar photovoltaic systems has been vigorously promoted in transportation and urban lighting.
Photovoltaic systems have different scales and application forms. For example, the system scale spans a wide range, ranging 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 the Dunhuang 10MW project. Its application forms are also diverse and can be widely used in many fields such as household, transportation, communications, and space applications. Although photovoltaic systems vary in size, their composition and working principles are basically the same. Figure 4-1 is a schematic diagram of a typical 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: Stores the electric energy generated by solar cell components. When the light is insufficient or at night, or the load demand is greater than the power generated by the solar cell components, the stored electric energy is released to meet the energy demand of the load. It is the storage battery of the solar photovoltaic system. functional parts. Currently, lead-acid batteries are commonly used in solar photovoltaic systems. For systems with higher requirements, deep-discharge valve-regulated sealed lead-acid batteries, deep-discharge liquid-absorbing lead-acid batteries, etc. are usually used.
Controller: It stipulates and controls the charging and discharging conditions of the battery, and controls the power output of the solar cell components and the battery 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, the functions of controllers are becoming more and more powerful, and there is a trend to integrate the traditional control part, inverter and monitoring system. For example, AES's SPP and SMD series controllers integrate the above three function.
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 power generated by the solar cell components or the DC power released by the battery into the AC power required by the load.
The basic working principle of the solar photovoltaic power supply system is to charge the battery with the electric energy generated by the solar cell components under the irradiation of the sun, or directly supply power to the load when the load demand is met. If the sunshine is insufficient or at night The battery supplies power to the DC load under the control of the controller. For photovoltaic systems containing AC loads, an inverter needs to be added to convert the DC power into AC power. Photovoltaic system applications come in many forms, but the basic principles remain the same. For other types of photovoltaic systems, only the control mechanism and system components differ according to actual needs. Different types of photovoltaic systems will be described in detail below.