Solar photovoltaic power generation system classification
Solar photovoltaic power generation systems can be divided into off-grid (independent) photovoltaic power generation systems and grid-connected photovoltaic power generation systems.
Figure 1 shows a schematic diagram of the working principle of an off-grid photovoltaic power generation system. The solar panel converts the light energy of sunlight into electric energy, and stores the electric energy output by the panel in the storage battery through the controller, and at the same time supplies power to the load. Since the output of the battery panel is direct current, it can be directly supplied to a direct current load. If it is an alternating current load, an inverter must be used to convert the direct current into alternating current before it can be used. The electric energy generated by the battery panel can be used immediately, or it can be stored in energy storage devices such as batteries and used when needed.
Figure 2 is a schematic diagram of the working principle of the grid-connected photovoltaic power generation system. Multiple solar panels are combined in series and parallel to form a square array of solar cells. After converting light energy into electrical energy, it enters the grid-connected inverter through the DC combiner box. Generally, grid-connected photovoltaic power generation systems do not need to be equipped with batteries, and some systems also need to be equipped with battery packs to store DC power in order to provide load backup power. The grid-connected inverter is composed of charge and discharge control, power regulation, inverter AC, and grid-connected protection switching. The AC power output by the grid-connected inverter is used by the load, and the surplus electric energy is fed into the grid through equipment such as power transformers (also known as electricity selling). When the grid-connected photovoltaic system has insufficient power generation or its own power consumption is large, the grid can supply power to the AC load (also known as buying electricity). In addition, the system is also equipped with monitoring, testing, and display systems, which are used for monitoring, testing, and generating data statistics of various parts of the state, and can also be remotely controlled and displayed using a computer network system.
Solar cell square array in the composition of solar photovoltaic power generation system
Solar cell square array. In order to meet the requirements of high-voltage and high-power power generation, the solar cell array is composed of multiple solar cell modules in series and parallel, and fixedly combined by a certain mechanical method. The basic circuit is composed of solar cell module strings, anti-reverse charge diodes, bypass diodes, and DC junction boxes with lightning arresters. The main forms are parallel, series or series-parallel hybrid square arrays, as shown in Figure 3 and Figure 4.
The diodes in the DC junction box in Fig. 3 and Fig. 4 are anti reverse charging diodes, which are used to prevent the current of the battery from flowing back to the battery array when the battery array does not generate power, and to avoid the current flowing back between the parallel branches of the array.
When the battery components are connected in series, the positive and negative output terminals of each battery plate need to be connected in reverse parallel with 1 (or 2 to 3) diodes. This diode is called a bypass diode. Its function is to prevent a certain component or part of the battery array string from being covered by shadows or the entire array string stopping working when the power generation is stopped due to a fault. At this time, the two ends of the bypass diode are turned on due to the forward bias voltage, and the component string current bypasses the faulty component and flows through the bypass diode without affecting the normal operation of other components. At the same time, it also protects faulty components from being subjected to higher forward bias or heat damage due to the hot spot effect.
The so-called hot spot effect is that when the solar cell module is covered by fallen leaves, dust and other obstructions to form a shadow, due to the existence of local shadow, the voltage and current of some single cells in the battery module change, and the product of local current and voltage increases, resulting in local temperature rise. This phenomenon is hot spot effect. The defects of some cells in the solar cell module may also cause the module to generate local heat. The hot spot effect will seriously damage the service life of the battery panel, and even cause the entire battery panel to be scrapped.