Photovoltaic module is the smallest indivisible solar cell assembly device with encapsulation and internal connection, which can provide direct current output separately, also called solar cell module.
Photovoltaic modules are the core part of the entire photovoltaic power generation system, and their function is to convert solar energy into DC power output through the photovoltaic effect. When sunlight shines on the solar cell, the cell absorbs light energy and generates photo-generated electron-hole pairs. Under the action of the built-in electric field of the battery, the photogenerated electrons and holes are separated, and the accumulation of different signs of electric charge appears at both ends of the battery, that is, a “photogenerated voltage” is generated, which is the “photovoltaic effect”. If the electrodes are drawn on both sides of the built-in electric field and the load is connected, the load will have “photo-generated current” flowing through it, thereby obtaining power output. At the same temperature, the greater the light intensity, the greater the open circuit voltage and short-circuit current of the solar panel, and the greater the maximum output power.
Photovoltaic modules are mainly composed of solar cells, tempered glass, EVA film, frame, backplane, junction box, diode connector and photovoltaic special cables (see Figure 1). Among them, the EVA film is used to bond and fix the tempered glass and the main body of power generation (such as cell). The sequence of the lamination process is as follows: tempered glass-EVA film-solar cell-EVA film-back sheet.
The main function of the diode is a unidirectional conduction function, which is usually divided into a bypass diode and an anti-recoil diode. The bypass diode will not work when the solar panel is working normally, but when it encounters the hot spot effect, the bypass diode will automatically pass the battery string and connect with other battery strings to continue working. The main function of using bypass diodes in the current component design is to prevent the battery from burning out. The main function of the anti-recoil diode is to prevent the battery current from flowing backward when the component is not illuminated.
The connectors and connecting wires have good insulation performance, and the male and female plugs have a self-locking function to make the solar panel and the electrical connection more convenient and reliable.
According to different manufacturing processes and materials, photovoltaic modules are usually divided into crystalline silicon and amorphous silicon modules. Among them, crystalline silicon components have different atomic structure arrangements due to different production processes, and can also be divided into polycrystalline silicon components and monocrystalline silicon components (see Figure 2).
①Polysilicon components
Polycrystalline silicon solar cells are generally produced by pouring, and their silicon atoms are arranged in disorder. From the appearance, the four corners of the cell of the polysilicon module are 90° right angles, and the surface has a pattern similar to ice flowers. The conversion efficiency of polycrystalline silicon solar cells is relatively low, about 18% on average. In addition, its manufacturing process is relatively simple, the production power consumption is lower, and the manufacturing cost per watt is lower than that of monocrystalline silicon solar cells, which reflects a better cost performance. Therefore, in the early development of the photovoltaic power generation industry, polycrystalline silicon modules have overall advantages.
②Single crystal silicon module
The manufacturing process of monocrystalline silicon components increases the reconstruction of the atomic structure, and the production process is relatively complicated, so the manufacturing cost is higher than other component types. However, the average photoelectric conversion efficiency of monocrystalline silicon modules is also 10% to 20% higher than that of monocrystalline silicon modules. If the current more advanced PERC process technology is adopted, the highest conversion efficiency of monocrystalline silicon modules is close to 25%, which is all Among the types of solar modules, the photoelectric conversion efficiency is the highest. In recent years, monocrystalline silicon components have become more mature in their manufacturing processes, and their production scale has been increasing. The cost of single-watt manufacturing has declined rapidly, and they are currently more competitive in the market.
③Amorphous silicon solar cell
Amorphous silicon solar cells mainly refer to thin-film solar cells, whose structure is characterized by the use of coating technology to deposit conductive films on glass substrates. According to different film materials, this type of battery can be divided into cadmium telluride, copper indium gallium selenide amorphous silicon, gallium arsenide and so on. Thin-film solar cell technology originated in the late 1970s. Due to the low photoelectric conversion efficiency, it has not been industrialized. However, with the continuous improvement of technology maturity, the current highest conversion efficiency has been close to that of polycrystalline silicon cells. Thin-film batteries generally use less materials, simple processes, low energy consumption, and can generate electricity under low light conditions. Their comprehensive cost performance is beginning to highlight, and they still have a good development prospect in the foreseeable future. In addition to thin-film solar cells, other amorphous silicon solar cells currently include perovskite cells, but most of them have not yet entered the stage of formal industrial application.
