The influence of raw materials on the power of photovoltaic modules

The power increase of solar cell modules is the main means to reduce costs and increase efficiency, and the power of modules also directly affects the promotion of solar energy systems and the return on investment. The general package structure of the module is: tempered glass, high-transmittance EVA-cell high-sun EVA-back plate, the above materials mainly affect the light loss during the power conversion process of the module. In addition, there are welding ribbons, bus bars, and junction boxes that may affect the power loss of the module during the power conversion process.

Raw materials have a relatively large impact on the power of photovoltaic modules, including the effect of the cell itself on the power of the module, the main role of glass and EVA in the photoelectric conversion process on the power of the module after packaging, and the difference in electrical conductivity The influence of the specifications of the welding ribbon and bus bar on the components.
(1) Photovoltaic glass
Improving the optical utilization efficiency of solar cell modules is an important means to increase the power of the modules. As can be seen from Figure 1, the reflection of glass is a major factor in the optical loss of solar cell modules. The optical loss ratio is about 20%, so reduce the glass Reflection and improving light transmittance are effective means to reduce optical loss. There are two main ways to increase the light transmittance of photovoltaic glass: one is to emboss the surface of the glass to make a diffuse reflection surface (such as the current photovoltaic rolled glass), but the light transmittance of this kind of glass can only reach 92%, and the other is Using the principle of light interference to add a layer of anti-reflection coating on the surface of the photovoltaic rolled glass, the light transmittance of the glass can reach up to about 95%. After research and comparison tests, it is found that the use of AR and AR coating coated glass can effectively reduce the light reflection loss, increase the output power of the solar cell module, and help reduce the initial cost of the entire system.

Figure 1 Optical loss of each component in solar cell module

(2) Welding materials
The welding materials of photovoltaic modules are divided into welding ribbons and bus bars. The welding ribbons are mainly used to connect the cells in series, and then connect them in parallel through the bus bars. For example, by selecting the same material and different specifications of welding ribbon for experimental comparison, it is found that the increase of the thickness of the welding ribbon and the bus bar can reduce the series resistance consumption of the module, the average power of the module has increased, and the power loss is correspondingly reduced. Therefore, increasing the thickness of the solder ribbon and the bus bar has certain advantages in improving the output power of the component and reducing the packaging loss.
(3)EVA
EVA (ethylene-vinyl acetate copolymer) film is currently the most commonly used material in the solar cell packaging process. It is mainly made by adding various additives such as ultraviolet absorbers, light stabilizers, antioxidants and crosslinking aids to the EVA base material. EVA film is used for the encapsulation of solar modules. It mainly has the following performance requirements: high light transmittance, suitable cross-linking degree, excellent resistance to ultraviolet aging and humidity and heat aging resistance, to ensure the 25-year service life of the module outdoors, and low The shrinkage rate guarantees the dimensional stability and strong bonding strength of the components. He Baohua and others prepared different samples by selecting coated glass of different manufacturers and different specifications and combining high-transmittance EVA film. The test results show that the high-transmittance EVA module has a significant power gain compared to the ordinary EVA module, and the maximum gain is 1.9% after combining with the coated glass. Ordinary EVA usually adds ultraviolet absorbers to reduce the damage of ultraviolet rays in the sun to the cells and backplanes. This EVA is called UV-cut EVA; and another EVA film with europium elements can protect the EVA. At the same time, it increases the transmittance of ultraviolet light, thereby improving the conversion efficiency of the battery module. This EVA is called EVA without UV cutoff. According to the test data, the average maximum output power of EVA modules without UV cutoff is 2. 1084W higher than those with UV cutoff EVA modules. In the test, the power loss of EVA without UV cutoff was 2.92%, and the power loss of EVA module with UV cutoff was 3.67%. The use of UV-free EVA reduces the packaging loss of components by 0.75%. The UV cut-off EVA module effectively utilizes part of the solar ultraviolet energy, thereby achieving the purpose of increasing the output power of the module and reducing the packaging loss of the module.
(4) Backplane
The back sheet film is the material that encapsulates the back of the solar cell, which protects and supports the cell. The service life of commercial solar cell modules is required to be 25 years, and the backsheet film, as a photovoltaic encapsulation material that directly contacts the external environment on a large area, must have excellent aging resistance (mixed heat, dry heat, ultraviolet), electrical insulation, and water resistance. Vapor barrier, dimensional stability and other properties. If the back film cannot meet the changing harsh environment test, and there are undesirable conditions such as delamination, cracking, blistering, yellowing, etc., which cause the battery module to fall off, the cell slips, and the effective output power of the battery decreases, the solar cell’s Reliability, stability and durability cannot be guaranteed, and even larger accidents can be caused. Backplanes mainly include: TPT backplane film, TPE backplane film, fluorine-coated backplane film, and fluorine-free backplane film. Photovoltaic module backsheets are usually painted black to improve power generation efficiency.
(5) Junction box
The photovoltaic junction box is a connector between the solar cell array composed of solar cell modules and the solar charging control device. It is a cross-domain comprehensive design body integrating electrical design, mechanical design and material science. The solar cell module according to the wire box is very important in the composition of the solar module, and the main function is to connect the power generated by the solar cell with the external circuit. The photovoltaic junction box is composed of three parts: box body, cable and connector. It is very important to choose a suitable junction box. For an excellent solar cell module junction box, the following requirements must be met: ①Meet the requirements for use under harsh outdoor environmental conditions; ②The shell has strong anti-aging and ultraviolet resistance; ③It has an excellent heat dissipation mode and reasonable The internal cavity volume effectively reduces the internal temperature to meet electrical safety requirements; ④It has good waterproof and dust-proof protection to provide users with a safe connection plan; ⑤It has a low body resistance to minimize the junction box Power loss. The materials, processing technology and structural design of the box body are not exactly the same for different types of junction boxes. Therefore, the body resistance of different junction boxes has certain differences; and different types of junction boxes will also choose different types and different packaging forms of diodes, mainly SMD type and axial type. These types of diodes have a certain reverse leakage current. difference.

The traditional junction box structure design includes a box cover, a box body, a diode device in the box, an input contact and an output wire. According to the input point of the solar cell module lead connection to the junction box, the current is output through the bypass diode in the box body through the output terminal of the output wire. The box body of this kind of junction box itself is too large, which increases the material cost accordingly; the diode device in the box body is Discrete components are connected and fixed by wire plug-ins; air is used as a heat-insulating medium, and the heat dissipation effect is often poor, and the power loss is also relatively large; as the power of the solar cell module continues to increase, the junction box body cannot be enlarged without restriction. In addition, the way in which discrete components are connected and fixed by wire plug-ins increases the contact resistance, which also brings certain safety hazards to the battery assembly itself. In order to improve the shortcomings of the above traditional junction box, a modular junction box is used, and 3 Schottky diodes are installed in the box. According to the pre-designed circuit, the aluminum substrate is welded into a PCB board form, and then the SMD Schottky is directly The base-pole tube is welded on the aluminum substrate to form a modularized wire The traditional junction box structure design includes a box cover, a box body, a diode device in the box, an input contact and an output wire. According to the input point of the solar cell module lead connection to the junction box, the current is output through the bypass diode in the box body through the output terminal of the output wire. The box body of this kind of junction box itself is too large, which increases the material cost accordingly; the diode device in the box body is Discrete components are connected and fixed by wire plug-ins; air is used as a heat-insulating medium, and the heat dissipation effect is often poor, and the power loss is also relatively large; as the power of the solar cell module continues to increase, the junction box body cannot be enlarged without restriction. In addition, the way in which discrete components are connected and fixed by wire plug-ins increases the contact resistance, which also brings certain safety hazards to the battery assembly itself. In order to improve the shortcomings of the above traditional junction box, a modular junction box is used, and 3 Schottky diodes are installed in the box. According to the pre-designed circuit, the aluminum substrate is welded into a PCB board form, and then the SMD Schottky is directly The base-pole tube is welded on the aluminum substrate to form a modularized wire box. Although different types of junction boxes have little effect on the power of the components, they have a great impact on the long-term performance of the components.

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