Photovoltaic module reflective bus bar structure and processing method thereof

Abstract

The invention discloses a photovoltaic module reflective bus bar structure and a processing method thereof, and relates to the technical field of photovoltaic equipment. The reflective bus bar is in a long strip shape and is provided with two opposite surfaces, one surface is a welding surface, and the other surface is a non-welding surface. The non-welding surface is of a curved surface structure, the curved surface structure is different from a plane structure, and a convex and concave continuous form is formed in the width direction and the thickness direction of the reflective bus bar; the processing method comprises the following steps: S1, preparing a reflective bus bar base material; s2, processing a curved surface of a non-welding surface; s3, welding surface treatment; and S4, surface anti-corrosion treatment. Through the design of the curved surface structure of a non-welding surface, the directional light recovery is realized by combining the mirror reflection and angle controllable principle, the reflective rate is greatly improved to promote the improvement of the assembly efficiency, and the dimensional precision and batch processing consistency of the curved surface structure are ensured by virtue of the precise mold pressing, laser engraving and electroplating processes, so that the production efficiency is improved. And finally, the requirements of efficient, reliable and stable mass production of the photovoltaic module are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic devices, in particular to a photovoltaic module light-reflecting busbar structure and a processing method thereof. BACKGROUND

[0002] With the increasing requirements of the photovoltaic industry on the power density and energy conversion efficiency of modules, light-reflecting busbars have become one of the core technical means for optimizing the performance of modules because they can increase the light absorption of cell pieces by reflecting incident light.

[0003] At present, the light-reflecting busbars in the industry generally adopt a combination of a non-welding surface plane design and a traditional flat solder strip, and the copper base material and the surface plating layer are used to ensure the conductivity and outdoor corrosion resistance, but in actual application, the existing technology still has many key problems, which are difficult to meet the needs of efficient, reliable and batch production of modules, as follows:

[0004] The non-welding surface of the existing light-reflecting busbar is a plane structure, and the light reflection is mainly diffuse reflection, which has weak directivity. After the incident light is reflected by the plane, only a small part of it can fall accurately on the effective light-receiving area of the cell piece, and the rest is reflected to the edge of the module, causing energy loss. At the same time, the plane structure is easy to form a light-reflecting blind area at the edge of the busbar in the length direction, resulting in a generally low overall light reflection rate.

[0005] Some improvement schemes try to increase the height of the protrusions on the non-welding surface to improve the light reflection rate, but the protrusion height is not accurately controlled, which leads to excessive plastic deformation of the busbar substrate and a significant decrease in the flatness of the welding surface. This not only reduces the contact area between the solder strip and the busbar and increases the contact resistance, but also causes virtual welding due to uneven heat distribution during welding, which is an industry pain point that sacrifices reliability in pursuit of high light reflection, and cannot balance both performances.

[0006] The existing busbar has shortcomings in the design of the substrate and the plating layer. If a low-purity copper substrate is used, the resistivity is large, and the joule heat loss during current conduction increases significantly. If the plating layer is not designed reasonably, the corrosion resistance will be insufficient, and it will be difficult to meet the dual requirements of low-resistance conduction and long-term corrosion resistance, affecting the long-term operation stability of the module.

[0007] In the existing module, the light reflection designs of the flat solder strip and the plane busbar are independent of each other. The light reflection rate of the flat structure of the flat solder strip is low, and the reflected light is concentrated directly below the solder strip, which cannot cover the blank area between the cell piece and the busbar. The reflected light of the plane busbar is easily blocked by the flat solder strip, forming a mutual exclusion of light, which cannot build a light recycling system inside the module, and the overall light utilization rate is difficult to improve. The performance of the light reflection design of a single component is obviously limited.

[0008] The processing technology of the existing curved surface type reflective bus bar lacks control of key parameters, improper pressure and time during mold pressing easily lead to curved surface depression or substrate cracking, and unreasonable wavelength and power selection during laser engraving can cause too large size deviation of the curved surface and high surface roughness, so that the reflectivity of the final batch product is greatly different, which cannot meet the requirement of performance stability for component mass production

[0009] Therefore, the application provides a photovoltaic component reflective bus bar structure and a processing method thereof. SUMMARY

[0010] An object of the application is to provide a photovoltaic component reflective bus bar structure and a processing method thereof. The application can realize directional light recycling by combining mirror reflection and angle controllable principle through the non-welding surface curved surface structure design, greatly improve the reflectivity to promote the component efficiency, and avoid the problem of sacrificing reliability for high reflectivity by strictly controlling the curved surface drop, considering the reflectivity and welding reliability, and also can synergistically optimize the low resistance conduction and long-term corrosion resistance of the bus bar by the combination of high-purity copper substrate and precise thickness plating layer, and further improve the light utilization rate by building the secondary light circulation in the component through the reflective synergistic effect of round wire welding strip and curved bus bar. In addition, the size precision of the curved surface structure and the batch processing consistency are ensured by the precise mold pressing, laser engraving and electroplating process, and finally the requirements of efficient, reliable and stable mass production of photovoltaic components are realized, and the industry pain points of the existing reflective bus bar in reflectivity efficiency, performance synergy and processing consistency are solved.

[0011] According to the photovoltaic component reflective bus bar structure of the application, the reflective bus bar is in a strip shape, has two oppositely arranged surfaces, one is a welding surface, and the other is a non-welding surface.

[0012] The non-welding surface is a curved surface structure, which is different from a planar structure, and forms a continuous shape of protrusions and depressions along the width direction and the thickness direction of the reflective bus bar, and the curved surface structure covers the entire area of the non-welding surface.

[0013] Further, the size X of the cross section of the curved surface structure along the width direction of the reflective bus bar is 0.1mm-0.2mm, the size Y of the cross section along the thickness direction of the reflective bus bar is 0.03mm-0.05mm, and the cross section of the curved surface structure forms an included angle Z, the included angle Z is the angle formed by the intersection of two adjacent curved surface segments of the curved surface structure at the cross section, and the angle value is 90°-150°.

[0014] Further, the curved surface structure has a curved surface drop, the curved surface drop is the vertical distance between the highest point and the lowest point of the curved surface structure along the thickness direction of the reflective bus bar, and the curved surface drop is less than 0.15mm, and the welding surface is a flat surface with a surface roughness Ra of less than or equal to 0.4μm.

[0015] Further, the curved surface is a continuous curved surface extending along the length direction of the light-reflecting bus bar, and the adjacent curved surface units in the continuous curved surface are designed to be smoothly transitioned without edges and breakpoints.

[0016] Further, the base material of the light-reflecting bus bar is copper material with a purity of not less than 99.9%, and the surface of the base material is covered with a corrosion-resistant plating layer, which is a tin plating layer or a silver plating layer, wherein the thickness of the tin plating layer is 5-10 μm, and the thickness of the silver plating layer is 8-15 μm.

[0017] Further, the method further comprises a cooperatively used solder strip, which is a round wire solder strip with a circular cross section, the diameter of which is adapted to the width of the light-reflecting bus bar, and one end of the round wire solder strip is fixedly attached to the soldering surface of the light-reflecting bus bar, and the area of the attached region is not less than 1 / 2 of the cross-sectional area of the round wire solder strip.

[0018] A processing method of a light-reflecting bus bar structure of a photovoltaic module, comprising the following steps:

[0019] S1, preparing a light-reflecting bus bar base material, selecting copper plate material with a purity of not less than 99.9%, and cutting the copper plate material into a long strip-shaped blank with a preset width and length by using a precision numerical control cutting device, or rolling the copper plate material into a long strip-shaped blank with a preset thickness, width and length by using a multi-pass rolling device, to obtain a bus bar base material; two opposite surfaces of the bus bar base material are marked as a soldering surface to be processed and a non-soldering surface, respectively;

[0020] S2, non-soldering surface curved surface processing, using a mold pressing process or a laser engraving process to process the non-soldering surface of the bus bar base material, and forming a curved surface structure meeting the size parameters on the non-soldering surface after processing;

[0021] S3, soldering surface treatment, using a fine sandpaper with a particle size of 800-1200 mesh to manually or mechanically polish the soldering surface of the bus bar base material, or using a sulfuric acid solution with a concentration of 5-10% to soak the soldering surface for 3-5 min, and then rinsing the soldering surface with deionized water to neutralize, and then placing the soldering surface in a drying oven at 60-80°C for 5-10 min;

[0022] S4, surface corrosion-resistant treatment, performing plating layer treatment on the bus bar base material after step S3 to form a tin plating layer or a silver plating layer on the surface of the bus bar base material, to obtain a finished light-reflecting bus bar structure.

[0023] Further, when the mold pressing process is used in the step S2, the mold comprises an upper mold and a lower mold, the lower surface of the upper mold is provided with a cavity matched with the preset curved surface structure, the surface roughness Ra of the cavity is ≤0.2 μm, when pressing, the non-welding surface of the bus bar substrate is placed upwards and combined with the lower mold, the upper mold is pressed downwards, the pressing pressure is 5 MPa-15 MPa, the pressing time is 10 s-30 s, and in the pressing process, the drop of the curved surface structure of the non-welding surface can be monitored in real time by the laser thickness gauge, so that the drop is ensured to be <0.15 mm.

[0024] Further, when the laser engraving process is used in the step S2, the fiber laser engraving equipment with a wavelength of 1064 nm is selected, and before engraving, the bus bar substrate is fixed on the workbench of the equipment, the engraving area of the non-welding surface is calibrated through the positioning system of the equipment, when engraving, the laser power is set to 50 W-200 W, the engraving speed is 100 mm / s-500 mm / s, the preset continuous curved surface path is engraved, and after the engraving is completed, the polishing solution with a volume ratio of phosphoric acid to sulfuric acid of 3:1 is prepared, the non-welding surface of the bus bar substrate is soaked in the polishing solution at 50 ℃-70 ℃ for 5 min-15 min, then the non-welding surface is washed with deionized water until neutral, and then dried.

[0025] Further, the plating treatment in the step S4 is carried out by using the electroplating process, and the specific steps comprise:

[0026] In the step S41, in the tin plating layer, the electroplating solution is a stannous sulfate system, the stannous sulfate concentration is 30 g / L-50 g / L, the sulfuric acid concentration is 80 g / L-120 g / L, and the polyethylene glycol concentration is 1 g / L-3 g / L, when electroplating, the current density is controlled to be 1 A / dm 2 -3 A / dm 2 , and the electroplating time is 10 min-20 min.

[0027] In the step S42, in the silver plating layer, the electroplating solution is a silver cyanide system, the silver cyanide concentration is 30 g / L-50 g / L, and the potassium cyanide concentration is 80 g / L-120 g / L, when electroplating, the current density is controlled to be 2 A / dm 2 -5 A / dm 2 , and the electroplating time is 8 min-15 min.

[0028] In the step S43, after electroplating, the bus bar substrate is washed with deionized water for 3-5 times, each time for 1 min-2 min, and then placed in a drying oven at 60 ℃-80 ℃ for drying for 10 min-20 min.

[0029] The beneficial effects of the application are:

[0030] 1. In this invention, the non-welded surface is designed as a curved structure, and the directional recovery of light is achieved based on the principle of mirror reflection and angle control. The convex and concave parts of the curved surface form multiple micro-reflective units. The cross-sectional angle of each unit can be preset through geometric optics calculation. When the light is incident at 30°-60°, the exit angle of the reflected light is limited to 45°-120°, which exactly covers the effective light-receiving area of ​​the battery cell. Secondly, the continuous curved surface design extends along the entire length of the busbar, avoiding light leakage caused by the reflective blind area of ​​the planar busbar, which greatly improves the reflectivity and ultimately promotes the improvement of module efficiency.

[0031] 2. In this invention, by strictly limiting the surface drop to <0.15mm, a performance balance is achieved by combining the principles of material mechanics and welding thermodynamics. The small surface drop ensures that the plastic deformation of the busbar substrate is controlled within the elastic range, and the surface roughness of the weld is maintained in a flat state with Ra≤0.4μm. This ensures that the contact area between the welding strip and the welding surface is not less than 1 / 2 of the cross-sectional area of ​​the welding strip, and the contact resistance is stable below 3.0mΩ. Furthermore, the flat welding surface makes the heat conduction during welding more uniform, avoiding damage to the substrate caused by local high temperature. This invention retains the reflective advantages of the curved surface structure and solves the industry pain point that high reflectivity and high reliability cannot be achieved simultaneously.

[0032] 3. The present invention achieves low resistance conduction through a combination of high-purity copper substrate and a precisely thick coating. The resistivity of the high-purity copper substrate is much lower than that of low-purity copper, reducing electron scattering loss within the substrate and effectively reducing Joule heat loss during current conduction. The coating is designed for different application scenarios. The tin coating utilizes the low melting point of tin to improve solder wettability, while the tin oxide product SnO2 has a dense structure that can block oxygen from contacting the copper substrate, achieving a salt spray corrosion resistance time of up to 72 hours. The silver coating utilizes the optimal conductivity of silver to further reduce surface resistance, and silver has higher chemical stability, achieving a salt spray corrosion resistance time of up to 120 hours, meeting the usage requirements of harsh environments such as high altitude and high humidity.

[0033] 4. In this invention, a combination of round wire welding strips and curved busbars is used to construct a secondary light cycle inside the module based on the principle of light superposition and complementarity. The circular cross-section of the round wire welding strips can reflect incident light to both sides, covering the blank area between the busbars and the cells, and making up for the reflective blind spot of the curved busbars in the area near the welding strips. The curved structure of the non-welded surface of the busbars reflects light to the central area of ​​the cells, complementing the reflective area of ​​the round wire welding strips. After the reflective coverage of the two is superimposed, the effective light-receiving area of ​​the cells is greatly improved. Some of the light reflected by the round wire welding strips will re-enter the curved busbars, and after secondary reflection, return to the surface of the cells, forming a light cycle. This synergistic effect can improve the light utilization rate of the module. Compared with the traditional combination of flat welding strips and planar busbars, the module power is improved, breaking through the performance limit of single component reflective design.

[0034] 5、The present application is based on the principle of metal plastic deformation and laser processing, design needle mold pressing process, laser engraving process and electroplating process control, mold pressing process through the control of pressing pressure and time, make copper base material in the process of plastic deformation stress distribution is uniform, avoid the curvature caused by insufficient pressure or pressure caused by substrate cracking, laser engraving process selects 1064nm wavelength of fiber laser, by adjusting the laser power and engraving speed, accurate control of the depth and width of the curved surface, avoid the substrate oxidation caused by high laser energy or incomplete engraving caused by insufficient energy, and electroplating process control tin or silver plating layer respectively set current density and time, ensure the plating thickness deviation is small, avoid the difference caused by uneven plating thickness of the conductive performance. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, together with the embodiments of the present application, to explain the present application, and do not constitute a limitation on the present application. In the drawings:

[0036] Figure 1 The overall structure of the cross section of the photovoltaic module light reflection bus bar structure is proposed in the present application;

[0037] Figure 2 The cross section structure of the light reflection bus bar of the photovoltaic module light reflection bus bar structure is proposed in the present application;

[0038] Figure 3 The welding strip comparison diagram of the photovoltaic module light reflection bus bar structure is proposed in the present application;

[0039] Figure 4 The continuous curved surface form of the photovoltaic module light reflection bus bar structure is proposed in the present application;

[0040] Figure 5 The flow chart of the photovoltaic module light reflection bus bar structure is proposed in the present application. DETAILED DESCRIPTION

[0041] In order to make the technical means and achieve the purpose and effect of the present application easy to understand, the embodiments of the present application are described in detail below combined with specific drawings.

[0042] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in one or more embodiments or examples.

[0043] As shown in Figures 1-4 The present application discloses a photovoltaic module light-reflecting busbar structure.

[0044] The photovoltaic module light-reflecting busbar structure is in the shape of a long strip, which is designed to match the current conduction path in the photovoltaic module and can efficiently collect and transmit the current generated by the battery piece to the junction box. The light-reflecting busbar has two oppositely arranged surfaces, one of which serves as a welding surface for fixed connection with the solder strip in the photovoltaic module, and the other is a non-welding surface. The non-welding surface is different from the flat design of the traditional busbar and adopts a curved surface structure. This curved surface structure is not locally arranged but covers the entire area of the non-welding surface, forming a continuous concave-convex pattern along the width and thickness directions of the light-reflecting busbar. This continuous curved surface pattern can increase the contact angle range of light and the non-welding surface, so that light with different incident angles can be reflected under the action of the curved surface, thereby improving the utilization rate of light.

[0045] For the specific size parameters of the curved surface structure, the size X of the cross section along the width direction of the light-reflecting busbar is set to be between 0.1mm and 0.2mm. When X is less than 0.1mm, the extension of the curved surface structure in the width direction is insufficient, resulting in too small a light-reflecting area and failing to fully utilize the incident light. When X is greater than 0.2mm, the overall width of the busbar will increase, which may exceed the installation space limit inside the photovoltaic module and affect the cooperation with other components.

[0046] The size Y along the thickness direction of the light-reflecting busbar is 0.03mm to 0.05mm. This size range is determined considering the overall thickness requirement of the busbar. If Y is less than 0.03mm, the convexity and concavity of the curved surface are insufficient, which makes it difficult to effectively change the direction of light reflection. If Y is greater than 0.05mm, the thickness of the busbar will increase, which not only increases the material cost but also may affect the overall thickness design of the photovoltaic module.

[0047] In addition, the cross section of the curved surface structure forms an included angle Z, which is an angle formed by the intersection of two adjacent curved surface segments of the curved surface structure at the cross section, and the angle value is 90°-150°. When the included angle Z is less than 90°, the curved surface is too steep, which can cause the reflection angle of part of the light to be too large, and the light cannot reach the surface of the battery piece; when the included angle Z is greater than 150°, the curved surface tends to be flat, and the reflection guiding effect of the light is weakened, which also reduces the light reflection effect.

[0048] The photovoltaic module light reflection bus bar structure disclosed in the embodiment has a significant influence on the light reflection performance and the efficiency of the photovoltaic module in actual application. By designing a control experiment, different size parameters of the curved surface structure are selected for testing, and the results are shown in Table 1 as follows:

[0049] Table 1: Comparison table of size parameters of curved surface structure and light reflection performance

[0050]

[0051] As shown in Table 1, when the size parameters of the curved surface structure are within the limited range, the light reflection rate can reach more than 85%, and the component efficiency is improved by more than 1.5%, which is significantly better than the scheme whose parameters exceed the range. The parameter combination of No. 3 performs best, with a light reflection rate of 91% and a component efficiency improvement of 2.3%, because the light reflection angle distribution of the curved surface under this parameter is more suitable for the light receiving requirement of the battery piece, and the light utilization rate is the highest.

[0052] It should be noted that the curved surface drop of the curved surface structure is a key parameter, which is defined as the vertical distance between the highest point and the lowest point of the curved surface structure along the thickness direction of the light reflection bus bar, and the curved surface drop is strictly controlled to be <0.15mm. Because if the curved surface drop is too large, the deformation of the bus bar in the thickness direction will be more obvious, which will affect the flatness of the welding surface, and when the welding surface is welded with the solder strip, the contact is poor, which will cause the welding quality to decrease, increase the resistance, and affect the current conduction. At the same time, the welding surface is designed as a flat surface, and the surface roughness Ra is ≤0.4μm. Such flatness can ensure that the solder strip and the welding surface have a large enough contact area, improve the firmness and conductivity of the welding, and reduce the contact resistance.

[0053] The experimental data of the influence of the curved surface drop on the welding performance are shown in Table 2 as follows:

[0054] Table 2: Comparison table of curved surface drop and welding performance

[0055]

[0056]

[0057] As shown in Table 1, when the surface fall is less than 0.15 mm, the roughness of the welding surface Ra is less than or equal to 0.4 μm, the welding strength is greater than or equal to 6N, and there is no false welding phenomenon, which meets the reliability requirements of photovoltaic modules for long-term use; when the fall is greater than or equal to 0.15 mm, the flatness of the welding surface decreases, the welding strength decreases significantly, and the false welding rate increases significantly.

[0058] The curved surface structure adopts a continuous curved surface design, which extends along the length direction of the reflective bus bar. This continuous extension design enables the non-welding surface to reflect light in the entire length range of the bus bar, avoiding the blind area caused by the discontinuity of the curved surface. In addition, the adjacent curved surface units in the continuous curved surface are designed to have a smooth transition, and there are no edges and breakpoints at the transition. This design can reduce the diffuse reflection of light at the curved surface transition, so that the light can be more regularly reflected to the surface of the cell, improving the utilization efficiency of the light.

[0059] The base material of the reflective bus bar is copper material, and the purity of the copper material is not less than 99.9%. The high-purity copper material has excellent electrical conductivity, which can effectively reduce the loss of current during transmission and improve the power generation efficiency of the photovoltaic module. If the purity of the copper material is less than 99.9%, the impurities contained therein will increase the resistance, resulting in more Joule heat during current transmission, reducing the energy conversion efficiency.

[0060] A corrosion-resistant plating layer, such as a tin plating layer or a silver plating layer, is covered on the surface of the base material.

[0061] The thickness of the tin plating layer is controlled to be 5 μm to 10 μm. Tin has good welding performance, which can improve the welding quality between the welding surface and the solder strip. At the same time, the tin plating layer can also play a certain anti-corrosion role to protect the copper base material from corrosion.

[0062] Secondly, the thickness of the silver plating layer is 8 μm to 15 μm. The electrical conductivity of silver is better than that of tin, which can further reduce the surface resistance of the bus bar and improve the electrical conductivity. At the same time, silver has good chemical stability and excellent corrosion resistance, which is suitable for photovoltaic module scenes with high performance requirements.

[0063] The performance test data of different base materials and plating layers are shown in Table 3 as follows:

[0064] Table 3: Performance comparison table of base material and plating layer

[0065]

[0066] As can be seen from Table 3, when the copper base material with a purity of not less than 99.9% is matched with a tin plating layer or a silver plating layer, the resistivity is significantly lower than that of a low-purity base material, and the corrosion resistance is greatly improved. Among them, the combination of 99.9% pure copper material + 12 μm silver plating layer performs best, with a resistivity of only 1.6 μΩ·cm and a salt spray corrosion resistance time of 120 h, fully proving the rationality of the material selection in claim 5.

[0067] The photovoltaic module light-reflecting busbar structure further comprises a welding strip used in cooperation, and the welding strip is a round wire welding strip with a circular cross section and a diameter matched with the width of the light-reflecting busbar. The arc surface of the round wire welding strip can reflect light, and cooperates with the curved surface structure of the non-welding surface of the light-reflecting busbar to form a synergistic light-reflecting effect, thereby further improving the utilization rate of light. One end of the round wire welding strip is fixedly attached to the welding surface of the light-reflecting busbar, and the attachment area is not less than 1 / 2 of the cross-sectional area of the round wire welding strip. Such an attachment area can ensure that the welding strip and the busbar have sufficient connection strength and good electrical conductivity, thereby avoiding affecting the performance of the photovoltaic module due to poor contact during use.

[0068] The performance test data of the welding strip and the busbar are shown in Table 4 as follows:

[0069] Table 4: Influence of welding strip type and attachment area on electrical conductivity

[0070]

[0071] As can be seen from Table 4, when the round wire welding strip is matched with the light-reflecting busbar, the contact resistance is lower than 3.0 mΩ, and the current transmission efficiency is more than 97% when the attachment area ratio is ≥50%, which is better than the combination of flat welding strips.

[0072] As shown in Figures 1-5 , the embodiment further discloses a processing method of the photovoltaic module light-reflecting busbar structure, which is used for processing the above-mentioned photovoltaic module light-reflecting busbar structure, and the method comprises the following steps:

[0073] S1, preparing a light-reflecting busbar base material.

[0074] First, a copper plate material with a purity of not less than 99.9% is selected, because a high-purity copper plate material can ensure that the subsequently manufactured busbar has good electrical conductivity. The selected copper plate material needs to be subjected to appearance inspection to ensure that the surface is free of obvious scratches, cracks, impurities and other defects.

[0075] Subsequently, according to the preset bus bar size, the copper plate is cut into a long strip-shaped blank with a preset width and length by using a precision numerical control cutting equipment. During the cutting process, the positioning accuracy of the numerical control equipment needs to be controlled within ±0.01 mm to ensure the dimensional accuracy of the blank. Alternatively, the copper plate can also be rolled into a long strip-shaped blank with a preset thickness, width and length by using a multi-pass rolling equipment. During the rolling process, the reduction of each pass needs to be accurately controlled. Generally, the reduction of the first pass is 10% to 15%, and the reduction of the subsequent passes gradually decreases to avoid cracks in the copper material due to excessive deformation. The thickness deviation of the final bus bar substrate needs to be controlled within ±0.005 mm.

[0076] After obtaining the bus bar substrate, its two opposite surfaces are marked as the welding surface and the non-welding surface to be processed, respectively, so as to be distinguished and processed in the subsequent processing process.

[0077] S2, the non-welding surface is processed by using a mold pressing process or a laser engraving process to form a curved surface structure that meets the size parameters.

[0078] When the mold pressing process is used, the mold includes an upper mold and a lower mold. The lower surface of the upper mold is provided with a cavity matching the preset curved surface structure, and the surface roughness Ra of the cavity is ≤0.2 μm. Such surface roughness can ensure that the surface of the curved surface structure after pressing is smooth and reduces the diffuse reflection of light.

[0079] Before pressing, the bus bar substrate needs to be cleaned to remove oil stains and impurities on the surface to avoid impurities being embedded in the surface of the substrate during the pressing process, which affects the quality of the curved surface.

[0080] During pressing, the non-welding surface of the bus bar substrate is placed upward against the lower mold. The upper surface of the lower mold needs to be flat, and the surface roughness Ra thereof is ≤0.4 μm to ensure that the substrate is placed stably. The upper mold is pressed downward, and the pressing pressure is 5 MPa to 15 MPa, and the pressing time is 10 s to 30 s. The selection of the pressing pressure and time needs to be adjusted according to the thickness and material characteristics of the bus bar substrate. For thicker substrates, the pressure needs to be appropriately increased and the time needs to be extended to ensure that the curved surface structure can be fully formed.

[0081] During the pressing process, the laser thickness gauge is used to monitor the drop of the curved surface structure of the non-welding surface in real time. The measurement accuracy of the laser thickness gauge needs to reach ±0.001 mm to ensure that the drop is <0.15 mm. If it is found that the drop exceeds the limit, the pressing parameters need to be adjusted in time until the requirements are met.

[0082] To explore the influence of the pressure and time parameters in the mold pressing process on the curved surface accuracy, a plurality of pressing experiments with different parameters are designed in this embodiment to test the curved surface dimensional deviation, roughness and product qualification rate. The results are shown in Table 5 as follows:

[0083] Table 5: Mold pressing process parameters and surface precision table

[0084]

[0085]

[0086] The data in Table 5 shows that when the pressing pressure is 5 MPa to 15 MPa and the pressing time is 10 s to 30 s, the surface size deviation is ≤±3 μm, the roughness Ra is ≤0.2 μm, and the product qualified rate is more than 96%; when the pressure or time exceeds the range, the precision and qualified rate decrease, proving the rationality of the process parameter range.

[0087] When the laser engraving process is used, a fiber laser engraving equipment with a wavelength of 1064 nm is selected. The laser with this wavelength has good metal processing performance and can accurately engrave on the surface of copper material while having less heat impact on the substrate.

[0088] Before engraving, the bus bar substrate is fixed on the workbench of the equipment, and the positioning accuracy of the workbench needs to reach ±0.005 mm. The non-welding surface engraving area is calibrated through the equipment positioning system to ensure the accuracy of the engraving position.

[0089] During engraving, the laser power is set to 50 W to 200 W, and the engraving speed is 100 mm / s to 500 mm / s. The combination of laser power and engraving speed needs to be adjusted according to the depth and width of the curved surface structure. For deeper curved surfaces, the engraving speed needs to be reduced or the laser power needs to be increased. The engraving is carried out according to the preset continuous curved surface path, and the engraving path is generated by computer-aided design software to ensure that the size and shape of the curved surface structure meet the design requirements.

[0090] After engraving, a polishing solution with a volume ratio of phosphoric acid to sulfuric acid of 3:1 is prepared, and the non-welding surface of the bus bar substrate is soaked in the polishing solution at 50°C to 70°C for 5 min to 15 min. The solution needs to be stirred regularly during polishing to ensure uniform polishing. Then, the substrate is rinsed with deionized water until it is neutral, and the rinsing time is not less than 3 min. Then, the substrate is placed in a drying oven at 60°C to 80°C for drying, and the drying time is 10 min to 15 min to remove the surface moisture.

[0091] To verify the influence of laser engraving parameters on the reflective performance of the curved surface, the laser power, engraving speed, and polishing time are adjusted for multiple experiments, the curved surface reflectivity and surface flatness are tested, and the data are shown in Table 6:

[0092] Table 6: Laser engraving parameters and curved surface reflectivity table

[0093]

[0094]

[0095] From table 6, when the power is 50W-200W, the speed is 100mm / s-500mm / s, and the polishing time is 5min-15min, the curved surface reflectivity can reach more than 87%, and the surface flatness is less than or equal to 3.5μm. Among them, the combination of 100W power, 300mm / s speed and 10min polishing time can reach 90% reflectivity, and the comprehensive performance is optimal.

[0096] S3, welding surface treatment, using fine sandpaper with a particle size of 800-1200 mesh to manually or mechanically polish the welding surface of the busbar substrate.

[0097] When manually polishing, the polishing direction should be consistent to avoid cross scratches, and the polishing force should be uniform until the oxidation layer and impurities on the welding surface are completely removed, exposing the fresh copper surface.

[0098] When mechanically polishing, an automatic polisher is selected, the speed of the polishing wheel is controlled at 1000-1500r / min, and the polishing time is 30-60s. At the same time, a coolant is needed to cool the polishing area to prevent the surface of the substrate from oxidizing due to frictional heat.

[0099] Alternatively, a 5%-10% sulfuric acid solution is used to soak the welding surface for 3-5min, and the temperature of the sulfuric acid solution is controlled at 20-30℃. The solution needs to be gently stirred during the soaking process to ensure that all parts of the welding surface can fully contact the solution to remove the oxidation layer.

[0100] After polishing or soaking, the welding surface is rinsed with deionized water until it is neutral. The water quality after rinsing can be detected by pH test paper to ensure that the pH value is between 6 and 7. Then, it is placed in a drying oven at 60-80℃ for 5-10min. The dried welding surface needs to be protected from further contamination.

[0101] S4, surface corrosion prevention treatment, the busbar substrate after step S3 is subjected to plating treatment to form a tin or silver plating layer on the surface of the busbar substrate to obtain a finished reflective busbar structure.

[0102] The plating treatment is carried out by electroplating process.

[0103] S41, when forming a tin plating layer, the electroplating solution is a stannous sulfate system, wherein the stannous sulfate concentration is 30 g / L-50 g / L, the sulfuric acid concentration is 80 g / L-120 g / L, and the polyethylene glycol concentration is 1 g / L-3 g / L. The stannous sulfate provides tin ions for electroplating, the sulfuric acid can improve the conductivity and stability of the solution, and the polyethylene glycol as a brightener can improve the appearance and uniformity of the plating layer. Before electroplating, the bus bar substrate needs to be activated by soaking in a 10% sulfuric acid solution for 1 min-2 min to remove the possible residual oxide film on the surface. During electroplating, the bus bar substrate is used as the cathode and a pure tin plate as the anode, which are placed in the electroplating solution, the current density is controlled at 1 A / dm 2 -3 A / dm 2 , and the electroplating time is 10 min-20 min. The control of current density and electroplating time directly affects the thickness of the plating layer, and needs to be accurately adjusted according to the preset plating layer thickness to ensure that the thickness of the tin plating layer is between 5 μm-10 μm.

[0104] S42, when forming a silver plating layer, the electroplating solution is a silver cyanide system, wherein the silver cyanide concentration is 30 g / L-50 g / L, and the potassium cyanide concentration is 80 g / L-120 g / L. Silver cyanide provides silver ions, and potassium cyanide as a complexing agent can stabilize silver ions and prevent their hydrolysis and precipitation. Before electroplating, the bus bar substrate needs to be degreased by soaking in an alkaline degreasing agent for 5 min-10 min to remove the oil on the surface, and then rinsed with deionized water. During electroplating, the bus bar substrate is used as the cathode and a pure silver plate as the anode, the current density is controlled at 2 A / dm 2 -5 A / dm 2 , the electroplating time is 8 min-15 min, and the thickness of the silver plating layer is ensured to be 8 μm-15 μm.

[0105] S43, after electroplating, the bus bar substrate is rinsed with deionized water for 3-5 times, each time for 1 min-2 min, to ensure that the surface residual electroplating solution is thoroughly rinsed and cleaned, avoiding corrosion of the residual electrolyte on the plating layer. After rinsing, the bus bar substrate is placed in a drying oven at 60°C-80°C for 10 min-20 min, and good ventilation is required during the drying process to ensure that the substrate surface is completely dry. The finished reflective bus bar structure needs to be inspected for appearance and performance, including whether the plating layer is uniform, has no pinholes, peeling, etc. defects, and performance tests including conductivity test and corrosion resistance test to ensure that the product meets the design requirements.

[0106] To determine the effect of electroplating process parameters on the performance of the plating layer, the thickness, adhesion and corrosion resistance of the plating layer under different current densities and electroplating times were tested for tin plating layer and silver plating layer respectively, and the results are shown in Table 7 below:

[0107] Table 7: Electroplating parameter and plating layer performance comparison table

[0108]

[0109] From Table 7, the tin plating layer is 1A / dm 2 ~ 3A / dm 2 , 10min~20min, the silver plating layer is 2A / dm 2 ~ 5A / dm 2 , 8min~15min, the plating layer thickness meets the design requirements, the adhesion reaches 5B level, the corrosion resistance is optimal, and out of the range will appear the problems of too thin plating layer, adhesion decline or too thick leading to cost increase and the like.

[0110] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement and the like within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A photovoltaic module reflective busbar structure, characterized by, The reflective bus bar is in a strip shape and has two opposite surfaces, one of which is a welding surface and the other is a non-welding surface. The non-welding surface is in a curved surface structure, which is different from a planar structure, and forms a continuous shape of protrusions and depressions along the width direction and the thickness direction of the reflective bus bar, and the curved surface structure covers the entire area of the non-welding surface.

2. The photovoltaic module reflective busbar structure of claim 1, wherein, The size X of the cross section of the curved surface structure along the width direction of the reflective bus bar is 0.1mm-0.2mm, the size Y of the cross section along the thickness direction of the reflective bus bar is 0.03mm-0.05mm, and the cross section of the curved surface structure forms an included angle Z, which is an angle formed by the intersection of two adjacent curved surface segments in the curved surface structure at the cross section, and the angle value is 90°-150°.

3. The photovoltaic module reflective busbar structure of claim 1, wherein, The curved surface structure has a curved surface difference, which is the vertical distance between the highest point and the lowest point of the curved surface structure along the thickness direction of the reflective bus bar, and the curved surface difference is <0.15mm, and the welding surface is a flat surface with a surface roughness Ra≤0.4μm.

4. The photovoltaic module reflective busbar structure of claim 1, wherein, The curved surface structure is a continuous curved surface extending along the length direction of the reflective bus bar, and the adjacent curved surface units in the continuous curved surface are designed with smooth transition, and there are no corners and breakpoints at the transition.

5. The photovoltaic module reflective busbar structure of claim 1, wherein, The base material of the reflective bus bar is copper material with a purity of not less than 99.9%, and the surface of the base material is covered with a corrosion-resistant plating layer, which is a tin plating layer or a silver plating layer, the thickness of the tin plating layer is 5μm-10μm, and the thickness of the silver plating layer is 8μm-15μm.

6. The photovoltaic module reflective busbar structure of claim 1, wherein, It also includes a solder strip used in cooperation, which is a round wire solder strip, the cross section of the round wire solder strip is circular, the diameter is matched with the width of the reflective bus bar, one end of the round wire solder strip is fixedly attached to the welding surface of the reflective bus bar, and the area of the attached area is not less than 1 / 2 of the cross section area of the round wire solder strip.

7. A method of processing a photovoltaic module light-reflecting busbar structure according to any one of claims 1 to 6, characterized in that, It includes the following steps: S1, preparing a reflective bus bar base material, selecting a copper plate material with a purity of not less than 99.9%, and cutting the copper plate material into a long strip-shaped blank with a predetermined width and length by using a precision numerical control cutting equipment, or rolling the copper plate material into a long strip-shaped blank with a predetermined thickness, width and length by using a multi-pass rolling equipment, to obtain a bus bar base material; two opposite surfaces of the bus bar base material are marked as a welding surface to be processed and a non-welding surface respectively; S2, non-welding surface curved surface processing, using a mold pressing process or a laser engraving process to process the non-welding surface of the bus bar base material, and forming a curved surface structure with size parameters on the non-welding surface after processing; S3, welding surface treatment, using a fine sandpaper with a particle size of 800-1200 mesh to manually or mechanically polish the welding surface of the bus bar base material, or immersing the welding surface in a 5%-10% sulfuric acid solution for 3-5 minutes, then rinsing the welding surface with deionized water until it is neutral, and then placing it in a drying oven at 60-80°C for 5-10 minutes; S4, surface corrosion prevention treatment, carrying out plating treatment on the bus bar base material completed in step S3 to form a tin plating layer or a silver plating layer on the surface of the bus bar base material, and obtaining a finished reflective bus bar structure.

8. The method of claim 7, wherein the method further comprises: When the mold pressing process is used in the step S2, the mold comprises an upper mold and a lower mold, the lower surface of the upper mold is provided with a cavity matched with the preset curved surface structure, the surface roughness Ra of the cavity is ≤0.2 μm, when pressing, the non-welding surface of the busbar substrate is placed on the lower mold, the upper mold is pressed downward, the pressing pressure is 5 MPa-15 MPa, the pressing time is 10 s-30 s, and in the pressing process, the drop of the curved surface structure of the non-welding surface can be monitored in real time by a laser thickness gauge, so that the drop is ensured to be <0.15 mm.

9. The method of claim 7, wherein the method further comprises the step of applying a reflective coating to the busbar. 9 When the laser engraving process is used in the step S2, a fiber laser engraving equipment with a wavelength of 1064 nm is selected, and before engraving, the busbar substrate is fixed on the workbench of the equipment, the engraving area of the non-welding surface is calibrated through the positioning system of the equipment, when engraving, the laser power is set to 50 W-200 W, the engraving speed is 100 mm / s-500 mm / s, and the engraving is carried out according to the preset continuous curved surface path, and after the engraving is completed, a polishing solution with a volume ratio of phosphoric acid to sulfuric acid of 3:1 is prepared, the non-welding surface of the busbar substrate is soaked in the polishing solution at 50 °C-70 °C for 5 min-15 min, then the non-welding surface is washed with deionized water until neutral, and then dried.

10. The method of claim 7, wherein the method further comprises: In the step S4, the plating treatment is carried out by using an electroplating process, and the specific steps comprise: S41, in the tin plating layer, the electroplating solution is stannous sulfate system, wherein the stannous sulfate concentration is 30g / L-50g / L, the sulfuric acid concentration is 80g / L-120g / L, the polyethylene glycol concentration is 1g / L-3g / L, during electroplating, the current density is controlled to be 1A / dm 2 ~3A / dm 2 , the electroplating time is 10min-20min; S42, in the silver plating layer, the electroplating solution is cyanide silver system, wherein the concentration of cyanide silver is 30g / L-50g / L, the concentration of potassium cyanide is 80g / L-120g / L, the current density is controlled to be 2A / dm 2 ~5A / dm 2 during electroplating, and the electroplating time is 8min-15min; S43, after electroplating, the busbar substrate is washed with deionized water for 3-5 times, each time for 1 min-2 min, and then placed in a drying oven at 60 °C-80 °C for 10 min-20 min.

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