Common problems and repair of photovoltaic modules
1. FAQ of battery chipThe reason for the network hidden crack on the surface of the module is mainly due to the external force acting on the battery sheet during welding or handling, or the expansion of the battery sheet after being subjected to high temperature in a short time without preheating under low temperature. The network crack will affect the power attenuation of the module, and after a long time, fragments, hot spots, etc. will directly affect the performance of the module.The quality problem of reticular cracks on the surface of the battery chip needs to be found by manual inspection. Once reticular cracks appear on the surface, they will appear in a large area three or four years later. Reticular cracks are hard to see with the naked eye in the past three years. Now, hot spot images are generally taken by UAVs. When measuring EL of components with hot spots, it can be found that cracks have been generated.The battery slice is generally caused by improper operation during welding, incorrect lifting method of personnel or failure of the laminator. Partial failure of the slice, power attenuation of a single battery slice or complete failure will affect the power attenuation of the module.At present, most component factories have half chip high power components. Generally speaking, the damage rate of half chip components is higher. At present, five large and four small enterprises require that such cracks are not allowed, and they will test the component EL in all aspects. First, test the EL image from the component factory after delivery to the site to ensure that there is no hidden crack during the delivery and transportation of the component factory; Secondly, the EL shall be tested after installation to ensure that there is no hidden crack during the installation of the project.In general, low-grade battery chips are mixed into sub assemblies (raw material mixing/or mixing in the process), which easily affects the overall power of the assembly to become lower. The power of the assembly attenuates greatly in a short period of time. In addition, the low-efficiency chip area will produce hot spots and even burn the assembly.Since the battery chips are generally divided into 100 or 200 pieces by the component factory, which is a power level, the power test will not be performed on each battery, but rather a random inspection. Therefore, this problem may occur with low-grade batteries in the automatic assembly line. At present, the mixed battery chips can be generally judged by infrared imaging, but the specific reason of the infrared image is caused by mixed battery chips, hidden cracks or other obstructions needs further EL analysis.Lightning streaks are generally caused by the hidden crack of the battery chip, or the combined effect of negative electrode silver paste, EVA, water vapor, air and sunlight. The mismatch between EVA and silver paste and the high water permeability of the backplane will also cause lightning streaks. The heat generated at the lightning stripe increases, and the thermal expansion and cold contraction lead to the hidden crack of the battery chip, which is easy to cause the hot spot of the module, accelerate the attenuation of the module, and affect the electrical performance of the module. An actual case shows that when the power station is not powered on for operation, many lightning streaks appear on the components after 4 years of exposure. Although the error of the test power is small, the EL image will still be much worse.There are many reasons that cause PID and hot spot. The hot spot and PID may be caused by foreign matter shielding, hidden crack of the cell, defects of the cell itself, and serious corrosion and decay of photovoltaic modules caused by the grounding mode of photovoltaic inverter array in high temperature and humidity environment. In recent years, with the improvement of the battery module process, there are few PID phenomena, but in the early years, power plants could not guarantee that PID did not exist. The repair of PID requires overall technical transformation, not only from the component itself, but also from the inverter side.2. Common problems of welding strip, bus bar and fluxToo low welding temperature or too little or too fast application of flux will lead to faulty welding, while too high welding temperature or too long welding time will lead to over welding. The phenomenon of faulty welding and over welding appeared more frequently in the components produced from 2010 to 2015, mainly because the assembly line equipment of Chinese manufacturers began to change from foreign imports to localization during this period, and the process standards of enterprises at that time would be lowered, resulting in poor quality of components produced during this period.False soldering will lead to delamination of the welding strip and the battery chip in a short time, affecting the power attenuation or failure of the module; Overwelding will cause damage to the internal electrode of the battery chip, directly affect the power attenuation of the module, reduce the service life of the module or cause scrapping.The components produced before 2015 often have a large area of weld strip offset, which is generally caused by the abnormal positioning of the welding machine. The offset will reduce the contact between the weld strip and the battery area, cause delamination or affect the power attenuation. In addition, if the temperature is too high, the bending hardness of the welding strip will lead to the bending of the battery chip after welding, resulting in the fragmentation of the battery chip. Now, with the increase of grid lines of battery cells, the width of the welding strip is becoming narrower and narrower, requiring higher accuracy of the welding machine, and the phenomenon of welding strip offset is becoming less and less.The contact area between the bus bar and the welding strip is small or the resistance of the faulty welding is increased and the heating is easy to cause the burning of the components. In a short period of time, the components will be seriously attenuated, and the components will be burned out after a long time of work, which will eventually lead to scrapping. At present, there is no effective way to prevent this problem, because there is no practical means to measure the resistance between the bus bar and the welding strip at the application end. Remove the replacement assembly only if the surface is visibly charred.The welding machine adjusts that too much flux is sprayed or too much flux is applied by personnel during repair, which will cause yellowing at the edge of the main grid line, affect the EVA delamination at the position of the main grid line of the component, and after a long time of operation, there will be black spots with lightning stripes, which will affect the power attenuation of the component, reduce the service life of the component or cause scrapping.3. EVA/backplane FAQEVA delamination is caused by unqualified crosslinking degree of EVA, foreign matters on the surface of raw materials such as EVA, glass and backplane, and uneven composition of EVA raw materials (such as ethylene and vinyl acetate), which lead to inability to dissolve at normal temperature. A small delamination area will affect the high power failure of the module. When the delamination area is large, it will directly lead to the failure and scrapping of the module. Once EVA delamination occurs, it is non repairable.EVA delamination is relatively common in the components in the past few years. In order to reduce costs, some enterprises do not have enough cross-linking degree of EVA, and the thickness is reduced from 0.5mm to 0.3mm and 0.2mm. The EVA is put into use in the factory without aging test, resulting in delamination.EVA bubbles generally occur because the vacuum temperature of the laminator is too short, the temperature setting is too low or too high, and bubbles may occur, or bubbles may also occur if there are impurities inside. Bubbles in components will affect the delamination of EVA backplane and lead to scrapping in serious cases. This problem usually occurs during the production of components. If it is small, it can be repaired.The yellowing of EVA insulation strips is generally caused by variation after long exposure to the air, or EVA is polluted by flux, alcohol, or chemical reaction with EVA from different manufacturers. On the one hand, customers will not accept the poor appearance, and on the other hand, delamination may occur, which will shorten the service life of components.4. Common problems of glass, silica gel and profilesThe shedding of the facial mask on the coated glass surface is irreversible. The coating process in the module factory can generally increase the power of the module by 3%, but after two to three years of operation of the power station, it will be found that the facial mask layer on the glass surface falls off unevenly, which affects the glass transmittance of the module, reduces the power of the module, and affects the power generation of the entire array. This kind of attenuation is usually hard to see in the first few years of the operation of the power station, because the error of attenuation rate and radiation fluctuation is not large. However, if compared with the power station without film removal, the difference of power generation can be seen.Silica gel bubbles are mainly caused by bubbles in the silica gel raw material or unstable air pressure of the air gun, and the gap is mainly caused by non-standard sealant application by employees. Silica gel is a layer of adhesive film between the component frame, the back plate and the glass, which separates the back plate from the air. If the sealing is not tight, the components will be directly delaminated, and rain will enter, and the insulation is not enough to cause electric leakage.Deformation of component frame profile is also a common problem. Generally, it is caused by unqualified profile strength, and the strength of aluminum alloy frame material decreases, which directly causes the frame of photovoltaic panel array to fall off or tear in strong wind. Profile deformation usually occurs in the process of moving the square array during technical transformation. For example, the following problem occurs in the process of loading and unloading components using mounting holes, and the insulation will fail during re installation, and the grounding continuity cannot reach the same value.5. Common problems of junction boxThe incidence of fire in junction box is very high. The causes include that the lead is not clamped in the slot and ignites, the welding area of lead and junction box is too small and the resistance is too large, which causes fire, and the lead is too long to contact the plastic parts of junction box and is heated for a long time, which causes fire. If the junction box catches fire, the components will be scrapped directly, which may cause fire in serious cases.Now, the high-power double glass module is generally divided into three junction boxes, which is better. In addition, the junction box is also divided into semi closed and fully closed ones. Some can be repaired if burned, and some can't be repaired.In the process of operation and maintenance, there will also be glue filling problems in the junction box. Inadequate production will cause glue leakage, and non-standard or careless operation of personnel will cause solder leakage. For example, if the full seal glue filling is solidified with AB glue, if the proportion of AB glue is incorrect, it will be difficult to cure. It may be found that the A glue in the junction box has evaporated completely after one year of use, and the sealing is not enough. If no sealant is applied, it will enter the rain or moisture and cause the connected components to catch fire. If the connection is poor, the resistance will increase, and the components will be burned due to ignition.The breakage of the wire in the junction box and the falling off of the MC4 head are also common problems. Generally, the wire is not placed according to the specified position, resulting in being crushed or the mechanical connection of the MC4 head is not firm. The damage of the wire will lead to the failure of the component power or the dangerous accident of electric leakage and connection., False connection of MC4 connector is easy to cause cable fire. This kind of problem is relatively easy to repair and transform on site.6. Repair of components and future visionSome of the problems of the above components can be repaired. The repair of components can quickly solve the problems, reduce power generation loss, and effectively use the original materials. Among them, some simple repairs such as junction box, MC4 connector, glass silica gel, etc. can be realized on the site of the power station, and since a power station is not equipped with many operation and maintenance personnel, the repair volume is not large, but the performance must be skilled and understood. For example, if the junction box is replaced, if the back plate is marked in the cutting process, then the back plate needs to be replaced, and the whole repair will be more complex.However, the problems of battery, welding strip and EVA backplane cannot be repaired on site. Due to the limitations of environment, process and equipment, they need to be repaired at the factory level. Because most of the repair processes need to be repaired in a clean environment, the frame should be removed. After cutting off the back plate, the defective battery pieces should be cut off by high temperature heating. * Welding recovery can only be achieved in the factory's repair workshop.The mobile component repair station is a vision for future component repair. With the improvement of component power and process, the problems of high-power components will be less and less in the future, but the problems of components in the early years are gradually emerging.At present, the competent operation and maintenance party or component undertaker will provide the operation and maintenance professionals with process technology transformation ability training. In large surface power stations, there are generally working areas and living quarters, which can provide repair sites. Basically, a small laminated press is enough, which is within the scope of responsibility for most operators and owners. Then, in the later stage, a small number of modules with battery chip problems will no longer be replaced and put aside directly, but will be repaired by special staff, which can be achieved in areas where photovoltaic power stations are concentrated.
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