——Battery Common Problems
The reason for the network-like cracks on the surface of the module is that the cells are subjected to external forces during welding or handling, or the cells are suddenly exposed to high temperatures at low temperatures without preheating, resulting in cracks. The network cracks will affect the power attenuation of the module, and after a long time, debris and hot spots will directly affect the performance of the module.
The quality problems of network cracks on the surface of the cell need manual inspection to find out. Once the surface network cracks appear, they will appear on a large scale in three or four years. Reticular cracks were difficult to see with the naked eye in the first three years. Now, the hot spot images are usually taken by drones, and the EL measurement of the components with hot spots will reveal that the cracks have already occurred.
Cell slivers are generally caused by improper operation during welding, incorrect handling by personnel, or failure of the laminator. Partial failure of the slivers, power attenuation or complete failure of a single cell will affect the power attenuation of the module.
Most module factories now have half-cut high-power modules, and generally speaking, the breakage rate of half-cut modules is higher. At present, the five large and four small companies require that such cracks are not allowed, and they will test the component EL in various links. Firstly, test the EL image after delivery from the module factory to the site to ensure that there are no hidden cracks during the delivery and transportation of the module factory; secondly, measure the EL after installation to ensure that there are no hidden cracks during the engineering installation process.
Generally, low-grade cells are mixed into high-grade components (mixing raw materials/mixing materials in the process), which can easily affect the overall power of the components, and the power of the components will decay greatly in a short period of time. Inefficient chip areas can create hot spots and even burn components.
Because the module factory generally divides the cells into 100 or 200 cells as a power level, they do not perform power tests on each cell, but spot checks, which will lead to such problems in the automatic assembly line for low-grade cells. . At present, the mixed profile of cells can generally be judged by infrared imaging, but whether the infrared image is caused by mixed profile, hidden cracks or other blocking factors requires further EL analysis.
Lightning streaks are generally caused by cracks in the battery sheet, or the result of the combined action 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 back sheet can also cause lightning streaks. The heat generated at the lightning pattern increases, and thermal expansion and contraction lead to cracks in the battery sheet, which can easily cause hot spots on the module, accelerate the decay of the module, and affect the electrical performance of the module. Actual cases have shown that even when the power station is not powered on, many lightning streaks appear on the components after 4 years of exposure to the sun. Although the error in the test power is very small, the EL image will still be much worse.
There are many reasons that lead to PID and hot spots, such as foreign matter blocking, hidden cracks in cells, defects in cells, and severe corrosion and degradation of photovoltaic modules caused by grounding methods of photovoltaic inverter arrays in high temperature and humid environments may cause hot spots and PID. . In recent years, with the transformation and progress of battery module technology, PID phenomenon has been rare, but the power stations in the early years could not guarantee the absence of PID. The repair of PID requires overall technical transformation, not only from the components themselves, but also from the inverter side.
- Solder Ribbon, Bus Bars and Flux Frequently Asked Questions
If the soldering temperature is too low or the flux is applied too little or the speed is too fast, it will lead to false soldering, while if the soldering temperature is too high or the soldering time is too long, it will cause over-soldering. False soldering and over-soldering occurred more frequently in components produced between 2010 and 2015, mainly because during this period, the assembly line equipment of Chinese manufacturing plants began to change from foreign imports to localization, and the process standards of enterprises at that time would be lowered Some, resulting in poor quality components produced during the period.
Insufficient welding will lead to delamination of the ribbon and the cell in a short period of time, affecting the power attenuation or failure of the module; over-soldering will cause damage to the internal electrodes of the cell, directly affecting the power attenuation of the module, reducing the life of the module or causing scrap.
Modules produced before 2015 often have a large area of ribbon offset, which is usually caused by abnormal positioning of the welding machine. The offset will reduce the contact between the ribbon and the battery area, delamination or affect power attenuation. In addition, if the temperature is too high, the bending hardness of the ribbon is too high, which will cause the battery sheet to bend after welding, resulting in battery chip fragments. Now, with the increase of cell grid lines, the width of the ribbon is getting narrower and narrower, which requires higher precision of the welding machine, and the deviation of the ribbon is less and less.
The contact area between the bus bar and the solder strip is small or the resistance of the virtual soldering increases and heat is likely to cause the components to burn out. The components are seriously attenuated in a short period of time, and they will be burned out after long-term work and eventually lead to scrapping. At present, there is no effective way to prevent this kind of problem in the early stage, because there is no practical means to measure the resistance between the bus bar and the soldering strip at the application end. Replacement components should only be removed when burnt surfaces are evident.
If the welding machine adjusts the amount of flux injection too much or the personnel apply too much flux during rework, it will cause yellowing on the edge of the main grid line, which will affect the EVA delamination at the position of the main grid line of the component. Lightning pattern black spots will appear after long-term operation, affecting the components. Power decay, reducing component life or causing scrapping.
——EVA/Backplane Frequently Asked Questions
The reasons for EVA delamination include unqualified cross-linking degree of EVA, foreign matter on the surface of raw materials such as EVA, glass, and back sheet, and the uneven composition of EVA raw materials (such as ethylene and vinyl acetate) that cannot be dissolved at normal temperatures. When the delamination area is small, it will affect the high-power failure of the module, and when the delamination area is large, it will directly lead to the failure and scrapping of the module. Once EVA delamination occurs, it is not repairable.
EVA delamination has been common in components in the past few years. In order to reduce costs, some enterprises have insufficient EVA cross-linking degree, and the thickness has dropped from 0.5mm to 0.3, 0.2mm. Floor.
The general reason for EVA bubbles is that the vacuuming time of the laminator is too short, the temperature setting is too low or too high, and bubbles will appear, or the interior is not clean and there are foreign objects. Component air bubbles will affect the delamination of the EVA backplane, which will seriously lead to scrapping. This kind of problem usually occurs during the production of components, and it can be repaired if it is a small area.
The yellowing of EVA insulation strips is generally caused by long-term exposure to the air, or EVA is polluted by flux, alcohol, etc., or it is caused by chemical reactions when used with EVA from different manufacturers. First, the poor appearance is not accepted by customers, and second, it may cause delamination, resulting in shortened component life.
——FAQs of glass, silicone, profiles
The shedding of the film layer on the surface of the coated glass 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 in the power station, the film layer on the glass surface will be found to fall off, and it will fall off unevenly, which will affect the glass transmittance of the module, reduce the power of the module, and affect the entire square Bursts of power. This kind of attenuation is generally difficult to see in the first few years of power station operation, because the error of the attenuation rate and irradiation fluctuation is not large, but if it is compared with a power station without film removal, the difference in power generation can still be seen.
Silicone bubbles are mainly caused by air bubbles in the original silicone material or unstable air pressure of the air gun. The main reason for the gaps is that the staff’s technique of glueing is not standard. Silicone is a layer of adhesive film between the frame of the module, the backplane and the glass, which isolates the backplane from the air. If the seal is not tight, the module will be delaminated directly, and rainwater will enter when it rains. If the insulation is not enough, leakage will occur.
The deformation of the profile of the module frame is also a common problem, which is generally caused by the unqualified profile strength. The strength of the aluminum alloy frame material decreases, which directly causes the frame of the photovoltaic panel array to fall off or tear when strong winds occur. Profile deformation generally occurs during the shifting of the phalanx during technical transformation. For example, the problem shown in the figure below occurs during the assembly and disassembly of components using mounting holes, and the insulation will fail during reinstallation, and the grounding continuity cannot reach the same value.
——Junction Box Common Problems
The incidence of fire in the junction box is very high. The reasons include that the lead wire is not clamped tightly in the card slot, and the lead wire and the junction box solder joint are too small to cause fire due to excessive resistance, and the lead wire is too long to contact the plastic parts of the junction box. Prolonged exposure to heat may cause fire, etc. If the junction box catches fire, the components will be scrapped directly, which may cause a serious fire.
Now generally high-power double-glass modules will be divided into three junction boxes, which will be better. In addition, the junction box is also divided into semi-enclosed and fully enclosed. Some of them can be repaired after being burned, and some cannot be repaired.
In the process of operation and maintenance, there will also be glue filling problems in the junction box. If the production is not serious, the glue will be leaked, and the personnel’s operation method is not standardized or not serious, which will cause the leak of welding. If it is not correct, then it is difficult to cure. You may open the junction box after one year of use and find that the glue A has evaporated, and the sealing is not enough. If there is no glue, it will enter the rainwater or moisture, which will cause the connected components to catch fire. If the connection is not good, the resistance will increase, and the components will be burned due to ignition.
Breakage of wires in the junction box and falling off of the MC4 head are also common problems. Generally, the wires are not placed in the specified position, resulting in being crushed or the mechanical connection of the MC4 head is not firm. Damaged wires will lead to power failure of components or dangerous accidents of electric leakage and connection. , The false connection of the MC4 head will easily cause the cable to catch fire. This kind of problem is relatively easy to repair and modify in the field.
Repair of components and future plans
Among the various problems of the above-mentioned components, some can be repaired. The repair of the components can quickly solve the fault, reduce the loss of power generation, and effectively use the original materials. Among them, some simple repairs such as junction boxes, MC4 connectors, glass silica gel, etc. can be realized on site at the power station, and since there are not many operation and maintenance personnel in a power station, the repair volume is not large, but they must be proficient and understand the performance, such as changing wiring If the backplane is scratched during the cutting process, the backplane needs to be replaced, and the whole repair will be more complicated.
However, problems with batteries, ribbons, and EVA backplanes cannot be repaired on site, because they need to be repaired at the factory level due to the limitations of the environment, process, and equipment. Because most of the repair process needs to be repaired in a clean environment, the frame must be removed, cut off the backplane and heated at high temperature to cut off the problematic cells, and finally soldered and restored, which can only be realized in the factory’s rework workshop.
The mobile component repair station is a vision of future component repair. With the improvement of component power and technology, the problems of high-power components will become less and less in the future, but the problems of components in the early years are gradually appearing.
At present, capable operation and maintenance parties or component undertakers will provide operation and maintenance professionals with process technology transformation ability training. In large-scale ground power stations, there are generally working areas and living areas, which can provide repair sites, basically equipped with a small The press is enough, which is within the affordability of most operators and owners. Then, in the later stage, the components that have problems with a small number of cells are no longer directly replaced and put aside, but have specialized employees to repair them, which is achievable in areas where photovoltaic power plants are relatively concentrated.
Post time: Dec-21-2022