The Brutal Truth of PV Module In Welding Defects!

The Power Grid Is Complex.

For many power generation technologies, the complexity lies in their complexity itself. GW-scale nuclear power plants and coal power plants themselves are complex and require a large number of on-site technicians and engineers to ensure safe and efficient operation.

The complexity of solar power generation lies in other aspects, though.

Compared with nuclear power plants, the basic structure of solar modules is relatively simple. The key to solar power is to do all the work over and over again, accurately —— specifications, manufacturing, transportation, and installation.

For example, a 200MW typical solar power station using a 600W module requires 333,000 modules.

Major technological changes in the solar industry have gained significant attention, including the application of double-sided cells, the conversion from PERC to TOPCon, and the continued growth of the module wattage. However， there is a less visible and less interesting change that improves the current collection capacity of each solar cell but requires the precision of the manufacturing process.

Over the past 10 years, the design of solar panels has shifted from using two to three large flat wires per cell to using 18 thin circular wires. This change reduces costs and significantly reduces the impact of cracks, but also at a cost.

It is easy to weld large flat lines in place, but it is much harder to accurately place new, smaller round lines. A small misalignment can lead to "cold solder joints," where the wire is not fully connected to the solar cell.

A review of our 200MW reference plant with 333,000 modules?reveals the scale of this challenge: each solar cell?has 18 leads, each solar cell?has multiple solder joints per wire, and each component has 144 half-cut cells, which means more than 1 billion solder joints!

To test the quality of the solder joints, most manufacturers perform offline destructive tests (called "pull tests") on very small samples every four hours. The goal is to determine whether there are systemic failures during the welding process, but this method is not effective in finding uncommon defects. Further complicated, the eligible / nonconformity criteria for pull testing may vary from plant to plant. Therefore, undetected errors are inevitable.

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Clean Energy Associates (CEA) recently summarized the results of in-plant quality assurance surveys at more than 300 plants covering the period from January 2023 to August 2024. solar cell?rupture used to be the most common defect, but now cold welding has become the most frequent problem found in electroluminescence (EL) testing before shipment.

These defects were found at the final stage of the manufacturing process, meaning that they escaped the quality assurance checks in the process and were ready for shipment to the site.

CEA‘s engineering services team recently conducted a similar survey of defects found on-site. The survey found that 78% of the field modules?had welding defects.

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Power reduction with catastrophic failure, thermal event.

A range of problems can occur when solar panels with welding defects are shipped to the field for installation. Bad solder joints will form resistance connection points, resulting in increased heat loss and lower power generation. The bad solder joint may cause the bypass diode to open and disconnect one-third of the batteries in the assembly, thus reducing the output power of the component by one-third. At worst, poor welding can lead to extreme temperatures, leading to catastrophic failures and thermal events.

To make matters worse, when a cluster has both good modules?and bad modules, the maximum power point tracker (MPPT) makes it harder to find the optimal voltage for the string, which further reduces the output power.

The good thing is that there are effective strategies to protect buyers from welding defects. The solution was started long before production began, namely, through a negotiated supply agreement. The buyer shall clearly define the welding defects in the agreement, require the factory to conduct 100% EL testing, and have the right to arrange for third-party quality assurance experts to enter the plant to observe the production situation.

During your PV module production process, your quality assurance representative can observe the production process, ensure that the equipment is properly calibrated, the process is followed, and an adequate pull test is conducted. Prior to daily shipment, your representative shall take a number of samples from the finished product to detect defects, including but not limited to welding defects.

There is no perfect and flawless manufacturing in the world. However, a fully negotiated supply agreement and a well-designed plant quality assurance plan can greatly reduce the risk.

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