Core Requirements and Technical Specifications for Solar Cell Module Testing

As the core energy conversion unit of a photovoltaic (PV) system, the quality and performance of solar cell modules directly determine the power generation efficiency, operational stability, and service life of the PV system. To ensure that modules meet practical application requirements and avoid power attenuation, safety hazards, and other issues caused by manufacturing defects, the industry has formulated strict module testing standards, defining comprehensive requirements from appearance to internal structure, and from electrical connections to assembly accuracy. Combining current PV module testing specifications, this article provides a detailed analysis of the core testing requirements for solar cell modules, offering technical reference for module production, quality inspection, and application.​

The core of solar cell module testing revolves around three dimensions: "appearance integrity, structural standardization, and connection reliability." Each testing requirement corresponds to a key performance indicator of the module, serving as both the foundation for ensuring the normal operation of the module and the core basis for standardized industrial production. Combined with the actual testing process, the specific testing requirements and their technical connotations are as follows:​

I. Requirements for Appearance Cleanliness and Monocrystalline Cell Integrity​

Appearance quality is the primary link in module testing, directly affecting the light-receiving efficiency and long-term weather resistance of the module, and is also a key step in identifying obvious defects.​

The outer surface of the module must be clean and free of dust, stains, scratches, and foreign objects. This is because surface contaminants can block sunlight, reduce the light absorption efficiency of the cell, and long-term accumulation may also corrode the module's surface packaging materials, accelerating module aging. Especially in harsh outdoor environments, contaminants may also cause local hot spot effects, damaging cell performance. Therefore, the inspection of appearance cleanliness is not only a simple visual check but also the basic premise for ensuring the photoelectric conversion efficiency of the module.​

As the core unit for energy conversion of the module, the integrity of monocrystalline cells directly determines the power generation capacity of the module. The testing requires that monocrystalline cells are free of fatal defects such as breakage, cracks, and pinholes. Broken or cracked cells will cause interruptions in current transmission, significantly reduce module power, and even trigger thermal runaway of the cells; pinhole defects may damage the sealing performance of the cells, leading to water vapor penetration and exacerbating cell corrosion and failure. This requirement is consistent with the core requirements of the appearance inspection (MQT 01) in the national standard GB/T 9535.2-2025, aiming to avoid obvious quality hazards of the module from the source.​

II. Control Standards for Cell Chipping and Corner Defects​

During the production, transportation, and assembly processes, cells are prone to mechanical damage such as chipping and corner defects. Although such defects are not fatal, they will affect the structural strength and current transmission stability of the cells, so the scope of defects must be strictly controlled.​

For cell chipping, the testing standard clearly stipulates: chipping along the thickness direction of the cell, with a depth not exceeding 1/2 of the cell thickness and an area not exceeding 2mm², and no more than two chippings per cell. The core purpose of this restriction is to avoid the cell becoming structurally fragile due to excessive chipping depth, which may further break during subsequent environmental tests such as thermal cycling and mechanical loading. At the same time, controlling the chipping area reduces the impact on the light-receiving area and current transmission path of the cell.​

The control of cell corner defects is more precise, with specific requirements: for each cell, there shall be no more than one corner defect with a depth less than 1.5mm and a length less than 5mm; no more than two corner defects with a depth less than 1mm and a length less than 3mm. In addition, the total number of chipping and corner defects in each module shall not exceed two. This requirement combines the structural characteristics of the cells and the overall performance of the module, allowing for minor mechanical damage while avoiding concentrated defects that may lead to significant attenuation of module power, and is consistent with the basic specifications for internal defect testing of PV modules.​

III. Reliability Requirements for Grid Line and Bus Bar Connections​

Grid lines and bus bars are the core channels for internal current transmission of the module, and their connection quality directly affects the electrical conductivity and power output stability of the module, which is also one of the core focuses of module testing. As the key structure for collecting and transmitting photogenerated carriers, the integrity and connection reliability of the cell grid lines are crucial to the photoelectric conversion efficiency of the module. The main grid lines are responsible for summarizing the current collected by the fine grid lines, while the fine grid lines directly contact the surface of the silicon wafer to efficiently collect photogenerated electrons. The connection quality between the two determines the degree of current transmission loss.​

In terms of grid line connections, the connection between the main grid and fine grid lines of the module cells allows for a breakpoint of ≤1mm, the fine grid lines allow for a detachment of ≤2mm, and the total number of breakpoints and grid line detachments shall not exceed 1/5 of the total number of grid lines. This requirement balances the rationality of the production process and the stability of current transmission: minor breakpoints and detachments will not cause interruptions in current transmission, while strictly controlling the total number of defects can avoid increased resistance and aggravated power loss caused by excessive grid line defects. If grid line defects exceed the limit, current transmission will be blocked, which not only reduces the module's power generation efficiency but also may cause local current concentration, leading to hot spot effects and damaging the cells.​

At the connection between the bus bar and the solder ribbon, the solder ribbon exceeding the bus bar and the bus bar exceeding the solder ribbon shall both be less than 1mm. The connection between the bus bar and the solder ribbon is a key node for current summarization and output. Excessive offset at the connection will lead to insufficient contact area, increased contact resistance, and local heating. In long-term operation, it may cause detachment of the soldered joint, thereby triggering module failure. At the same time, reasonably controlling the offset can also avoid concentrated mechanical stress on the solder ribbon or bus bar due to offset, improving the structural stability of the module, which is highly consistent with the core technical requirements of the PV module soldering process.​

IV. Precision Control of Assembly Clearance and Displacement​

The assembly accuracy of solar cell modules directly affects the structural stability, current transmission efficiency, and appearance consistency of the module. It is necessary to strictly control the clearance and displacement deviation between various components, which is also an important part of the module's mechanical performance testing.​

In terms of clearance control, the distance between cells, between cells and bus bars, and between bus bars shall be more than 0.3mm. Sufficient clearance can avoid damage, short circuits, and other problems caused by mutual extrusion of various components during the thermal expansion and contraction of the module; at the same time, reasonable clearance also facilitates the implementation of the module packaging process, ensuring that the packaging material can be fully filled, improving the sealing performance of the module, and preventing water vapor, dust, and other impurities from entering the interior of the module, damaging the cells and connecting components.​

In terms of displacement control, the testing requirements clearly stipulate: the horizontal misalignment of cells ≤2mm; the difference between the two ends of the vertical gap ≤2mm; when the module is displaced as a whole, the difference in the distance between the cells on both sides and the edge of the glass ≤3mm. The control of horizontal and vertical misalignment can ensure that the cells are arranged neatly, avoiding uneven light reception and inconsistent current transmission paths caused by misalignment; the control of the overall displacement of the module can ensure the appearance consistency of the module, and at the same time avoid concentrated packaging stress caused by excessive displacement, extending the service life of the module.​

V. Sealing Requirements for Solder Ribbon and Grid Line Connections​

There shall be no detachment between the solder ribbon and the grid lines, which is the core requirement for ensuring the continuity of current transmission of the module. As a key component connecting cells and transmitting current, the tight connection between the solder ribbon and the grid lines is the basis for avoiding interruptions in current transmission and reducing power loss. Detachment will block the current transmission between cells, not only reducing the overall power generation efficiency of the module but also may cause local heating due to excessive resistance at the detachment point, leading to hot spot effects, and further damaging the cells and surrounding components. In addition, detachment may also cause water vapor to enter the interior of the module through the detachment gap in harsh outdoor environments, accelerating cell corrosion and grid line oxidation, and significantly shortening the service life of the module, which is highly consistent with the hazards of false soldering defects in PV modules.​

VI. Industrial Significance and Application Value of Testing Requirements​

The above testing requirements are not isolated technical indicators but are interrelated and complementary, together forming a quality assurance system for solar cell modules. Combined with industry standards such as NB/T 11081—2023 "Technical Specification for Infrared Thermographic (TIS) Testing of PV Modules" and GB/T 9535.2-2025 "Terrestrial Photovoltaic Modules - Design Qualification and Type Approval - Part 2: Test Procedures", these testing requirements are not only in line with the mainstream international trend of PV module testing but also adapt to the needs of high-quality development of China's PV industry.​

From the production side, strictly implementing the testing requirements can effectively avoid process defects during the production process, improve the qualification rate of module production, and reduce the rework and scrap costs caused by quality problems; from the application side, modules that meet the testing standards can ensure the long-term stable operation of the PV system, reduce operation and maintenance costs, and improve the return on investment of PV projects; from the perspective of industrial development, unified testing standards can regulate the market order, promote the development of the PV module industry towards standardization and high quality, and help the large-scale application of the PV industry.​

Conclusion​

The testing requirements for solar cell modules are formulated based on the working principle, structural characteristics, and application environment of the modules. Each indicator is directly related to the performance, reliability, and service life of the module. With the continuous development of PV technology, the module testing standards will also be continuously improved to adapt to the needs of new products such as high-efficiency modules and flexible modules. For module manufacturers, it is necessary to strictly implement various testing requirements and strengthen quality control during the production process; for PV project investors and operators, it is necessary to attach importance to the module testing link and select modules that meet the standards to ensure the stable and efficient operation of the PV system. Only by adhering to the quality bottom line and strictly implementing the testing specifications can we promote the sustainable and healthy development of the PV industry and give full play to the core value of solar energy as a clean energy source.