I: EL Testing

EL stands for Electro Luminescence, also known as electroluminescence testing. By applying voltage across the Pv module based on the electroluminescence principle of crystalline silicon, electrons within the module emit visible light. A high-resolution infrared camera captures near-infrared images of the crystalline silicon. Image analysis software processes these images to detect defects in solar modules, including microcracks, fragments, cold solder joints, broken grids, bright/dark spots, and mixed-cell issues.

As shown in the figure, these are partial EL imaging results of the modules. During module production, EL testing is primarily applied in the following processes:

① Pre-dicing inspection to detect hidden cracks in solar cells, integrated into dicing machines or cell sorting equipment

② Post-stringing inspection to detect cold solder joints, hidden cracks, etc., in cell strings

③ Conducting comprehensive testing of internal cells before lamination. Since faulty cells after lamination necessitate downgrading the module, EL testing must be performed beforehand—referred to as pre-lamination EL.

④ Inspecting modules after lamination to identify internal issues such as hidden cracks, fragments, or blackened cells—known as post-lamination EL.

II: IV Testing

Purpose of Testing: Photovoltaic IV testing serves as a key metric for evaluating solar cell performance. It primarily assesses critical parameters such as conversion efficiency and output power by analyzing the current-voltage (I-V) characteristic curve of photovoltaic materials under varying light and temperature conditions.

Principle of PV IV Testing: Testing is conducted based on photoelectric effect circuit analysis. The photoelectric effect refers to the conversion of photon energy absorbed by the cell into electron energy, causing electrons to migrate and flow within the material, thereby generating current. The variable load method, also known as the scanning method, is commonly used in IV testing. It simulates sunlight exposure using a flash lamp while gradually increasing the light intensity to a set value (typically 1000 W/m²). The current and voltage output of the Pv module are measured throughout this process to derive the IV characteristic curve.

IV testing is the most critical component in factory testing, directly reflecting a module's power output and efficiency. Specific IV data can indicate the quality of module encapsulation. (Typically, 80% of modules in a shift should exceed 590W. If this suddenly drops to 60%, production line anomalies must be investigated, issues analyzed, and adjustments made promptly to ensure encapsulation stability.)