Overview
IEC 62788-6-2:2020 is an international standard published by the International Electrotechnical Commission (IEC) that specifies measurement procedures for moisture permeation testing of polymeric materials used in photovoltaic (PV) modules. This part of the IEC 62788 series focuses on general test methods to evaluate the water vapor transmission rate (WVTR), water vapor permeability (P), diffusivity (D), solubility (S), and moisture breakthrough time (Ƭ10) of common polymeric materials such as encapsulants, edge seals, frontsheets, and backsheets in PV module construction. The standard outlines procedures for testing these materials under various temperatures and humidity levels to assess their performance and durability against moisture ingress, which is critical for PV module longevity.
IEC 62788-6-2 employs a model based on Fickian diffusion theory to analyze transient water vapor transmission data, making it especially relevant for monolithic polymer films. For multilayer films, only apparent values of diffusivity and solubility are derived, albeit accurate steady-state permeation properties are still attainable.
Key Topics
- Water Vapor Transmission Rate (WVTR): Measurement of the rate at which water vapor permeates through polymeric films, expressed in g·m⁻²·day⁻¹.
- Permeability (P): The inherent ability of a polymeric material to allow moisture to permeate through it.
- Diffusivity (D): Quantifies how fast moisture molecules diffuse through a polymer, a critical factor in understanding moisture ingress kinetics.
- Solubility (S): Represents the amount of moisture a polymeric material can absorb.
- Moisture Breakthrough Time (Ƭ10): Time required for the water vapor transmission rate to reach 10% of its steady-state value-essential for predicting early moisture exposure.
- Fickian Diffusion Analysis: A modeling approach assuming constant diffusivity, facilitating the interpretation of transient WVTR curves.
- Testing Conditions: Procedures allow for measurements at different temperature and humidity settings to simulate various environmental exposures.
- Applicability to Other Gases: While primarily targeting water vapor, the standard's methodologies also apply to other permeants like oxygen (O₂).
Applications
- Photovoltaic Module Material Evaluation: Ensuring that encapsulants, edge seals, and backsheets meet moisture resistance requirements for long-term outdoor exposure.
- Product Development: Guiding manufacturers in selecting and optimizing polymeric materials with superior moisture barrier properties to enhance module reliability.
- Quality Control: Standardizing moisture permeation testing in production to detect potential defects or variability.
- Lifetime Prediction: Using breakthrough time and permeation data to model degradation pathways influenced by moisture ingress.
- Research and Innovation: Supporting innovation in new polymeric materials and multilayer films with advanced moisture barrier characteristics.
The standard is vital for manufacturers, testing laboratories, and researchers dealing with moisture ingress, polymeric film assessment, and photovoltaic module durability.
Related Standards
IEC 62788-6-2 references and aligns with international standards and test methods relevant to moisture permeation and polymer testing, including:
- IEC TS 61836 - Solar Photovoltaic Energy Systems – Terms, Definitions, and Symbols.
- ISO 2528 - Determination of Water Vapour Transmission Rate (WVTR) by Gravimetric Method.
- ISO 9932 - Water Vapour Transmission Rate of Sheet Materials by Dynamic and Static Gas Methods.
- ISO 15106 Series - Water Vapour Transmission Rate Determinations using various sensor methods (humidity detection, infrared, electrolytic, and gas chromatographic).
- ASTM F1249-06 - Standard Test Method for WVTR through Plastic Films via Modulated Infrared Sensor.
These standards complement IEC 62788-6-2, ensuring comprehensive, harmonized approaches for evaluating polymeric films used in photovoltaic applications.
By following IEC 62788-6-2:2020, stakeholders gain a scientifically rigorous, internationally recognized procedure to assess moisture permeation in PV module materials-crucial for optimizing module reliability, reducing corrosion risks, and enhancing photovoltaic system performance over decades.