International Electrotechnical Commission

Measurement procedures for materials used in photovoltaic modules – Part 1-2: Encapsulants – Measurement of volume resistivity of photovoltaic encapsulants and other polymeric materials - Edition 1.0
 N 62788-1-2

Annotation

This part of IEC 62788 provides a method and guidelines for measuring the volume resistivity of materials used as encapsulation, edge seals, front-sheets, backsheets, or any other insulating material in a photovoltaic (PV) module. The test is performed on dry, humid or wet preconditioned samples. In the case of frontsheets and backsheets comprised of multiple layers, the measured resistivity is an effective value. This test is designed for room temperature measurement, but can also be utilized at higher temperatures.

Degradation of PV modules is known to occur in part by electrochemical corrosion, and other potential induced degradation processes. These processes may be dependent upon the resistivity of a polymeric component. Therefore, the DC resistivity of polymeric components is relevant to module design and durability in the field. The resistivity may depend on cure state, temperature, water content, and voltage history. A number of options are included to allow the measurement to be performed in a manner consistent with representative fielded module conditions.

Most resistivity measurement methods and equipment typically become inaccurate and variable for materials with volume resistivity above 1016 ? cm [5]1.Therefore, this standard is used for measurements less than 1?1017 ? cm.

Both monolithic and multilayer materials (e.g. frontsheets and backsheets) are suitable for measurement. Methods are described for room temperature measurement, with guidelines included for testing at elevated temperatures.

Results will vary with moisture content, therefore materials should be tested in a manner anticipatory of usage. Preconditioning procedures for dry, humid and wet environments are included.