IEC 62788-6-2-2020 pdf download.Measurement procedures for materials used in photovoltaic modules – Part 6-2: General tests – Moisture permeation testing of polymeric materials.
This document provides methods for measuring the steady-state water vapour transmission rate (WVTR), water vapour permeability (P), diffusivity (D), solubility (S), and moisture breakthrough time (Ƭ 1 0 ) (defined as the time to reach 1 0 % of the steady state WVTR) for polymeric materials such as encapsulants, edge seals, frontsheets and backsheets. These measurements can be made at selected temperatures and humidity levels as deemed appropriate for evaluation of their performance in PV modules. Measurement is accomplished by inspection of the transient WVTR curve and by fitting it to a theoretical Fickian model.
This document is best applied to monolithic films. If multilayer films are used, the D and S values are only apparent values, but the steady-state values can still be measured. This document was written for the measurement of water permeation, but it can equally be used for other permeants such as O 2 . In this case the same diffusion equations, fitting procedures, and scaling arguments are used.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC TS 61 836, Solar photovoltaic energy systems – Terms, definitions and symbols
ISO 2528, Sheet materials – Determination of water vapour transmission rate (WVTR) – Gravimetric (dish) method
ISO 9932, Paper and board – Determination of water vapour transmission rate of sheet  materials – Dynamic sweep and static gas methods
ISO 1 51 06-1 , Plastics – Film and sheeting – Determination of water vapour transmission Rate – Part 1: Humidity detection sensor method
ISO 1 51 06-2, Plastics – Film and sheeting – Determination of water vapour transmission Rate – Part 2: Infrared detection sensor method
ISO 1 51 06-3, Plastics – Film and sheeting – Determination of water vapour transmission Rate – Part 3: Electrolytic detection sensor method
ISO 1 51 06-4, Plastics – Film and sheeting – Determination of water vapour transmission Rate – Part 4: Gas-chromatographic detection sensor method
ASTM F1 249-06, Standard test method for water vapour transmission rate through plastic film and sheeting using a modulated infrared sensor
3 Terms, definitions and symbols
For the purposes of this document, the terms and definitions the terms and definitions given in
IEC TS 61 836 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Terms and definitions
3.1.1 edge seal
polymeric material designed to be placed between two impermeable (or with extremely low permeability) frontsheet and backsheet materials to restrict moisture ingress from the sides
3.1.2 Fickian
material for which the diffusivity is constant, independent of concentration of the permeant within the experimental uncertainty
3.1.3 permeability
state or quality of a material or membrane that causes it to allow liquids or gases to pass through it
3.1.4 diffusivity
measure of the capability of a substance to be diffused or to allow something to pass by diffusion
4 Apparatus
Any instrument capable of measuring the transient permeation through a membrane shall be used. Many examples of apparatus that are suitable for these measurements are described in ASTM F1 249-06, ISO 2528, ISO 9932, ISO 1 51 06-1 , ISO 1 51 06-2, ISO 1 51 06-3, and ISO 1 51 06-4. The key characteristics to look for are high precision and small timescales for the response to changes. At low permeation rates, the amount of moisture adsorbed onto instrument surfaces becomes a problem, because it limits the useful precision of some instruments.IEC 62788-6-2 pdf download.