Testing and Comparison of the Moisture Behavior and Mechanical Strength of Photovoltaic Encapsulants
By Kristof Proost1, Jane Kapur2, Steve Bennison2
1 DuPont de Nemours Belgium, Antoon Spinoystraat 7, 2800 Mechelen, Belgium
2 E. I. du Pont de Nemours & Company, Wilmington, Delaware, USA
This paper will present a technical comparison of several incumbent and candidate encapsulants that can be used for thin-film photovoltaic module manufacturing. We will focus on moisture ingress behavior and mechanical properties of several polymers. Most thin-film technologies are moisture sensitive; meaning, they can experience decreases in power output as a result of moisture ingress. One of the most important tests for this is a "damp heat" test defined by IEC 61646, where a module is placed for a period of time at 85oC and 85% relative humidity. Moisture ingress data measured in from the sides of glass-glass laminates after 1000 to 5000 hours of damp heat testing will be discussed. Resulting data for PVB, EVA and several ionomer-based encapsulants (commercial and experimental ionomers) will be compared.
Besides its role in protecting a cell from moisture and other environmental factors, an encapsulant also contributes to mechanical strength in a module. Finite Element Modeling (FEM) can be used to calculate the strength behavior of modules made with alternative encapsulants, under mechanical wind load test conditions (2.4 kPa uniform pressure for 1 hour). FEM modeling using a theoretical module will be discussed, where the variables are:
- type of encapsulant (we will discuss all encapsulants mentioned);
- support system (2-sided versus 4-sided);
- glass thickness; and
- encapsulant thickness.
We will compare some of these calculations with real mechanical load tests.