Abstract: The water vapor transmission rate (WVTR) is a crucial performance parameter used to evaluate the moisture barrier properties of solar backsheet materials. It plays a vital role in monitoring the protection of internal components within solar panels, such as photovoltaic cells, and helps prevent oxidation caused by external moisture. This paper presents a study conducted using the W3/330 water vapor transmission rate test system, independently developed by Jinan Languang Electromechanical Technology Co., Ltd. The system was employed to assess the WVTR of a solar backsheet film, with a detailed description of its parameters, application scope, and testing procedures. The findings provide valuable insights for the solar equipment manufacturing industry in verifying the moisture barrier capabilities of backsheet materials.
Keywords: water vapor transmission rate, moisture barrier, solar backsheet, solar cell, water vapor barrier, WVTR test system, photovoltaic module
1. Introduction
Solar panels are the core components of solar energy systems, responsible for converting sunlight into electricity. As these systems are designed to operate for over 25 years, it is essential that the solar backsheet (also known as the backplane) provides strong protection to the internal photovoltaic cells. A typical solar module consists of a "photovoltaic glass-EVA film-solar panel-EVA film-backboard" structure, enclosed within an aluminum frame. Common backsheet materials include TPT, BBF, TPE, and EVA films, with TPT being widely used due to its excellent moisture barrier properties, composed of a three-layer PVF/PET/PVF structure.
Since solar modules are often installed outdoors, the backsheet must exhibit high insulation, water resistance, and aging resistance. It should also have good peel strength, tensile strength, and low heat shrinkage. Among all these properties, the water vapor transmission rate is the most critical, as it determines how well the backsheet can block moisture from entering the module. If the WVTR is too high, moisture can penetrate the backsheet, degrading the EVA adhesive and causing delamination. This can lead to increased exposure of the solar cells to moisture, potentially causing oxidation and reducing the efficiency and lifespan of the module.
In this study, the W3/330 water vapor transmission rate test system was used to evaluate the moisture barrier performance of a commercial solar backsheet film, ensuring its reliability and durability under real-world conditions.
Figure 2: Solar backing material
2. Current Status
Currently, several methods exist for measuring the water vapor transmission rate of flexible plastic materials, including the gravimetric (cup) method, electrolytic method, humidity method, and infrared method. Standards such as GB 1037-1988, GB/T 16928-1997, GB/T 21529-2008, and GB/T 30412-2013 provide guidelines for these tests. In this study, the electrolytic sensor method (GB/T 21529-2008) was employed to measure the WVTR of the solar backsheet sample.
3. Test Samples
A commercially available solar backsheet (film) was selected for the experiment.
4. Test Equipment
The W3/330 water vapor transmission rate test system, developed by Jinan Languang Electromechanical Technology Co., Ltd., was used for the test. This system is specifically designed for accurate measurement of WVTR in various materials, including films, sheets, and containers.
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