Water Vapor Moisture Barrier Property Test of PV Backsheets

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Solar panel refers to a panel designed to absorb the sun’s rays as a source of energy for generating electricity or heating. As the main component of solar panel, the PV back sheets must protect the solar cells properly, because the solar panel is usually exposed to the external environment.

Commonly used materials for PV back sheets include TPT, BBF, TPE, EVA, among which TPT has the highest barrier property. TPT is one kind of composite film, which consists of 3-layer structure of PVF (or PVDF), PET and PVF (or PVDF).

The PV back sheet must have sufficient moisture barrier property, otherwise the water vapor may enter the external part of the solar panel and cause damage to the cells. Therefore, it is necessary to control the moisture barrier property of the back sheet through water vapor transmission rate tests.

This article provides a simplified testing method for water vapor transmission rate of PV back sheet for your reference. The testing instrument used in the tests is Labthink’s W3/330 Water Vapor Transmission Rate Test System.

Figure 1. Schematic Drawing of Solar Panel

Figure 2. Solar PV Back Sheets

There are mainly two categories of test methods for water vapor transmission rate i.e. gravimetric method (also known as cup method and divided into dry cup method and wet cup method) and sensor method (including electrolytic sensor method, infrared sensor method and humidity sensor method).

Labthink’s W3/330 Water Vapor Transmission Rate Test System employs electrolytic sensor in determination of water vapor transmission rate of flexible packaging materials. The gas transmission cell is designed in such way that, with the specimen inserted, it is divided into dry chamber and a controlled-humidity chamber. The dry side if swept by a flow of dry carrier gas, and water vapor permeating through the specimen from the controlled-humidity chamber is carried by the carrier gas into the electrolytic cell. Then the water vapor transmission rate can be determined by the electrolytic sensor.

The tests can be performed according to the following procedures.

1)      Cut 3 pieces, 108mm by 108mm specimens with special sample cutter.

2)      Mount the 3 pieces of specimens on the 3 test cells respectively.

3)      Set thickness, test temperature, test humidity and other test parameters.

4)      Adjust the pressure of carrier gas and make sure the humidity inside the test cell reaches the preset value. Adjust the flow rate of carrier gas to standard value.

5)      Click Start Test to start the test. The instrument will record the content changes of water vapor between the dry side and humidified side and calculate the test results automatically.

For more details about W3/330 Water Vapor Transmission Rate Test System, please visit www.labthink.com

About Labthink Instruments Co., Ltd:

Labthink Instruments Co., Ltd is one leading supplier of packaging testing instruments, which is headquartered in Jinan, China and operated in Boston, U.S.A.