Testing method for moisture permeability of EVA film for solar photovoltaic backsheet

EVA film is a thermosetting transparent film used in the encapsulation process of solar panels. Its main function is to form a tight bonding layer between the cell and the upper and lower layers of glass or backplane, and it can also serve as an optical medium to increase light transmittance, thereby increasing the power generation efficiency of solar panels. EVA film has good weather resistance, electrical insulation performance and anti-ultraviolet aging ability.

During the manufacturing process of solar panels, EVA film is placed between the cell and the front cover glass (or transparent plastic plate), and between the cell and the backplane. The EVA film is melted and solidified by heating and pressurizing to form a solid sealing structure. This process not only fixes the cell firmly in place, but also effectively isolates the influence of external environmental factors on the cell, ensuring the long-term stable operation of the solar panel.

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Why test the moisture permeability of EVA film

It is very important to test the moisture permeability of the EVA film of the solar photovoltaic backplane, because the moisture permeability directly affects the reliability and service life of the solar panel.

Prevent water vapor penetration:

Water vapor penetration will reduce the performance of the panel. Water vapor can enter the interior of the panel, causing problems such as corrosion, oxidation or short circuit of the cell, thus affecting the electrical performance and stability of the panel. In a high humidity environment, moisture may also accelerate the aging process of the internal materials of the panel and shorten its service life.

Keep the interior dry:

Low moisture permeability means that less moisture can penetrate the backsheet or EVA film into the panel. This helps keep the internal components dry, which is essential for maintaining the long-term performance of the panel.

Improve reliability:

Through rigorous moisture permeability testing, it can be ensured that the backsheet and EVA film used can maintain a good sealing effect for a long time under various climate conditions, thereby improving the reliability of the entire solar panel system.

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Testing method

Gravimetric method

This is one of the most traditional moisture permeability test methods. It determines the moisture permeability by measuring the mass change caused by the humidity difference on both sides of the sample. The specific steps are as follows:

Fix the EVA film sample on the WTR-06 gravimetric water vapor transmission rate tester container, which is divided into two parts, one for high humidity environment and the other for low humidity environment.

Under constant temperature and humidity conditions, water vapor is allowed to diffuse through the EVA film from the high humidity side to the low humidity side.

The mass change of the container is weighed regularly, and the amount of water vapor that passes through a unit area per unit time, i.e., the moisture permeability, is calculated based on the mass change.

Humidity Sensor Method

This method uses a humidity sensor to directly measure the change in water vapor concentration that passes through the EVA film. The specific steps are as follows:

Use the WTR-G3 electrolytic water vapor transmission rate tester to set up high and low humidity environments.

Use a humidity sensor to monitor the change in water vapor concentration on the low humidity side.

The moisture permeability is determined by calculating the change in water vapor concentration per unit time.

Infrared Detection Method

The process of water vapor passing through the EVA film is monitored by infrared technology. The specific steps are as follows:

Use the WTR-T3 infrared water vapor transmission rate tester to monitor the amount of water vapor that passes through the EVA film.

Since water vapor absorbs certain wavelengths of infrared light, the moisture permeability is indirectly inferred by measuring the change in infrared intensity.