Solar Module EVA Film Introduction 1
In order to improve the power generation efficiency of solar cell modules, provide protection against the loss caused by environmental climate change, and ensure the service life of solar modules, EVA plays a very important role. EVA is non-adhesive and anti-adhesive at room temperature. After hot pressing under certain conditions during the solar cell packaging process, EVA will produce melt bonding and adhesive curing. The cured EVA film becomes completely transparent and has quite high light transmittance. The cured EVA can withstand atmospheric changes and has elasticity. The solar cell wafer is wrapped and bonded with the upper glass and lower TPT by vacuum lamination technology.
Basic functions of EVA film:
1. Secure the solar Cell and connecting circuit wires to provide cell insulation protection
2. Perform optical coupling
3. Provide moderate mechanical strength
4. Provide a heat transfer pathway
EVA Main features:
1. Heat resistance, low temperature resistance, moisture resistance and weather resistance
2. Good followability to metal glass and plastic
3. Flexibility & Elasticity
4. High light transmission
5. Impact resistance
6. Low temperature winding
Thermal conductivity of solar cell related materials: (K value of thermal conductivity at 27 ° C (300'K))
Description: EVA is used for the combination of solar cells as a follow-up agent, because of its strong follow-up ability, softness and elongation, it is suitable for joining two different expansion coefficient materials.
Aluminum: 229 ~ 237 W/(m·K)
Coated aluminum alloy: 144 W/(m·K)
Silicon wafer: 80 ~ 148 W/(m·K)
Glass: 0.76 ~ 1.38 W/(m·K)
EVA: 0.35W /(m·K)
TPT: 0.614 W/(m·K)
EVA appearance inspection: no crease, no stain, smooth, translucent, no stain edge, clear embossing
EVA material performance parameters:
Melting index: affects the enrichment rate of EVA
Softening point: The temperature point at which EVA begins to soften
Transmittance: There are different transmittance for different spectral distributions, which mainly refers to the transmittance under the spectral distribution of AM1.5
Density: density after bonding
Specific heat: the specific heat after bonding, reflecting the size of the temperature increase value when the EVA after bonding absorbs the same heat
Thermal conductivity: thermal conductivity after bonding, reflecting the thermal conductivity of EVA after bonding
Glass transition temperature: reflects the low temperature resistance of EVA
Breaking tension strength: The breaking tension strength of EVA after bonding reflects the mechanical strength of EVA after bonding
Elongation at break: the elongation at break at EVA after bonding reflects the tension of EVA after bonding
Water absorption: It directly affects the sealing performance of battery cells
Binding rate: The binding rate of EVA directly affects his impermeability
Peel strength: reflects the bond strength between EVA and peel
EVA reliability test purpose: to confirm the weather resistance, light transmission, bonding force, ability to absorb deformation, ability to absorb physical impact, damage rate of pressing process of EVA... Let's wait.
EVA aging test equipment and projects: constant temperature and humidity test chamber (high temperature, low temperature, high temperature and high humidity), high and low temperature chamber (temperature cycle), ultraviolet testing machine (UV)
VA Model 2: Glass /EVA/ conductive copper sheet /EVA/ glass composite
Description: Through the on-resistance electrical measurement system, the low resistance in EVA is measured. Through the change of the on-resistance value during the test, the water and gas penetration of EVA is determined, and the oxidation corrosion of copper sheet is observed.
After three tests of temperature cycle, wet freezing and wet heat, the characteristics of EVA and Backsheet change:
(↑ : up, ↓ : down)
After three tests of temperature cycle, wet freezing and wet heat, the characteristics of EVA and Backsheet change:
(↑ : up, ↓ : down)
EVA：
Backsheet：
Yellow↑
Inner layer yellow ↑
Cracking ↑
Cracks in the inner layer and PET layer ↑
Atomization ↑
Reflectivity ↓
Transparency ↓
Solar Module EVA Film Introduction 2
EVA-UV test:
Description: Test the attenuation ability of EVA to withstand ultraviolet (UV) irradiation, after a long time of UV irradiation, EVA film will appear brown, penetration rate decreased... And so on.
EVA environmental test project and test conditions:
Humid heat: 85℃ / RH 85%; 1,000 hrs
Thermal cycle: -40℃ ~ 85℃; 50 cycles
Wet freezing test: -40℃ ~ 85℃ / RH 85%; 10 times UV: 280~385nm/ 1000w/200hrs (no cracking and no discoloration)
EVA Test Conditions (NREL) :
High temperature test: 95℃ ~ 105℃/1000h
Humidity and heat: 85℃/85%R.H./>1000h[1500h]
Temperature cycle: -40℃←→85℃/>200Cycles
(No bubbles, no cracking, no desticking, no discoloration, no thermal expansion and contraction)
UV aging: 0.72W/m2, 1000 hrs, 60℃(no cracking, no discoloration) Outdoor: > California sunshine for 6 months
Example of EVA characteristics change under Damp heat test:
Discoloration, atomization, Browning, delamination
Comparison of EVA bond strength at high temperature and humidity:
Description: EVA film at 65℃/85%R.H and 85℃/85%R.H. The degradation of the bond strength was compared at 65℃/85%R.H under two different wet and hot conditions. After 5000 hours of testing, the degradation benefit is not high, but EVA at 85℃/85%R.H. In the test environment, the adhesion is quickly lost, and there is a significant reduction in bond strength in 250 hours.
EVA-HAST unsaturated pressurized vapor test:
Objective: Since EVA film needs to be tested for more than 1000 hours at 85℃/85%R.H., which is equal to at least 42 days, in order to shorten the test time and accelerate the test speed, it is necessary to increase the environmental stress (temperature & humidity & pressure) and speed up the test process in the environment of unsaturated humidity (85%R.H.).
Test conditions: 110℃/85%R.H./264h
EVA-PCT pressure digester test:
Objective: The PCT test of EVA is to increase the environmental stress (temperature & humidity) and expose EVA to wetting vapor pressure exceeding one atmosphere, which is used to evaluate the sealing effect of EVA and the moisture absorption status of EVA.
Test condition: 121℃/100%R.H.
Test time: 80h(COVEME) / 200h(toyal Solar)
EVA and CELL bond tensile force test:
EVA: 3 ~ 6Mpa Non-EVA material: 15Mpa
Additional information from EVA:
1. The water absorption of EVA will directly affect its sealing performance of the battery
2.WVTR < 1×10-6g/m2/day(NREL recommended PV WVTR)
3. The adhesive degree of EVA directly affects its impermeability. It is recommended that the adhesive degree of EVA and cell should be greater than 60%
4. When the bonding degree reaches more than 60%, thermal expansion and contraction will no longer occur
5. The bonding degree of EVA directly affects the performance and service life of the component
6. Unmodified EVA has low cohesion strength and is prone to thermal expansion and contraction leading to chip fragmentation
7.EVA peeling strength: longitudinal ≧20N/cm, horizontal ≧20N/cm
8. The initial light transmittance of the packaging film is not less than 90%, and the internal decline rate of 30 years is not less than 5%
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