No matter how the battery is iterated, for double-glass components, single-glass components, or flexible components, whether to choose POE (polyolefin elastomer), EVA (ethylene vinyl acetate copolymer), or EPE Encapsulation is always an unavoidable and hotly debated topic.
Heat, oxygen, water, ultraviolet rays and biological activity in the environment are the most important factors causing material failure. In the outdoor application of photovoltaic modules, in addition to excluding biological activity, the other four environmental factors cannot be ignored. Therefore, when selecting materials, we must first consider the impact of these four factors on materials.
This article compares the impact of EVA and POE under these four major environmental factors, and provides you with a new idea and method for selecting materials.
1. Heat
Both EVA and POE materials can withstand short-term high temperature exposure of about 150°C after cross-linking. However, if the temperature continues to increase, above 200°C, EVA will decompose and release a large amount of acetic acid. The thermal decomposition temperature of POE needs to be at least 300°C.
2.Oxygen
Both EVA and POE are not easily oxidized at room temperature, but because there is always a small amount of free acetic acid monomer in EVA, it will be oxidized at high temperatures, but POE is all carbon-hydrogen bonds with stable chemical properties, and the temperature of chemical reaction with oxygen Much higher than EVA.
3.Water
From a molecular structure perspective, EVA contains ester groups, which are prone to hydrolysis. The terminal carboxyl groups produced by hydrolysis will further promote the hydrolysis reaction, causing the material to age rapidly. The full hydrocarbon chain of POE has high chemical stability and is not affected by hydrolysis. On the other hand, the water vapor transmission rate of EVA film at 38℃ and 90%RH is about 25g/m^2·24h, and the water vapor transmission rate of POE film is 3g/m^2·24h. In other words, the water vapor transmission rate of POE is much lower than that of EVA film, which makes POE not only difficult to hydrolyze itself, but also has a water-blocking ability much higher than that of EVA, thus providing strong protection to other components inside the module.
4.Ultraviolet rays
Similarly, POE is a full hydrocarbon chain structure. The chemical bond energy of this molecule is very high. The C-H bond energy is 414kJ/mol and the C-C bond energy is 332kJ/mol. It is not easy to break in the ultraviolet rays irradiated to the ground, while the ester group in EVA is The C-O bond energy is less than 330kJ/mol, which makes it more susceptible to breakage by ultraviolet radiation.
To sum up, in the use of packaging materials, POE is better than EVA in the four major factors of outdoor application reliability: heat, oxygen, water, and ultraviolet performance. As batteries become more and more "high-efficiency", " Today, with strict requirements, POE is still the best choice to ensure long-term stable and continuous "output" of the battery.
