By Rufeng Dou
With the application of crystalline silicon PV modules spreading, conventional structure of modules, such as photovoltaic glass + EVA + crystalline silicon cell + EVA + TPT + aluminum frame + junction box, cannot satisfy the requirement of special occasions. Among them, the EVA as packaging film is copolymer of ethylene and the vinyl acetate, and the TPT for backsheet material, is composite membrane of fluorine ethylene.
For example, the reflected light from the modules surface will produce glare which could make traffic risks where the modules installed in the airport, near road, etc. In the area with serious dust or other contaminants, PV modules need periodic cleaning to avoid power output attenuation because of the pollutants covered in the module surface. Those buildings which have limited carrying capacity need pass the structure design of the roof or expensive structure transformation to have the ability to carry PV modules. These series of demands led to design of new materials of the crystalline silicon PV module. The application of ETFE in crystalline silicon PV modules can meet the above requirements.
The Characteristics and Application of ETFE
ETFE is used in the transparent curtain wall and roof as superior quality materials. The Chinese National Aquatics Center (known as Water Cube) adopts ETFE film which is the most complicated membrane system in the world. This film is made by artificial high-strength fluorine polymer, which has high light transmittance, light, corrosion resistance, high stain resistant, easy-to-clean, B1 level of fire prevention, long service life (25 to 30 years) and other characteristics. The performance parameter is shown as Table 11).
Based on the characteristics of ETFE materials, it can be used as the ideal materials to replace the photovoltaic glass, which could be combined with other packaging materials to make PV modules. Uni-Solar (an American company) has used ETFE materials as the outermost layers of packaging materials to make flexible module successfully. In this article, the application of ETFE materials in the crystalline silicon PV modules will be introduced.
Crystalline Silicon PV Modules Encapsulated by ETFE
The crystalline silicon PV modules encapsulated by ETFE materials whose structure is ETFE + EVA + crystalline silicon cell + EVA + backsheet materials. Because ETFE materials do not have the structural performance, the module need the a back sheet which has a good structural performance to make up, such as thin of tempered glass or light FRP materials, etc.
The module production process is similar as the conventional crystalline silicon PV modules, which flow is welding, lamination, junction box and frames fixing, power output testing, and packaging. There are several differences, for example, 1) the material is put as this order before laminated shown in Figure 1. 2) We can choose certain mould with decorative pattern to cover the ETFE materials on the lamination process, and the embossed lines will be formed in the surface of laminates. 3) The pressure parameters can reference to the EVA laminated parameters with appropriate adjustment.
ETFE materials in construction applications have been proved their superior long-term aging performance. With reference to the standards IEC61215 test, the crystalline silicon PV modules encapsulated by ETFE materials can through the hot and damp experiment 1000 hours, temperature circulation experiment and wet frozen experiment.
The Advantages of ETFE Used in Crystalline Silicon PV Modules
ETFE material has the characteristics of high transmission performance, lightness, and easy process molding, which give the crystalline silicon PV modules powerful function.
High Transmission Performance
The transmission of ETFE material is above 95%. Photovoltaic cells can accept more light, and produce higher power output. Contrast temped glass for the front plate materials of crystalline silicon PV modules, can increase the power output by 2.5%-3%.
High Stain Resistant, Easy to Clean
The surface of conventional PV modules can be covered with leaves, dirt, etc., which will make quite significant influence of power output, and even produce hot spot2). It is necessary to make regular cleaning for conventional PV modules. However, cleaning will not only take energy and financial resources, but improper cleaning method may be damage the components or cause accidents. ETFE film with low surface energy and extreme scanty water characteristic has the high stain resistant and easy cleaning features. The rain down on the surface cannot stay, and soon fall down. At the same time, dirt can easily washed away with rain, the module surface will not leave pollutants.
The carrying capacity of a building should be considered when the PV modules are installed on the building. And the dead weight of the photovoltaic module itself is main building load factors. Thickness of ETFE materials is only about 0.5 millimeter. The weight of the PV modules encapsulated by ETFE can be reduced by 50%.
The application of ETFE materials in crystalline silicon PV modules can bring a variety of performance improvements of PV modules. It not only can improve the output power of crystalline silicon photovoltaic modules, and aslo can expand the application field of crystalline silicon PV modules.
Rufeng Dou has served as ET Solar (www.etsolar.com)’s Project Manager of R&D Department since July 2009, She received her master’s degree in Measuring, Testing Technologies and Instruments.
1) ETFE product performance. http://www.dhhb.com.cn/ETFExneng.htm
2) Chen Jufang. The influence of photovoltaic power station with air cleanliness of Guangzhou area. Solar journal.2011
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