Photovoltaic Modules with No Back Sheet

The research and development of this project is related to photovoltaic (PV) modules with no back sheet. The typical PV module consists of a glass sheet, ethylene vinyl acetate (EVA) as encapsulant, crystalline silicon (c-Si) solar cells that are inter-connected in series and a back sheet. A team in Japan reported that minimizing the concentration of acetic acid which is generated by hydrolysis of EVA is the key issue for high reliability (28th EU PVSEC p.2828, M. Miyashita). To minimize the concentration of acetic acid, one approach is to use back sheets of extremely low water vapor transmission rate (WVTR), such as back sheets with Aluminum layer. However, those back sheets increase the cost of modules. Another approach can be to use back sheets of extremely high acetic acid transmission rate or to use no back sheet, so that low concentration of acetic acid in the modules can be maintained. As far as manufacturing cost is concerned, the approach of no back sheet is very attractive. Therefore, Plains Cupid, LLC has been focusing on and studying the concept of No Back Sheet modules. After the latest two years’ study, what we confirmed include the initial module output is the same as the conventional, better reliability from Dump Heat test, significant potential of cost reduction with less material consumption, about 10% lighter module weight. Our latest experimental results show that some types of NBS modules have good reliability. However, the other kinds of NBS modules have poor reliability (Figure1). The poor reliability seems to be because of corrosion of metals on the rear side of solar cells (Figure2). In this project, what to be done on No Back Sheet Modules include; optimize rear side structure, treatments and materials for cost reduction, confirm and optimize output and reliability (Thermal Cycle test and Dump Heat test), find the best process and machine for mass production. For the conventional module, the cost of a back sheet and EVA is about $10.4 in total per module (1.8m x 1.0m). With the new concept, we found that the cost of $10.4 will be reduced to $4.3/module, which means $6.1/module cost reduction. Besides the cost benefit, the modules are expected for higher manufacturing yield due to no mechanical stress from back sheets as well as better reliability as shown Figure1 NBS1. The light weight of the modules would be a good benefit for Roof Top usage.