Encapsulation Performance Comparison of PV Modules in Outdoor Arrays

Abstract

Encapsulation of photovoltaic (PV) modules using ethylene vinyl acetate (EVA) has been broadly utilized by the solar industry since the early 1980s. Prior to the use of EVA encapsulant, silicone materials were applied as an encapsulant for PV modules. A significant effort to utilize silicone was made by BP Solar, in Frederick, MD, USA. Several hundred modules were produced and installed at the old Solarex facility in Frederick. Several panels from this array were tested in 2008 and showed less than 5% degradation in Pmax from the original rating. Silicone encapsulation was eventually replaced by EVA due to cost and processing advantages. Recently new materials and processes for silicone encapsulation were developed by Dow Corning Corporation to improve the cost structure and manufacturing speed under the United States Department of Energy Photovoltaic Manufacturing Research and Development (PV MR&D) project. These new materials and processes were utilized to encapsulate modules under the BP Solar and the United States Department of Energy Technology Pathways Partnership program. The silicone-encapsulated modules were installed as half of two separate arrays. The first was a 10 kilowatt array using BP Solar 125 mm multi-crystalline cells (BP3170N product) at the Dow Corning Solar Solutions Application Center in Freeland, MI, USA in 2009. The second installation was a 6 kilowatt array using BP Solar 125 mm mono-crystalline cells (BP4175T product) at a Zero Energy Home Project in Bay City, MI, USA commissioned in 2010. The cell strings and finished assemblies from BP Solar at Frederick, MD, USA were encapsulated on a lamination pilot line at Dow Corning’s Solar Solutions Application Center in Freeland, MI, USA. At both array sites, the selection of the cells and the subsequent module build for the side by side comparison was a key design factor to minimize systematic errors that could lead to measurement inaccuracies. The balance of the arrays was constructed using EVA encapsulated modules supplied by BP Solar, using identical glass, cell and back sheet technology. Both types of modules were installed in an alternating pattern. i.e. silicone, EVA, silicone, EVA, and so on, to compare side by side efficiency and durability performance. Currently, the array in Freeland, and Bay City MI, USA shows the silicone modules performing at a 1.04% and 1.26% advantage in power output respectively. This paper will provide a detailed description of the arrays and their comparative performance in outdoor conditions.