Table Of Content

K12310_cover 4/18/11 8:47 AM Page 1 C M Y CM MY CY CMY K MATERIALS SCIENCE P SSoollaarr MMoodduullee o l i s k i e SSoollaarr MMoodduullee PPaacckkaaggiinngg PPaacckkaaggiinngg Polymeric Requirements and Selection SS “Excellent, targeted material encompassing packaging in the PV industry, manufacturing oo and state of industry, economic trends, and a global framework for state of the science ll aa and state of the industry niche for solar cells and products.” rr —Karen Rayment, MSEE, P.E., Licensed Professional Engineer, State of California, USA MM “There is continual pressure on the solar industry to reduce cost and, like the electronics oo industry before it, solar companies will continue to integrate low-cost polymers to dd reduce their costs. This expected focus for product integration makes this a timely uu ll publication in the industry. … I thank Dr. Poliskie for putting this information together ee for the solar community; there is a strong need for this desk reference.” PP —Todd J. Menna, Ph.D., Packer Engineering, Inc., Naperville, Illinois, USA aa cc Solar Module Packaging: Polymeric Requirements and Selection explores current and kk future opportunities in photovoltaic (PV) polymeric packaging, emphasizing how it can aa simultaneously reduce cost, increase weatherability, and improve the power of a PV gg ii module. The text offers an insider’s perspective on the manufacturing processes and nn needs of the solar industry and reveals opportunities for future material development gg and processing. Suitable for nonspecialists in polymer science, this book provides a basic understanding of polymeric concepts, fundamental properties, and processing techniques commonly Polymeric Requirements used in solar module packaging. It presents guidelines for using polymers in commercial PV modules as well as the tests required to establish confidence in the selection process. and Selection K12310 MMiicchheellllee PPoolliisskkiiee 6000 Broken Sound Parkway, NW Suite 300, Boca Raton, FL 33487 711 Third Avenue an informa business New York, NY 10017 www.crcpress.com 2 Park Square, Milton Park www.crcpress.com Abingdon, Oxon OX14 4RN, UK Composite Solar Module Packaging Polymeric Requirements and Selection Solar Module Packaging Polymeric Requirements and Selection Michelle Poliskie Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2011 by Michelle Poliskie CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works International Standard Book Number-13: 978-1-4398-5074-9 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information stor- age or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Contents Preface ......................................................................................................................ix Acknowledgments .................................................................................................xi 1. Introduction to Polymers ..............................................................................1 1.1 A Brief Historical Perspective .............................................................1 1.2 Chemical Structure, Nomenclature, and Morphology ....................2 1.3 Polymeric Classification Based on Thermal and Mechanical Properties ................................................................11 1.3.1 Thermoplastics .......................................................................15 1.3.2 Thermosets..............................................................................16 1.3.3 Ionomers ..................................................................................18 1.3.4 Elastomers ...............................................................................18 References .......................................................................................................19 2. Certification and Characterization of Photovoltaic Packaging ...........21 2.1 Overview of Photovoltaic Installations............................................21 2.2 Selection Requirements for Photovoltaic Packaging .....................22 2.2.1 Certification and Compliance Criteria ................................25 2.2.1.1 Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE) Directives .............................26 2.2.1.2 Underwriters Laboratories ....................................27 2.2.1.3 International Electrotechnical Commission ............................................................28 2.2.1.4 American Standard for Testing Materials ..........28 2.3 Optical Properties ...............................................................................29 2.3.1 Material Properties ................................................................30 2.3.1.1 Refractive Index Measurements ...........................31 2.3.1.2 Yellowness Index ....................................................34 2.3.2 Photovoltaic Module Performance ......................................37 2.3.2.1 Quantum Efficiency Measurements ....................38 2.3.2.2 Current-Voltage (IV) Measurements ....................40 2.4 Thermal Properties .............................................................................44 2.4.1 Material Properties ................................................................44 2.4.1.1 Morphology .............................................................44 2.4.1.2 Coefficient of Thermal Expansion .......................46 2.4.1.3 Thermal Conductivity ...........................................48 2.4.2 Photovoltaic Module Performance ......................................51 2.4.2.1 Frame Warp .............................................................51 2.4.2.2 In-Service Temperature Measurements ..............52 © 2011 by Taylor & Francis Group, LLC v vi Contents 2.5 Mechanical Properties ........................................................................52 2.5.1 Material Properties ................................................................53 2.5.1.1 Durometer ...............................................................54 2.5.1.2 Peel Strength ...........................................................55 2.5.1.3 Tensile and Compression ......................................56 2.5.1.4 Impact Resistance ...................................................60 2.5.1.5 Flexural Testing ......................................................61 2.5.2 Photovoltaic Module Performance ......................................62 2.5.2.1 Thermal Cycling and Humidity Testing ............63 2.5.2.2 Salt Fog .....................................................................65 2.5.2.3 Snow Loading .........................................................65 2.6 Electrical Properties ............................................................................66 2.6.1 Material Properties: Dielectric Properties ..........................67 2.6.2 Photovoltaic Module Performance ......................................69 2.6.2.1 Wet-Leak Testing ....................................................69 2.6.2.2 High-Potential Testing ...........................................70 2.7 Flammability .......................................................................................70 2.7.1 Material Properties ................................................................71 2.7.2 Photovoltaic Module Performance ......................................75 2.8 Weathering Stability ...........................................................................77 2.8.1 Material Properties ................................................................78 2.8.1.1 Stabilizer Package...................................................78 2.8.1.2 Transmission Rates ................................................81 2.8.1.3 Hydrolytic Degradation ........................................86 2.8.1.4 Oxidative Degradation ..........................................87 2.8.2 Photovoltaic Module Performance ......................................88 2.8.2.1 Accelerated UV Aging Techniques ......................89 2.8.2.2 Developing an Accelerated Test ...........................91 2.8.2.3 Data Analysis ..........................................................96 References .......................................................................................................99 3. Polymer Specifications for Photovoltaic (PV) Packaging and Balance of System (BOS) Components...........................................107 3.1 Commercial Formulations ...............................................................107 3.1.1 Polymeric Stabilizers ...........................................................107 3.1.2 Polymeric Modifiers ............................................................109 3.1.3 Other Classifications ...........................................................111 3.2 The Effect of Additives on Polymeric Properties .........................111 3.3 Common Failure Mechanisms in Photovoltaic Packaging ...........................................................................................112 3.4 Encapsulants ......................................................................................113 3.4.1 Polysiloxane ..........................................................................115 3.4.2 Polyvinyl Acetate and Polyethylene ..................................118 3.4.3 Ethylene Vinyl Acetate Copolymer ...................................120 3.4.4 Polyvinyl Butyral .................................................................123 © 2011 by Taylor & Francis Group, LLC Contents vii 3.4.5 Ionomers ................................................................................124 3.4.5.1 Surlyn® ...................................................................125 3.5 Frames .................................................................................................126 3.6 Junction Boxes ...................................................................................127 3.7 Backsheets ..........................................................................................128 3.7.1 Fluorinated Polyolefins .......................................................129 3.7.2 Laminate Structures ............................................................130 References .....................................................................................................131 4. Polymer Processing Techniques Used in Photovoltaic Packaging and Balance of Systems (BOS) Component Fabrication .....................135 4.1 Common Polymer Processes for Photovoltaic Packaging and BOS Components ......................................................................135 4.2 Polymer Viscosity ..............................................................................135 4.2.1 Viscosity Measurement .......................................................137 4.3 Lamination .........................................................................................138 4.4 Injection Molding ..............................................................................141 4.5 Adhesive Dispense ...........................................................................145 References .....................................................................................................149 5. Economic Theory and Photovoltaic Packaging ....................................151 5.1 The First U.S. Energy Crisis .............................................................151 5.2 The Current Energy Crisis ...............................................................154 5.3 Technology Development Theory and Photovoltaic Energy ......155 5.4 Operational Optimization for Photovoltaic Companies .............162 5.5 Photovoltaic Markets Abroad ..........................................................168 5.5.1 China’s Solar Market ...........................................................172 5.5.2 Saudi Arabia’s Solar Market ...............................................174 5.6 The U.S. Polymer Market .................................................................175 References .....................................................................................................177 6. Other Polymeric Applications in Photovoltaic Modules ....................181 6.1 Emerging Polymeric Applications ..................................................181 6.1.1 Soiling Behavior of Photovoltaic Modules .......................181 6.1.1.1 Considerations for Developing a Soiling Protocol ..................................................................182 6.1.1.2 Experiments to Characterize Antisoiling Coatings .................................................................186 6.1.1.3 Antisoiling Coatings ............................................188 6.1.2 Antiscratch Coatings ...........................................................191 6.1.3 Antireflective Coatings .......................................................192 6.1.4 High Index of Refraction Polymers ...................................193 6.2 Concentrated and Organic Photovoltaics ......................................194 6.2.1 Lenses ....................................................................................195 6.2.2 Metallic Films .......................................................................196 © 2011 by Taylor & Francis Group, LLC viii Contents 6.2.3 Luminescent Solar Concentrators (LSCs) .........................198 6.2.4 Polymeric Photovoltaic Solar Cells ....................................202 References .....................................................................................................204 Appendix A: Conversion Factors and Common Units of Measurement ................................................................................................207 Appendix B: Glossary .......................................................................................209 © 2011 by Taylor & Francis Group, LLC Preface The core technology of a photovoltaic (PV) company is the PV cell, a semiconductor material responsible for turning light into electricity. Despite the importance of this technology, most PV companies currently do not manufacture their solar cells within the United States. In fact, PV modules, also known as panels, are the larger portion of U.S. PV exports. The module is composed of a series of electrically connected solar cells packaged in glass, polymers, and typically, a metallic frame. Currently, only two companies manufacture both the cell and module in the United States [1]. Due to this anemic manufacturing presence, the U.S. government has passed legislation to promote growth. Specifically, after the U.S. financial market tight- ened in 2007, the Obama administration and Congress passed the American Recovery and Reinvestment Act of 2009. As part of this legislation, the Department of Energy (DOE) was allowed to award loans, grants, and proj- ects to create economic growth in the renewable energy sector. Recognizing the importance of solar cell technology to PV manufacturing, the DOE revised the Buy American provisions to favor government investment in products from those companies with the largest amount of domestic manufacturing. Despite this new legislation, increasing cell manufacturing in the United States is a daunting task, because the U.S. PV industry has already lost its technological advantage. This technological deficit occurred decades ago when the U.S. semiconductor industry began offshoring its manufacturing capabilities. The semiconductors used to make solar cells are similar to those used to make integrated circuits. Integrated circuits, commonly referred to as chips, are the core technology for various electronics, such as cell phones, flash drives, and computers. While American manufacturing once dominated semiconductor production, today the highest volume of semiconductors comes from Malaysia, Taiwan, and China. The ero- sion of American manufacturing has been followed by the depletion of research and development (R&D) investments. Today, the majority of U.S. firms perform their R&D overseas in close proximity to their manufacturing lines [2]. With both the semiconductor innovation and production offshored, the United States is at a distinct disadvantage by designing future economic growth around improvements to PV cell technology. However, a potential competitive advantage does exist if there is innovation in other aspects of manufacturing that are currently overlooked by most government and industrial R&D efforts. Specifically, polymer packaging is an unrealized opportunity that has been underfunded in both the semiconductor and PV industries. © 2011 by Taylor & Francis Group, LLC ix