Performance Improvements in PV Modules Using Ionomer Encapsulants

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1 Performance Improvements in PV Modules Using Ionomer Encapsulants Mark Jacobson Sr. Accounts Manager, DuPont Encapsulants Cleveland, OH April 9, 2011

2 2 Agenda Encapsulant requirements Failure modes Moisture Ingress and WLC NREL results Strength enhancement Other benefits DuPont encapsulant offerings

3 3 Examples of Required Encapsulant Attributes Encapsulant Requirements for Thin Film Glass/ Glass Modules Low System Cost Durability 25 years no delamination Cell efficiency over life of module Meets operating temperature requirements Compatibility with Top Coat Material Low Moisture Permeability Protect the Cell from Corrosion High Resistivity = Low Current Leakage Safety requirement Important in maintaining cell efficiency over lifetime Ease of Processing with High Thru-put Autoclave Vacuum laminator No Lamination Defects No bubbles Ease of Handling

4 The Importance of Encapsulants in Module Design Common Causes of failure in Thin Film Modules 4 Failure occurs predominantly in the damp heat test (85C/85%RH, 1000hrs) The cause of failure is typically due to excessive wet current leakage after aging (wet resistance) Current leakage is most often dependent on module package integrity (encapsulant, J-box, front/back cover) Tamizhmani, G., et.al. Failure Analysis of Module Design Qualification Testing III 35 th IEEE PVSC Proceedings, 2010, Honolulu, Hawaii

5 5 Minimal Wet Current Leakage After Extended Aging Wet Current Leakage after Damp Heat Testing Electrical Resistance (M Ohms) Thin Film Glass-Glass module* with DuPont PV5400 Minimum resistance required to pass IEC standard after 1000hrs damp heat Excellent initial resistance Low resistance decline after aging Easy pass in IEC damp heat test No edge sealing or frame required Hours Damp Heat (85 o C / 85% RH) * No edge sealing (tape or caulk) used, frameless

6 6 % Moisture The Benefits of DuPont PV5400 Ionomer Low Moisture Ingress Glass laminate moisture ingress after 2000hr DH Diffusion coefficient is 4-6x less than EVA encapsulant Equilibrium Moisture level is half of EVA encapsulants EVA DuPont PV 5400 Ionomer Distance from Edge (cm) Provides excellent protection and insulation for electronic components over the module lifetime Introduces the possibility of a stable module without edge seal compounds High Resistivity Polymer Encapsulant Material Surface Resistivity ASTM D257 23C, 50%RH Enables low cost frameless module design DuPont PV5400 Ionomer Cross-linked EVA

7 Why Ionomer? Performance in Independent Studies 7 Samples with a quartz face or soda-lime glass in combination with an ionomer encapsulant did not degrade. (unlike glass/sio 2 barrier or EVA) For the hydrocarbon based materials, only the ionomer is demonstrating UV stability for 10X CPV applications Fig. 10. Loss of pseudo fill factor (FF) and open-circuit voltage (Voc) after 140 h at 45 C/30% RH with 1000 V bias applied to the active layer for five mini module constructions (plus controls). P.Hacke et. al., NREL (US), ECN (NL), Characterization of Multi-Crystalline Silicon modules with System Bias Voltage Applied in Damp Heat, 25 th EU PVSEC, DuPont 2010, Photovoltaic Valencia, Solutions Figure 8. QE- and solar-weighted transmission for a thermoplastic polyurethane (TPU), an ionomer, and polyvinyl butyral (PVB) as a function of exposure to 42 UV suns. The changes in YI for the ionomer, PVB and TPU correlate well with changes in optical transmission. M.D. Kempe et. al., NREL (US), Accelerated StressTesting of Hydrocarbon-based Encapsulants for Medium Concentration CPV Applications, 34 th IEEE PVSC, 2009, Philadelphia

8 8 High Modulus Enables Low Cost Mounting Finite Element Analysis of Module Mechanical Properties 3 Layers for Panel Glass-Encapsulant-Glass Four clamp support system Aluminum clamps with EPDM gaskets Clamps fixed at center points 4 Clamp Module: +2.4 kpa 1 hr 22 C 3.2 mm Glass / t mm Encapsulant / 3.2 mm Glass Maximum Principal Glass Stress (MPa) Encapsulant Thickness, t (mm) 65% Breakage Probability PV 5400: 150 mm Clamp PV 5400: 70 mm Clamp PVB: 150 mm Clamp PVB: 70 mm Clamp 3% Breakage Probability Glass stress minimally impacted by encapsulant thickness Glass stress is sensitive to clamp size Ionomer laminate with 150 mm clamp strong enough when used with all annealed glass

9 9 Other Benefits of Unique Ionomer Chemistry Ionomer Chemical Structure COO H COOH COO H Ion (X) exchanged with Na, Zn, Mg COOH COOH Acid-functionalized hydrocarbon copolymer COOX COO- COOH X++ -OOC COOH COO- ++X OOC Ionomer clusters form pseudocross-links No potential for acetic acid formation minimizes possibility of corrosion Inherent adhesion to glass (no adhesion promoters needed) Excellent adhesion to a variety of metals (such as Al, chrome and Zn) Excellent adhesion retention due to low moisture ingress Melt temperature and flow enable fast lamination on existing vacuum laminators Easy handling, no need to refrigerate or interleaf sheeting

10 10 DuPont now Offers Five Encapsulant solutions DuPont TM PV5200 series (PVB sheet) DuPont TM PV5300 series (High Clarity Ionomer sheet) DuPont TM PV5400 series (Low Moisture Ionomer sheet) DuPont PV8600 series (Modified Ionomer sheet) Developed by DuPont-Mitsui Developed by the leader in the glass industry with over 60 years of innovation DuPont TM Elvax PV1000 series (EVA Resin) - sold into PV market for 30 years Continuous pipeline of innovative encapsulants

11 11 Copyright 2012 DuPont or its affiliates. All rights reserved. The DuPont Oval Logo, DuPont, The miracles of science and all products denoted with or are registered trademarks or trademarks of E. I. du Pont de Nemours and Company or its affiliates.

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