2014 NREL Photovoltaic Reliability Workshops
The 2014 Photovoltaic Module Reliability Workshop featured more than 100 presentations and posters from workshop participants. The following topics were covered:
- Field Experience
- Potential Induced Degradation
- Physics of Failure
- Field Imaging
- Inverter Reliability
- Thin Film Technologies
- Packaging Materials and Accelerated Testing
- Quality Management
- Standards Work
- IEC Task Force Update
- Session Notes
The presentations listed are available as Adobe Acrobat PDFs. A compilation of the 2014 PVMRW proceedings is also available for download.
This annual workshop is sponsored by the U.S. Department of Energy Solar Energy Technologies Office.
Introduction and Plenary
- Welcome—Bill Tumas, National Renewable Energy Laboratory (NREL)
- Welcome—Shubhra Bansal, U.S. Department of Energy (DOE)
- Accessing Low Cost Financing Through Standardization, Best Practices, and Risk Scoring—Michael Mendelsohn, NREL
Session Chair: John Wohlgemuth, NREL
- Reliability Evaluation of PV Power Plants: Input Data for Warranty, Bankability, and Energy Estimation Models—Tamizhmani Govindasamy, ASU
- Recent Photovoltaic Performance Data in the United States—Dirk Jordan, NREL
- Analysis of Photovoltaic Installations: A Commercial Owner Perspective on PV Plant Operation and Optimization—Alexander Bradley, DuPont
- Lessons Learned: Field Observations of Module Failure and Damage—Ralph Romero, B&V Energy
- The PV Reliability O&M Database: Current Efforts by Sandia and EPRI to Improve PV System Reliability—Geoff Klise, Sandia National Laboratories
- Results of I-V Curves and Visual Inspection of PV Modules Deployed at TEP Solar Test Yard—Peter McNutt, NREL
- Data Science Approach to Time Series Analysis of Real-World PV—Yang Hu, Case Western Reserve University
- PV Performance and Energy Harvest Over Time—Joseph McCabe, Energy Ideas
- Regional Influence on Module Design Quality: Qualification Testing Failure Rate Results from Six Regional Labs of TUV Rheinland Around the World—GovindaSamy TamizhMani, TUV Rheinland
- Initiation of Reliability Studies at Green-IPUC/PUCMINAS, Brazil—Antonia Sonia Cardoso Diniz, PUCMINAS
- 20-Year Field Exposed Polycrystalline Silicon PV Modules, Detailed Visual Inspection and Analysis—Tony Sample, European Commission
- Risk of PV Fire Caused by Solder Bond Failure—Uichi Itoh, AIST
- Outdoor Exposure Testing for Glass-to-Glass PV Module for Building—Hanbit Kang, Korea Conformity Laboratories
- Case Study of Using a Modified "DC/POA" Method in Determining PV System's Degradation Rate and the Impact of Data Filters—Wilson Zexu Zhang, REC Solar Pte. Ltd.
- Effect of Soiling on Quantum Efficiency, Spectral Reflectance and Incident Angle on PV Modules—Jim Joseph John, Indian Institute of Technology Bombay
- Highly Redundant Inverter Architecture—Timothy Johnson, Tenksolar
- Soiling Losses of Utility-Scale PV Systems in Hot-Dry Desert Climates: Results from Four 4–16 Year Old Power Plants—Jaya Krishna Mallineni, ASU
- Uncertainty Analysis for Photovoltaic Degradation Rates—Dirk Jordan, NREL
Potential Induced Degradation
Session Chair: Max Koentopp, Hanwha Q CELLS GmbH
- Determining PID-resistance Based on Accelerated Tests Extrapolated to Field Stress Levels—Kent Whitfield, SunEdison
- Testing Modules for Potential-Induced Degradation–A Status Update of IEC 62804—Peter Hacke, NREL
- PID-Shunting and Electrical Characterization of Module-Like (Si Cell, Polymer Foil, Glass) Layer Stacks—Volker Naumann, Fraunhofer CSP
- Toward a Predictive Model for Potential-Induced Degradation (PID) Based on Climate Data—Simon Koch, Photovoltaik Insitut Berlin
Physics of Failure
Session Chair: David Miller, NREL
- Guidelines for Comparing Indoor Accelerated Stress Tests to Outdoor Use—Michael Kempe, NREL
- Experimental Evaluation of the Acceleration Factors and Activation Energies for Humidity-Based Degradation Phenomena in C-Si Modules—Michael Koehl, Fraunhofer ISE
- Development of Reliable Interconnect Systems for Photovoltaic Modules—Abhijit Namjoshi, Dow
- Adhesion and Debonding Kinetics in PV Devices and Structure—Reinhold H. Dauskardt, Stanford University
- Accelerated UV Photothermal Degradation of Polymer Encapsulants used in Low Concentration Photovoltaics (LCPV)—Itai Suez, Cogenra
Session Chair: Peter Hacke, NREL
- DaySy: Daylight Luminescence for PV Systems: How to Check 400kWpeak Per Day With Electroluminescence—Michael Reuter, Solarzentrum Stuttgart
- Reviewing the Practicality and Utility of Electroluminescence and Thermography Images at Various Stages of the Value Chain—Marc Köntges, ISFH
Session Chair: Rob Sorensen, Sandia National Laboratories
- PV Inverter Performance and Component-Level Reliability—Jack Flicker, Sandia National Laboratories
- Application of "Surge and Ring" Test in Qualifying Solar PV Inverters—Dutch Uselton, Lennox IND
- System Reliability for Utility PV Inverters—Ron Vidano, Advanced Energy Industries
- Application of Accelerated Testing and Modeling to Reliability Analysis of Microinverters—Paul Parker, SolarBridge Technologies
Thin Film Technologies
Session Chair: Tim Silverman, NREL
- Thin Film PID Field Failures and Root Cause Determination—Anders Olsson, Pearl Laboratories
- Direct Analysis of the Current-Voltage Curves Applied to an Outdoor-Degrading CdTe Module—Carolin Ulbrich, Forschungszentrum Jülich
- Stability of CdTe Cells with Different Device Structures—Jim Sites, CSU
- Stabilizing Thin-Film Module Performance for Indoor Measurements—Michael Deceglie, NREL
Packaging Materials and Accelerated Testing
- Nanoscale Cross-Sectional Analysis of a Multilayer Polymeric Backsheet Used in Commercial Photovoltaic Modules—Peter Krommenhoek, National Institute of Standards and Technology
- Silicone Encapsulation of Solar Cells Enhances Durability, Efficiency, and Enables New PV Cell and Module Technologies—Jeff Thompson, Momentive Performance Materials
- Role of Encapsulants in Improved Reliability of PV Modules—Kumar Nanjundiah, The Dow Chemical Company
- UV Degradation Study of Encapsulate Backsheet System for PV Modules—Shuying Yang, SunEdison
- Exploring the Behavior of PV Edge Seals on Glass in a Boeing Wedge Test Configuration—Lori Postak, Quanex Building Products Corporation
- Prevention of Potential-Induced Degradation with Thin Ionomer Film—Jane Kapur, E.I. DuPont
- Weathering Performance of PV Backsheets—Amy Lefebvre, Arkema
- A Framework for Characterization and Prediction of Edge Seal Performance in PV Modules—Kedar Hardikar, Miasole
- Evaluation of Oxygen and Wavelength Effects on UV Degradation of EVA—Xiaohong Gu, National Institute of Standards and Technology
- The Impacts of PV Module Encapsulation Quality on the Module Reliability—Hengyu Li, École Polytechnique Fédérale de Lausanne (EPFL), IMT, PVLAB
- Voids Evolution in the Encapsulation Process of Photovoltaic Modules—Hengyu Li, École Polytechnique Fédérale de Lausanne (EPFL), IMT, PVLAB
- Encapsulant Dependence of Ag-ion Migration Phenomenon During Damp Heat Test with Voltage Bias—Hirofumi Zenkoh, Mitusi Chemicals Tohcello, Inc.
- Moisture Ingress Rate and Route Into C-Si PV Modules—Hideyuki Morita, Photovoltaic Power Generation Technology Research Association
- Stability of Encapsulants Using Cu Electrode—Naoto Imada, Panasonic Group
- Improvements on PID for C-Si Based Solar Cells—Yi Cin Chen, Gintech Energy Corporation
- Towards PV Module Lifetime Prediction—Jiang Zhu, Centre for Renewable Energy Systems Technology, Loughborough
- Model for Predicting Thermal Runaway In Bypass Diodes—Narendra Shiradkar, University of Central Florida
- Durability of Photovoltaic Modules to UV and Weathering in Accelerated and Outdoor Exposure—William Gambogi, DuPont
- Evaluation of Mechanical Stress Beyond IEC 61215—Ryan Desharnais, Yingli Green Energy Americas
- Photovoltaic BOS Connector Accelerated Test for Reliability Model Development and Arc-Fault Risk Assessment—Benjamin Yang, Sandia National Laboratories
- Stress Testing a Non-Glass Crystalline Silicon Module—Tom Hood, Giga Solar FPC, Inc.
- Temperature Coefficients Measured Before and After IEC 61215 Stress Testing—Nicholas Riedel, CFV Solar Test Laboratory
- Durability Against the Effects of Weathering: Lessons from the Development of ASTM D7869—Sean Fowler, Q-Lab Corporation
- Analysis of Commercial PV Modules After PID Test—Takuya Doi, National Institute of Advanced Industrial Science and Technology (AIST-Kyushu)
- Acceleration of Potential-Induced Degradation (PID) by Salt-Mist Preconditioning in Crystalline Silicon Photovoltaic Modules—Tadanori Tanahashi, ESPEC
- An Examination of the Acceleration Method of Thermal Cycling Test for Crystalline Silicon PV Modules—Soh Suzuki, PVTEC
- Extended Degradation Tests of NICE Modules to Investigate Long Term Reliability—Roland Einhaus, Apollon Solar
- Non-Intrusive Cell Quantum Efficiency Measurements of Accelerated Stress Tested Photovoltaic Modules—Halden Field, PV Measurements, Inc.
- Utilization of PV Module Microclimates to Establish Pathways to Accelerated Weathering Protocols—Kurt Scott Atlas, Materials Testing Technology
- Photovoltaic Module Failure Analysis by Static Mechanical Load Stress—Dohyun Baek, Samsung SDI
- Analysis of Degradation of Multi-Crystalline Silicon Solar Cells After Damp Heat Tests—Wonwook Oh, Korea University
- Adhesion and Debond Kinetics of PV Encapsulants and Backsheets—Reinhold H. Dauskardt, Stanford University
- Cell Defect Analysis Post Dynamic Mechanical Load and Thermal Cycling Testing—Vivek Gade, Jabil
- NREL's Ultrasensitive, High-Throughput Moisture-Permeation Test—Arrelaine Dameron, NREL
Session Chair: Sarah Kurtz, NREL
- Reliability and the SunShot Initiative—Rebecca Jones-Albertus, DOE
- Status of the IECRE—George Kelly, IEC
- Overview of the Proposed PV Quality Management System—Govind Ramu, SunPower
- Experience with Modules Made Under Poor QMS—Ralph Romero, Black and Veatch
Standards Work and Thin-Film Technologies
- Performance Analysis of CIGS Thin-Film Photovoltaic System After 10 Years in the Hot and Humid Climate of Florida—Eric Schneller, Florida Solar Energy Center
- Update on Edition 2 of IEC 61724: "Photovoltaic System Performance Monitoring and Analysis"—Michael Gostein, Atonometrics
- Current Status of QA Taskforce TG5 Region-Japan—Tsuyoshi Shioda, Mitsui Chemicals, Inc.
- Japanese TG4 Activities of QA Forum—Yasunori Uchida, JET
- Japanese TG8 Activities in International PV Module Quality Assurance—Keiichiro Sakurai, PVTEC
- Standards Contributing to Reliability of Photovoltaic Modules and Systems—Tanya Dhir, Natural Resources Canada
- Activities of TG8 on Thin Film PV Module Reliability—Ramesh Dhere, Episolar
- Tightening Nameplate Rating Tolerance Below 5%: Can It Be Rationally and Objectively Required in Test Standards?—Bill Shisler, TUV Rheinland (U.S.)
- What is the US TAG?—Alex Mikonowicz, Powermark Inc.
- PV Standards- IEC TC82—George Kelly, Sunset Technology, Inc.
- A New PV Module Reliability Laboratory in Qatar—Diego Martinez Plaza, QEERI-Qatar Foundation
- Searching Stable CuxS Structure for Photovoltaic Application—Yufeng Zhao, NREL
- Developing a Roadmap for the Establishment of PV Weathering Standards—Nancy Phillips, 3M
IEC Task Force Update
Session Chair: Nick Bosco, NREL
- TG2: Thermal and Mechanical Fatigue—Tadanori Tanahashi, ESPEC
- TG3: Humidity, Temperature and Voltage—John Wohlgemuth, NREL
- TG4: Diodes, Shading and Reverse Bias—Vivek Gade, Jabil
- TG5: UV, Temperature and Humidity—David Miller, NREL
- TG8: Thin-Film Testing—Neelkanth Dhere, University of Central Florida
- TG9: CPV Testing—Nick Bosco, NREL
- TG10: Junction Box Connectors—Juris Kalejs, American Capital Energy
Session: Field Experience
- Broken glass appeared to be the results of thermal expansion issues associated with the racking system.
- The solder bond failures reported in "Reliability Evaluation of PV Power Plants: Input data for Warranty, Bankability and Energy Estimation Models" were judged to be more related to workmanship than design, but the detailed cause has not been determined.
- The bypass diode failures reported in "Reliability Evaluation of PV Power Plants: Input data for Warranty, Bankability and Energy Estimation Models" resulted in open-circuited bypass diodes. Almost all of these were found in a system that had shading.
Session: Potential Induced Degradation
- The comparison of damp heat and foil testing presented in "Testing Modules for Potential-Induced Degradation — A Status Update of IEC 62804" would have given a better comparison if weight had been applied to the foil.
- Some attendees raised the question of using a foil test that applies the stress across the entire module instead of simulating the situation in the field. Others noted that the foil test does a good job of simulating the leakage when it is raining and that they like the foil test because it helps to easily identify whether there is a problem. The current draft of IEC 62804 includes both the damp heat and the foil method.
- Volker Naumann reported that after a regenerative bias has been applied (after degradation induced by application of a bias voltage), they have observed evidence that the sodium migrated back out of the stacking faults. Annealing can also lead to regeneration, but takes a longer time.
Session: Physics of Failure
- In "Guidelines for Comparing indoor Accelerated Stress Tests to Outdoor Use," it was assumed that there was a single reaction occurring with a single activation energy, but in some situations there are multiple processes occurring that have different activation energies. In some cases, the rate-limiting step may be the diffusion of the moisture, which gives a different result than modeling the activation energy of the chemical reaction.
- We need to be cognizant of the difference between the application of damp heat and the photolysis process that occurs in the field. To be quantitative, we need to model the specific reactions.
- Measuring the activation energy may give a clue to the mechanism.
- When looking at the effects of moisture ingress, one should include thermal cycling. Inclusion of thermal variation may open paths for moisture ingress that one would not see in an isothermal damp-heat test.
Session: Inverter Reliability
- A separate study showed that 1000 cycles corresponded to 10 y in the field, but the details of the temperature fluctuations during those 10 y are unknown.
- When comparing the effect of temperature fluctuations in the field with thermal cycling in a chamber, the order of the fluctuations may change the damage done by a specific change in temperature. There's a hysteresis effect.
- The temperatures experienced for microinverters are higher than ambient. Typically, SolarBridge keeps the inverters 3-4 inches off of the roof, which keeps the temperature in a manageable range.
- During testing, Advanced Energy installs as many as 200 thermocouples to monitor every IGBT, every PC board, and many other places.
- To enable the writing of good standards, we need the manufacturers to communicate about the failures modes that are being seen.
- There is talk of people disconnecting from the grid, but battery storage is still expensive and unreliable, so its time has not yet come.
- There is a trend toward undersizing the inverter, then clipping the power (by operating the modules in forward bias) when the inverter rating is exceeded. Advanced Energy reports that some of their 1 MW inverters may clip as much as 8 hours in a day. The design intent is to have a steep power-up curve.
- The operating voltage and power point (clipping) need to be considered when testing for degradation and failure mechanisms.
- Testing the firm ware is essential. Advanced Energy uses a hardware emulator to test the firmware in the laboratory and also tests firmware on site in beta testing. Much of this testing is directed by UL standards.
- Customers want longer reliability from inverters. However, this message isn't driving the standards development — customers need to participate in standards writing to demand that testing is done to give the confidence that customers look for.
Session: Quality Management
- Hand-soldering can yield superb results, but movement toward automation may help to provide better consistency when there is a diverse work force.