Quality and long-term reliability are two of the most important issues facing the solar industry today. In no segment of the industry is this more critical than panels. Solar Power World has written extensively on the issue ourselves, but we wanted to get an insider’s perspective on them. Sam Tsou, VP of Quality Management Center at Motech, produced a three-part series on the subject, exclusively for us. This is Part I of the series. Parts II and III will be posted respectively on May 13 and May 27.
Prior to joining Motech, Sam Tsou was VP of USA Sales/Marketing at Semiconductor Manufacturing International Corporation, Director of Customer Engineering/Planning at TSMC-Wafertech, Assistant Vice President (AVP) of Quality and Reliability Assurance and AVP of Facility at Worldwide Semiconductor Manufacturing Co., and GM of Field Operation, Taiwan and Singapore, at Lam Research. Mr. Tsou graduated from the National Taiwan University with a bachelor’s degree in physics and received his master’s degree in Administration and Consoling from Harvest Seminary, USA.
For anyone making the decision to move to a renewable energy system, solar power can be a daunting challenge if one only considers the impressions left over from earlier years that do not reflect the true economic picture of today. Current U.S. government statistics aggressively support the idea that commercial and residential installations are proving to be a valuable approach, with a return on investment that means the payoff schedule is becoming shorter and shorter.
In fact, the choice of solar power in the United States as an option is growing at an amazing rate. This has occurred in part because solar system prices are falling toward grid parity and are making installations more affordable.
According to a recent report by Time.com, energy from the sun was the second-biggest source of new electricity generation capacity in 2013. In the United States, this strong growth has occurred across the three prime sectors, including utility, commercial, and residential, with the greatest performance seen across six top states including California, Arizona, North Carolina, Massachusetts, New Jersey and Hawaii.
And while the industry, as a whole, continues to work toward delivering a reliable, more efficient product, one of the critical considerations is to ensure that quality and long-term reliability remain the primary target points in offering the solar approach. What’s more, installers and designers will build a significant and predictable revenue stream by developing reputations for delivering systems based on quality and long-term reliability. In other words, designing or installing a solar system based on price alone will not likely support the pattern of growth recently seen. Instead, adopting a path aimed at the longer-term target will create a heightened benefit for the solar industry and end-users alike.
Beyond Basic Safety and Design Qualification:
From our perspective as a cell and module manufacturer, quality is all about longevity: How do you know that your module can really be expected to last? It is practically a given that most solar panels have undergone the ubiquitous IEC 61215, IEC 61730, and CSA/UL1703 design and safety qualification tests as a prerequisite to marketplace participation. In their current form, these tests are widely acknowledged to weed out designs susceptible to many unnecessary failure mechanisms. Unfortunately, important degradation mechanisms are left completely unexamined or inadequately probed by this basic suite of tests. A manufacturer must be cognizant of and eliminate these blind spots by extending the duration of a subset of the basic qualification tests, and conducting supplemental tests to access sensitivity to otherwise untested degradation pathways.
There are a host of “beyond the basics”tests that a manufacturer should conduct to assure its customers of a quality product. For example, due diligence can mean asking manufacturers about tests involving such things as:
- Extended Temperature Cycling (2x to 3x the IEC61215 standard)
- Potential Induced Degradation Testing (7x IEC62804)
- Extended UV Light Exposure (10x to 20x IEC61215)
- Bypass Diode Thermal Runaway Testing
- Dynamic Mechanical Load Testing
- Interlayer Adhesion Testing after chamber exposures
- Extended Humidity Freeze Cycle testing
- Salt Mist testing
- Transportation testing of module packaging
Until the basic prerequisite tests have undergone proper revision, extended and supplemental testing will remain a requirement to ensure a panel design is generally reliable for its 25- to 30-year warranted service life. But this type of design validation testing is only the first step towards delivering a quality PV module.
Backsheet yellowing.
Manufacturing Quality Management System:
Initial design and qualification of a few panels has little to do with the successful creation of a durable utility-scale PV power plant. A large scale PV power plant contains thousands upon thousands of individual panels. Each one of these PV modules must be produced consistently. In many cases, manufacturing occurs at multiple factories in different countries, each with a different equipment set. These disparate manufacturing conditions must be unified by a consistent Quality Management System (QMS). All sites must manufacture product to the same in-process inspection criteria, material handling procedures, verification frequency, calibration standards, defect definitions and operator-training levels. More specifically, the QMS helps ensure:
- First in First Out material usage
- Incoming Material Inspection to ensure compliance with engineering specifications
- Module power measurement calibration and adjustment procedures
Process audit measurement of:
- Solder peel strength
- EVA encapsulant degree of crosslinking
- Interface t-peel adhesion strength at all material interfaces
- Unannounced challenges to the QMS with known defects
- Electroluminescence equipment and inspection criteria are capable of reliable defect detection
- Quarantine and review of noncompliant products and materials
- Periodic (quarterly) reliability testing of finished product
The above is just a short list of items the QMS is required to enforce. A manufacturer should be able to produce the pedigree of any PV module which includes: date of manufacture; material lots used in the production of that module; incoming inspection results of those materials; flash and final test results; and process audit records that bookend the module’s production date. These records must be readily available years, even decades, past the manufacturing date. Otherwise, the cycle of design, production, deployment, and improvement cannot be completed for such a long lived product.
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