【DNV GL】2016 年光伏组件可靠性计分卡

PV Module Reliability Scorecard Report 2016 Report Contributors Jenya Meydbray, VP Strategy the measurement methods and calibrations were clearly described and were generally similar at each measurement point; details on the installation (disregarding proprietary considerations) are provided. The results of the NREL study shown in Figure 2-2 and Figure 2-3 indicate a mean degradation of about half a percent per year (for the high quality dataset) which is generally in line with expectations. However, there is a long tail with degradation beyond one percent annually. This long tail is likely driven by equipment issues caused by poor quality manufacturing, materials, or product design. Source: “Compendium of Photovoltaic Degradation Rates”, D.C. Jordan, et al, NREL, 2015 Figure 2-3 Results of Kurtz-Jordan NREL study on PV degradation Dataset # of modules surveyed Mean Degradation Rate Median Degradation Rate P90 Degradation Rate High Quality 1,936 0.5 – 0.6 % / year 0.4 – 0.5 % / year 1.2 % / year All Module Data 9,977 0.9 – 1.0 % / year 0.9 – 1 % / year 1.7% / year Source: “Compendium of Photovoltaic Degradation Rates”, D.C. Jordan, et al, NREL, 2015 Figure 2-2 Results of Kurtz-Jordan NREL study of PV degradation DNV GL PVEL Page 4 In another large study, DuPont performed extensive field inspections (visual inspection and thermal imaging) of 60 global sites totaling 1.5 million PV modules from 45 manufacturers to evaluate aging behaviors in the real world. System ages ranged from 0 to 30 years. Their findings are outlined in Figure 2-4, issues were identified on 41% of the modules surveyed. Source: courtesy of DuPont Photovoltaic Solutions, “Quantifying PV Module Defects in the Service Environment”, Alex Bradley, et al, 2.2 The objective of laboratory testing The most accurate way to determine if a product can last 20 years in the field is to instrument it and deploy it for 20 years. This level of testing is obviously prohibitive. Laboratory testing should be leveraged to understand PV equipment aging behavior in a commercially reasonable timeframe. Quite a bit can be learned about PV modules in only a few months in the laboratory. Unfortunately, extrapolating lab results to precisely predict field degradation rate is not possible today. However, relative performance in the laboratory is expected to translate to the field. For example, if module A outperforms module B in Thermal Cycling in the lab it will very likely outperform in the field as well for the aging mechanisms captured by this test. In addition to degradation analysis the stress tests available today are very effective at screening for PV module defects that cause severe degradation or safety issues such as bad solder joints or a poorly adhered junction box. Figure 2-5 outlines failure modes targeted by each laboratory stress test as published by NREL. Failure Categorizations Glass / Superstrate Broken, etched, hazed glass Encapsulant Discoloration or delamination Cell / Interconnect Corrosion, hot spot, broken interconnect, snail trails, cracks, burn marks Backsheet Cracking, yellowing, delamination Figure 2-4 DuPont inspection of field PV modules DNV GL PVEL Page 5 Figure 2-5 PV module failure modes per laboratory test Accelerated Stress Failure Mode Thermal Cycling Broken Interconnect Broken Cell Solder Bond Failures Junction Box Adhesion Module Connection Open Circuits Open Circuits leading to Arcing Damp Heat Corrosion Delamination of Encapsulant Encapsulant loss of adhesion & elasticity Junction Box Adhesion Electrochemical corrosion of TCO Inadequate edge deletion Humidity Freeze Delamination of Encapsulant Junction Box Adhesion Inadequate edge deletion UV Exposure Delamination of Encapsulant Encapsulant loss of adhesion & elasticity Encapsulant Discoloration Ground Fault due to backsheet degradation Source: “Reliability Testing Beyond Qualification as a Key Component in Photovoltaic’s Progress Toward Grid Parity”, Wohlgemuth, et al, NREL, 2011 DNV GL PVEL Page 6 3 MODULE RELIABILITY AND TESTING 3.1 A brief history of module reliability When discussing the origins and early phases of terrestrial module reliability assessment, two bodies of work are typically cited: the Jet Propulsion Laboratory’s Block Buy program and the Joint Research Center’s European Solar Test Installation. Figure 3-1 Jet Propulsion Laboratory’s block buy modules Source: Jet Propulsion Laboratory The JPL Block Buy program started in the mid-1970s as terrestrial PV module development started to gain traction. Throughout the program’s lifetime, it had the goal of developing and implementing environmental tests for crystalline silicon modules. By the project’s end, it had established many of the tests that are still used for reliability assessment today, including temperature cycling, humidity freeze and mechanical load. The European Solar Test Installation (ESTI) project was initiated in the late 1970s and focused on both testing modules and creating standard performance metrics for solar cells. The project is ongoing and is currently focusing on developing an industry standard for module power verification. These two programs formed a foundation for today’s basic module qualification test, the International Electrotechnical Commission (IEC) 61215, and safety test, the Underwriters Laboratories (UL) 1703. DNV GL PVEL Page 7 3.2 The limitations of existing certification standards Though most projects require UL and/or IEC certification to ensure a minimum bar of module robustness, it is widely accepted that these certification standards are not sufficient to demonstrate PV module reliability nor consistency. First, it should be noted that UL 1703 is purely a safety test. The goal of the test is to ensure that the module does not pose a hazard during operation. The IEC 61215 standard is the minimum baseline industry-accepted module assessment program, applying environmental stress tests first developed in the JPL’s Block Buy program. However, the scope of these tests accounts only for so-called infant mortality and leaves aside a number of common potential causes of failure. For instance, resilience to PID is not tested at all (more on that later). This means that the IEC 61215 tests are only well suited to weed out modules that would be likely to fail within the first years in the field (screening for defects). Certification testing is performed on only on a small number of samples and isn’t necessarily representative of high volume commercial production over time. Besides, the manufacturer is free to select the physical modules sent for testing and no random selection out of the production line is necessary. Furthermore, maintaining certification does not require periodic re-testing unless materials or designs change. Applying these IEC tests for PV module defect screening is becoming a common and effective Batch Acceptance test, screening for serial defects for PV module procurement in large residential or commercial procurements or utility scale projects, but it is not sufficient to start to quantify long-term reliability of the module construction. Based on DNV GL’s experience at least 6% of commercial PV modules do not pass the IEC 61215 Thermal Cycling test – see Figure 3-2 below. Additionally, the IEC certification only functions as a pass/fail set of tests. It does not report the actual magnitude of degradation after the tests, nor does it seek to discern the root cause of performance loss. Figure 3-2 DNV GL’s historical Thermal Cycling degradation results Source: DNV GL Laboratory Services Group DNV GL PVEL Page 8 3.3 Degradation versus failure Power degradation over time is built into project expectations and is warranted by the manufacturers. The current standard 25-year warranty is typically triggered if modules degrade more than 3% within the first year and at a linear rate down to 80% of its initial nameplate power in year 25. Small levels of power degradation in the field are difficult to accurately measure due to the uncertainty of measurement tools. Warranty claims are therefore typically only executed for gross underperformance or complete failure. Prior to module purchase measurement of the resilience of modules to the most common degradation mechanisms is therefore of essential importance. DNV GL PVEL Page 9 4 THE PRODUCT QUALIFICATION PROGRAM DNV GL (formerly PV Evolution Labs a.k.a. PVEL) developed the Product Qualification Program to support the downstream solar community back in 2013. The objectives of the program are twofold. First, it provides PV equipment buyers and PV power plant investors with independent and consistent reliability and performance data to help implement effective supplier management process (such as an Approved Product or Vendor List). Additionally, it provides module manufacturers focused on the reliability of their products the visibility they need to be successful in this competitive market. The Product Qualification Program provides DNV GL’s downstream partners with 3 rd party performance data (PAN files, IAM, NOCT, and LID) as well as reliability data as outlined in the table below. Data in the PV Module Reliability Scorecard is pulled from this Product Qualification Program. In the past 2 years DNV GL has executed 40 Qualification Programs across 30 manufacturers. Figure 4-1 DNV GL’s Product Qualification Program compared to IEC 61215 Test Thermal Cycling Damp Heat Humidity Freeze Mechanical Load PID Product Qualification Program 800 TC cycles 3,000 DH hours 30 HF cycles Dynamic Load 600 hours IEC 61215 Standard 200 TC cycles 1,000 DH hours 10 HF Cycles Static mechanical load None Source: DNV GL Laboratory Services Group 4.1 Module selection and sampling process Independent PV module sampling is a critical step in testing and qualification. This step builds confidence that the production process and Bill of Materials (BOM) are representative of commercial production. DNV GL works with independent inspectors from SolarBuyer and CEA for all modules tested in the PV Module Reliability Scorecard. This is a standard part of the Product Qualification Program. 4.2 Light-induced degradation Upon initial exposure to light, modules experience a permanent reduction in power output. The phenomenon is called light induced degradation or LID. On average, LID for crystalline silicon modules ranges from 0.5% to 3%, with some modules exhibiting a loss of up to 5%. Manufacturers using n-type silicon cells such as SunPower exhibit no LID loss. Manufacturers take this into account by factoring in a 3% power loss (typically) during the first year of the module warranty. To ensure that light-induced degradation does not jeopardize the conclusions of the chamber testing, all PV modules in the PV Module Reliability Scorecard were light soaked for at least 40 kWh / m 2 before entering the testing chambers. DNV GL PVEL Page 10