Service life prediction through the quality management system

Transcription

1 Service life prediction through the quality management system Timothy J Silverman Nick Bosco Sarah Kurtz NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

2 Product-specific tests Type qualification and comparative testing are difficult; lifetime prediction is even trickier Small changes can have a major effect on lifetime, but cost reductions are desirable Close integration with production is necessary There can be no one-size-fits-all lifetime test 2

3 The quality management system The QMS is a company s formal statement of its quality procedures Traceability of raw materials and final products Testing of products to meet customer requirements Corrective and preventive action Auditing The QMS is the ideal place to formalize a service life prediction test 3

4 Why product-specific testing? The module is a highly coupled system Lifetime can be sensitive to small changes in material, process or service conditions Some products are doing fine 4

5 Interaction within the module Discoloration mono-si after 18 years (left) and 27 years (right) in Sacramento (warm temperate/ summer dry/hot summer) Delamination can accompany discoloration 5

6 Interaction within the module Corrosion EFG Si after 23 years in Marin County, Florida mono-si after 15 years in Cocoa, Florida Delamination can let in moisture, causing corrosion, but some corrosion occurs without delamination 6

7 Interaction within the module Delamination multi-si after 10 years in Perrysburg, Ohio mono-si after 15 years in Cocoa, Florida Delamination at the encapsulant-cell interface often follows ribbons and grid fingers 7

8 Interaction within the module Delamination multi-si after 10 years in Perrysburg HIT after 10 years in Tucson Al-containing backsheet traps outgassing Backsheet layers can separate from each other or from the encapsulant 8

9 Interaction within the module Interconnect degradation This module has a hot area where adhesive bus tapes intersect Encapsulant is discoloring here 8 years in Toledo, Ohio 9

10 Interaction within the module Interconnect degradation 75% of the modules in this field were affected 10

11 Interaction within the module Interconnect degradation Broken solder bonds lead to high series resistance and loss of FF They also result in highly localized dissipation of heat mono-si after 8 years in Tucson 11

12 Interaction within the module Interconnect degradation mono-si after 10 years in Perrysburg, Ohio Highly localized heating from broken solder bonds damages adjacent materials 12

13 IEC qualification tests IEC IEC IEC These standards specify accelerated tests but they are design qualification and type approval tests for products suitable for long-term operation 13

14 Levels of Accelerated Testing IEC Qualification Comparative Service Life Purpose Minimum design qualification Comparison of products Reduction of cost while still meeting warranty Quantification Pass/fail Relative Absolute Climate or application (mounting) Not differentiated Differentiated Differentiated Specificity Silicon, thin-film, CPV Package specific? Product specific Chamber test times Modules: < 2 months Up to 6 months 3 years?

15 Getting acceleration right Accelerated aging 100 o C, 5 minutes Shelf-life aging 25 o C, 30 days Henhouse aging 30 days

16 Timeline Challenge 3 mo 6 mo 1 y 2 y 3 y Common product development cycle today (even shorter?) Qualification test can be completed Preferred quality management testing X10 acceleration to simulate 25 y X100 acceleration to simulate 25 y Henhouse aging 30 days Too much acceleration may answer the wrong question!

17 Steps to a service life prediction 1. Identify failure/degradation mechanisms that determine end of life 2. Quantify the rate of these mechanisms 3. For given use environment, apply rates within a model to estimate expected lifetime 4. Verify model by comparing with field data The steps are clear but the tests are not 17

18 Creating a standard for life prediction If long tests are required, product development cycle needs to slow down Start today: Screen for and eliminate design flaws In parallel, begin to quantify failure/degradation rates for stubborn problems for this specific product Implement standard for service life prediction through the quality management system 18

19 Importance of uncertainty Properly quantifying uncertainty in lifetime prediction enables Better quantification of risk Differentiation in testing between established products and new ones 19

20 PV-specific QMS supplement The international PVQAT has proposed a supplement to ISO 9001 for PV manufacturers Serves as a guideline for manufacturing consistency 20

21 Gaps Kinetics of each failure mechanism and how these depend on product specifics Inexpensive, rapid tests that will identify changes early Methods for uncertainty management Role of the QMS