The first speaker (Keynote speaker) was Mr. John Lushetsky (Program Manager – United States Department of Energy (DOE), Office of Energy Efficiency & Renewable Energy) and his topic was “PV Module / System Reliability – A Critical Part of Total Industry Growth”.
John introduced U.S. Department of Energy which had two major parts that were Energy Efficiency, and Renewable Energy (EERE). Renewable Energy section had Solar Energy Technologies Program (SETP). He mentioned “Rapid production scale-up and new PV technologies and system designs, driven by increasing private investment, are making “reliability” a growing priority.”He explained why China should focus on PV reliability. It was because more than 22% of global PV production came from China in 2007 and it was approximate 98% of PV exported.
He also summarized several common reliability problems of PV product as follows:
i) Tracking, soiling / Dirt, Overheating / Heat Sinks;
ii) Interconnects and Junction Box Seals; and
iii) De-lamination, Glass Breakage and Corrosion.
The second speaker: Prof. CUI RongQiang come from Solar Energy Institute, Physics Department, Shanghai Jiao Tong University. Topic: “Development of Photovoltaic in China”. Prof. CUI predicted the development (Up to 2020) and forecast (Up to 2050) for renewable energy generation in China.
Then he introduced the Ideal Model for Chinese PV Growth.
Solar Energy (SE) + Energy Storage (ES) = Whole Energy Demand (WED)
He proposed Five-Stage of PV application in China as follows:
Stage 1: Off-grid PV system
Stage 2: On-grid roof PV system
Stage 3: PV Station in desert
Stage 4: PV Station coastal area
Stage 5: PV Power roof over road
At last, Prof CUI concluded that it needed to acquire more policies support from Chinese government and learn more experiences from PV developed countries (e.g. Japan, US, Germany and European countries) so as to benefit Chinese citizens to enjoy green, clear and safe PV energy.
Then he introduced the Ideal Model for Chinese PV Growth.
Solar Energy (SE) + Energy Storage (ES) = Whole Energy Demand (WED)
He proposed Five-Stage of PV application in China as follows:
Stage 1: Off-grid PV system
Stage 2: On-grid roof PV system
Stage 3: PV Station in desert
Stage 4: PV Station coastal area
Stage 5: PV Power roof over road
At last, Prof CUI concluded that it needed to acquire more policies support from Chinese government and learn more experiences from PV developed countries (e.g. Japan, US, Germany and European countries) so as to benefit Chinese citizens to enjoy green, clear and safe PV energy.
The third speaker: Dr. Ruiping Wang (General Manager, Solar Business Group China, Applied Materials China).
Topic: “Finally, Solar Power on the SCALE the Planet has been waiting for.”
She introduced the technology transformation from Integrated Circuit, Flat Panel Display to Solar Cell; and the PV Module price reduction from year to year. Applied SunFab Module Reliability and Testing Lab (SMRT Lab) employed SunFabTM PECVD 5.7m2. It aimed to lower the cost of PV modules by combining proven silicon thin film technology, with very large area manufacturing and industry standard equipment set. She had shown video of the demonstration for solar cell module test.
The forth speaker: Dr. Jennifer Granata (Member of the Technical Staff, Solar System Department, Sandia National Laboratories, US DOE).
She presented two topics entitled “Cell and Indoor PV Module Measurements” and “Outdoor PV Module and System Measurements”.
For Indoor cell testing, Jennifer considered the following points:
- Light Current-Voltage (LIV): Baseline performance testing, binning, pre-/post- reliability stress test (e.g. IEC 60891:1987 and 1992 Amendment; IEC 60904 series, etc.)
- Dark Current-Voltage (DIV): Assess diode quality; shunt and series resistance; use pre-/post- reliability stress testing
- Spectral Response: Bandgap determination; deduce optical loss regions; reference cell choice
- Reverse Bias Stress Test: Screen for shunted / weak diode cells; determine appropriate by-pass diode requirements
- Reflection/Transmission: Deduce optical losses; assess anti-reflective coatings
- Temperature Coefficients: Temp accuracy, solar simulator calibration, etc.
- Cell-level Reliability Testing: Accelerated Life Testing, FMEA, Lifetime predictions
For Indoor module testing, she considered the following points:
- Light Current-Voltage (LIV) Flash Test: Baseline module performance testing at STC; module name plate , pre-/post- reliability stress test (e.g. IEC 60904 series, ASTM E927-04a, ASTM E1036 etc.)
- Dark Current-Voltage (DIV): Assess shunted cells in module; use pre-/post- reliability stress testing
- Temperature Coefficients: Module temperature coefficient needed for energy output ratings at operating conditions.
- Chamber testing: Damp Heat, Humidity Freeze, Thermal Cycling – used for Qualification, product development, stress testing, reliability
- Reliability Stress Tests: Accelerated Life Testing, FMEA, Lifetime predictions
- Application standards include: IEC 61215, IEC 61646
For Outdoor module testing, she considered the following points:
- Electrical Performance: Baseline performance testing; performance under various Air Mass Conditions; pre-/post-reliability stress tests
- Standard Test Conditions (STC) – 1000W/m2 & 25oC module temp., Nominal Operating Cell Temperature (NOCT) – 800 W/m2 & 20oC & wind speed of 1m/s, PV USA Test Condition (PTC) - 1000 W/m2 & 20oC ambient, 1m/s wind
- Thermal Performance: Calculate module-level temperature coefficient; needed to model module output for any climate
- Angle of Incidence / Optical Reflectance Loss: Calculate module-level performance offset for off-normal conditions; determine optical reflectance losses in the field.
- Long-term testing: Measure derate factors; degradation rates
For System testing, following points were considered:
- Time of year considerations: Test when Air Mass 1.5 occurs at incident angles less than 45 degrees.
- Safety considerations: Improper hazards assessment can cause injury to personnel or electrical damage to PV system
- On-site measurements: Assess power rating, system energy yield, performance ratio, reliability over time
The fifth speaker: Prof. YU Peinuo (Tianjin Institute of Power Sources).
Topic: “China Photovoltaic Calibrating & Testing techniques Review”. He introduced the history of PV Calibrating and Testing techniques development.
He also introduced the following calibrations:
- Natural Sunlight Calibration
- Spectral Calibration
- Measure Solar Irradiance (W/m2) and Solar Irradiation (Wh/m2) using Pyranometer and PV Modules Calibrated
Finally, he summarized the spectral response of PV devices included Power Efficiency, Normal Power Efficiency, Energy Yield Efficiency and Ratio of two PV Modules Yield Efficiency.
The sixth speaker: Mr. Liang Ji from Underwriters Laboratories Inc. (UL).
Topic: “PV Module Design and Manufacturing Issues related to Safety and Reliability”.
He introduced several types of test which were Qualification, Safety, Reliability and Engineering evaluation. Then he showed us the failure cases of Lamination, Frame, J-Box and Connector.
The failure cases were:
- Lamination bubble
- Encapsulant overflow
- Gel content too high
- Cell touching
- Frame loading
- Corner key & screw
- Installation / Grounding Holes
- Corrosion
- J-Box wire (should be separated the electrical connection with mechanical connection)
- Connector Design & Installation
End-of-Life Failure included:
- Gradually reducing power output
- Suddenly lost power
- Open circuit
- Short circuit
- Current leakage to frames or/and grounding path
- Arcing or catching fire, etc.
Lastly, he concluded “Statistically, when millions of modules are installed, there will be some failures, but we have to prevent disasters.”
The seventh speaker: Dr. Yuepeng Wan (CTO, LDK Solar Co., Ltd.).
Topic: “Quality Control for the Production of Multi-crystalline Silicon Ingots and Wafers”.
He introduced the PV industry chair from Silicon ore, Metallurgical silicon, pure silicon raw material, to Ingot & Bricks, wafers, solar cell, module to solar system.
He introduced the PV industry chain from Silicon ore, Metallurgical silicon, pure silicon raw material, to Ingot & Bricks, wafers, solar cell, module to solar system.
Topic: “Finally, Solar Power on the SCALE the Planet has been waiting for.”
She introduced the technology transformation from Integrated Circuit, Flat Panel Display to Solar Cell; and the PV Module price reduction from year to year. Applied SunFab Module Reliability and Testing Lab (SMRT Lab) employed SunFabTM PECVD 5.7m2. It aimed to lower the cost of PV modules by combining proven silicon thin film technology, with very large area manufacturing and industry standard equipment set. She had shown video of the demonstration for solar cell module test.
The forth speaker: Dr. Jennifer Granata (Member of the Technical Staff, Solar System Department, Sandia National Laboratories, US DOE).
She presented two topics entitled “Cell and Indoor PV Module Measurements” and “Outdoor PV Module and System Measurements”.
For Indoor cell testing, Jennifer considered the following points:- Light Current-Voltage (LIV): Baseline performance testing, binning, pre-/post- reliability stress test (e.g. IEC 60891:1987 and 1992 Amendment; IEC 60904 series, etc.)
- Dark Current-Voltage (DIV): Assess diode quality; shunt and series resistance; use pre-/post- reliability stress testing
- Spectral Response: Bandgap determination; deduce optical loss regions; reference cell choice
- Reverse Bias Stress Test: Screen for shunted / weak diode cells; determine appropriate by-pass diode requirements
- Reflection/Transmission: Deduce optical losses; assess anti-reflective coatings
- Temperature Coefficients: Temp accuracy, solar simulator calibration, etc.
- Cell-level Reliability Testing: Accelerated Life Testing, FMEA, Lifetime predictions
For Indoor module testing, she considered the following points:
- Light Current-Voltage (LIV) Flash Test: Baseline module performance testing at STC; module name plate , pre-/post- reliability stress test (e.g. IEC 60904 series, ASTM E927-04a, ASTM E1036 etc.)
- Dark Current-Voltage (DIV): Assess shunted cells in module; use pre-/post- reliability stress testing
- Temperature Coefficients: Module temperature coefficient needed for energy output ratings at operating conditions.
- Chamber testing: Damp Heat, Humidity Freeze, Thermal Cycling – used for Qualification, product development, stress testing, reliability
- Reliability Stress Tests: Accelerated Life Testing, FMEA, Lifetime predictions
- Application standards include: IEC 61215, IEC 61646
For Outdoor module testing, she considered the following points:
- Electrical Performance: Baseline performance testing; performance under various Air Mass Conditions; pre-/post-reliability stress tests
- Standard Test Conditions (STC) – 1000W/m2 & 25oC module temp., Nominal Operating Cell Temperature (NOCT) – 800 W/m2 & 20oC & wind speed of 1m/s, PV USA Test Condition (PTC) - 1000 W/m2 & 20oC ambient, 1m/s wind
- Thermal Performance: Calculate module-level temperature coefficient; needed to model module output for any climate
- Angle of Incidence / Optical Reflectance Loss: Calculate module-level performance offset for off-normal conditions; determine optical reflectance losses in the field.
- Long-term testing: Measure derate factors; degradation rates
For System testing, following points were considered:
- Time of year considerations: Test when Air Mass 1.5 occurs at incident angles less than 45 degrees.
- Safety considerations: Improper hazards assessment can cause injury to personnel or electrical damage to PV system
- On-site measurements: Assess power rating, system energy yield, performance ratio, reliability over time
The fifth speaker: Prof. YU Peinuo (Tianjin Institute of Power Sources).
Topic: “China Photovoltaic Calibrating & Testing techniques Review”. He introduced the history of PV Calibrating and Testing techniques development.
He also introduced the following calibrations:
- Natural Sunlight Calibration
- Spectral Calibration
- Measure Solar Irradiance (W/m2) and Solar Irradiation (Wh/m2) using Pyranometer and PV Modules Calibrated
Finally, he summarized the spectral response of PV devices included Power Efficiency, Normal Power Efficiency, Energy Yield Efficiency and Ratio of two PV Modules Yield Efficiency.
The sixth speaker: Mr. Liang Ji from Underwriters Laboratories Inc. (UL).
Topic: “PV Module Design and Manufacturing Issues related to Safety and Reliability”.
He introduced several types of test which were Qualification, Safety, Reliability and Engineering evaluation. Then he showed us the failure cases of Lamination, Frame, J-Box and Connector.
The failure cases were:
- Lamination bubble
- Encapsulant overflow
- Gel content too high
- Cell touching
- Frame loading
- Corner key & screw
- Installation / Grounding Holes
- Corrosion
- J-Box wire (should be separated the electrical connection with mechanical connection)
- Connector Design & Installation
End-of-Life Failure included:
- Gradually reducing power output
- Suddenly lost power
- Open circuit
- Short circuit
- Current leakage to frames or/and grounding path
- Arcing or catching fire, etc.
Lastly, he concluded “Statistically, when millions of modules are installed, there will be some failures, but we have to prevent disasters.”
The seventh speaker: Dr. Yuepeng Wan (CTO, LDK Solar Co., Ltd.).
Topic: “Quality Control for the Production of Multi-crystalline Silicon Ingots and Wafers”.
He introduced the PV industry chair from Silicon ore, Metallurgical silicon, pure silicon raw material, to Ingot & Bricks, wafers, solar cell, module to solar system.
He introduced the PV industry chain from Silicon ore, Metallurgical silicon, pure silicon raw material, to Ingot & Bricks, wafers, solar cell, module to solar system.
The impact on efficiency (wafer to cell/module):
1. Impurities and defects in bulk
2. Light induced degradation effect (LID)
Hot spot effect could be caused by impurities, cracks and defects.
The following slides were the Wafer Production Processes (for multi-crystalline).
Quality control points in the wafering processes were:
- Inspection of Ingots
- Inspection of Bricks
- Inspection of Wafers
Most customers need wafer lifetime inspection; the common method is to test the Passivation wafer.
The eighth speaker: Prof. Deren Yang (楊德仁) (Zhejiang University).
Topic: “The impact of impurity and defect on silicon to solar cell”.
The figure was the based solar cell with defect.
The effect of oxygen in which source were raw material & quartz crucible were shown below.
The effect of carbon in which source were raw material & graphite heater are shown below.
The effect of hydrogen in which source were SiN anti-reflective layer plus passivation.
The effect of metal in which source were raw material, wafer process & cell process.
The effect of dislocation in which source were crystal growth & cell process are shown below. 
The effect of grain boundary in which source was crystal growth.
Lastly, Prof. Yang concluded:
- Oxygen and carbon related complexes/precipitates have an influence on the efficiency;
- Metal including complexes/precipitates deteriorate the efficiency;
- Hydrogen can passivate electrical active centers, improving the efficiency; and
- Dislocation and grain boundary, interacted with metal to form electrical active centers, decrease the efficiency.
The ninth speaker: Dr. John Pern (Sr. Scientist II, National Center for Photovoltaics – NCPV; National Renewable Energy Laboratory – NREL, USA).
Topic: “Module Encapsulation Materials, Processing and Testing”.
He also showed the different degradation of field modules included yellow-browning, back-sheet blistering & delamination, corrosion by moisture ingress, glass cracking by stress, etc. Finally, he concluded that
- Encapsulation method and processing conditions can affect the laminate quality and reliability of PV modules.
- Adequate accelerated exposure tests can be useful to assess the performance expectation of materials and quality of processed components.
- Overall module reliability is determined by all component materials and processing factors.
The tenth speaker: Mr. Zhihuang Fei (Chief Engineer – Jolywood (Suzhou) Solar Material Technology Co., Ltd.).
Topic: “The Tetrafluoro-based Solar cell Backsheet – its properties and Application for PV Modules”.
He introduced the technology reliability and economic level of the tetrafluoro-based solar cell backsheet, and the research of plasma surface modification.
Their product used FFC Solar cell Backsheet (FFC + PET + FFC) where FFC – using Plasma Fluoro-Silicone surface modification and PET – using Plasma Titanium-Silicon surface modification.
They had researched the change of PET and FCC Backsheet surface contact angles with the different plasma modification time, as well as, with the different plasma modification function density after 10s plasma modification, respectively. In their research laboratory, several equipments were employed for this study such as GC, UV, LC, NMR, SEM, IR, TGA, etc.
The eleventh speaker: Dr. Mani G. Tamizh-Mani (President – TUV Rheinland PTL, LLC).
Topic: “Qualification Testing vs Reliability Testing”.
His paper entitled “Failure analysis of design qualification testing: 2007 vs. 2005” in IEEE 2008 was introduced. About 1200 and 1000 modules were tested in the 1997-2005 and 2005-2007 periods, respectively. According to the IEC 61215 Edition 2, the major new tests are wet leakage current and Diode tests, and major modified test is TC200 with current injection.
He reported the failure analysis of the qualification test results, indicating a large increase in the failure rates for the 2005-2007 periods as compared to the 1997-2005 periods. It could be attributed to the market entry of a large number of new manufacturers in the 2005-2007 periods in which the highest failure rate in c-SI PV modules and Thin-Film PV modules was the wet resistance test after damp heat (1000 hour).
For reliability testing, he summarized the typical field failures and stresses as below:
Stress by Thermal, mechanical electrical:
- Broken interconnects
- Broken cells
- Solder bond failures
- Hot spots
Stress by Moisture ingress with high temp:
- Corrosion
- Delamination
- Junction box
Stress by UV with high temp:
- Encapsulant discoloration
The final speaker of day one was Mr. Michael A. Quintana (Sandia National Laboratories) and his topic was “Photovoltaic Module Reliability”. He also introduced different module failures as follows:
Corrosion (45.3%), Cell or Interconnect Break (40.7%), Output Lead Problem (3.9%), Junction Box Problem (3.6%), Delamination (3.4%), Overheated wires/diodes/terminal strip (1.5%), Mechanical Damage (1.4%) and Defective Bypass Diodes (0.2%).
He summarized forth points at the end.
- Module reliability is being studied extensively from materials to commercial component.
- Module reliability continues to be a very high priority for manufacturers as new products continue to be introduced and new materials and processes are integrated into existing products.
- Diagnostics needs have not been met completely and need to be a focal point of R&D efforts.
- Predictive models need data from fielded installations as well as accelerated tests.
1. Impurities and defects in bulk
2. Light induced degradation effect (LID)
Hot spot effect could be caused by impurities, cracks and defects.
The following slides were the Wafer Production Processes (for multi-crystalline).
Quality control points in the wafering processes were:- Inspection of Ingots
- Inspection of Bricks
- Inspection of Wafers
Most customers need wafer lifetime inspection; the common method is to test the Passivation wafer.
The eighth speaker: Prof. Deren Yang (楊德仁) (Zhejiang University).
Topic: “The impact of impurity and defect on silicon to solar cell”.
The figure was the based solar cell with defect.
The effect of oxygen in which source were raw material & quartz crucible were shown below.
The effect of carbon in which source were raw material & graphite heater are shown below.
The effect of hydrogen in which source were SiN anti-reflective layer plus passivation.
The effect of metal in which source were raw material, wafer process & cell process.
The effect of dislocation in which source were crystal growth & cell process are shown below.
The effect of grain boundary in which source was crystal growth.
Lastly, Prof. Yang concluded:
- Oxygen and carbon related complexes/precipitates have an influence on the efficiency;
- Metal including complexes/precipitates deteriorate the efficiency;
- Hydrogen can passivate electrical active centers, improving the efficiency; and
- Dislocation and grain boundary, interacted with metal to form electrical active centers, decrease the efficiency.
The ninth speaker: Dr. John Pern (Sr. Scientist II, National Center for Photovoltaics – NCPV; National Renewable Energy Laboratory – NREL, USA).
Topic: “Module Encapsulation Materials, Processing and Testing”.
He introduced the PV Module Production Line and Manufacturing bottleneck in (c-Si) PV Module Fabrication Process. He said only one company could be totally automatic production in Germany.
There were three typical PV Module Encapsulation Configurations:
1. Crystalline Si-based Module
2. Superstrate-Deposited Thin Film Module
3. Substrate-Deposited Thin Film Module
Dr. John Pern introduced different types of module encapsulation materials and selection criteria. For polymeric encapsulants, the most commonly used and cheapest was EVA.
The following shows “Testing vs. Performance Reliability”.
There were three typical PV Module Encapsulation Configurations:
1. Crystalline Si-based Module
2. Superstrate-Deposited Thin Film Module
3. Substrate-Deposited Thin Film Module
Dr. John Pern introduced different types of module encapsulation materials and selection criteria. For polymeric encapsulants, the most commonly used and cheapest was EVA.
The following shows “Testing vs. Performance Reliability”.
He also showed the different degradation of field modules included yellow-browning, back-sheet blistering & delamination, corrosion by moisture ingress, glass cracking by stress, etc. Finally, he concluded that
- Encapsulation method and processing conditions can affect the laminate quality and reliability of PV modules.
- Adequate accelerated exposure tests can be useful to assess the performance expectation of materials and quality of processed components.
- Overall module reliability is determined by all component materials and processing factors.
The tenth speaker: Mr. Zhihuang Fei (Chief Engineer – Jolywood (Suzhou) Solar Material Technology Co., Ltd.).
Topic: “The Tetrafluoro-based Solar cell Backsheet – its properties and Application for PV Modules”.
He introduced the technology reliability and economic level of the tetrafluoro-based solar cell backsheet, and the research of plasma surface modification.
Their product used FFC Solar cell Backsheet (FFC + PET + FFC) where FFC – using Plasma Fluoro-Silicone surface modification and PET – using Plasma Titanium-Silicon surface modification.
They had researched the change of PET and FCC Backsheet surface contact angles with the different plasma modification time, as well as, with the different plasma modification function density after 10s plasma modification, respectively. In their research laboratory, several equipments were employed for this study such as GC, UV, LC, NMR, SEM, IR, TGA, etc.
The eleventh speaker: Dr. Mani G. Tamizh-Mani (President – TUV Rheinland PTL, LLC).
Topic: “Qualification Testing vs Reliability Testing”.
His paper entitled “Failure analysis of design qualification testing: 2007 vs. 2005” in IEEE 2008 was introduced. About 1200 and 1000 modules were tested in the 1997-2005 and 2005-2007 periods, respectively. According to the IEC 61215 Edition 2, the major new tests are wet leakage current and Diode tests, and major modified test is TC200 with current injection.
He reported the failure analysis of the qualification test results, indicating a large increase in the failure rates for the 2005-2007 periods as compared to the 1997-2005 periods. It could be attributed to the market entry of a large number of new manufacturers in the 2005-2007 periods in which the highest failure rate in c-SI PV modules and Thin-Film PV modules was the wet resistance test after damp heat (1000 hour).
For reliability testing, he summarized the typical field failures and stresses as below:
Stress by Thermal, mechanical electrical:
- Broken interconnects
- Broken cells
- Solder bond failures
- Hot spots
Stress by Moisture ingress with high temp:
- Corrosion
- Delamination
- Junction box
Stress by UV with high temp:
- Encapsulant discoloration
The final speaker of day one was Mr. Michael A. Quintana (Sandia National Laboratories) and his topic was “Photovoltaic Module Reliability”. He also introduced different module failures as follows:
Corrosion (45.3%), Cell or Interconnect Break (40.7%), Output Lead Problem (3.9%), Junction Box Problem (3.6%), Delamination (3.4%), Overheated wires/diodes/terminal strip (1.5%), Mechanical Damage (1.4%) and Defective Bypass Diodes (0.2%).
He summarized forth points at the end.
- Module reliability is being studied extensively from materials to commercial component.
- Module reliability continues to be a very high priority for manufacturers as new products continue to be introduced and new materials and processes are integrated into existing products.
- Diagnostics needs have not been met completely and need to be a focal point of R&D efforts.
- Predictive models need data from fielded installations as well as accelerated tests.
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