Download - Solar PV Module Durability Testing
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May 2014
Mani G. TamizhMani
Solar PV Module Durability Testing
Short Course on “Solar PV Modules and System Testing and Characterization” IIT Bombay, Nov 26, 2014
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Slide 2
• Difference between durability and reliability • Importance of durability • Outdoor durability evaluation • Indoor durability evaluation • Summary
Presentation Outline
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Slide 3
• Difference between durability and reliability • Importance of durability • Outdoor durability evaluation • Indoor durability evaluation • Summary
Presentation Outline
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Slide 4
Difference between durability and reliability
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Slide 5
kWh is dictated by durability loss and reliability loss Durability loss = Degradation rate below warranty rate Reliability loss = Degradation rate above warranty rate Note: Safety failed modules shall be replaced and these modules should be excluded from the degradation rate calculations
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Possible degradation trends
A.W. Czanderna and G.J. Jorgensen; Presented at Photovoltaics for the 21st Century Seattle, Washington, May 4, 1999
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Practical implication of these issues for stakeholders:
Higher $/kWh
Not bankable (high risk premium rate and O&M insurance backup!)
Both durability & reliability issues: A hypothetical representation
Source: ASU-PRL (Solar ABCs report)
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Solder bond fatigue
Source: IEA-PVPS-2014
Both durability & reliability issues: A hypothetical representation
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Slide 9
• Difference between durability and reliability • Importance of durability • Outdoor durability evaluation • Indoor durability evaluation • Summary
Presentation Outline
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Slide 10
Importance of durability
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Slide 11
Goal of project developers:
Securing low interest bank loan with no risk premium adders Interest Rate
=
Interest Rate @ Zero Risk
+
Risk Premium Rate
Note: The typical 20/20 warranty is assumed in the above example.
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SF = Safety Failure (Qualifies for safety returns); Identified by: Visual inspection, IR and Circuit/diode checker RF = Reliability Failure (Qualifies for warranty claims); Identified by: I-V
DL = Durability Loss (Does not qualify for warranty claims); Identified by: I-V
Technical Levelized Cost of Energy (T-LCOE) of PV Module
$/kWh = Bankability
“$/kW” dictated by: • Material cost ($): Materials
and process cost per unit area • Device Quality (kW): Module
efficiency per unit area
Performance
“h” dictated by:
• Packaging / Design Quality: Safety failures (SF) over time (obsolete)
• Manufacturing Quality: Reliability failures (RF) over time (under-performance; >1%/year degradation)
• Material Quality: Durability / Degradation loss (DL) over time (better-performance; <1%/year degradation)
Safety, Reliability and Durability
$/kW h
To decrease levelized cost of energy ($/kWh) by decreasing “$/kW” value and
increasing “h” value.
Reliability evaluation: Importance to stakeholders
Source: ASU-PRL
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Slide 13
• Difference between durability and reliability • Importance of durability • Outdoor durability evaluation • Indoor durability evaluation • Summary
Presentation Outline
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Slide 14
Outdoor durability evaluation
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< 1% dr/y
SF
with <1% dr/y
Durability Loss with or without cosmetic defects
(DL)
Defects
(D)
Safety Issues
Safety Failure
(SF)
METRIC/NUMERIC Definition of Failures and Degradation
> 1% dr/y
- SF
with >1% dr/y
Reliability Failure with or without cosmetic defects
(RF)
with
- SF = Safety Failure (100% risk; Qualifies for safety returns;) RF = Reliability Failure (1-100% risk proportional to DR; Qualifies for warranty claims) DL = Durability Loss (0% risk; Does not qualify for warranty claims)
DR = Degradation Rate
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Review: Module Construction, Full I-V curves (STC and LowEs), Previous Reports, System Layout, Metered kWh and Weather Data
Visual Inspection: All modules per NREL
checklist
Thermal Imaging: All modules
I-V & Megger Tests: All hotspot modules
I-V Test and SunEye: All strings
(before cleaning)
I-V Test: All modules in three
best, worst and median strings
(before cleaning)
Diode/Circuit Test: All modules
I-V & Megger Tests: All diode-failed modules
I-V Test (1000, 800 and 200 W/m2):
Three best modules from the best strings (after cleaning)
Cell-Crack Test: All modules in the best strings (after cleaning)
PID Check: All modules in the best strings (after cleaning)
Safety and Reliability Evaluation Primary Goal: Identification of Safety Failures (SF) and Reliability Failures (RF)
Durability and Reliability Evaluation Primary Goal: Identification of degradation rates (DR) [Reliability Failure (RF) = if DR>1%/y; Durability Loss (DL)= if DR<1%/y)]
Inverter Ground Fault Events: All safety failed
strings
Field Evaluation of PV Modules: Application of ASU-PRL’s Definitions on Field Failures and Degradation Determinations
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Defects (mono-Si; glass/polymer)
SF SF SF
SF = Safety Failure; RF = Reliability Failure; DL = Degradation Loss Defects with safety issues are identified on the plot.
Other defects shown on the plot are classified as either RF or DL depending on degradation rates
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Examples of Safety Failures
Hotspot leading to backsheet burning (along the busbars)
Ribbon-ribbon solder bond failure (with backsheet burning )
Failed Diodes (with no backsheet burning ) Backsheet Delamination
(frameless modules)
12 Years – 1-axis Tracker
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Mapping of Safety Failures (Model G – Site 3)
Hotspot issues leading to backsheet burn (37/2352)Ribbon-ribbon solder bond failure with backsheet burn (86/2352)Failed diode wih no backsheetburn (26/2352)Hotspot issues with backsheet burn + Ribbon-ribbon solder bond with backsheet burn (1/2352)Backsheet Delamination (10/2352)Backsheet Delamination + Ribbon-ribbon solder bond failure (2/2352)
Safety failure rate at the plant level = 162/2352 = 7%
Framed - 12 Years – 1-axis Tracker
Pri
mar
y fa
ilure
mo
de
: R
ibb
on
-rib
bo
n s
old
er
bo
nd
fai
lure
wit
h b
acks
kin
bu
rnin
g
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Distribution of Reliability Failures and Degradation Losses (Model G – Site 3)
2.11.81.51.20.90.60.3
40
30
20
10
0
Degradation of Power (%/year)
Fre
qu
en
cy
Mean 0.9476
StDev 0.3110
N 285
Histogram of Degradation of Power (%/year) of Model-G ModulesNormal
Median 0.964
Both Durability and Reliability Issues (both materials and
design/manufacturing issues)
Only Durability Issues (only material issues)
Total number of modules = 285 (safety failed modules excluded) Average degradation = 0.95%/year
12 Years – 1-axis Tracker
Primary degradation mode: Solder bond degradation
No Potential Induced Degradation (PID) observed probably due to dry glass surface and/or positive bias
strings
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Distribution of Reliability Failures and Degradation Losses (Model G – Site 3)
(Safety failed modules excluded)
12 Years – 1-axis Tracker
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Distribution of Safety Failures, Reliability Failures and Degradation Losses (Model G – Site 3)
93 x 0.55 = 51% 93 x 0.45 = 42%
12 Years – 1-axis Tracker (combination of previous two slides)
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Linking Field Evaluation Data with Premium Risk Rate Calculation
A Conceptual Representation
Risk Premium Rate Calculation
Interest Rate
= Interest Rate @ Zero Risk
+ Risk Premium Rate
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0.94
2.83
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Model-G non-hotspotmodules
Model-G hotspot Modules
De
grad
atio
n R
ate
(%
/ye
ar)
Model G: Pmax degradation rate comparison between
non-hotspot and hotspot modules
31#
296#
# No. of Modules
Hotspot modules degrade at higher rates (>3 times) (Model G – Site 3)
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Best Modules Experienced Only Durability Issues (Model G – Site 3)
W P
ma
x
M P
ma
x
B P
ma
x
W F
F
M F
F
B F
F
W V
ma
x
M V
ma
x
B V
ma
x
W V
oc
M V
oc
B V
oc
W I
ma
x
M I
ma
x
B I
ma
x
W I
sc
M I
sc
B I
sc1.25
1.00
0.75
0.50
0.25
0.00
-0.25
-0.50De
gra
dati
on R
ate
(%/
yea
r)
Field Age = 12 years
Best,Median,Worst Strings- Best Modules (6 Strings; 18 Modules)
Balck Square(Median)
Blue Square(Mean)
Agua Fria (Model-G)
Pmax loss FF loss Rs increase BEST modules = 18 (safety failed modules excluded if any) Mean degradation = 0.5%/year Median degradation = 0.5%/year
Due to only intrinsic (materials) issues contributing to real wear out mechanisms
1-axis Tracker
B = Best string; M = Median string; W = Worst string Primary degradation mode: Solder bond degradation
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Worst Modules Experienced Both Reliability and Durability Issues (Model G – Site 3)
W P
ma
x
M P
ma
x
B P
ma
x
W F
F
M F
F
B F
F
W V
ma
x
M V
ma
x
B V
ma
x
W V
oc
M V
oc
B V
oc
W I
ma
x
M I
ma
x
B I
ma
x
W I
sc
M I
sc
B I
sc
9
8
7
6
5
4
3
2
1
0
De
gra
da
tio
n R
ate
(%
/y
ea
r)
Field Age = 12 years
Best,Median,Worst Strings- Worst Modules (6 Strings; 18 Modules)
Balck Square(Median)
Blue Square(Mean)
Agua Fria (Model-G)
W
Both ribbon-ribbon solder bonds failed.
1 of 2 ribbon-ribbon solder bonds failed
Zero power
WORST modules = 18 (safety failed modules included) Mean degradation = 1.8-5.6%/year Median degradation = 1.4-4%/year
Due to both intrinsic (materials) and extrinsic (design/manufacturing) issues
1-axis Tracker
Pri
mar
y fa
ilure
mo
de
: R
ibb
on
-rib
bo
n s
old
er
bo
nd
fai
lure
wit
h b
acks
kin
bu
rnin
g
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Source: IEA-PVPS-2014
Germany (cold-dry climate); 2 Years & 2 million modules
FAILURE & DEGRADATION MODES WITHOUT RISK PRIORITIZATION
Not all defects are failures: Cosmetic defects should not be considered;
Modes shall be risk prioritized for each climatic condition and each module construction type
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Souce: ASU-PRL
Arizona (hot-dry climate); 6-16 Years & 6000 modules
FAILURE & DEGRADATION MODES WITH RISK PRIORITIZATION
Not all defects are failures: Cosmetic defects should not be considered;
Modes shall be risk prioritized for each climatic condition and each module construction type
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Slide 29
• Difference between durability and reliability • Importance of durability • Outdoor durability evaluation • Indoor durability evaluation • Summary
Presentation Outline
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Slide 30
Indoor durability evaluation
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0%
20%
40%
60%
80%
100%
120%
1997-2005 2005-2007 2007-2009 2009-2011 2011-2013
Nominal rating compliance-3% tolerance compliance
Degradation rate calculation may be influenced by nameplate rating
practice which in turn is influenced by demand & supply of the market
31
# Modules
39%
mo
du
les o
ver-
rate
d
27%
mo
du
les o
ver-
rate
d
389 278 304 478 825
51%
mo
du
les o
ver-
rate
d
50%
mo
du
les o
ver-
rate
d
37%
mo
du
les o
ver-
rate
d
Under-rated modules will show POSITIVE degradation rate
Over-rated modules will show OVERLY NEGATIVE degradation rate
Cross check the degradation rate with kWh based degradation rate using Performance
Index (PI) method
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Degradation rate may depend on the country of production
32
Stark design quality variation between the regions has been observed.
• HF10 test: Region/country 3 (RL-3) has the highest and abnormal failure rate
Potential reasons: Polymeric material and/or interface issue
• Hotspot test: Region/country 2 (RL-2) has the highest and abnormal failure rate
Potential reasons: Cell quality and/or tabbing issue
• TC200 test: Almost all the regions/countries suffer
Potential reasons: Metallic material and/or interface issue
c-Si
RL = Country not identified; random order
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33
Source:
Kurtz et al, NREL, IEEE PVSC 2013; TamizhMani et al, ASU, SolarABCs report, 2013
New test Existing
Degradation rate can be decreased through beyond-Qualification tests
such as Qualification Plus, Comparative and Lifetime tests
Qualification PLUS
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Degradation rate can be decreased through beyond-Qualification tests
such as Qualification Plus, Comparative and Lifetime tests
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35
Qualification PLUS Testing
December 2013
http://www.nrel.gov/docs/fy14osti/60950.pdf (available for free downloading)
Degradation rate can be decreased through beyond-
Qualification tests such as Qualification PLUS
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Parameter Qualification Qualification PLUS
Module Testing
Duration < 3 months < 3 months
Sample size for each sequence 2 5
Thermal cycling test 200 cycles 500 cycles
Dynamic load test before the humidity freeze
sequence tests
None 1000 cycles of 1000Pa
Potential induced degradation (PID)* Not required 60°C/85%RH for 96 hours
Hot spot Test method not adequate Use ASTM E2481-06 method
Component Testing
Duration Not required < 6 months
Sample size for each sequence None 3-12
UV exposure test for encapsulants,
backsheets, connectors, and junction boxes
15 kWh/m2 @ 60oC and
humidity not controlled
224-320 kWh/m2 @ 50-70oC
and humidity controlled
Bypass diode test 1 hour 96 hours
Manufacturing Quality
Quality Management System (QMS) Not required Addition of PV-specific
requirements to ISO9001
Source: NREL, Photovoltaic Module Qualification Plus Testing, Kurtz et al, Dec. 2013 http://www.nrel.gov/docs/fy14osti/60950.pdf (available for free downloading)
* Discussed further
Qualification PLUS Testing Comparison with Qualification Testing
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Slide 37
PID No PID
Aluminum
frame
E-field
Transformerless Inverter
Potential induced degradation (PID) is a major degradation issue in humid/rainy locations
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PID: Not fully recovered
Source: J. Oh et al (ASU-PRL), IEEE PVSC 2014 (submitted)
• Only about 96% recovered • Reponses from blue photons are not
recovered
PID (aluminum method): 60°C, -600V, 88h
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Slide 39
• Difference between durability and reliability • Importance of durability • Outdoor durability evaluation • Indoor durability evaluation • Summary
Presentation Outline
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Slide 40
Summary
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Slide 41
• Differences between durability and reliability losses are defined and the definitions have been applied in the outdoor evaluations
• Importance of durability for bankability is explained • A systematic outdoor durability evaluation approach to
determine climate specific degradation rate is presented
• A few key indoor durability evaluations are presented
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Thanks for your attention!
May 2014
Theses of ASU-PRL students can be freely downloaded at:
repository.asu.edu
(search under “TamizhMani”)