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The influence of different climates
on module performance
Hui Shen, Qiangzhong Zhu, Zhichao Ji, Jianmei Xu,
Pierre J.Verlinden, Wei Zhou, Zhiqiang Feng
October 4th 2016
目录Catalogue
Outline
1. Field application challenges
Problem analysis
2. Reliability test: Region 1 (hot and humid)
2.1 Electrical performance of Modules after DH and HAST
2.2 Mechanism analysis by HAST test
3. Reliability test: Region 2 (hot and dry)
3.1 Mechanical load performance of modules
3.2 Mechanism analysis of modules after TC and TS test
4. Conclusions
目录Catalogue
1. Field application challenges
Outline
4
EVA & backsheetyellowingSnail TrackPID
Delamination Backsheet crack
1. Field Application Challenges
Hot spot
5
Fig 2. Map of IrradiancesFig 1. Map of World climates
1. Field Application Challenges
Do different types of PV module’s failures co-relate to specific climates?
What is the mechanism of failure in tropical and desert regions?
How do we choose the most suitable modules in harsh environments?
6
1.1 Analysis of module data
Place Climate
Yearly Mean
Insolation
/kwh*m-2
Yearly Mean
Temperature
/℃
Daily Mean
Temperature
Range /℃
Mean
Precipitation
/mm*year-1
Averaged Relative
Humidity /%
Shenzhen Subtropical Monsoon 1427 25.7 4.7 1800 75.6
DunhuangTemperate continental
(Arid region)1704 8.7 15.2 55 36.7
-20
-10
0
10
20
30
0
20
40
60
80
100
1 2 3 4 5 6 7 8 9 101112
Precipitation Temperature
Pre
cip
itatio
n /m
m
Tem
pera
ture
/℃
Climagraph of Dunhuang
Month0
5
10
15
20
25
30
0
100
200
300
400
1 2 3 4 5 6 7 8 9 101112Precipitation Temperature
Pre
cip
itatio
n /m
m
Tem
pera
ture
/℃
Climagraph of Shenzhen
Month
7
Place Module Type Layout Quantity Glass Encapsulant Backsheet
ShenzhenPolycrystalline
12*3 3pcs 3.2mm
patterned glassEVA
TPT
38/75/38umDunhuang 11*3 2pcs
1.1 Analysis of module data
• Cell blackening from EL image
Shenzhen(hot and humid)
• Glass abrasion• Cell cracking• Reduced the adhesive
strength between TPT layers
Dunhuang(hot and dry)
8
Electrical performance
1.1 Analysis of module data
-30 -25 -20 -15 -10 -5-30
-25
-20
-15
-10
-5
Perf
orm
an
ce d
eg
rad
ati
on
(%)
Pmax degradation(%)
FF
Voc
Isc
Vpm
Ipm
Pmax
Dunhuang(hot and dry)
Shenzhen(hot and humid)
Module 1 2 3 4 5
Fig. 1 Electrical performance of modules in Shenzhen and Dunhuang
0 5 10 15 200.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Cu
rrre
nt/
A
Voltage/V
Module 4
Module 5
Dunhuang( hot and dry)
Isc
Fig. 3 IV curve of Dunhuang modules
0 5 10 15 200.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Cu
rren
t /A
Voltage /V
Module 1
Module 2
Module 3
Shenzhen(hot and humid)
FF
Fig. 2 IV curve of Shenzhen modules
9
Resistance between
electrodes
(front side)
Resistance between
electrodes
(back side)
Cell 1 Cell 2 Cell 3 Cell 1 Cell 2 Cell 3
Shenzhen 477 108 101 63 60 61
Dunhuang 68 55.6 55.3 55.8 55.7 54.4
1.1 Analysis of module data
Electrical performance
3
2
1
Dunhuang
2
1
3
Shenzhen
Cell temperature of Shenzhen modules is not uniform under 8A current.
The resistance between electrodes on the front side in modules from Shenzhen greatly increased.Acetic acid produced by the moisture and UV could affect the solder
performance.
Cell Resistance:
IR image of modules under 8A current
10
1.1 Analysis of module data
Electrical performance
Dunhuang(hot and dry)
Si
Ag
Ag3Sn
Sn
Cu
Pbd ≈ 2.6um
𝑑 = 𝑑0 + 𝐷0exp −𝑄
𝑅𝑇𝑡 [1]
[1] Chen W. H.,Yu, C. F.,Cheng,H.C., Tsai Yu-min,Lu S.T., Microelectronics Reliability, 2013, 53, 30-40
Thickness of Intermetallic compound (IMC):
Shenzhen Dunhuang
Fig.1 IR image of modules under 8A current
Fig.2 Cross-sectional view of ribbon
Shenzhen(hot and humid)
Si
Ag
Ag3Sn
Sn
Cu
Pbd ≈ 4um
目录Catalogue
Outline
2. Reliability test in hot and humid environment
2.1 Electrical performance of Modules after DH and HAST
2.2 Mechanism analysis by HAST test
12
2.1 Electrical performance of Modules after DH and HAST
DH 0 DH 1000 DH 2000 DH 3000-3
-2
-1
0
Ave
rag
e F
F d
eg
rad
ati
on
(%)
Damp Heat (DH) test cycles
Dual-glass modules
Traditional modules
DH0 DH1000 DH2000 DH3000-7
-6
-5
-4
-3
-2
-1
0
Avera
ge Isc d
eg
rad
ati
on
(%)
Damp Heat (DH) test cycles
Dual-glass modules
Traditional modules
1. Damp Heat 3000h (85℃, 85%R.H.)
Dual-glass modules
Traditional modules
Fig.1 Electrical performance of traditional module and dual-glass module
13
2.1 Electrical performance of Modules after DH and HAST
1. Damp Heat 3000h (85℃, 85%R.H.)
Traditional module:Dual-glass module
Traditional module
Fig.2 Yellowing index of modulesFig.3 Corrosion in the bus bar region after DH 3000h
Moisture and oxygen penetration, through the backsheet, lead to EVA aging and yellowing , and to corrosion in the bus bar.
14
0 96 192 288 384 480 576-100
-80
-60
-40
-20
0
Pm
ax d
egra
da
tion
(%
)
HAST (h)
TM (EVA with high VAc)
DG (EVA with high VAc)
DG (POE)
0 96 192 288 384 480 576
-60
-40
-20
0
FF
de
gra
da
tio
n(%
)
HAST (h)
TM (EVA with high VAc)
DG (EVA with high VAc)
DG (POE)
2. Highly Accelerated Stress Test (HAST):121℃,100% R.H.
2.1 Electrical performance of Modules after DH and HAST
The FF degradation and power loss of the traditional module, compared with Dual-glass modules, is
clear.
The trend of power loss in Dual-glass modules using EVA was almost the same as in modules using
POE. The power is reduced to about 18% after HAST 576h.
15
Test TM SamplesResistance between electrodes
(front side) /mΩ
Resistance between electrodes
(backside) /mΩ
InitialEVA with high
VAc(vinyl acetate)26.7 14
Hast 576h
EVA with high VAc 43.9 907
EVA with low VAc 41.9 844
POE 40.4 909
DH 3000 EVA with high VAc 48.5 289
Resistance between electrodes in traditional modules after reliability testing
The power reduction is related to the resistance between electrodes (backside) after HAST and DH test.
In the field, the resistance degradation seems to appear on the front side. UV and moisture act together in the field to accelerate the degradation of front EVA, affect the
activation energy and solder performance.
Future research will add the UV factor in the environmental chamber to simulate field conditions.
2.1 Electrical performance of Modules after DH and HAST
16
2.2 Mechanism analysis by HAST test
Hast 576h TM (EVA with high VAc)
TM (EVA with low VAc)
DG(EVA with low VAc)
EL image
IR image under 8A current
The traditional modules using EVA with high VAc are going black near the ribbon.
In traditional modules using EVA with high Vac, almost all the solder points have degraded badly.However the traditional module using EVA with low VAc, only have some degradation.
17
Hast 576h: 121℃,100%R.H.
POE
d≈5um
EVA with high VAc
d≈13um
EVA with low VAc
d≈6um
Acetic acid
2.2 Mechanism analysis by HAST test
The thickness of Ag3Sn increased with rising VAc. Acetic acid could decrease the reaction activation energy and accelerate the growth of Ag3Sn.
Ag3Sn
Cu
Pb
Ag
Ag3Sn
Cu
Pb
Ag
Ag3Sn
Cu
Pb
Fig. 1 Cross section view of ribbon in TM
18
H2O
Hast 576h: 121℃,100%R.H.
2.2 Mechanism analysis by HAST test
The thickness of Ag3Sn reduced along the direction of moisture permeation.
Traditional module using POE
Water influence
Ag3Sn thickness reduce
Si
AgAg3SnSn-Pb
Cu
19
Traditional modules using EVA with high VAc
d ≈ 3um
Hast : 121℃,100%R.H. 96h Oven: 121℃, 96h
H2O
2.2 Mechanism analysis by HAST test
After HAST 96h, the thickness of Ag3Sn is greater than after oven aging test.
Si
AgAg3Sn
Sn
Cu
Pb
Si
AgAg3Sn
Sn
Cu
Pb
20
How to recreate the cracking between Ag3Sn and Pb-Sn alloy at front side of cells in the Shenzhen modules?
Thickness of Ag3Sn
Temperature
Acetic acid H2O
Si
Ag
Ag3Sn
Sn
Cu
Pb
Cracking in the field
2.2 Mechanism analysis by HAST test
TC stress? UV factor?
目录Catalogue
3. Reliability test in hot and dry environment
3.1 Mechanical load performance of modules
3.2 Mechanism analysis of modules after TC and TS test
Outline
22
TM
Glass
EVACells
EVA, Back sheet
3.1 Mechanical load performance of modules
The middle layer of a structure is the “stress
neutral layer”, according to
structural mechanics theory.
In a 2.5+2.5mm dual-glass structure, the cells are located at the position of “stress neutral layer”. During bending, the mechanical stress applied to the cells is negligible.
Longitudinal symmetry plane
The symmetry axis of cross section
Neutral axis Neutral layer
Stress analysis
In TM, the cells are located far from the “stress neutral layer” and the cells bear the maximum stress during bending.
Dual-glass is a symmetrical “sandwich” structure, providing better protection to cells
DG
2.5mm toughened Glass
2.5mm toughened Glass
Cells
EVANeutral Fiber
Cells
Fig.1 structure diagram Fig.2 structure of DG modules Fig.3 structure of traditional modules
23
Frame module DG module
EL after test for 3weeks
Power loss(%) -1.8 -0.1
Land Movement Simulation
Land subsidence: 150mm
3.1 Mechanical load performance of modules
1. Land Movement Simulation
2. Mechanical Load test (5400Pa)
The power loss was for both less than 0.5%;
Cell micro-cracking appeared in traditional
modules.
24
3.2 Mechanism analysis of modules after TC and TS test
TC0 TC200 TC400 TC600
-4
-3
-2
-1
0
Pm
ax
de
gra
da
tio
n(%
)
TC(Cycles)
Traditional Modules
Dual-glass modules
TC0 TC200 TC400 TC600
-2.0
-1.5
-1.0
-0.5
0.0
FF
de
gra
da
tio
n(%
)
TC(Cycles)
Dual-glass modules
Traditional modules
1. Thermal Cycle 600
Dual-glass modules’ power and FF degradation trend is slower than traditional modules in TC test.
25
TS500 TS1250 TS2000 TS2750
-14
-12
-10
-8
-6
-4
-2
0
2
Traditional modules
A
ve
rag
e P
max d
eg
rad
ati
on
(%)
Thermal Shock Tests Cycles
Dual-glass modules
Due to Rs
2. Thermal shock (TS3000)
Traditional module
Finger broken
Broken interconnections
Dual-glass moduleVS.
TS500 TS1250 TS2000 TS2750
0
10
20
30
40
50
60
Avera
ge R
s d
eg
rad
ati
on
(%)
Thermal Shock Tests Cycles
Traditinal modules
Dual-glass modules
3.2 Mechanism analysis of modules after TC and TS test
Fig.1 Electrical performance after TS test
Fig.2 EL of the traditional module Fig.3 EL of the dual-glass module
26
0 20 40 60 80
-40
-20
0
20
40
60
80
100
120
Tem
pera
ture(℃
)
Time(Min)
Chamber
TM
DG
Back surface
Material Thickness (d)/mm
Density (ρ)/g/cm3
specific heat capacity(C)/KJ/Kg/K
Glass 2.5 2.35 0.75
Backsheet 0.3 1.37 2.2
Ramp rate(Max)℃/min
Ramp rate(Average)℃/min
Chamber 190 5.25
Traditional module 94 4.98
Dual-glass module 56 3.45TS:-40~110℃
3.2 Mechanism analysis of modules after TC and TS test
QT
SdC
Fig.1 Temperature change in the TS chamber
Table.1 Ramp rate of the modules and the TS chamber
Table.2 Parameters of the formula
27
0 20 40 60 80
-40
0
40
80
120
Tem
pera
ture(℃
)
Time(Min)
Chamber
Back surface
Inside
Traditional Module
0 20 40 60 80
-40
0
40
80
120
Tem
pra
ture
(℃)
Time(Min)
Chamber
Back surface
Inside
Dual-glass Module
Dual-glass and traditional modules have almost the same heat conduction performance.The result is essentially in agreement with the theoretical calculation.
TS:-40~110℃TS:-40~110℃
3.2 Mechanism analysis of modules after TC and TS test
Fig.1 Traditional modules Fig.2 Dual-glass modules
Materialheat conductivity coefficient (K)
/ W/(m*K)Thickness (d)
/mmThermal Resistance(R)
/m2*K/W
Glass 1.04 2.5 0.0024
Backsheet 0.14 0.3 0.0021
目录Catalogue
1. The failure of PV modules is climate dependent.
2. In hot and humid climates:
TC stress, UV and DH factors influence the power degradation.
Preventing moisture from entering the modules is important.
Dual-glass modules provide better protection for cells against
moisture.
3. In hot and dry climates:
Dual-glass modules, with their symmetrical structure, protect the
cells from mechanical stress.
Dual-glass modules have a slower rate of temperature change.
4. Conclusion
Thank You!
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