the influence of different climates on module performance · pdf filethe influence of...

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


• 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


-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



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


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



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




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


Si

Ag

Ag3Sn

Sn

Cu

Pbd ≈ 4um

目录Catalogue

Outline

2. Reliability test in hot and humid environment



12


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


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.


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.


16


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


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.


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


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


TC stress? UV factor?

目录Catalogue

3. Reliability test in hot and dry environment



Outline

22

TM

Glass

EVACells

EVA, Back sheet


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


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


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


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℃


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℃


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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