Accelerated UV Test M

for Encapsulants of Photovoltaic Modules

Michael D. Kempe

National Renewable Energy Laborat

1617 Cole Blvd. Golden, CO 8040

NREL/PR-520-43309Presented at the 33rd IEEE Photovoltaic Specialist Conference held May 11-16, 20
Encapsulant Selection 

 Optically Couples Glass to C

 High Photon Transmission. Can’t Yellow Significantly Ov

 Cost Must Be Balanced Wit

Performance.

 Must Provide Good Adhesio

 Resistant to Heat, Humidity, 

and Thermal Cycling.
Light Transmission is 

Encapsulant Selection

(t pp

)

glass eTT

−

α

=

Tglass = 88.94% and is the transmission 

through 6.35 mm plate glass. 

tp is the polymer layer thicknessαp is the solar weighted photon 

absorptivity in the polymer. 

(

) ( ) pp glass t

cell

e

T

T

+

−

α

=

2

100

Light

Light
Cost and Photon Transm

are Important Selection 

The approximate cost factor relative to EVA is based on costs quoted by the manufactnegotiate a better price. The true cost factor could easily be different by a factor of two.

AM 1.5 Solar 

Weighted 

Absorptivity 

200 nm to 

1100 nm

Transmission to 

Cells through 

3.18 mm glass 

and 0.45 mm 

Encapsulant

(1/mm)

%

GE RTV615 0.000 ± 0.003 94.5 ± 0.3 4.45 PDMS, AdditDow Corning Sylgard 184 0.001 ± 0.004 94.4 ± 0.3 6.97 PDMS, AdditDow Corning 527 0.001 ± 0.003 94.4 ± 0.3 2.33 PDMS Gel, APolyvinyl Butraldehyde 0.014 ± 0.005 93.9 ± 0.4 1.50EVA 0.014 ± 0.005 93.9 ± 0.4 1.00NREL Experimental 0.025 ± 0.006 93.4 ± 0.4 1.28Thermoplastic Polyurethane 0.027 ± 0.004 93.3 ± 0.3 2.00Thermoplastic Ionomer #1 0.052 ± 0.007 92.3 ± 0.4 1.00 Copolymer oDC 700 0.067 ± 0.004 91.7 ± 0.3 0.94 PDMS, AcetiThermoplastic Ionomer #2 0.147 ± 0.007 88.4 ± 0.4 2.00 Copolymer o

Encapsulant

Approximate 

Cost 

Relative to 

EVA
Long Term UV Resistan

Evaluated in IEC Standa

 IEC 61215, 61646 and 61730-2

 “UV Preconditioning Test” 15 kWh/m

2 between 280 nm and 

 Equivalent to 17.7 days of AM 1.5 

 >5 kWh/m

2 between 280 nm and 

 Equivalent to 137 days of AM 1.5

 IEC 62108

 “UV Conditioning Test” 50 kWh/m

2 below 400 nm

 Equivalent to 45 days of AM 1.5
Lap Shear Used to Ev

Adhesion

6.35 mm

Schematic and photo o

F

≈5000 N

76.2 m

76.2 mm

19 mm
Ce Doped Glass Redu

Samples labeled “solarized” had been exposed to 114 W/m2 (30

Ci4000 weatherometer at 60oC and 60% RH.

0

102030405060708090

100

260 280 300 320 340 360 

Wavelength (nm)

Percent Transmittance

5.6 mm Old Starphire Glass5.6 mm Old Solarized Starphire6.06 mm KK Glass3 mm KK Glass3 mm Solarized KKHemispherical Tilt Irriadiance

Non-Ce Glass

AM 1.5

Ce Gla

UV-B UV-AII UV-AI
UV-B/AII Radiation R

Adhesion 8 Times Fas

Lap shear strength after exposure to 60 oC/60% RH/2.5 UV suns. to slightly different formulations from the same manufacturer.

02468

1012

1 10 100 1000 10000 

Exposure Time (hr)

Lap Shear Strength (MPa) Non-Ceriated Glass #1 Non-Ceriated Glass #2 Ce Containing Glass #2
High UV Light Transm

Increases Deadhesion

Estimated irradiance at the glass/EVA interface

0

0.20.40.60.8

1

1.2

290 300 310 320 330 340 350 360 370 3

Wavelength (nm)

Transmitted Energy (W/m2/nm)

AM 1.5 Global IrradiationStarphire Solarized 5.61 mmKrystal Klear Solarized 6.35 mmDifference Between Starphire to and 6.35mm Krystal Klear
Greater Damage is Pr

for UV Transparent G

0

0.10.20.30.40.50.60.70.80.9

1

290 300 310 320 330 340 350 3

Wavelength (nm)

Activation Spectrum (AU)

( )

∫

− λλλ λ deID B

~

(

)

B

λ

e

−

~

() ()

λ λλλ

B eIE

−

~

Action Spectrum

Activation Spectrum

Photon Damage

B=0.07 (1/nm)

A. L. Andrady, Wavelength Sensitivity in Polymer Photodegradation, Advances in Polymer Science 128, 49-94 
Other Arbitrary Action 

Give Similar Factors

Step Function Linea

At 2.5 UV suns, running 24 h/day (~4X), with 3.4 it takes 6.2 to 7.0 months to get a 20 year equiva

B =0.07 (1/nm)

λo=368 (nm)

Tefzel 0.036 (mm) 4.83 4.30 

Vintage Starphire 5.61 (mm) 3.85 3.40 

Krystal Klear 3.18 (mm) 1 1 Krystal Klear 6.35 (mm) 0.48 0.43 

Exponential Linear 

Action Spectrum
Conclusions

 IEC PV Qualification tests do not a

UV stability.

 Using highly transmissive glass in 

can increase the severity of stress exposure of the correct order of m

 Cost and light transmission must a

considered in selecting an encapsu

 The use of non-ceriated glass will 

likelihood of glass/EVA delaminatio
Acknowledgements

 This work was supported b

Department of Energy undNo. DE-AC36-99GO10337 wNational Renewable Energy