Performance Improvements in PV
Modules Using Ionomer Encapsulants
Mark Jacobson
Sr. Accounts Manager, DuPont Encapsulants
Cleveland, OH
April 9, 2011
2
Agenda
•Encapsulant requirements
•Failure modes
•Moisture Ingress and WLC
•NREL results
•Strength enhancement
•Other benefits
•DuPont encapsulant offerings
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3
Examples of Required Encapsulant Attributes
Encapsulant Requirements for Thin Film Glass/ Glass Modules
Low System Cost
Durability
•
•
•
25 years no delamination
Cell efficiency over life of module
Meets operating temperature requirements
Compatibility with Top Coat Material
Low Moisture Permeability
Protect the Cell from Corrosion
High Resistivity = Low Current Leakage
•
•
Safety requirement
Important in maintaining cell efficiency over
lifetime
Ease of Processing with High Thru-put
•
•
Autoclave
Vacuum laminator
No Lamination Defects
•
No bubbles
Ease of Handling
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The Importance of Encapsulants in Module Design
Common Causes of failure in Thin Film Modules
• Failure occurs predominantly in
the damp heat test (85C/85%RH,
1000hrs)
• The cause of failure is typically due
to excessive wet current leakage
after aging (wet resistance)
• Current leakage is most often
dependent on module package
integrity (encapsulant, J-box,
front/back cover)
Tamizhmani, G., et.al.”Failure Analysis of Module
Design Qualification Testing – III” 35th IEEE PVSC
Proceedings, 2010, Honolulu, Hawaii
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Minimal Wet Current Leakage After Extended Aging
Wet Current Leakage after Damp Heat Testing
Electrical Resistance (M Ohms)
400
Thin Film Glass-Glass module* with DuPont™ PV5400
• Excellent initial
resistance
350
300
• Low resistance
decline after aging
250
200
• Easy pass in IEC
61646 damp heat test
150
Minimum resistance required to
pass IEC 61646 standard after
1000hrs damp heat
100
50
0
0
500
1000
2000
o
Hours Damp Heat (85 C / 85% RH)
* No edge sealing (tape or caulk) used, frameless
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3000
• No edge sealing or
frame required
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The Benefits of DuPont™ PV5400 Ionomer
Low Moisture Ingress
Glass laminate moisture ingress after 2000hr DH
0.45
Diffusion coefficient is 4-6x less than EVA encapsulant
Equilibrium Moisture level is half of EVA encapsulants
% Moisture
0.40
0.35
0.30
EVA
0.25
• Provides excellent protection
and insulation for electronic
components over the module
lifetime
DuPont™ PV 5400 Ionomer
0.20
0.15
0.10
0.05
0.00
0
2
4
6
8
10
12
14
16
18
Distance from Edge (cm)
High Resistivity Polymer
Encapsulant
Material
Surface Resistivity
DuPont™ PV5400
Ionomer
1016
Cross-linked EVA
1014
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ASTM D257 23C, 50%RH
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• Introduces the possibility of a
stable module without edge seal
compounds
• Enables low cost frameless
module design
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Why Ionomer? Performance in Independent Studies
“Samples with a quartz face or soda-lime glass
in combination with an ionomer encapsulant did
not degrade.” (unlike glass/SiO2 barrier or EVA)
Fig. 10. Loss of pseudo fill factor (FF) and open-circuit
voltage (Voc) after 140 h at 45°C/30% RH with –1000 V
bias applied to the active layer for five mini module
constructions (plus controls).
“For the hydrocarbon based materials,
only the ionomer is demonstrating UV
stability for 10X CPV applications”
Figure 8. QE- and solar-weighted transmission for a
thermoplastic polyurethane (TPU), an ionomer, and polyvinyl
butyral (PVB) as a function of exposure to 42 UV suns. The
changes in YI for the ionomer, PVB and TPU correlate well with
changes in optical transmission.
M.D. Kempe et. al., NREL (US), “Accelerated StressTesting of
P.Hacke et. al., NREL (US), ECN (NL), “Characterization of Multi-Crystalline
Hydrocarbon-based Encapsulants for Medium Concentration CPV
Silicon modules with System Bias Voltage Applied in Damp Heat”, 25th EU
Applications”, 34th IEEE PVSC, 2009, Philadelphia
DuPont
Photovoltaic
Solutions
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DuPont
PVSEC, 2010, Valencia,
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High Modulus Enables Low Cost Mounting
Finite Element Analysis of Module
Mechanical Properties
3 “Layers” for Panel
• Glass-Encapsulant-Glass
Four clamp support system
• Aluminum clamps with EPDM gaskets
• Clamps fixed at center points
4 Clamp Module: +2.4 kPa 1 hr 22 C
3.2 mm Glass / t mm Encapsulant / 3.2 mm Glass
Maximum Principal Glass Stress
(MPa)
50
• Glass stress minimally impacted
by encapsulant thickness
45
65% Breakage Probability
40
PV 5400: 150 mm Clamp
35
PV 5400: 70 mm Clamp
PVB: 150 mm Clamp
30
• Glass stress is sensitive to clamp
size
PVB: 70 mm Clamp
25
3% Breakage Probability
20
0.2
0.4
0.6
0.8
1
Encapsulant Thickness, t (mm)
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• Ionomer laminate with 150 mm
clamp strong enough when used
with all annealed glass
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Other Benefits of Unique Ionomer Chemistry
Ionomer Chemical Structure
COOH
COO
H
• No potential for acetic acid formation –
minimizes possibility of corrosion
COO
H
COOH
COOH
Acid-functionalized hydrocarbon
copolymer
Ion (X) exchanged
with Na, Zn, Mg
• Inherent adhesion to glass (no adhesion
promoters needed)
• Excellent adhesion to a variety of metals
(such as Al, chrome and Zn)
• Excellent adhesion retention due to low
moisture ingress
COOX
COOH
• Melt temperature and flow enable fast
lamination on existing vacuum laminators
COOX++
-OOC
COOH
++X
OOC
COOIonomer clusters form pseudocross-links
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• Easy handling, no need to refrigerate or
interleaf sheeting
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DuPont now Offers Five Encapsulant solutions
• DuPontTM PV5200 series (PVB sheet)
• DuPontTM PV5300 series (High Clarity Ionomer sheet)
• DuPontTM PV5400 series (Low Moisture Ionomer sheet)
• DuPont™ PV8600 series (Modified Ionomer sheet)
• DuPontTM Elvax® PV1000 series (EVA Resin)
- sold into PV market for 30 years
Continuous pipeline of innovative encapsulants
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Developed by
DuPont-Mitsui
Developed by
the leader in
the glass
industry with
over 60 years
of innovation
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