performance improvements in pv modules using...

Performance Improvements in PV Modules Using Ionomer Encapsulants

Mark JacobsonSr. Accounts Manager, DuPont EncapsulantsCleveland, OHApril 9, 2011

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DuPont Photovoltaic Solutions © DuPont

Agenda

•Encapsulant requirements

•Failure modes

•Moisture Ingress and WLC

•NREL results

•Strength enhancement

•Other benefits

•DuPont encapsulant offerings

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Examples of Required Encapsulant Attributes

Low System Cost

Durability• 25 years no delamination• Cell efficiency over life of module• Meets operating temperature requirements

Compatibility with Top Coat MaterialLow Moisture PermeabilityProtect the Cell from CorrosionHigh 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

Encapsulant Requirements for Thin Film Glass/ Glass Modules

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The Importance of Encapsulants in Module DesignCommon Causes of failure in Thin Film Modules

Tamizhmani, G., et.al.”Failure Analysis of Module Design Qualification Testing – III” 35th IEEE PVSC Proceedings, 2010, Honolulu, Hawaii

• 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)

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Minimal Wet Current Leakage After Extended Aging

Wet Current Leakage after Damp Heat Testing

Hours Damp Heat (85 oC / 85% RH)

Ele

ctric

al R

esis

tanc

e (M

Ohm

s)

Thin Film Glass-Glass module* with DuPont™ PV5400

0

50

100

150

200

250

300

350

400

0 500 1000 2000 3000

Minimum resistance required to pass IEC 61646 standard after 1000hrs damp heat

* No edge sealing (tape or caulk) used, frameless

• Excellent initial resistance

• Low resistance decline after aging

• Easy pass in IEC 61646 damp heat test

• No edge sealing or frame required

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The Benefits of DuPont™ PV5400 Ionomer

• Provides excellent protection and insulation for electronic components over the module lifetime

• Introduces the possibility of a stable module without edge seal compounds

• Enables low cost frameless module design

Glass laminate moisture ingress after 2000hr DH

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 2 4 6 8 10 12 14 16 18 20Distance from Edge (cm)

% M

oist

ure

EVA

DuPont™ PV 5400 Ionomer

1014Cross-linked EVA

1016DuPont™ PV5400 Ionomer

Surface ResistivityASTM D257 23C, 50%RH

Encapsulant Material

Low Moisture Ingress

High Resistivity Polymer

Diffusion coefficient is 4-6x less than EVA encapsulant Equilibrium Moisture level is half of EVA encapsulants

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Why Ionomer? Performance in Independent Studies“For the hydrocarbon based materials, only the ionomer is demonstrating UV

stability for 10X CPV applications”

M.D. Kempe et. al., NREL (US), “Accelerated StressTesting of Hydrocarbon-based Encapsulants for Medium Concentration CPV Applications”, 34th IEEE PVSC, 2009, Philadelphia

“Samples with a quartz face or soda-lime glass in combination with an ionomer encapsulant did not degrade.” (unlike glass/SiO 2 barrier or EVA)

P.Hacke et. al., NREL (US), ECN (NL), “Characterization of Multi-Crystalline Silicon modules with System Bias Voltage Applied in Damp Heat”, 25th EU PVSEC, 2010, Valencia,

Fig. 10. Loss of pseudo fill factor (FF) and open-c ircuitvoltage (Voc) after 140 h at 45°C/30% RH with –1000 Vbias applied to the active layer for five mini modu leconstructions (plus controls).

Figure 8. QE- and solar-weighted transmission for athermoplastic polyurethane (TPU), an ionomer, and p olyvinylbutyral (PVB) as a function of exposure to 42 UV sun s. Thechanges in YI for the ionomer, PVB and TPU correlat e well withchanges in optical transmission.

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High Modulus Enables Low Cost Mounting

4 Clamp Module: +2.4 kPa 1 hr 22 C 3.2 mm Glass / t mm Encapsulant / 3.2 mm Glass

20

25

30

35

40

45

50

0.2 0.4 0.6 0.8 1

Encapsulant Thickness, t (mm)

Max

imum

Prin

cipa

l Gla

ss S

tres

s (M

Pa) PV 5400: 150 mm Clamp

PV 5400: 70 mm Clamp

PVB: 150 mm Clamp

PVB: 70 mm Clamp

65% Breakage Probability

3% Breakage Probability

• Glass stress minimally impacted by encapsulant thickness

• Glass stress is sensitive to clamp size

• Ionomer laminate with 150 mm clamp strong enough when used with all annealed glass

3 “Layers” for Panel• Glass-Encapsulant-Glass

Four clamp support system• Aluminum clamps with EPDM gaskets• Clamps fixed at center points

Finite Element Analysis of Module Mechanical Properties

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Other Benefits of Unique Ionomer Chemistry

Ion (X) exchanged with Na, Zn, Mg

COOH

COOH

COOH

COOH

COOH

Ionomer Chemical Structure

Acid-functionalized hydrocarbon copolymer

• No potential for acetic acid formation –minimizes possibility of corrosion

• 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

• Melt temperature and flow enable fast lamination on existing vacuum laminators

• Easy handling, no need to refrigerate or interleaf sheeting

COOH

COOH

COO-

COO-

X++

COOX

-OOC

++X OOCIonomer clusters form pseudo-cross-links

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• DuPont TM PV5200 series (PVB sheet)

• DuPont TM PV5300 series (High Clarity Ionomer sheet)

• DuPont TM PV5400 series (Low Moisture Ionomer sheet)

• DuPont™ PV8600 series (Modified Ionomer sheet)

• DuPont TM Elvax® PV1000 series (EVA Resin) - sold into PV market for 30 years

Continuous pipeline of innovative encapsulants

DuPont now Offers Five Encapsulant solutions

Developed by the leader in the glass industry with over 60 years of innovation

Developed by DuPont-Mitsui

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Copyright © 2012 DuPont or its affiliates. All rights reserved. The DuPont Oval Logo, DuPont™, The miracles of science™and all products denoted with ™ or ® are registered trademarks or trademarks of E. I. du Pont de Nemours and Company or its affiliates.

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