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Acceleration of Degradation by HAST and air-HAST in c-Si PV Modules

Tadanori Tanahashi2, Soh Suzuki1, Takuya Doi2, and Atsushi Masuda2 (1ESPEC CORP., 2AIST)

SAYURI-PV 2016 (Tsukuba, JP) 2016/10/4

Main parts of this presentation have been published in The Japanese Journal of

Applied Physics, Vol. 55, No. 2, p. 22302, Feb. 2016.

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2

EL Images of c-Si PV Modules Exposed in Identical Outdoor Site (ca. 30 Years)

Mfg. in 1983 Pmax: -40.5% Isc: -19.0% Voc: -1.2% FF: -25.6% (vs. Name Plate)

Mfg. In 1984 Pmax: -43.9% Isc: -9.5% Voc: -0.6% FF: -31.7% (vs. Name Plate)

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-100

-80

-60

-40

-20

0

% C

han

ge o

f IV

Par

amet

er

Model: a Model: g Model: d Model: e Model: f Model: b

% Changes of PV Parameters in Long-Term Exposed c-Si PV Modules under Outdoor Conditions

Large Reduction of Isc & FF

A Little Reduction of Voc

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0.2

0.4

0.6

0.8

1.0

No

rmal

ize

d P

max

A-1 B-1 C E F G H I J K M N 0

Massive Survey for the Degradation Profiles of Commercial PV Modules Extended Damp Heat Test: 13 Models (multi- / mono-c-Si, FY2011~)

Initial Value

DH: 1,000 h

DH: 2,000 h

DH: 3,000 h

Mean +/- SD (N = 10 or 5)

5% P / F Criteria

Asia Standards and Conformity Assessment Promoting Project (METI), 2011-2014

Mono-c-Si

Multi-c-Si

4

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0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1000 2000 3000

Pmax

Isc

Voc

FF

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1000 2000 3000

Pmax

Isc

Voc

FF

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1000 2000 3000

Pmax

Isc

Voc

FF

Massive Survey for the Degradation Profiles of Commercial PV Modules Extended Damp Heat Test: 13 Models (multi- / mono-c-Si, FY2011~)

Asia Standards and Conformity Assessment Promoting Project (METI), 2011-2014

Model C Model I Model E

Duration of DH Test (h)

No

rmal

ize

d P

V P

aram

ete

r

Large Reduction of Isc & FF

A Little Reduction of Voc Similar Reduction

with those Observed in Outdoor Exposed PV Modules

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Motivation

Hygrothermal Stress Test defined in IEC 61215: 10.13 Damp Heat Test: 85oC / 85% rh, 1,000 h

“To determine the ability of the module to withstand the effects of long-term penetration of humidity”

Moisture Ingress (Penetration of Humidity): -> Corrosion, Delamination, Discoloration, Loss of Elasticity / Adhesion in Polymer Materials, and Other failures ====> Power Loss of PV Modules (> 2,000 h)

Objectives To Precisely Address the Effects of Hygrothermal Stress (i.e., Identification of Power-Loss Mechanisms) To Establish a Novel-Accelerating-Hygrothermal Stress Test (Time Saving, Actual Stress reflecting field exposure)

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Encapsulant (EVA)

Glass

Encapsulant (EVA) PV cell

Backsheet（T / P / T)

Mini-Module Architecture

No Frame / No Edge Seal

= practically “No Guard” to Moisture Ingress

Mini-Module (1 cell)

Experiment: c-Si PV Mini-Module

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Power Loss with Hygrothermal Stresses

Time (h)

D P

max

(%

)

Mean +/- Std. Error

85 / 85

95 / 95

HAST 105 /100

HAST 120 /100

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Artificial Degradation in HAST: 120 / 100 (200 h)

PVF (T)

PET

PVF (T)

EVA Module Architecture

Delamination of Backsheet Component(s)

EVA

Glass

EVA PV cell

Backsheet（T / P / T)

View from Backside of PV Module

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Temp. (oC)

Humid. (% RH)

Total Pressure(kPa [A])

Water Vapor P. (kPa [A])

Air Pressure (kPa [A])

Air P. / Water V. Ratio

Air P. / Total P. Ratio

Atmos. 25 60 101.3 1.6 99.7 62.3 0.98

DH 85 85 101.0 49.2 51.8 1.1 0.51

HAST

105 100 120.8 120.8 0 0 0

110 85 121.6 121.6 0 0 0

120 100 198.5 198.5 0 0 0

air-HAST

110 85 249.8 121.6 128.2 1.1 0.51

These values (Pressures, Ratios) are calculated from ideal gas composition.

Hygrothermal Conditions (DH, HAST, air-HAST)

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HAST / air-HAST

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Power Loss under DH / HAST / air-HAST Stress Conditions

Jpn. J. Appl. Phys. 55 (2): 22302, 2016

Rate of Power-Loss in HAST and air-HAST was ca. 5-Folds that in DH Stress Test.

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Correlation of Power Loss (ΔPmax) with the Decreases in PV Parameters (ΔVoc, ΔIsc, and ΔFF)

Voc

Voc

Isc

Isc

FF

FF

Jpn. J. Appl. Phys. 55 (2): 22302, 2016

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I–V Curves for Three hygrothermal Stress Tests

DH 85/85 air-HAST110/85 HAST 110/85

In severe degraded conditions, n (diode factor) is Over 2, due to Non-Uniform Contact Resistance .

Ref: A. S. H. van der Heide, A. Schönecker, J. H. Bultman, and W. C. Sinke, “Explanation of high solar cell diode factors

by nonuniform contact resistance,” Prog. Photovoltaics Res. Appl., vol. 13, no. 1, pp. 3–16, Jan. 2005.

Jpn. J. Appl. Phys. 55 (2): 22302, 2016

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Dark I–V Curves at 0 and 800 h after HAST or air-HAST

Jpn. J. Appl. Phys. 55 (2): 22302, 2016

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Jpn. J. Appl. Phys. 55 (2): 22302, 2016

Contents of Acetate Ions in the Peripheral and Central Encapsulant Regions of PV Modules

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Jpn. J. Appl. Phys. 55 (2): 22302, 2016

Visual Images of PV Modules after the Exposure to DH stress, HAST, or air-HAST

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1 2

3 4

5

1 2

3 4

1 2

3 4

5

Colorimetric Positions in c-Si PV Module

Front w/o Cell

Front w/ Cell

Rear

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Brightness : z Difference in Saturation: r Hue: f

Color Difference Level = Distance (d)

L*a*b*Color Space Cylindrical (Axis) System Rectangular Coordinate System

A = Origin B = Terminal

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Jpn. J. Appl. Phys. 55 (2): 22302, 2016

Discoloration in the Front Sites w/o Cell of tested PV Modules

A = Origin (Initial State)

DH

HAST

air-HAST

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Jpn. J. Appl. Phys. 55 (2): 22302, 2016

Increase in Distance (d) in PV modules during the Exposure to DH stress, HAST, and air-HAST Conditions

DH – air-HAST: Apparent Acceleration Factor (AF) Identified by Discoloration Rates in All Sites was Approximately 10-Folds.

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Jpn. J. Appl. Phys. 55 (2): 22302, 2016

Brightness (z) Hue (f) Saturation (r)

Changes in three color attributes (z, f, and r) in PV Modules during the Exposure to DH stress, HAST, and air-HAST Conditions

Front w/o Cell

Rear

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http://dx.doi.org/10.1016/j.polymdegradstab.2013.06.024

in HAST Condition: Inert Conditions due to Exhaust of Air Thermal Oxidation of EVA is Completely Restricted by Inert Conditions

in DH / air-HAST conditions: Oxygen penetrated into EVA Thermal Oxidation of EVA was Occurring with the Penetrated Oxygen

DLO: Diffusion Limited Oxidation M. C. Celina, “Review of polymer oxidation and its relationship with materials performance

and lifetime prediction,” Polym. Degrad. Stab, vol. 98, no. 12, pp. 2419–2429, 2013.

We assume that the ‘Thermal Oxidation’ of EVA proceeded under DH / air-HAST conditions, but not under HAST condition

Of Course, Thermal Oxidation is a Common Reaction Observed in Outdoor Conditions Then, We Should Address the Precise Effect of Oxygen on Discoloration of EVA

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Summary

- air-HAST (110 oC/85% rh, containing air) can accelerate the power-loss,

the accumulation of acetate ions in the front EVA, the discoloration of the encapsulant

similarly to the DH stress test (85 oC/85% rh).

- HAST (110 oC/85% rh, non-containing air) can accelerate the power-loss,

the accumulation of acetate ions in the front EVA, the discoloration of the encapsulant

similarly to the DH stress test (85 oC/85% rh).

- The required duration of the DH stress test will at least be significantly shortened using air-HAST, but not HAST.

X

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