Energy and Power Engineering, 2013, 5, 455-458 Published Online September 2013 (
High Voltage Stress Impact on P Type Crystalline Silicon
PV Module
Han-Chang Liu*, Chung-Teng Huang, Wen-Kuei Lee, Mei-Hsiu Lin
Green Energy and Environment Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
Email: *
Received July 18, 2013; revised August 18, 2013; accepted August 25, 2013
Copyright © 2013 Han-Chang Liu et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The effects of the high voltage stress and other environmental conditions on crystalline silicon photovoltaic module
performance have not been included in the IEC 61215 or other qualification standards. In this work, we are to evaluate
the potential induced degradation on p type crystalline silicon PV modules by three cases, one case is in room tempera-
ture, 100% relative humidity water bath, another is in room temperature, the front sheet coverage with aluminum foil
and the other is in the 85˚C, 85% relative humidity climate chamber. All the samples are applied with the 1000 V bias
to active layers, respectively. Our current-voltage measurements and electroluminescence results showed in these mod-
ules power loss of 37.74%, 11.29% and 49.62%, respectively. These test results have shown that among high voltage
effects the climate chamber is the harshest and fastest test. In this article we also showed that the ethylene vinyl acetate
volume resistivity and soda-lime glass ingredients are important factors to PID failure. The high volume resistivity
which is more than 1014 ·cm and Na less contents glass will mitigate the PID effect to ensure PID free.
Keywords: Potential Induced Degradation; High Voltage; Volume Resistivity
1. Introduction
In photovoltaic (PV) solar modules, reliability is the very
important issue for solar power performance, as light
induced degradation is a well-known phenomenon. It has
long been included in the performance guarantees offered
by producers in the industry or the calculations of project
developers and system operators. Light induced degrada-
tion can cause an approximate 2% decrease in system
performance in the first few hours of operation of any
new PV installation. In 2005, a new form of performance
degradation began to be noticed and now called potential
induced degradation (PID) [1] which is high voltage
stress effect in negative potential field relative to ground.
With the more and more growing PV system and in-
creasing system voltages the PID effects are more seri-
ously and the leakage currents are the characterizations.
Possible pathways for the leakage currents from the en-
capsulated cell to the frame are described by J. A. del
Cueto [2]. The domain pathway to cause PID is via the
front sheet as glass to the frame. Higher leakage currents
can be caused by water entering the solar module causing
the encapsulation material to become more conductive.
So far the potential degradation mechanism is not
monitored by the typical PV tests listed in IEC 61215 [3].
Some researchers were trying to find out it. It is known
that metal ions such as Na+ formed from the oxides of the
module glass can drift toward the cell if the cell is biased
negatively [4]. Recently P. Hacke et al. found the in-
creased Na concentrations in the surface and sub-surface
area of PID affected samples were shown by secondary
ion mass spectroscopy (SIMS) [5] and Na precipitates
were found on the surface of such samples [6]. M.
Schütze et al. show that PID can also be caused by other
ions usually not present in photovoltaic modules indicat-
ing that the chemical nature of the ions is not relevant for
PID [7]. The Dr. Liu et al. in their study directly verified
that the PID caused by Na+ from their saline water bath
experiment [8]. Until now, there is no agreement with
evidence that observed metal concentration increasing in
the vicinity or inside the cell is responsible for shunting
of PID affected modules. The effect of the high voltage
and other environmental conditions on module perform-
ance has not been included in the IEC61215 or other
qualification standards. In this work we discussed the
PID effects in different environmental conditions. The
case one is 100% relative humidity (RH) water bath, an-
other is covered with conductive aluminum foil and the
other is tested in the 85˚C/85% RH chamber to provide
*Corresponding autho
opyright © 2013 SciRes. EPE
the different test methods for PV manufacturer to ensure
their solar cell modules to have PID free.
2. Experimental
Three commercial silicon PV modules with 6 × 10 mc-Si
solar cells were applied to the PID test. Three methods
are applied to the high voltage test, one is in the water
baths with room temperature and 100% RH environ-
mental factors for 168 hr, another one is in room tem-
perature and full area coverage with aluminum foil of the
modules’ front surface for 168 hr [9], the third method is
using 85˚C and 85% RH damp heat chamber for 48 hr
[10], then application of 1000 V between the cells (via
the junction box) and the aluminum frame, respectively.
In addition, a 4 × 3 mini module which without soda-
lime glass was made and applied 1000 V between the
ells (via the junction box) and the aluminum frame to
identify the PID formation issue.
For characterization of these modules prior and after
the PID test a Berger PSS30 flash tester [11] and a high
resolution electroluminescence (EL) camera were used.
The volume resistivity test was according to ASTM-
D257 [12] “Standard Test Methods for DC Resistance or
Conductance of Insulating Materials” using 500 ± 5 V as
the applied direct voltage and charged with 60 sec to
measure the volume resistivity variety.
3. Results and Discussion
Three commercial silicon PV modules were produced in
order to compare different options for PID test conditions.
The degree of PID was measured in terms of the standard
test condition (STC) module power as shown in Table 1.
In Table 1 all the samples after PID testing are shown
the power loss more than 5% during 168 hr or 48 hr test.
From our results the PID test under water bath had about
three times power loss than that was covered with alu-
minum foil that means water acceleration the PID rate. In
another method by chamber test we find the same result
as test under water bath. The chamber PID test reducing
70% time is more effective than water bath.
Table 1. PID test data under different conditions.
Test time Voc Isc Vmp Imp PmaxΔPmax
NO [hr] [V] [A] [V] [A] [W] [%]
0 36.670 8.290 29.160 7.700 224.430
bath 168 34.184 8.356 21.774 6.410 139.737
0 36.690 8.420 28.860 7.770 224.310
Al foil
168 36.562 8.467 27.372 7.270 198.988
0 37.410 8.530 30.071 8.024 241.284
48 33.600 8.203 23.381 5.199 121.551
Furthermore we used electroluminescence technology
to check these cells performance. Figure 1 was EL im-
age after PID test in water bath condition.
We can see that serious dark areas more than two
strings after PID test, relevant the Voc decreased about
2.5 V and power loss 38% that means weakening of
cell’s depletion zone, resulting in a reduction of Voc and
Pmax. In the Figure 2, there was EL image after PID test
coverage with aluminum foil.
From the Figure 2 there are random dark areas distri-
bution in the EL images, and relevant Voc decreased
slightly about 0.1 V and loss power 11%. Compared to
the two testing results humidity played an important role
on acceleration PID testing. Humidity can enhance the
leakage currents flow from module-cells through module
insulation and packaging materials, to the module frames,
to earth-ground via module supports, moreover moisture
entrancing the module can induce encapsulant degrada-
tion and reduce insulation of encapsulant to form PID
(a) (b)
Figure 1. EL images of a module (a) pre and (b) post PID
test in water bath.
(a) (b)
Figure 2. EL images of a module (a) pre and (b) post PID
test with front sheet coverage with aluminum foil.
Copyright © 2013 SciRes. EPE
H.-C. LIU ET AL. 457
prone, the encapsulant especially meaning ethylene vinyl
acetate (EVA). Figure 3 was EL image after PID test in
85˚C/85% RH climate chamber which also had the seri-
ously dark areas after 48 hr PID test. In the chamber ex-
cept moisture we added heat to accelerate the PID test. It
can more quickly and effectively check the photovoltaic
solar cell module whether it have PID prone.
Furthermore we studied the volume resistivity relative
to PID effect. Two different EVA films A and B were
aged in 85˚C and 85% RH climate chamber monitored
one week as showed in Figure 4.
The film A showed that volume resistivity from 1014
order decreased to 1013 order, opposite to A the film B
appearance good performance during aged period. From
the results we can deduce that increasing EVA film con-
ductivity caused the module to PID prone. The Figure 4
also showed that the excellent encapsulant can restrain
moisture entrance to module and mitigate PID occur-
rence. Because no prediction of PID effect without test-
ing is possible so far, hence test can protect manufacturer
from massive customer complains.
In order to study the PID mechanism we designed a 4
× 3 mini module without soda-lime glass as front sheet
for the PID testing. The testing was performed in the
(a) (b)
Figure 3. EL images of a module (a) pre and (b) post PID
test in 85˚C/85% RH climate chamber.
Figure 4. The volume resistivity varies of EVA film A and B
after 85˚C and 85% RH climate chamber test.
climate chamber with 85˚C and 85% RH conditions ap-
plying 1000 V until 48 hr. The test result was showed in
Table 2.
There is only 1% power loss after PID test which
shows good performance than that with soda-lime glass
specimens testing previously. EL image without glass
module had no obvious difference before and after PID
test as showed in Figure 5 that means the module was
PID free.
From the result we can speculate some compounds in
the soda-lime glass which also plays important role for
PID effect. The compounds especially sodium ions can
migrate easily from glass to cell if strong negative elec-
tric field exists between cell and module aluminum frame.
Above all result, we can suppose the PID process as fol-
lows: moisture permeate into module which causes EVA
degradation to become more conductive and helpful Na
migration to cell surface or P/N junction, finally causes
the cell shunting to loss output power.
4. Conclusions
The lifetime of PV modules are reduced by various deg-
radation factors such as: harsh environments, high sys-
tem voltages and material failures over long periods of
Table 2. PID test data without Soda-lime glass module.
Test TimeVocIsc Vmp Imp PmaxΔPmax
NO. [hr] [V][A] [V] [A] [W]%
0 7.4858.552 5.799 7.888 45.742
glass 48 7.4808.449 5.767 7.856 45.305
Figure 5. EL images of a module (a) pre and (b) post PID
test without Soda-lime glass module.
Copyright © 2013 SciRes. EPE
Copyright © 2013 SciRes. EPE
operation. In this article we investigated the high system
voltage effect or PID effect. Our PID test results showed
that PID in chamber is the harshest and fastest test
method than in water bath and coverage with aluminum
foil. Our results also verified that the volume resistivity
and soda-lime glass ingredients are important factors to
PID failure.
Nowadays, PID effects are focused by every PV
manufacturer to assure their products PID free. In the
future how to reduce module PID effect to increase reli-
ability and performance will lead PV modules to more
competitiveness and wide acceptance of PV technolo-
5. Acknowledgements
The financial support provided by Bureau of Energy
(contract No.: 102-D0305) is gratefully acknowledged.
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