CIEMAT PVLabDER has largely increased its demand on testing and characterizing PV plants, according to the fast growth of PV installed capacity in Spain. One of the topics in which manufacturers, promoters, and owners of the plants are more interested in, is the possible degradation of PV modules and its relationship to guarantee contracts, as it is related to subsidies. This paper presents some findings in campaigns of PV plants evaluation carried out during last years. This evaluation usually consists of visual inspection, I-V curve measurement in the fields (the whole plant or selected areas), thermal evaluation by IR imaging, and, in some cases, measurement of the I-V characteristic and thermal behaviour of selected modules in the plant, chosen by the laboratory. It must be noticed that new defects that grow when the module is into operation may appear in modules initially free of them (named as hidden manufacturing defects). Usually some of these hidden defects that only appear in normal operation are not detected in reliability tests (EN61215 or EN 61646) [4][5] due to the different operational conditions of the module in the standard tests and in the field (serial-parallel connection of many PV modules, power inverter influence, over voltage on wires, etc.

Alonso Garcia, M. Carmen

Chenlo, Faustino

Muñoz-García, Miguel Angel

Archivo Digital UPM

Early degradation of PV modules and guaranty conditions

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

EARLY DEGRADATION OF PV MODULES AND GUARANTY CONDITIONS 
  
 
M.A. Munoz, M.C.  Alonso-García, F. Chenlo 
Photovoltaic Laboratory, Renewable Energy, CIEMAT 
Avda. Complutense, 22; 28040 Madrid, Spain 
miguelangel.munoz@ciemat.es Phone: +34 913466497; Fax: +34 913466037 
 
 
ABSTRACT:  CIEMAT PVLabDER has largely increased its demand on testing and characterizing PV plants, according to 
the fast growth of PV installed capacity in Spain. One of the topics in which manufacturers, promoters, and owners of the 
plants are more interested in, is the possible degradation of PV modules and its relationship to guarantee contracts, as it is 
related to subsidies. This paper presents some findings in campaigns of PV plants evaluation carried out during last years. 
This evaluation usually consists of visual inspection, I-V curve measurement in the fields (the whole plant or selected areas), 
thermal evaluation by IR imaging, and, in some cases, measurement of the I-V characteristic and thermal behaviour of 
selected modules in the plant, chosen by the laboratory. It must be noticed that new defects that grow when the module is 
into operation may appear in modules initially free of them (named as hidden manufacturing defects). Usually some of these 
hidden defects that only appear in normal operation are not detected in reliability tests (EN61215 or EN 61646) [4][5] due to 
the different operational conditions of the module in the standard tests and in the field (serial-parallel connection of many PV 
modules, power inverter influence, over voltage on wires, etc.) 
 
Keywords: PV Module, Degradation, Defects 
 
1. INTRODUCTION 
 
Photovoltaic market in Spain has grown rapidly in 
past years. It has passed from 250 MW to more than 
2.500 MW installed only in last year.  
This increase led to the fact that more than twelve million 
PV modules were installed. And also that more than eight 
hundred million of solar cells were necessary to 
manufacture them. It is quite clear that in such huge 
population sometimes we find PV modules with 
problems. Besides this, when a problem appears, affects 
to a higher number of modules. 
Problems not always were detected during the 
manufacturing of the PV modules or the silicon but they 
can appear later when the modules are already installed 
and working in the plant. 
 At the moment this fast increase has been calmed 
due to the new regulation that allows the installation of 
500 MW/year in the next years, but a demand for testing 
laboratories to analyse early degradation and hidden 
defects studies in PV modules and plants has arisen. This 
topic is related to guaranty contracts, and manufacturers, 
promoters and owners are uncertain whether these defects 
or early degradations should cause the rejection and 
reposition of PV modules.  This paper shows different 
kinds of PV module defects and analyses its effects over 
peak power of the module.  
Other questions are mentioned, such as IR 
characterization analysis (taking into account three 
possibilities: maximum power point, short circuit 
condition and middle range operation), the consideration 
of visual defects as only cosmetic or a serious 
manufacturing defect, etc. 
 
Among the most common visible effects we can outline: 
- Yellowing 
- Delaminations 
- Bubbles 
- Cracks in the cells 
- Defects in the antirreflexive coating 
- Burnt cells 
 
These problems found in plants that are in operation 
for a not too long period of time, make necessary the 
definition of certain criteria in order to determine which 
can be consider a major defect that implies the 
replacement of a module under guaranty. To do that, the 
categorization of defect types and the evolution of them 
with time is required. 
 
2. ANALYSIS PROCEDURE. 
 
The analysis of the defects listed in the previous 
section was performed by means of different tests. First, 
the I-V characteristic curve was measured in order to 
detect power losses that could be related to cell changes. 
I-V curve measurement was performed according to IEC 
60904-1[1][2], what permits to obtain main parameters, 
Isc, Voc, Im, Vm Pm and FF in Standard Test Conditions 
(STC): 
- Irradiance: 1000 W/m² 
- Cell temperature: 25°C 
- Spectral distribution: AM1.5G (according to 
IEC 60904-3) 
- Normal incidence 
Measurements were performed indoors, with a flash 
pulsed class AAA IEC 60904-3 [3] solar simulator (10 
ms pulse). All measurements were done at temperature 
and irradiance conditions very closed to STC (1000 ± 
5 W/m2 and 25 ± 2° C). Short circuit current and open 
circuit voltage were extrapolated to 1000 W/m² and 25°C 
using a and b coefficients respectively. The influence of 
these corrections is minor, due to the small difference 
between measured and standard conditions. 
Besides, infrared imaging and electroluminescence 
tests were performed in some modules.  
IR characterisations can be performed in different 
conditions, being the most significant, short circuit, a 
working point close to maximum power and forward bias 
of the module at a current similar to short circuit current. 
Worst case with respect to temperature increase and hot 
sport occurrence is the module in short circuit conditions. 
This can be achieved in laboratory but not in the plant, 
unless it is disconnected and the sample taken out of the 
24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany
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circuit. Furthermore, temperature differences in module 
surface are different depending on the operation point of 
the module. Modules that in short circuit conditions 
could show large temperature increases in one of their 
cells may not increase their temperature in normal 
operation conditions. On the other hand, there are other 
local effects that may affect the thermal behaviour of the 
module working in the plant, that are not present in the 
hot-spot tests carried out in laboratories.  
Electroluminescence tests were performed in the 
laboratory, applying a forward voltage slightly higher 
than open circuit voltage to get a similar current to short 
circuit current. In these conditions, the module emits 
light in the wavelengths where it is sensitive. An 850nm 
filter was used, with acquisition times from 5 to 30 s. 
These conditions were chosen to minimize noise and 
increase sensitivity. Darker areas in the images 
correspond to less active areas, suggesting defective 
regions. Besides, it is easy to detect with this method 
contact finger breakages, shunts and microcracks. [7][8]  
  
 
3. RESULTS AND DISCUSSION. 
 
Following are presented and commented main defects 
found. 
  
3.1. Yellowing 
Consist of a tedlar colour change or a colour change 
in the material in the back side of the module from white 
to yellow. With the tests performed it can not be asses the 
influence of this defect in the power losses of the module. 
Despite this, the yellowing could be a problem if it would 
start a lack of adherence between the tedlar and the 
module, causing water penetration inside the module.   
In some PV modules, yellowing appear in some areas 
but not in adjacent areas with a different tedlar of a 
different origin or characteristics. This should mean that 
yellowing appears in tedlar instead in the adherent 
element (usually EVA). 
Figure 1 shows an example of how the yellowing 
effect is due to a change in the colour of the tedlar 
instead to changes in EVA. 
 
 
Figure 1.- Yellowing over an area of a PV module. 
3.2. Delamination 
It consists of the tedlar adherence loss with the 
subsequent unstuck. It is a major problem because it can 
cause water penetration inside the module structure. It is 
more severe if it occurs in the borders of the module 
because, apart of the power losses, it causes electric risk 
for the module and the installation.  
 
3.3. Bubbles 
It is a type of delamination combining the lack of 
adherence between the tedlar and the back side of the 
module with the blowing of the areas where this 
adherence has been lost. These bubbles make more 
difficult the heat dissipation of the cells in these areas, 
overheating them with the subsequent reduction of cell 
lifetime.   
On Figure 2 we can see an example of a module with 
many bubbles in the back side. Usually they appear in the 
centre of a cell, maybe due to a different adherence of the 
cell. 
 
 
Figure 2.- Bubbles in the back side of a PV module. 
 
On Figure 3 we can see how bubbles can also appear 
in the front side of a PV module, between the glass and 
the silicon cells. In this case it is a detachment between 
part of the cell and the glass. The influence in the front 
side of the module is minor in this case, because cells are 
more rigid than tedlar. Air or gas is again accumulated in 
the bubbles, probably due to some chemical reaction. 
Here, apart from heating effects it is added the fact that 
light incidence in the cell can be reduced.  
 
 
 
Figure 3.- Bubbles in the front side of a PV module. 
 
 
3.4. Cracks in cells 
The market of silicon solar cells has changed the 
thickness of cells in few years from 300µm to less than 
200µm.  
This thickness reduction makes the cells more fragile 
and susceptible to breakages during its manipulation, 
module lamination or storage.  
Microcracks consist of small cell cracks usually not 
visible, that may affect both sides of the cell. They 
produce a loss in cell consistence and a possible carrier 
recombination path. Sometimes, different colour lines 
can be appreciated in the cell, although the cracks are not 
visible at a sight. When modules with these different 
WHITE 
YELLOW 
TEDLAR-a 
TEDLAR-b 
24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany
3566
coloured lines are tested by electroluminescence, there is 
good accordance between these lines and the microcracks 
observed by EL. Microcracks areas are darker in EL 
because either they do not produce light emission, or this 
emission is lower. In some cases the cracks isolate parts 
of the cell avoiding current generation as we can see in 
Figure 4.  
  
 
Figure 4.- Cracks in cells. B&W image an simulated 
colour image. 
 
The IR characterisation of these modules both in 
short circuit conditions and in the operation point did not 
show a particular temperature increase in the damaged 
areas. Forward bias IR characterisation showed some 
temperature distributions with the same shape as those 
found by EL, but temperature differences were rather 
small (a few degrees, sometimes lower, others higher, 
than the adjacent areas) making difficult the 
interpretation of temperature patterns. 
 
3.5. Defects on antireflexive layer 
The layer that covers each cell of the module suffers a 
change that induces a change in the colouring (Figure 5). 
The antireflection properties may suffer changes as well 
and in this case the light that achieves the cells may be 
lower than expected. Nonetheless, this colour change 
should not cause a decrease in the wavelengths that the 
cells use, affecting only to visible Light. 
IR characterisation of these modules in different 
conditions did not show any particular effect that could 
be associated with the changes in the colour of the AR 
layer. 
A follow up of the affected modules should be done 
in order to detect if this defect lead to another that could 
be severe.  
 
 
 
Figure 5.- Decolouring of cells due to a change in 
antireflexive coat. 
 
3.6. Other defects. 
- Lines and blemishes that appear in the cells. 
Lines sometimes are indicating a crack in the cell. 
Probably this crack leads to a chemical reaction or a 
migration that affects the antireflexive layer and the line 
appears (Figure 6). 
 
 
Figure 6.- Two defects detected with EL image. One of 
them not visible at a sight. 
 
- Detachment of the frame.  
It sometimes appears after the PV module has been 
installed. It could be due to an incorrect installation 
where the module supports an excessive weight or 
because the adherence between the frame and the glass is 
24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany
3567
not strong enough. We can see an example of this in 
Figure 7. 
 
 
Figure 7.- Detachment of the frame. 
- Power losses higher than guaranteed.  
Manufacturers usually give a tolerance for module 
nominal power in standard test conditions [6]. They also 
guarantee power delivered by the module within a range 
for a certain time (usually 10% during 10 or 15 years), 
increasing the time in some cases to 20 or 25 years with 
80% of the nominal power. Nevertheless, power losses 
higher than the ones indicated in guarantee contracts 
have been found in some cases when measuring modules 
taken out of the plants.  
In some cases, a significant degradation is reported. 
After obtaining a I-V curve of a module where clearly 
can be seen that a string has bad cells a EL image can be 
taken to confirm this situation (Figure 8).  
 
Figure 8.- Supposed string with bad cells. 
Besides this, an I-V curve analysis string by string 
can be performed. In this case, the I-V curve can be 
obtained from the leads of diodes after opening the 
connections box. Figure 9 shows the same module where 
the I-V curve was obtained from each string.  
 
string 2
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1.0
2.0
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5.0
6.0
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Figure 9.- I-V analysis string by string. 
The analysis show how central string (string 2) has 
worse cells than the other ones (current is lower) and it 
affects the complete module. 
These power losses can be only detected by 
measuring a representative sample of the total population 
of the solar plant periodically. 
 
 
4. CONCLUSIONS. 
 
An initial follow-up of the modules of a plant should 
be done in order to be able to detect early degradations in 
modules during the initial guaranty period. To do this, 
the first inspection should be a visual inspection looking 
for defects as mentioned like bubbles, delamination, 
decolouring or any strange figure that could appear over 
the cells and that could indicate an initiating defect. 
After this, a sample of these modules should be sent 
to a laboratory in order to determine if it is a real defect 
and could lead to a claim to the manufacturer of the 
modules. 
Cracks over the cells could appear not only during 
the lamination process but during the storage or the 
installation of the module. These cracks could be a 
problem in the future. 
 
 
 
 
 
5. REFERENCES. 
 
[1] International Electrotechnical Commission. Standard 
IEC-EN 60904-1: Photovoltaic Devices. Part 1: 
Measurement of Photovoltaic Current-Voltage 
Characteristics. 
[2] International Electrotechnical Commission. 
“Standard IEC-EN 60904-3: Photovoltaic Devices. Part 
3: Measurement principles for terrestrial photovoltaic 
(PV) solar devices with reference spectral irradiance 
data”. 
[3] International Electrotechnical Commission. 
“Standard IEC-EN 60904-9: Photovoltaic Devices. Part 
9: Solar Simulator Performance Requirements”. 
[4] International Electrotechnical Commission. 
“Standard IEC-EN 61215: Crystalline silicon terrestrial 
photovoltaic (PV) modules. Design qualification and 
type approval”. 
[5] International Electrotechnical Commission. 
“Standard IEC-EN 61646: Thin-film terrestrial 
photovoltaic (PV) modules. Design qualification and 
type approval”. 
[6] International Electrotechnical Commission. 
“Standard IEC –EN 50380: Datasheet and nameplate 
information for photovoltaic  modules”. 
[7] T. Fuyuki. "Luminoscopy. A versatile tool for the 
diagnosis of crystalline silicon solar cells utilizing 
electroluminescence". 9th International Conference on 
Polycrystalline Semicoductors, POLYSE 2006. 
complete module
0.0
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Early degradation of PV modules and guaranty conditions

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