Microcracks in photovoltaic modules were studied to understand their effect on power output. Various crack detection techniques were examined including optical transmission, infrared ultrasound lock-in thermography, and electroluminescence imaging. Cracks were classified based on orientation and effects. While small cracks may not impact power initially, as cracks grow and become Mode B or C, power loss increases due to reduced active cell area. The conclusion is that silicon wafer cracks can cause up to 2.5% power loss if electrical connection is maintained, and modules can tolerate up to 8% loss of cell active area before impacting output.

1. MICRO CRACKS IN
PHOTOVOLATIC(PV)
MODULES
BY
O.RENUKA

3. ABSTRACT
Degradation of power output of a
photovoltaic( PV) module
Study of microcracks is essential to answer
how these degrade the performance

4. content
INTRODUCTION
ORIGIN OF CRACKS
CRACK DETECTION TECHNIQUES
CLASSIFICATION OF CRACKS
EFFECTS OF CRACKS
CORRELATION OF CRACKS WITH
MODULE PARAMETER
CONCULSION

5. INTRODUCTION
• Micro cracks in a solar cell is an important issue for PV module
• Cause power loss and effect the reliability
• Cracks developed in young modules initially not effect power
output
• Module experience heat, wind, humidity, mechanical loading
• Cells having cracks above a limit are rejected before integration of
cell string
• Done by ultrasonic methods, flux thermograph,
electroluminescence imaging
• The exact effect of cracks are not well known because the growth
of cracks depends on the handling of module, location of module,
climate and other environment conditions.
• Two modules with same amount of crack may give different power
output at two different places.
• Impact of these cracks on power output to reduce the number of
rejected cells and reduce loss of manufacturer.

6. ORIGIN OF CRACKS
 PV cells are made of silicon & brittle in nature
 Occurrences of micro cracks in a PV module are of
three categories
During Production
Due to poor equipment & inexperienced operator
During Transport
Mitigated by a good packaging with more protection
Installation
Bad installation may develop cracks and also 0ther
damage to modules

7. CRACK DETECTION TECHNIQUES
Non destructive methods :
Optical Transmission:
cracks are detected by IR light
size of crack detection depend on
CCD camera
Not good for detection in finished
solar cell

8. Infrared ultrasound lock-in thermography:
Ultrasound energy in feed periodically into wafe
Transducer generates ultrasound energy at 20KHz
Energy is fed to silicon wafer by ultrasound coupler
Information is converted into an image by lock in
thermography

9. Electroluminescence imaging:
o It is also called as contact
technique
o Used for finished PV modules
o Usually done in dark
environment
o Cracks appears as dark gray line

10. Photoluminescence imaging:
It is non contact method for
detection of cracks
Acquition time of less than a
second
Fluorescence:
In EL outdoor images taken are
of poor quality and reuires change
of circuit
Fluroscence detects cracks with
aging

11. Method Advantage Disadvantage
Optical transmission
Detect small cracks up to
1um, throughput 1 wafer
per sec.
Used in production stage, inapplicable
for finished cells
Ultrasound lock-in
thermography
Can be used for both
wafers and solar cells
Long acquisition time
Electroluminescence High throughput Interference with other defects, contact
method used only for finished cells
Photoluminescence High throughput,
contactless
Interference with other defects e.g.
scratches
Fluorescence High throughput , also Interference with defects

12. CLASSIFICATION OF CRACKS
Cracks are of various sizes and
characteristic
A classification of cracks according to
orientation
No crack:
A cell which has no crack as
reference
Dendritic crack:
present at any part of cell & any
direction
+45/-45 degree crack are oriented with
respect to reference cell

13. Parallel to bus bar:
Perpendicular to bus bars:
Cross line crack:

14. Relative occurrence of cracks

15. Mode A crack:
Not influence the current flow
No crack resistance and are still
electrically connected to cell
Mode B crack
Affects the current through cell
Crack resistance
Area more than mode A
Mode C Crack :
Isolate the crack area from cell
Degrade power output
Critical than two mode cracks
Current from the cell is directly proportional to
active area

16. EFFECTS OF CRACKS
Impact of micro cracks on power output not
significant in initial stage of crack
Initially crack is electrically connected
with cell
Different cracks impact the power differently
depending on their orientation,size,location
Based on orientations into 3 categories
according to how much they degrade power
category 1:- low criticality
category 2:-Moderate criticality
category 3:- High criticality
Type of crack category
Dendritic III
+45 degree II
-45 degree II
Parallel to busbars III
Perpendicular to
busbars
I
Cross line II
Several direction III

17. In 60 PV cell modules if half of the cells
have mode A crack
power loss about 1% and if all cell
have A crack then power loss 2.5%
Graph showing power loss with no. of
cracks after mechanical load test
How various crack modes impact the
power output of PV modules montages
has done experiment
Cell micro cracks impact power loss
very little extent if they do not generate
inactive area

18. Relating power loss with a number of cracks
after humidity freeze cycle
Power loss is more for modules
having more no. of cracks
Maximum degration of around
10%
After humidity freeze test EL
image shows that many modes
A crack has changed to mode B
and C

19. CORRELATION OF CRACKS WITH
MODULE PARAMETER
Correlate effects of cracks with
location, Pmax degradation
Location of cracks in module can
guess source of crack
Divide the module into 3 zones
central,intermidate and
periphery
All India survey, most cracks are
located at periphery

20. DRAK AREA THE DEGRATION
Micro cracks of solar cell effects the
short circuit current
Mode C and Mode B cracks mainly
effects the IC
Increasing dark area the degradation
in IC increases
Old modules shows high degradtion
than younger modules

21. CONCLUSION
Si wafer cannot degrade the power output of a PV module by
more than 2.5%
if the crack does not harm the electrical connection from the
active cell area.
A PV module can tolerate up to 8% loss of active area of a
cell without impacting the power output of the module
A good way to avoid power loss due to micro cracks is to
avoid cell breakage and use more flexible cell metallization
The flexible metallization will prevent isolation of cell parts in a
cracked cell.